Q. I have two large Mesquite trees in my yard and both drop a huge quantities of seed pods annually. I have heard that Mesquites can be sprayed with the same chemical used on Olive trees to prevent them from setting fruit, does this material work on Mesquite trees? If so, what is the optimal time of year to spray, what is the name of the spray and can I purchase it at my local nursery?
A. Theoretically you can. The problem is two-fold. Technically the chemical to be used falls under the label requirements for a pesticide even though it really doesn’t kill a pest. Because it is categorized as a pesticide, it falls under the legalities of pesticide use.
If mesquite trees and the purpose of preventing seed pod formation are not on the label, no one can legally recommend it for that use or it violates federal law.
Secondly, to prevent pod formation from the flowers you would need to know the right timing and the right dosage to get results. Neither appear on the label to my knowledge. If someone were to attempt to control the pods, that person would have to "guestimate" what the right concentration would be (how many tbs or teaspoons per gallon for instance) and the right stage in flower and pod formation to make the application.
Some of these chemicals have to be applied only when the flowers are open. Since the flowers don’t all open at the same time, the tree would have to be sprayed multiple times.
Some types of chemicals that cause flower drop, or prevent pod or fruit formation, have to actually land inside the flowers to cause the flower, pod or fruit to abort. Other chemicals can be sprayed before flowering, taken up by the plant and systemically moved around inside the tree where it can cause the flower to abort.
So even if I was legally permitted to tell you to try it, I would not know what concentration to use unless it is stated on the label. The timing of the spray is pretty straight forward. The label would tell you to spray when the flowers are open or at some other time before or during flower development.
You should be aware that some of these products can damage or even kill other plants if this type of spray were to land on them. So theoretically it will probably work if you knew the right dosage and time of application but I am not recommending it.