Q: I am starting to see some odd growths on parts of my oleander hedge. I understand they are galls but I am not sure what to do about them.
A: Oleander (Nerium oleander) is one of the most popular evergreen shrubs in Arizona and the gall disease you are seeing is widespread. Oleander gall is caused by the bacterium Pseudomonas syringae savastanoi.
The galls occur on twigs, branches, leaves, flowers, and seedpods. Initially galls appear as small protuberances that subsequently develop into wart-like growths with roughened, fissured surfaces. Galls vary in size but average about a half to 1 inch in diameter. Large galls are usually made up of several small galls that have grown together.
Galls are the result of the growth and multiplication of the bacterium. The bacteria enter and infect oleanders through leaf and blossom scars, wounds produced by pruning, frost injury, and natural openings. Rain, sprinkler water, and pruning tools can spread bacteria from diseased to healthy plants.
When purchasing oleanders, examine them carefully to be sure they are free of galls. The vast majority of nursery stock is free from disease but prevention is always the most effective method of disease control. For diseased oleanders, prune out infected plant parts and apply disinfection solution (a 10 percent solution of household bleach) to each cut surface.
Always dip pruning tools in the disinfectant solution between cuts to reduce the possibility of spreading the bacteria. Pruning operations should be conducted during the dry seasons to avoid infection of wounds. Avoid sprinkler irrigation. Severe infection of large shrubs is difficult to control by selective pruning. If the entire shrub is cut down, the new succulent growth is extremely susceptible to infection. In certain situations, removal of the diseased plant and replanting may be the best method of control.
Q: What are the luminescent critters found in the Tucson region? Back East there are fireflies or lightning bugs, but I have not seen them here.
While taking a predawn hike in Sabino Canyon several years ago, we spotted a small wingless luminescent crawling insect on the roadway. It was about a half inch long with a termite-like appearance, and put off a light bluish light. A few dark nights ago looking out past our back fence line on the ground I spotted my second luminescent critter, I think. It was an LED-like spot of white-bluish light that persisted for several minutes. Our home is at about 2,750 feet in elevation in north Tucson. Any suggestions as to what we are seeing? Sober on both occasions.
A: Lightning bugs are one of my favorites from back east. We used to feed them to toads and watch them light up in their bellies, making the toads glow. What we have in the West are a couple dozen other species, although none as common as the ones back East.
What you were likely seeing are the immature beetles of one of these species. According to retired bugman Carl Olson, now is a great time for people to see the larval stage that usually has an eerie green light. Most of the ones seen in Rincons and Catalinas are pink as you will see in his photo of Microphotis dilatatus from the Vail area.
Q: We have tons of mesquite pods and they are a huge pain. A yard guy we met said he could spray the tree next April and that would take care of it. Then I read that spraying doesn’t work well on Mesquites because the timing has to be accurate and the pods mature over too broad a time period. Also, our tree is huge and I worry about the spray harming nearby plants. What do you say?
A: The spraying doesn’t work well on most trees, it is costly and time consuming, and it could harm surrounding plants and other organisms, depending on the chemical used and if not done correctly.
There are many factors at play including timing, environmental conditions, and making thorough applications. Due to the gradual development you mentioned, it might take repeat sprays to do a sufficient job. It would likely be more environmentally sound and cheaper to hire someone to rake the pods. Another alternative is to harvest the pods before the monsoon begins and have them milled into mesquite flour. Mesquite flour is a popular alternative to wheat flour among local and heritage foodies and a nice gluten free alternative for those that require one in their diets. Milling events are available in various locations during the harvest season and they charge a nominal fee to grind them for you.Check out DesertHarvesters.org for one group that does this and instructions on how to harvest.
Q: I have many Penstemon parryi seedlings that have been growing through the summer. Within the last two weeks they have begun to develop “burned” scale patches on the leaves that are accompanied by black “seedy” areas. The black beads could be the seeds for future plants, except that these haven’t ever bloomed. The black beads don’t appear to be adult insects, but could be eggs. Do you have any idea what’s going on?
A: Very small caterpillars, the chalcedon checkerspot (Euphydryas chalcedona) most likely, are eating your Penstemon plants and the black “seeds” are actually caterpillar poop or frass as we call it when it comes out of insects.
The plants will likely be OK regardless and you are supporting a healthy butterfly population but if you see active caterpillars chewing your plants to the ground you can spray the leaves with Bacillus thuringiensis, aka Bt. This organic compound will make the plant poisonous to the caterpillars that eat it and will not harm other organisms on the plant. There are multiple strains of Bt, so if you choose to buy some, make sure you are getting the strain designed to kill caterpillars.
