Question of the Week
Answer: There are two species of chestnut weevil--the 'lesser' and the 'greater,’ and though the life cycles are slightly different, the control methods are the same. Only one pesticide (see below) is labeled for treatment of chestnut weevil, so the best way to control their proliferation is through good sanitary practices. Every fall, be certain to collect all burs, nuts, and leaf matter from under chestnut trees and burn them. Try to collect nuts within one or two days of falling from the bur (if not before).
As soon as possible after harvest, treat nuts by putting them in 120-degree (Fahrenheit) water for 20 minutes. This process kills the egg/small larvae but does not affect the viability of the seed. If the temperature is too low (less than 117 degrees F), the weevil will not be killed. If the temperature is too high, you will kill the embryo and, thus, the seed.
Because the weevil spends pupation and even part of adulthood in the soil under the tree, it’s possible that light tillage twice (or more) a year—once in spring and once in late summer (or sometime before the nuts are ripe in fall)—might help with control. However, this is not a proven method; we’re suggesting this as a possibility because it works with other weevils in this same family (cucurlionidae), including the plum curculio, a major pest of fruits in the eastern United States.
If you decide to use an insecticide, be aware that the only insecticide labeled for chestnut weevil control is carbaryl (Sevin), and you’ll have to have a sprayer capable of spraying up and through the tree canopy. Moreover, insecticides have proven effective only when applied to adults during the mating and early egg-laying period. For small chestnut weevils, this is mid-August to early September. Spraying should begin when adult weevils begin arriving in the tree crowns. Spreading a large sheet on the ground and shaking branches is a good way to monitor weevil presence (weevils have a habit of dropping to the ground whenever they are disturbed). Spraying should be done when the weevils are active, i.e., on warm, calm days. The interval between spray applications should range from three to seven days depending on weather and the presence of weevils. Two to four spray applications per season should be sufficient to provide adequate control.
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