Root Weevil Control At Last?
by Warren Berg, Kent, Washington
If you are as tired of looking at all those chewed rhododendron leaves as I am, you will be happy to know there is a new chemical control that may be the answer to our problem. This past season (1976), I had the opportunity to test a product called Orthene which is put out by the Ortho Division of Chevron Chemical Company. Hopefully it will be cleared for specific use on rhododendrons this year. It was developed about 11 years ago, but has taken this long to test and get approval for public use. Orthene is a systemic that is safe and easy to handle. When applied as a full-cover spray to foliage it is very effective against root weevils in the adult, or beetle, stage. Its effect on the larval stage is still under study.
Dr. Lee Campbell of the Western Washington Research and Extension Center, has worked with Orthene for some time. In 1976 one of his tests was on a plot of rhododendrons that I grow in the Kent Valley. The results were very good, showing a feeding reduction of 99, 97, and 94% over the untreated check at application rates of 1, 3/4 and 1/2 lbs. actual / 100 gallons, respectively. (1 lb. actual = 1 level tablespoon of 75 S or 1½ tablespoons of the 15.6% liquid per gallon of water.)
My tests were made in two other areas of Western Washington at the same rates. The results were almost identical to Dr. Campbell's. Applications were begun on June 1st and continued at 30-day intervals for 5 months. Usually this would be sufficient, however, in 1976 we had a very long warm autumn in the Seattle area and weevils continued active feeding until the middle of November, so treatment should have continued for 2 more months.
We will, no doubt, never eliminate the root weevil, since it is impossible to keep them from moving in from surrounding native plants and with newly acquired specimens, but there should be a big improvement in the appearance of our rhododendrons for some time to come if this new tool is used.