Q: I found these insects eating my potato leaves. What are they and what can I do about them?
A: The insects are called tortoise beetles because of the shape of their exoskeleton, which resembles a tortoise shell. They are plant-feeding beetles and can be an occasional pest on a variety of vegetables and weeds. The good news is the vegetable plants can handle the holes in the leaves that they make so you really donβt need to do anything to manage them. More good news is that these insects are helpful in keeping some weeds in check and have, in some cases, been raised and released to manage specific weed species.
Q: Over the course of about 5 years we have lost three 20- to 30-year-old Australian willows (we think thatβs what they were) on the west side of our home. We also lost a vine on the wall surrounding the tress that has been here as long as we have, which is about 18 years. The plants in the flowerbeds around the trees such as verbena, mint and lantana also died. Irrigation has never been an issue. Our tree trimmer suggested that we might have a fungus in the earth around the trees. Coincidently, we have noticed mushrooms popping up in this area after a rain. They are the size and shape of an adultβs finger and are quite malodorous. Can you tell us how to confirm this suspicion and more importantly how to determine what is killing our plants and what we can do about it? The west side of our yard is a dead zone and I am afraid whatever is causing this is spreading.
A: Australian willows (Geijera parviflora) are evergreen trees that grow up to 25 to 30 feet tall. Branches sweep up and out and long, narrow leaves hang down giving the appearance of a weeping willow. Small white flowers are produced in the spring and fall. Because they are on the west side of your home, it would be important to screen them from western afternoon sun because their bark is susceptible to cracking from sunscald. I wonder if the other plants you mentioned were being screened by the trees that died and then they suffered a similar fate from being over exposed to the western afternoon sun. Fungi may be seen after a rain if there is any organic matter in the soil. We often see this in mulched areas or areas with trees that allows organic matter and water to mix. Your area may have built up some organic matter from the trees being there so many years. Our desert soils donβt usually have much organic matter. Without seeing the fungus in question, I suspect you are seeing what is called stinkhorn fungus. These are more common east of the Rocky Mountains but can be seen in the west. Their distinct shape, smell and orange color make them easy to spot. Fortunately, there is nothing bad to say about them except that they stink. If you donβt want to marvel at their random occurrence, you can simply rake them into the soil or dispatch them to the trash bin. I recommend planting some tougher plants that can handle the western sun on the west side of your house. If you need recommendations, please contact the Pima County Extension Office. The Master Gardener Volunteers would be glad to help.
Q: About 1 Ζ years ago I purchased four white flowering oleander plantsβthe tall not the petite variety. They have been deep watered regularly, fed in May and have only grown about 1/16th of an inch. They have original leaves, have flowered but have no new growth or leaves. My hope was these would grow quickly in front of my screened in porch. I have other oleanders in the back and side yards that are huge, some of which I have planted. I wonder if the soil is old as I have lived here 31 years and the home was built in 1968. There had been huge juniper trees that died over the years. Perhaps this area of soil is not rich enough to support new growth. Iβve considered moving the oleanders and putting in birds of paradise.
A: Many woody plants will take up to three years to grow a lot after planting so I think you should give it more time. Another factor could be the roots of your old junipers. If they were cut down recently and simply cut at the soil level, the stump and roots are still in the ground. That means the roots will decompose over time and in the process take nitrogen from the surrounding soil for that process, leaving less for your new plants. Not knowing the exact situation with your junipers, I am doing a little guesswork here so it would be good to have more information about the timing of their demise and the planting of your oleanders. Having your soil tested is a good idea if you are still concerned about this. There are a few labs in the area that will test it and you can call the Pima County Extension Office to ask for their contact information.
Q: I have elm leaf beetles chewing up the leaves of my Siberian elm tree. Is there an organic solution to this problem?
A: The elm leaf beetle is a serious pest of American and European elm species and less so on the Siberian elm. Since there are other pests that can cause similar shot hole damage as these beetles, it is good to be sure. The beetles are one-quarter of an inch long, olive-green with black, longitudinal stripes along the margin and center of the back. While the adult beetles chew holes through the leaves, the larvae skeletonize the leaves by feeding on the green surface tissue of the leaves. It is important to take good care of elm trees to make them able to withstand some feeding damage. A healthy tree can handle up to 40 percent defoliation, especially if this threshold is reached toward the end of the growing season. We are fortunate to have a few natural enemies that parasitize these beetles. A fly species and two wasp species are often found where these beetles thrive and as long as we can refrain from using insecticides against the beetles, these beneficial insects should do well and help keep their population under a manageable level.
