I have seen many palo verde trees impacted by the palo verde root borer: truck and limbs turning golden brown, leaves drop. All these symptoms develop after the damage has been done. But this year I ran across something I have only ever described after the palo verde begins rapidly declining.
As the agaves begin wilting out there, I am getting more and more questions about the proper treatment for prevention. The first questions is whether or not to treat. Not treating you take a risk of infestation, which may or may not happen this year or even next year. However, if infested, consider the agave a goner. If you have a large number of plants you want to protect, it can be quite costly to treat.
The key to successfully treating agaves is in the timing of your pesticide applications. Your first application of the season needs to be just prior to insect activity in the spring, which is most often dependent on soil temperatures. As temperatures increase in March, activity of the agave weevil will begin. If using a ‘protective’ systemic insecticide, you want to make your application before the weevil’s activity. Contact insecticides labelled for drenching can also be helpful in killing existing infestations. Make sure both chemicals control Coleoptera insects, otherwise you will waste time and money with your treatments.
Follow-up with a second application of the systemic insecticide just before the residual runs out. Most professional products provide up to 90 days control if used at the high rates. Contact insecticides often only last 1-2 weeks in the high temperatures so don’t count on them for control for more than a short period.
If the agave weevil does feed on an agave, you won’t know it until the rot begins to destruct the agave, most often in the mid to late summer in the Phoenix area. If they are wilting, don’t bother treating these plants. Remove the agave along with the soil around the root ball and try not to plant back immediately. When you do replant, treat the new agave with the systemic insecticide for future protection.
If you would like specific chemical recommendations and the proper timing of your applications, please call me for a customized management program. Remember to keep them healthy- careful not to overwater them throughout the year!
Every summer, I get calls from landscapers in Phoenix about Agave suddenly wilting and dying. It has to be a fungus, right? Well, sort of, but it is actually a rot that has been caused by the feeding of an insect called the Agave Snout Weevil. The Agave Snout Weevil enters the plant at the base where the larva eats the tissue, inviting decaying organisms also to start working on the Agave.
Once the larva has done its damage, the adult- that’s the one with the ‘snout’, will move on to lay eggs on its next victim. The weevil loves the Agave americana, Agave weberi and other larger agave species. Though multiple generations per season can sometimes occur, it is best to treat in the fall and again in the late spring when life stages are most susceptible. Preventative treatments are your best bet. If you see wilting, remove the plant and surrounding soil immediately so they don’t move to other nearby Agave.