Garden Sage - Some grasses OK; whitefly problem; transplanting agaves
- Updated
Answers to your gardening questions from an expert in Southern Arizona.
- By Peter L. Warren Special to the Arizona Daily Star
- Updated
Q: We have several acacia trees that are about 12 years old. Our landscaper had described them as sweetgum acacia, but I am not sure if that is really what we have. They have grown up from an initial height of 5 feet to 15, but they are not looking healthy. Especially over the last five years, the leaves have gotten very sparse and they are often covered with small, white insects. Some of the branches have died and have no leaves at all. Our landscaper has repeatedly sprayed them with pesticide, but the white insects always return. These trees are irrigated with a drip system. Other neighbors all across Oro Valley seem to have the same problem . Also on our property we have other native acacias, which we did not plant and they are doing fine. They have the small orange-yellow colored balls and they have never been sprayed and they are not even irrigated. Should I just give up on these trees and replace them with mesquites, which seem to do fine here, or do you have other solutions for us?
A: It would be helpful to see the insects up close to be sure of the problem. Please let me know if you can bring a sample of infested leaves to my office or if I may stop by your trees and see them in person.
One likely possibility is that sweet acacias (Vachellia farnesiana) are occasionally infested with insects called whiteflies. They are very small white insects in their adult form. As immature insects they are wingless, darker in color and suck sap from the leaves, sometimes causing the tree to drop leaves prematurely. Repeated infestations can be hard on the tree, but in many cases the infestation is not severe and natural enemies reduce the population to tolerable levels. In recent years these whiteflies seem to be more common in the Tucson area, probably due to warmer weather.
Whiteflies in general have been a sporadic problem at our elevation, whereas in lower and warmer areas such as Pinal and Maricopa counties, they are a regular occurrence. I would be interested to know which insecticide your landscaper is using. There might be other options for pest management. I wouldn’t recommend giving up on your trees yet.
Peter L. Warren is the urban horticulture agent for the Pima County Cooperative Extension and the University of Arizona. Email questions and photos to tucsongardensage@gmail.com
- By Peter L. Warren Special to the Arizona Daily Star
- Updated
Q: Please tell me when I can transplant two small agaves that I raised from the little ones off a large plant. I was thinking of doing it now that it has cooled off, but I thought it would be better to get your advice.
A: Agaves are easily propagated from the offsets, aka pups, or little ones as you called them. Now is a fine time to plant them. If you removed them from the parent plant by cutting the stolons (the underground branches by which they are attached), it’s a good idea to let them dry for a few days to form a callus on the cut end. Agaves do best in well-drained soil such as a mix sold for cacti and succulents. You can simply push them into the soil, although they might get a better start if you put them in a container in a shady area until they establish roots.
The root establishment can take up to four weeks. Once rooted, they will start growing and then you can apply a soluble fertilizer, but only once or twice per year. Watering should be done as often as the container dries out. It’s not great for them to stay wet all the time, so allow the soil to dry between watering. If you eventually transplant them into the ground, watering should be done less frequently. In the summer, water every 10 to 14 days unless there was rain. In the spring and fall, every three to four weeks and none in the winter.
Peter L. Warren is the urban horticulture agent for the Pima County Cooperative Extension and the University of Arizona. Email questions and photos to tucsongardensage@gmail.com
- By Peter L. Warren Special to the Arizona Daily Star
- Updated
Q: I just moved to Arizona from Wisconsin. Is there any indication when the drought might end or is this long-term condition due to climate change? And if it doesn’t improve, what will be the impact for places like Tucson?
A: The drought we are experiencing has reportedly been going on for more than 20 years with no end in sight. Climate scientists predict it will likely get worse. The big challenge in the Southwest has always been a shortage of water. Even the earliest explorers thought the region was not a great place to build towns and cities, but we humans are sometimes determined to find a way. There are many articles and books on this subject, so there is no shortage of information if you’re interested in learning more.
“Cadillac Desert” by Marc Reisner is one of the classic books on this topic. Something more current would be the CLIMAS website at the University of Arizona, climas.arizona.edu, that assesses climate in the Southwest and includes research findings, blogs, and podcasts on many aspects of climate.
Peter L. Warren is the urban horticulture agent for the Pima County Cooperative Extension and the University of Arizona. Email questions to tucsongardensage@gmail.com
- By Peter L. Warren Special to the Arizona Daily Star
- Updated
Q: Grasses? They are awful. What’s wrong with these landscape architects and their lack of concern for the desert and their poor plant material choices and layouts?
A: There are some native grasses that are fine for the desert and our landscapes. Extensive research has been and continues to be done to determine the best plants for our region. We even have a research operation in Tucson. It is called the United States Department of Agriculture Natural Resources Conservation Service Tucson Plant Materials Center.
You can schedule a tour if you are interested to learn more about grasses that are appropriate for our region. Google AZPMC if you want to learn more .
There are, however, other species that are invasive and should not be planted here. In some cases, these problems are self-inflicted because humans failed to see the downside to species that were once thought to be a great solution to erosion or nutrition for livestock . I like to think that nowadays we are much more careful about planting grasses that can reseed and become invasive.
Unfortunately, this only works if we are aware of the potential problems. Some grass species that are marketed as sterile are not 100 percent so and unfortunately they are popular landscape plants. I wouldn’t blame the landscape architects for all these troubles. Many of them are schooled in proper plant selection through their degrees and their experience. Part of the blame can be spread to consumers who buy the plants and nurseries that sell them.
In the end, it is something we all need to educate ourselves about when considering which plants to use no matter where we live.
Peter L. Warren is the urban horticulture agent for the Pima County Cooperative Extension and the University of Arizona. Questions and photos may be emailed to tucsongardensage@gmail.com.
- By Peter L. Warren Special to the Arizona Daily Star
- Updated
Q: I have a mature Valencia orange tree that has yellowing leaves and dead end tip branches. It also has some dried yellow fruit. The tree is watered three times a week for 45 minutes each time with three bubbler type irrigation system heads at the tree drip line. Any thoughts on what may be the problem?
A: Although yellowing leaves can also indicate a lack of nitrogen, the dead end branches and your current irrigation schedule tells me the tree needs more water. If you are fertilizing three times per year as recommended in late winter, spring, and fall, the other important input is water. While your placement of bubblers is appropriate, the scheduled watering is not ideal. Citrus trees do best with deeper watering on a less frequent basis. During the summer, every 7 to 10 days to a depth of 36 inches is recommended. In the spring and fall you can back that off to every 10 to 14 days and in the winter to every 14 to 21 days.
Peter L. Warren is the urban horticulture agent for the Pima County Cooperative Extension and the University of Arizona. Questions and photos may be emailed to tucsongardensage@gmail.com.
- By Peter L. Warren Special to the Arizona Daily Star
- Updated
Q: We planted this Satsuma Mandarin Orange two years ago, and last spring it had good foliage and produced two or three small fruit. But now, it appears to lose leaves on lower branches, put out new leaves on upper branches, but has not gained any new branches or height. It is on a drip system. I don’t see evidence of anything chewing on it. Any suggestions on how to help out thrive?
A: This is typical for newly planted trees. The stress of transplanting sometimes causes some leaf drop and/or fruit and flower drop. Assuming you are watering and fertilizing properly, I expect you will see new growth in the coming year. Trees typically take between two and three years to get established in their new surroundings before they show a lot of growth. This is mainly due to the large amount of root damage they incur during transplanting.
Peter L. Warren is the urban horticulture agent for the Pima County Cooperative Extension and the University of Arizona. Questions and photos may be emailed to tucsongardensage@gmail.com.
- By Peter L. Warren Special to the Arizona Daily Star
- Updated
Q: What is wrong with this saguaro cactus?
A: The brown and black areas show signs of bacterial necrosis. This is a common affliction of cacti in the desert and unfortunately once it gets into the main stem and spreads that wide there is nothing you can do to fix the problem. Eventually the cactus will succumb and fall over. It would be wise to plan for that eventuality and make sure there aren’t any potential hazards such as the chance people or property could be damaged if it fell unannounced. Contracting with an experienced landscaper or certified tree professional to take it down would be appropriate if any hazards are present.
Peter L. Warren is the urban horticulture agent for the Pima County Cooperative Extension and the University of Arizona. Questions and photos may be emailed to tucsongardensage@gmail.com.
- By Peter L. Warren Special to the Arizona Daily Star
- Updated
Q: Can you tell me what is going on with this sage bush? I took a sample to the nursery and was told it is new growth. The bush has been this way for a couple of years and stays on the same side of the bush. Is this a problem or just new growth?
A: New growth is correct in so far as it’s newer than the shrub you planted. Unlike normal new growth, it won’t take on the appearance of old growth after a period of time. It appears that your Texas ranger has reverted back to it’s original form, at least in part.
Many of the interesting cultivars we see in landscapes originate from some mutation with desirable characteristics from the original parent plant. These interesting mutations can be propagated into new cultivars and then introduced into the horticulture trade. Unfortunately, not all of these cultivars are stable and they sometimes revert back to the original plant. The original is likely more vigorous than the designer cultivar and could take over the space by outgrowing the shrub you planted. So if you like the one you planted more than the new original version, you can prune out the offending parts. As long as we’re discussing them, these plants are commonly called sages but are actually not related to the true sages in the Salvia genus. Rather they are in the figwort family, Scrophulariaceae.
Peter L. Warren is the urban horticulture agent for the Pima County Cooperative Extension and the University of Arizona. Questions and photos may be emailed to tucsongardensage@gmail.com.
- By Peter L. Warren Special to the Arizona Daily Star
- Updated
Q: I’ve got a previously healthy stand of Mexican fence post cactus that has been infested with a white scale pest of some kind. Can you tell me what it is — and how I might get rid of it?
A:Your scale insect was identified as Diaspis echinocacti. They are found on a variety of cacti and other plants. The recommended management strategy for scale insects is a combination of integrated pest management tactics including natural enemies, physical removal, and applications of horticultural oil or insecticide. Because their outer covering protects scale insects, the ideal time to spray them is during the time in their life cycle when the young have recently emerged from their eggs and are crawling about unprotected. The timing is not always easy to determine but you have options to figure it out. Late winter is a good time to start watching. Carefully examine the infested plant to see if crawlers are present. A magnifying glass or loupe will come in handy when looking for these tiny insects. Alternatively, place double-sided tape around the cacti in affected areas of the plant when crawlers are expected. The tiny insect bodies get stuck in the adhesive. Once you see them you will have a general idea when they emerge. The next trick is to notice what else is happening nearby with your other plants. For example, what is recently blooming in your landscape? Year to year variation in insect development can be estimated by the use of phenology (the known influences of weather variations on plant and animal life cycles). By watching known phenological indicator plants you can accurately predict when particular scale insect eggs will hatch in your area in following years and thus you will be better prepared to manage the scale insects.
Peter L. Warren is the urban horticulture agent for the Pima County Cooperative Extension and the University of Arizona. Email questions to tucsongardensage@gmail.com
- By Peter L. Warren Special to the Arizona Daily Star
- Updated
Q: I have a love/hate relationship with this “weed.” For about 10 years I cut it off at the ground. It came up as one puny stalk with a reddish stem and then got other stems growing next to it and I’ve seen it in other places where it volunteers near drip emitters. I always wanted a real tree in that corner but couldn’t afford it. About three years ago I thought: maybe if I let it grow and tied it up, it would get a strong enough stem to become a tree, sort of… so I did that. Looking it up on line, I thought it looked very like an African Willow. So now it is strong enough to support itself, but I really don’t feel like giving it a tree status. What the heck is it? Its perseverance has finally got my grudging admiration. It won the battle.
A: Your tree is called African sumac (Rhus lancea) and it is a very common plant in our area. They can grow to a height and width of 30 to 40 feet. Once they become large trees, some people like them for the shade they provide. They are tough and do well with little care and may be used as street trees or in places where little else will grow well. Unfortunately, they are invasive and can spread easily in urban areas. Their seeds will grow wherever there is available water. As you know, persistence is required to keep them down once they start growing. Some people report allergies to the pollen so that is another concern. It’s hard to say no to a free tree but this is one that you might consider removing given the associated problems it brings.
Peter L. Warren is the urban horticulture agent for the Pima County Cooperative Extension and the University of Arizona. Email questions to tucsongardensage@gmail.com
- By Peter L. Warren Special to the Arizona Daily Star
- Updated
Q: What kind of cactus is this (pictured above, left), what are the fruits called, and are they edible?
A: It’s called Cereus repandus, the Peruvian apple cactus. It’s a South American species as you probably guessed from the name. It does well in our area except when we have a frost or freeze. The growing tips are damaged by below-freezing temperatures and need to be pruned as a result. In ideal locations protected from cold temperatures this plant may grow quite large. The fruit are edible and you may find birds, insects, and desert tortoises eating them as they ripen and fall to the ground.
Peter L. Warren is the urban horticulture agent for the Pima County Cooperative Extension and the University of Arizona. Questions may be emailed to tucsongardensage@gmail.com
- By Peter L. Warren Special to the Arizona Daily Star
- Updated
Q: This is not a question about plants, but I thought you might know the answer. We enjoy sitting on the patio but haven’t been able to for several weeks. The problem is we’re out there for just a few minutes, and then our ankles and feet start to itch like crazy. I have sprayed the deck, but that hasn’t seemed to help.
A: Mosquitoes are fairly common ankle biters this time of year. While there are landscape sprays you can use for short-term effect, I recommend you use an insect repellent on your legs to see if that stops or at least mitigates the problem. The most effective repellents are those that contain the active ingredient DEET.
Peter L. Warren is the urban horticulture agent for the Pima County Cooperative Extension and the University of Arizona. Questions may be emailed to tucsongardensage@gmail.com
- By Peter L. Warren Special to the Arizona Daily Star
- Updated
Q: I have a sick orange tree. One side is doing somewhat well, but the other side is dying, and the leaves are curled up. There is no sign of insect infestation. I have to water the tree every four to five days, otherwise the leaves begin to shrivel. I think the tree is about 6 years old but could be more. Originally it was on a drip system, but I stopped that about a year ago and use a sprinkler spray.
A: The tree is old enough to be established in its current location. The sprinkler you are using is likely not delivering enough water and not deep enough. I recommend you adjust your irrigation schedule to deliver enough water to reach a depth of 36 inches at the drip line once every two weeks. You can still use the sprinkler but it will not be as efficient as a drip system. More is lost to evaporation when it is airborne. You can check the depth the water is reaching by using a soil probe. The simplest kind is a three-foot piece of rebar with a handle that you can push into the ground after irrigation. It will meet resistance when you hit dry soil.
Peter L. Warren is the urban horticulture agent for the Pima County Cooperative Extension and the University of Arizona. Questions may be emailed to tucsongardensage@gmail.com
- By Peter L. Warren Special to the Arizona Daily Star
- Updated
Q: When field mice eat the top tips of sweet potatoes (while still in the soil), are the tubers safe for home consumption?
A: While the practical me says just wash it off really well, I checked with our food safety microbiologist, and she says no way. The chewed part may not be the only part of the plant that the rodent touched. The problem is that the rodent may have touched its own feces or other rodent feces and if that gets anywhere on the produce, and it is not washed properly (with an actual sanitizer), it could harbor foodborne pathogens. My advice would be to put those veggies in the compost pile.
Peter L. Warren is the urban horticulture agent for the Pima County Cooperative Extension and the University of Arizona. Questions may be emailed to tucsongardensage@gmail.com
- By Peter L. Warren Special to the Arizona Daily Star
- Updated
Q: What is this pretty little weed plant (above, right)?
A: Your plant is called broom snakeweed (Gutierrezia sarothrae). It’s a native plant and regarded as a weed, especially where livestock graze, because it is poisonous.
Peter L. Warren is the urban horticulture agent for the Pima County Cooperative Extension and the University of Arizona. Questions may be emailed to tucsongardensage@gmail.com
- By Peter L. Warren Special to the Arizona Daily Star
- Updated
Q: I have heard from a number of people that mistletoe does not kill a tree. That might be true, but it weakens the tree so much that anything that comes along after the infestation of mistletoe will kill the tree—like our drought. I think people want to hear that it doesn’t kill the tree so they don’t have to act on ridding the tree of it. Or maybe people don’t care that much about their trees. Even the Rillito River Path trees have a lot of it in them, and the city pays to plant and water the trees.
A: There are many species of mistletoe and they are parasitic plants. In general, the species we are familiar with in the low elevations of the Sonoran Desert attach to their host plant to absorb water and nutrients. The healthier the host plant, the healthier the parasitic mistletoe that depends on it. If the host plant is suffering from other problems, such as drought, the mistletoe can take enough water and nutrients to weaken the host and that can lead to the death of the host. A common species in our area is called mesquite mistletoe (Phoradendron californicum). This is a native plant that has a place in our desert ecology in that it provides food and shelter for some animals. The birds that eat the seeds will spread mistletoe by pooping them out in other trees along with a dollop of their own brand of fertilizer. It would be impossible to eradicate mistletoe from our environment because it of the way it is spread by birds. It would also be hard to generalize about the relationship between people and mistletoe. I am fairly certain there are a few different reasons why mistletoe is allowed to thrive on landscape trees. Depending on the person, these may include the knowledge that it is food for birds, that it’s not always easy or affordable to cut it out of every tree, and that there is an endless supply of this plant in the open desert from which it can spread. I am familiar with the city’s lack of resources and I expect they are doing the best they can with limited staff and funds to manage trees and other plants on public property.
Peter L. Warren is the urban horticulture agent for the Pima County Cooperative Extension and the University of Arizona. Questions may be emailed to tucsongardensage@gmail.com
- By Peter L. Warren Special to the Arizona Daily Star
- Updated
Q: How can I get rid of the squirrels that are destroying my backyard? They have three huge (apparently connecting) holes around the large palo verde tree. They keep the gravel all messed up with their digging. Of course, my cat (who is an indoor cat) loves watching them from the door. The chipmunks have many holes around a large cholla on the bank outside the front wall, so I assume that is where they are coming from.
A: Round-tailed ground squirrels are not likely something you can eradicate. As you noticed, they can migrate from outside a wall by digging or climbing if it’s not made of slippery material. The best strategy is an integrated approach that includes systematic destruction of their habitat, trapping to reduce the population, and protecting the plants you like best with some sort of fencing. Since they are fairly small, using hardware cloth with smaller holes that can be buried a few inches into the soil may help. Since they climb, this means you also have to protect from that likelihood with either a cover or lining your barrier with flashing or some other material on which they cannot get traction. You can contain them but you can’t stop them.
Peter L. Warren is the urban horticulture agent for the Pima County Cooperative Extension and the University of Arizona. Questions may be emailed to tucsongardensage@gmail.com
- By Peter L. Warren Special to the Arizona Daily Star
- Updated
Q: My father has a tangelo tree that will sometimes have a second bloom in the summer. This year on one of the branches there are two grapefruit! Usually I would think if there is another fruit it would come from a branch that sprouted from below the graft but this did not. He picked and cut one open and the flesh was a very light orange and tasted like a bland tangelo.
A: The tangelo is a hybrid citrus created by crossing a tangerine with a pomelo or grapefruit. Occasionally hybrids or part of them revert back to one of the original parents by producing plant parts such as foliage, flowers, or fruit that more resemble the parent plants. These growths are sometimes referred to as a ‘sport.’ So the odd fruit is likely a sport but probably something other than a pure grapefruit. Hopefully, they taste good. If not, you can prune that branch out of the tree or just let it be.
Peter L. Warren is the urban horticulture agent for the Pima County Cooperative Extension and the University of Arizona. Questions may be emailed to tucsongardensage@gmail.com
- By Peter L. Warren Arizona Daily Star
- Updated
Q: How do you keep bees out of the hummingbird feeders effectively enough that the little hummers have a chance to feed? Despite their aggressive nature, it seems that our hummers don’t want to challenge the bees. What to do?
A: Bees are seeking nectar and water for the same reasons as the hummingbirds and they both prefer actual plant nectar to sugar water if they can get it. I recommend providing a variety of flowering plants for the bees to distract them from your feeders. Hummingbirds prefer flowers that are tubular in shape but bees can’t access the nectar in these because they lack the long tongues of hummingbirds. Bees would more likely be found on plants that have a wide-open bloom with a place for them to land and access the nectar and pollen up close. Sunflowers are an example of the shape they prefer.
Peter L. Warren is the urban horticulture agent for the Pima County Cooperative Extension and the University of Arizona. Questions and photos may be emailed to tucsongardensage@gmail.com.
- By Peter L. Warren Arizona Daily Star
- Updated
Q: I have two well-established lilac bushes that always did well with minimal care until about two years ago. I used to water them for 2 to 3 minutes every day, but stopped doing that at one point. When I realized that they were getting stressed I started watering them again — once a week for 20 to 30 minutes. That was a year ago. But they haven’t recovered. They’ve had mildew on the leaves for the last year or more. They grow well, but most of the leaves get mildew and wither up. Now I’m watering them every day for 2 to 3 minutes again. Am I overwatering now that it’s November? What can I do to help them recover at this point? The house is about 50 years old, we’ve been here 14 years, and so the lilacs could be quite old.
A: Non-native shrubs such as lilacs do best when watered infrequently and deeply. The recommended schedule is once every seven to 14 days in the summer to a depth of 24 to 36 inches. In the spring and fall you can reduce this to once every 10 to 21 days and in the winter every 14 to 21 days. Powdery mildew can be a problem in certain situations when the climate is suitable. Like any successful disease story, you need a susceptible host, the presence of the disease pathogen, and a suitable environment. If you were planting a new lilac I would encourage you to select a mildew resistant variety. To prevent an infestation, the first thing to do is remove any diseased leaves from the ground or on the plant. This will prevent the disease from overwintering nearby and spreading to new growth. Second, you can selectively prune your lilacs to provide space between the branches for air circulation and sunlight penetration. Dense areas will favor the infection. There are also fungicides you can use to spray the mildewed leaves. Choose a fungicide specifically labeled for mildew and spray according to instructions. Typically, they recommend beginning to spray when new leaves are emerging.
Peter L. Warren is the urban horticulture agent for the Pima County Cooperative Extension and the University of Arizona. Questions and photos may be emailed to tucsongardensage@gmail.com.
- By Peter L. Warren Arizona Daily Star
- Updated
Q: My tomatoes show an unknown leaf disease that has slowly spread over 35 percent of all tomato plants. Based on my observations, it started approximately four weeks ago within the center of one plant and has slowly advanced. Also, there is a very fine spider like web covering some of the browned leaf areas. I am familiar with “leaf curl” problems, but this is a new one for me.
A: From the photos and your description, I suspect spider mites. The symptom that is most noticeable is the color change on the leaves as a result of their feeding. Their tiny mouthparts pierce the leaves and remove sap. Just one mite feeding wouldn’t be noticeable but after weeks of feeding by a number of them, the change in leaf color becomes more noticeable. The fine spider-like webbing is a sign as well. Spider mites, just like many of their spider relatives, produce webbing where they live. This is also something that may go unnoticed with a small number of mites but becomes apparent with a significant population. Identifying mites often requires a 10X magnifier and it’s good to make sure you have live ones before spending time and money treating for them. Sometimes we only see the damage after they moved on. Spider mites thrive in our arid climate and can be a problem on a variety of plants. They aren’t all bad though, since some mites are predatory and feed on the pest mites. When they become a problem there are a few tactics you can use to manage them. Sprays of water, horticultural oil, or insecticidal soap are usually effective in reducing their numbers. Mites often hang out on the underside of leaves so sprays should be directed to contact them there. Make sure your plants are properly irrigated because stressed-out plants are less tolerant of their feeding damage. Spider mites sometimes become a problem after spraying insecticides. The reason is that their natural predators are often victims of insecticides and the mites are less susceptible. That is why less toxic chemicals, such as oils and soaps, are recommended over stronger products to spare the predators.
Peter L. Warren is the urban horticulture agent for the Pima County Cooperative Extension and the University of Arizona. Questions and photos may be emailed to tucsongardensage@gmail.com.
- By Peter L. Warren Special to the Arizona Daily Star
Q: We have several acacia trees that are about 12 years old. Our landscaper had described them as sweetgum acacia, but I am not sure if that is really what we have. They have grown up from an initial height of 5 feet to 15, but they are not looking healthy. Especially over the last five years, the leaves have gotten very sparse and they are often covered with small, white insects. Some of the branches have died and have no leaves at all. Our landscaper has repeatedly sprayed them with pesticide, but the white insects always return. These trees are irrigated with a drip system. Other neighbors all across Oro Valley seem to have the same problem . Also on our property we have other native acacias, which we did not plant and they are doing fine. They have the small orange-yellow colored balls and they have never been sprayed and they are not even irrigated. Should I just give up on these trees and replace them with mesquites, which seem to do fine here, or do you have other solutions for us?
A: It would be helpful to see the insects up close to be sure of the problem. Please let me know if you can bring a sample of infested leaves to my office or if I may stop by your trees and see them in person.
One likely possibility is that sweet acacias (Vachellia farnesiana) are occasionally infested with insects called whiteflies. They are very small white insects in their adult form. As immature insects they are wingless, darker in color and suck sap from the leaves, sometimes causing the tree to drop leaves prematurely. Repeated infestations can be hard on the tree, but in many cases the infestation is not severe and natural enemies reduce the population to tolerable levels. In recent years these whiteflies seem to be more common in the Tucson area, probably due to warmer weather.
Whiteflies in general have been a sporadic problem at our elevation, whereas in lower and warmer areas such as Pinal and Maricopa counties, they are a regular occurrence. I would be interested to know which insecticide your landscaper is using. There might be other options for pest management. I wouldn’t recommend giving up on your trees yet.
Peter L. Warren is the urban horticulture agent for the Pima County Cooperative Extension and the University of Arizona. Email questions and photos to tucsongardensage@gmail.com
- By Peter L. Warren Special to the Arizona Daily Star
Q: Please tell me when I can transplant two small agaves that I raised from the little ones off a large plant. I was thinking of doing it now that it has cooled off, but I thought it would be better to get your advice.
A: Agaves are easily propagated from the offsets, aka pups, or little ones as you called them. Now is a fine time to plant them. If you removed them from the parent plant by cutting the stolons (the underground branches by which they are attached), it’s a good idea to let them dry for a few days to form a callus on the cut end. Agaves do best in well-drained soil such as a mix sold for cacti and succulents. You can simply push them into the soil, although they might get a better start if you put them in a container in a shady area until they establish roots.
The root establishment can take up to four weeks. Once rooted, they will start growing and then you can apply a soluble fertilizer, but only once or twice per year. Watering should be done as often as the container dries out. It’s not great for them to stay wet all the time, so allow the soil to dry between watering. If you eventually transplant them into the ground, watering should be done less frequently. In the summer, water every 10 to 14 days unless there was rain. In the spring and fall, every three to four weeks and none in the winter.
Peter L. Warren is the urban horticulture agent for the Pima County Cooperative Extension and the University of Arizona. Email questions and photos to tucsongardensage@gmail.com
- By Peter L. Warren Special to the Arizona Daily Star
Q: I just moved to Arizona from Wisconsin. Is there any indication when the drought might end or is this long-term condition due to climate change? And if it doesn’t improve, what will be the impact for places like Tucson?
A: The drought we are experiencing has reportedly been going on for more than 20 years with no end in sight. Climate scientists predict it will likely get worse. The big challenge in the Southwest has always been a shortage of water. Even the earliest explorers thought the region was not a great place to build towns and cities, but we humans are sometimes determined to find a way. There are many articles and books on this subject, so there is no shortage of information if you’re interested in learning more.
“Cadillac Desert” by Marc Reisner is one of the classic books on this topic. Something more current would be the CLIMAS website at the University of Arizona, climas.arizona.edu, that assesses climate in the Southwest and includes research findings, blogs, and podcasts on many aspects of climate.
Peter L. Warren is the urban horticulture agent for the Pima County Cooperative Extension and the University of Arizona. Email questions to tucsongardensage@gmail.com
- By Peter L. Warren Special to the Arizona Daily Star
Q: Grasses? They are awful. What’s wrong with these landscape architects and their lack of concern for the desert and their poor plant material choices and layouts?
A: There are some native grasses that are fine for the desert and our landscapes. Extensive research has been and continues to be done to determine the best plants for our region. We even have a research operation in Tucson. It is called the United States Department of Agriculture Natural Resources Conservation Service Tucson Plant Materials Center.
You can schedule a tour if you are interested to learn more about grasses that are appropriate for our region. Google AZPMC if you want to learn more .
There are, however, other species that are invasive and should not be planted here. In some cases, these problems are self-inflicted because humans failed to see the downside to species that were once thought to be a great solution to erosion or nutrition for livestock . I like to think that nowadays we are much more careful about planting grasses that can reseed and become invasive.
Unfortunately, this only works if we are aware of the potential problems. Some grass species that are marketed as sterile are not 100 percent so and unfortunately they are popular landscape plants. I wouldn’t blame the landscape architects for all these troubles. Many of them are schooled in proper plant selection through their degrees and their experience. Part of the blame can be spread to consumers who buy the plants and nurseries that sell them.
In the end, it is something we all need to educate ourselves about when considering which plants to use no matter where we live.
Peter L. Warren is the urban horticulture agent for the Pima County Cooperative Extension and the University of Arizona. Questions and photos may be emailed to tucsongardensage@gmail.com.
- By Peter L. Warren Special to the Arizona Daily Star
Q: I have a mature Valencia orange tree that has yellowing leaves and dead end tip branches. It also has some dried yellow fruit. The tree is watered three times a week for 45 minutes each time with three bubbler type irrigation system heads at the tree drip line. Any thoughts on what may be the problem?
A: Although yellowing leaves can also indicate a lack of nitrogen, the dead end branches and your current irrigation schedule tells me the tree needs more water. If you are fertilizing three times per year as recommended in late winter, spring, and fall, the other important input is water. While your placement of bubblers is appropriate, the scheduled watering is not ideal. Citrus trees do best with deeper watering on a less frequent basis. During the summer, every 7 to 10 days to a depth of 36 inches is recommended. In the spring and fall you can back that off to every 10 to 14 days and in the winter to every 14 to 21 days.
Peter L. Warren is the urban horticulture agent for the Pima County Cooperative Extension and the University of Arizona. Questions and photos may be emailed to tucsongardensage@gmail.com.
- By Peter L. Warren Special to the Arizona Daily Star
Q: We planted this Satsuma Mandarin Orange two years ago, and last spring it had good foliage and produced two or three small fruit. But now, it appears to lose leaves on lower branches, put out new leaves on upper branches, but has not gained any new branches or height. It is on a drip system. I don’t see evidence of anything chewing on it. Any suggestions on how to help out thrive?
A: This is typical for newly planted trees. The stress of transplanting sometimes causes some leaf drop and/or fruit and flower drop. Assuming you are watering and fertilizing properly, I expect you will see new growth in the coming year. Trees typically take between two and three years to get established in their new surroundings before they show a lot of growth. This is mainly due to the large amount of root damage they incur during transplanting.
Peter L. Warren is the urban horticulture agent for the Pima County Cooperative Extension and the University of Arizona. Questions and photos may be emailed to tucsongardensage@gmail.com.
- By Peter L. Warren Special to the Arizona Daily Star
Q: What is wrong with this saguaro cactus?
A: The brown and black areas show signs of bacterial necrosis. This is a common affliction of cacti in the desert and unfortunately once it gets into the main stem and spreads that wide there is nothing you can do to fix the problem. Eventually the cactus will succumb and fall over. It would be wise to plan for that eventuality and make sure there aren’t any potential hazards such as the chance people or property could be damaged if it fell unannounced. Contracting with an experienced landscaper or certified tree professional to take it down would be appropriate if any hazards are present.
Peter L. Warren is the urban horticulture agent for the Pima County Cooperative Extension and the University of Arizona. Questions and photos may be emailed to tucsongardensage@gmail.com.
- By Peter L. Warren Special to the Arizona Daily Star
Q: Can you tell me what is going on with this sage bush? I took a sample to the nursery and was told it is new growth. The bush has been this way for a couple of years and stays on the same side of the bush. Is this a problem or just new growth?
A: New growth is correct in so far as it’s newer than the shrub you planted. Unlike normal new growth, it won’t take on the appearance of old growth after a period of time. It appears that your Texas ranger has reverted back to it’s original form, at least in part.
Many of the interesting cultivars we see in landscapes originate from some mutation with desirable characteristics from the original parent plant. These interesting mutations can be propagated into new cultivars and then introduced into the horticulture trade. Unfortunately, not all of these cultivars are stable and they sometimes revert back to the original plant. The original is likely more vigorous than the designer cultivar and could take over the space by outgrowing the shrub you planted. So if you like the one you planted more than the new original version, you can prune out the offending parts. As long as we’re discussing them, these plants are commonly called sages but are actually not related to the true sages in the Salvia genus. Rather they are in the figwort family, Scrophulariaceae.
Peter L. Warren is the urban horticulture agent for the Pima County Cooperative Extension and the University of Arizona. Questions and photos may be emailed to tucsongardensage@gmail.com.
- By Peter L. Warren Special to the Arizona Daily Star
Q: I’ve got a previously healthy stand of Mexican fence post cactus that has been infested with a white scale pest of some kind. Can you tell me what it is — and how I might get rid of it?
A:Your scale insect was identified as Diaspis echinocacti. They are found on a variety of cacti and other plants. The recommended management strategy for scale insects is a combination of integrated pest management tactics including natural enemies, physical removal, and applications of horticultural oil or insecticide. Because their outer covering protects scale insects, the ideal time to spray them is during the time in their life cycle when the young have recently emerged from their eggs and are crawling about unprotected. The timing is not always easy to determine but you have options to figure it out. Late winter is a good time to start watching. Carefully examine the infested plant to see if crawlers are present. A magnifying glass or loupe will come in handy when looking for these tiny insects. Alternatively, place double-sided tape around the cacti in affected areas of the plant when crawlers are expected. The tiny insect bodies get stuck in the adhesive. Once you see them you will have a general idea when they emerge. The next trick is to notice what else is happening nearby with your other plants. For example, what is recently blooming in your landscape? Year to year variation in insect development can be estimated by the use of phenology (the known influences of weather variations on plant and animal life cycles). By watching known phenological indicator plants you can accurately predict when particular scale insect eggs will hatch in your area in following years and thus you will be better prepared to manage the scale insects.
Peter L. Warren is the urban horticulture agent for the Pima County Cooperative Extension and the University of Arizona. Email questions to tucsongardensage@gmail.com
- By Peter L. Warren Special to the Arizona Daily Star
Q: I have a love/hate relationship with this “weed.” For about 10 years I cut it off at the ground. It came up as one puny stalk with a reddish stem and then got other stems growing next to it and I’ve seen it in other places where it volunteers near drip emitters. I always wanted a real tree in that corner but couldn’t afford it. About three years ago I thought: maybe if I let it grow and tied it up, it would get a strong enough stem to become a tree, sort of… so I did that. Looking it up on line, I thought it looked very like an African Willow. So now it is strong enough to support itself, but I really don’t feel like giving it a tree status. What the heck is it? Its perseverance has finally got my grudging admiration. It won the battle.
A: Your tree is called African sumac (Rhus lancea) and it is a very common plant in our area. They can grow to a height and width of 30 to 40 feet. Once they become large trees, some people like them for the shade they provide. They are tough and do well with little care and may be used as street trees or in places where little else will grow well. Unfortunately, they are invasive and can spread easily in urban areas. Their seeds will grow wherever there is available water. As you know, persistence is required to keep them down once they start growing. Some people report allergies to the pollen so that is another concern. It’s hard to say no to a free tree but this is one that you might consider removing given the associated problems it brings.
Peter L. Warren is the urban horticulture agent for the Pima County Cooperative Extension and the University of Arizona. Email questions to tucsongardensage@gmail.com
- By Peter L. Warren Special to the Arizona Daily Star
Q: What kind of cactus is this (pictured above, left), what are the fruits called, and are they edible?
A: It’s called Cereus repandus, the Peruvian apple cactus. It’s a South American species as you probably guessed from the name. It does well in our area except when we have a frost or freeze. The growing tips are damaged by below-freezing temperatures and need to be pruned as a result. In ideal locations protected from cold temperatures this plant may grow quite large. The fruit are edible and you may find birds, insects, and desert tortoises eating them as they ripen and fall to the ground.
Peter L. Warren is the urban horticulture agent for the Pima County Cooperative Extension and the University of Arizona. Questions may be emailed to tucsongardensage@gmail.com
- By Peter L. Warren Special to the Arizona Daily Star
Q: This is not a question about plants, but I thought you might know the answer. We enjoy sitting on the patio but haven’t been able to for several weeks. The problem is we’re out there for just a few minutes, and then our ankles and feet start to itch like crazy. I have sprayed the deck, but that hasn’t seemed to help.
A: Mosquitoes are fairly common ankle biters this time of year. While there are landscape sprays you can use for short-term effect, I recommend you use an insect repellent on your legs to see if that stops or at least mitigates the problem. The most effective repellents are those that contain the active ingredient DEET.
Peter L. Warren is the urban horticulture agent for the Pima County Cooperative Extension and the University of Arizona. Questions may be emailed to tucsongardensage@gmail.com
- By Peter L. Warren Special to the Arizona Daily Star
Q: I have a sick orange tree. One side is doing somewhat well, but the other side is dying, and the leaves are curled up. There is no sign of insect infestation. I have to water the tree every four to five days, otherwise the leaves begin to shrivel. I think the tree is about 6 years old but could be more. Originally it was on a drip system, but I stopped that about a year ago and use a sprinkler spray.
A: The tree is old enough to be established in its current location. The sprinkler you are using is likely not delivering enough water and not deep enough. I recommend you adjust your irrigation schedule to deliver enough water to reach a depth of 36 inches at the drip line once every two weeks. You can still use the sprinkler but it will not be as efficient as a drip system. More is lost to evaporation when it is airborne. You can check the depth the water is reaching by using a soil probe. The simplest kind is a three-foot piece of rebar with a handle that you can push into the ground after irrigation. It will meet resistance when you hit dry soil.
Peter L. Warren is the urban horticulture agent for the Pima County Cooperative Extension and the University of Arizona. Questions may be emailed to tucsongardensage@gmail.com
- By Peter L. Warren Special to the Arizona Daily Star
Q: When field mice eat the top tips of sweet potatoes (while still in the soil), are the tubers safe for home consumption?
A: While the practical me says just wash it off really well, I checked with our food safety microbiologist, and she says no way. The chewed part may not be the only part of the plant that the rodent touched. The problem is that the rodent may have touched its own feces or other rodent feces and if that gets anywhere on the produce, and it is not washed properly (with an actual sanitizer), it could harbor foodborne pathogens. My advice would be to put those veggies in the compost pile.
Peter L. Warren is the urban horticulture agent for the Pima County Cooperative Extension and the University of Arizona. Questions may be emailed to tucsongardensage@gmail.com
- By Peter L. Warren Special to the Arizona Daily Star
Q: What is this pretty little weed plant (above, right)?
A: Your plant is called broom snakeweed (Gutierrezia sarothrae). It’s a native plant and regarded as a weed, especially where livestock graze, because it is poisonous.
Peter L. Warren is the urban horticulture agent for the Pima County Cooperative Extension and the University of Arizona. Questions may be emailed to tucsongardensage@gmail.com
- By Peter L. Warren Special to the Arizona Daily Star
Q: I have heard from a number of people that mistletoe does not kill a tree. That might be true, but it weakens the tree so much that anything that comes along after the infestation of mistletoe will kill the tree—like our drought. I think people want to hear that it doesn’t kill the tree so they don’t have to act on ridding the tree of it. Or maybe people don’t care that much about their trees. Even the Rillito River Path trees have a lot of it in them, and the city pays to plant and water the trees.
A: There are many species of mistletoe and they are parasitic plants. In general, the species we are familiar with in the low elevations of the Sonoran Desert attach to their host plant to absorb water and nutrients. The healthier the host plant, the healthier the parasitic mistletoe that depends on it. If the host plant is suffering from other problems, such as drought, the mistletoe can take enough water and nutrients to weaken the host and that can lead to the death of the host. A common species in our area is called mesquite mistletoe (Phoradendron californicum). This is a native plant that has a place in our desert ecology in that it provides food and shelter for some animals. The birds that eat the seeds will spread mistletoe by pooping them out in other trees along with a dollop of their own brand of fertilizer. It would be impossible to eradicate mistletoe from our environment because it of the way it is spread by birds. It would also be hard to generalize about the relationship between people and mistletoe. I am fairly certain there are a few different reasons why mistletoe is allowed to thrive on landscape trees. Depending on the person, these may include the knowledge that it is food for birds, that it’s not always easy or affordable to cut it out of every tree, and that there is an endless supply of this plant in the open desert from which it can spread. I am familiar with the city’s lack of resources and I expect they are doing the best they can with limited staff and funds to manage trees and other plants on public property.
Peter L. Warren is the urban horticulture agent for the Pima County Cooperative Extension and the University of Arizona. Questions may be emailed to tucsongardensage@gmail.com
- By Peter L. Warren Special to the Arizona Daily Star
Q: How can I get rid of the squirrels that are destroying my backyard? They have three huge (apparently connecting) holes around the large palo verde tree. They keep the gravel all messed up with their digging. Of course, my cat (who is an indoor cat) loves watching them from the door. The chipmunks have many holes around a large cholla on the bank outside the front wall, so I assume that is where they are coming from.
A: Round-tailed ground squirrels are not likely something you can eradicate. As you noticed, they can migrate from outside a wall by digging or climbing if it’s not made of slippery material. The best strategy is an integrated approach that includes systematic destruction of their habitat, trapping to reduce the population, and protecting the plants you like best with some sort of fencing. Since they are fairly small, using hardware cloth with smaller holes that can be buried a few inches into the soil may help. Since they climb, this means you also have to protect from that likelihood with either a cover or lining your barrier with flashing or some other material on which they cannot get traction. You can contain them but you can’t stop them.
Peter L. Warren is the urban horticulture agent for the Pima County Cooperative Extension and the University of Arizona. Questions may be emailed to tucsongardensage@gmail.com
- By Peter L. Warren Special to the Arizona Daily Star
Q: My father has a tangelo tree that will sometimes have a second bloom in the summer. This year on one of the branches there are two grapefruit! Usually I would think if there is another fruit it would come from a branch that sprouted from below the graft but this did not. He picked and cut one open and the flesh was a very light orange and tasted like a bland tangelo.
A: The tangelo is a hybrid citrus created by crossing a tangerine with a pomelo or grapefruit. Occasionally hybrids or part of them revert back to one of the original parents by producing plant parts such as foliage, flowers, or fruit that more resemble the parent plants. These growths are sometimes referred to as a ‘sport.’ So the odd fruit is likely a sport but probably something other than a pure grapefruit. Hopefully, they taste good. If not, you can prune that branch out of the tree or just let it be.
Peter L. Warren is the urban horticulture agent for the Pima County Cooperative Extension and the University of Arizona. Questions may be emailed to tucsongardensage@gmail.com
- By Peter L. Warren Arizona Daily Star
Q: How do you keep bees out of the hummingbird feeders effectively enough that the little hummers have a chance to feed? Despite their aggressive nature, it seems that our hummers don’t want to challenge the bees. What to do?
A: Bees are seeking nectar and water for the same reasons as the hummingbirds and they both prefer actual plant nectar to sugar water if they can get it. I recommend providing a variety of flowering plants for the bees to distract them from your feeders. Hummingbirds prefer flowers that are tubular in shape but bees can’t access the nectar in these because they lack the long tongues of hummingbirds. Bees would more likely be found on plants that have a wide-open bloom with a place for them to land and access the nectar and pollen up close. Sunflowers are an example of the shape they prefer.
Peter L. Warren is the urban horticulture agent for the Pima County Cooperative Extension and the University of Arizona. Questions and photos may be emailed to tucsongardensage@gmail.com.
- By Peter L. Warren Arizona Daily Star
Q: I have two well-established lilac bushes that always did well with minimal care until about two years ago. I used to water them for 2 to 3 minutes every day, but stopped doing that at one point. When I realized that they were getting stressed I started watering them again — once a week for 20 to 30 minutes. That was a year ago. But they haven’t recovered. They’ve had mildew on the leaves for the last year or more. They grow well, but most of the leaves get mildew and wither up. Now I’m watering them every day for 2 to 3 minutes again. Am I overwatering now that it’s November? What can I do to help them recover at this point? The house is about 50 years old, we’ve been here 14 years, and so the lilacs could be quite old.
A: Non-native shrubs such as lilacs do best when watered infrequently and deeply. The recommended schedule is once every seven to 14 days in the summer to a depth of 24 to 36 inches. In the spring and fall you can reduce this to once every 10 to 21 days and in the winter every 14 to 21 days. Powdery mildew can be a problem in certain situations when the climate is suitable. Like any successful disease story, you need a susceptible host, the presence of the disease pathogen, and a suitable environment. If you were planting a new lilac I would encourage you to select a mildew resistant variety. To prevent an infestation, the first thing to do is remove any diseased leaves from the ground or on the plant. This will prevent the disease from overwintering nearby and spreading to new growth. Second, you can selectively prune your lilacs to provide space between the branches for air circulation and sunlight penetration. Dense areas will favor the infection. There are also fungicides you can use to spray the mildewed leaves. Choose a fungicide specifically labeled for mildew and spray according to instructions. Typically, they recommend beginning to spray when new leaves are emerging.
Peter L. Warren is the urban horticulture agent for the Pima County Cooperative Extension and the University of Arizona. Questions and photos may be emailed to tucsongardensage@gmail.com.
- By Peter L. Warren Arizona Daily Star
Q: My tomatoes show an unknown leaf disease that has slowly spread over 35 percent of all tomato plants. Based on my observations, it started approximately four weeks ago within the center of one plant and has slowly advanced. Also, there is a very fine spider like web covering some of the browned leaf areas. I am familiar with “leaf curl” problems, but this is a new one for me.
A: From the photos and your description, I suspect spider mites. The symptom that is most noticeable is the color change on the leaves as a result of their feeding. Their tiny mouthparts pierce the leaves and remove sap. Just one mite feeding wouldn’t be noticeable but after weeks of feeding by a number of them, the change in leaf color becomes more noticeable. The fine spider-like webbing is a sign as well. Spider mites, just like many of their spider relatives, produce webbing where they live. This is also something that may go unnoticed with a small number of mites but becomes apparent with a significant population. Identifying mites often requires a 10X magnifier and it’s good to make sure you have live ones before spending time and money treating for them. Sometimes we only see the damage after they moved on. Spider mites thrive in our arid climate and can be a problem on a variety of plants. They aren’t all bad though, since some mites are predatory and feed on the pest mites. When they become a problem there are a few tactics you can use to manage them. Sprays of water, horticultural oil, or insecticidal soap are usually effective in reducing their numbers. Mites often hang out on the underside of leaves so sprays should be directed to contact them there. Make sure your plants are properly irrigated because stressed-out plants are less tolerant of their feeding damage. Spider mites sometimes become a problem after spraying insecticides. The reason is that their natural predators are often victims of insecticides and the mites are less susceptible. That is why less toxic chemicals, such as oils and soaps, are recommended over stronger products to spare the predators.
Peter L. Warren is the urban horticulture agent for the Pima County Cooperative Extension and the University of Arizona. Questions and photos may be emailed to tucsongardensage@gmail.com.
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