Insect Infestation On Sweet Acacia Trees - Knowledgebase Question

Peoria, AZ
Question by joedsw
November 29, 1999
My trees are infested with spidermites, white flies, thrips, and we think they have some sort of boring insect as well. The trees are 15 years old and we would like to save them. In addition to the problems with the acacias most of the other trees and shrubs on the site have spidermites. I've had advice that we do a Merit soil drench treatment to posibly remedy the problem. Since Merit is a systemic the label indicates 60 days for full effect. I would like to know if the Merit treatment is the way to go or is there a better solution? Also will the trees survive 60 days?


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Answer from NGA
November 29, 1999

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I suggest you contact a professional arborist or the Master Gardeners at County Cooperative Extension office, 4341 E. Broadway Rd., Phoenix, 602-470-8086, ext. 301.You can bring in a sample of the boring insect or plant parts that show the symptoms. There is a Master Gardener satellite office near you in Sun City West. The main office number can provide you with the address and hours. I hope this info helps! with the beneficials coming in to control the bad guys.

As a tree grows, its new roots tips, where nutrients are being absorbed, spread out laterally. If you are watering only within a four-foot area at the base of the tree, it's not really being watered effectively. Expand your watering zone out PAST the tree's canopy. As the tree grows, continue expanding that water zone. If you have an irrigation system, you need to move the emitters out. If you use a hose, just drag it out further. In any case, water slowly and deeply to ensure water penetration.

When leaves completely dry out, the problem is often salt burn. This is common in our area with low rainfall, alkaline soil and water high in salts. Browning usually occurs on the old leaves first. This excess salt accumulates in the leaf edges, where it kills the tissue and the leaf dries out and turns brown. It's important to water deeply, slowly and infrequently. At least once a month, water deeply enough to "leach" or push salts below the root zone. Frequent, light "sprinklings" allow salts to accumulate in the top layers of soil, where the roots are, which is bad news, as the salty soil can actually draw moisture out of roots.

Similar symptoms occur when too much fertilizer has been applied. (Note that even if you didn't apply fertilizer directly to this plant, it could have absorbed it from elsewhere, such as turf, which is often heavily fertilized with nitrogen.)

When fertilizing, moisten the soil well before and after application. Follow package directions exactly. (A little bit more is never better!) Fertilize just before the growing season begins (late February-early March) and lightly again in the fall (mid- to late September). Fertilizing during the hot weather isn't a good idea because the potential for burn is increased.

I don't think the soil drench treatment is the solution at this point. I suggest you contact a professional arborist or the Master Gardeners at County Cooperative Extension office, 4341 E. Broadway Rd., Phoenix, 602-470-8086, ext. 301.You can bring in a sample of the boring insect or plant parts that show the symptoms. There is a Master Gardener satellite office near you in Sun City West. The main office number can provide you with the address and hours. I hope this info helps!

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