New Solution for Weevil Problem
E. White Smith
Weevils, weevils, weevils. We all have some be it the black vine weevil, the strawberry root weevil, or the obscure root weevil. And we really do not care which one it is. We just don't want them eating our rhodies. Root weevils do two kinds of damage. The real obvious thing they do is take notches out of the rhododendron leaves and that is what most people see and object to. The less obvious damage that root weevils do is produce larvae which eat the roots of the plants. Eating the roots can and does kill plants or makes them so weak that they die from other things like a small lack of water.
The only good chemical we have had available for years was Orthene™1. For root weevil control with Orthene™ the plants needed to be drenched. It also needed to be used over and over and over. Drenching might kill the larvae. And if you don't kill the larvae you will have adults eating the leaves and laying eggs to make more larvae. Commercial growers have had another chemical that really works well - Talstar™2. Talstar™ was originally registered for use on termites and it was very, very good. It also was used to control ants where they were a problem. It provides long-term protection from ants, crickets, ticks, fleas, fire ants, chinch bugs, armyworms, termites, mealybugs and weevils plus many more insects.
Talstar™ is a synthetic pyrethroid, low odor chemical that comes in two different forms: granular at 0.20% active ingredient and as a liquid concentrate at 7.9% active ingredient that was sprayed on (cost about $125 for 3/4 gallon). Both work very well on root weevils. Talstar™ itself is not available to the public. But now you can get the same thing with a different name. The chemical name is bifenthrin or sometimes it is listed as Bifen IT. I went to Home Depot and found this chemical in two products: Ortho® Home Defense® Max® at 0.05% for a 24-ounce ready-to-use sprayer at $4.99. Ortho also has a concentrate called Ortho® Ortho-Klor® Termite & Carpenter Ant Killer Concentrate at 2.4% active ingredient for $38 a quart. Yes, $38 seems to be a high price, but this chemical is so good that you will get rid of root weevils (or almost), whereas Orthene™ really did not do a good job. The "ready-to-use" product probably is not a good buy because you would need to use a lot of it at a time to get control.
The modern way to control pests in the garden is to use a product that does the job the first time. With Talstar™-type products you only treat the plants once (or at least not very often) and only the ones that have a problem. Never spray the entire area, just the damaged plants and the groundcovers surrounding them. Talstar™ and the chemical bifenthrin are said to be very safe products and have a low toxicity. But it is bad for fish so keep away from flowing water. Again these products are a "synthetic pyrethroid." Pyrethrums are natural insecticides produced by certain species of the chrysanthemum plant.
Like most rhododendron growers and hobbyists we had weevils at Bovees Nursery. But not any more. There will always be some around because they can come in from the neighbors, but with only a few treatments we are free of this pest. I have not used an insecticide of any kind for the last two years (twice with Orthene™ in the greenhouse for aphids is all). We also spend quite a lot for wild birdseed and the little birds do a great job of insect control. Birdseed is a lot better than spraying insecticide any day.
1 Orthene™ is the trademark name for the chemical acephate and is an Ortho® product.
2 Talstar™ is the trademark name for the chemical bifenthrin and is an Ortho® product.
E. White Smith is a member of the Tacoma Chapter and the Portland Chapter and, with Lucie Sorensen-Smith, runs the Bovees Nursery in Portland, Oregon.