Rice Water Weevil and Rice Stink Bug Update

Jeff Gore, Research and Extension Entomologist
By Jeff Gore, Research and Extension Entomologist June 17, 2011 07:00

Rice water weevil densities appear to be very high at some locations in Mississippi this year. I looked at two fields over the last week where adult feeding was actually affecting plants. Adult numbers were running as high as 4-5 weevils per plant.  Neither one of those fields had an insecticide seed treatment.   The fields treated with Cruiser seemed to be holding up fairly well, but with the high pressure we are seeing more feeding scars behind the Cruiser than we usually see. Dermacor seed treatment does not have much activity against the adults, so some fields treated with Dermacor may see some significant feeding from the adult weevils. Adult feeding generally does not affect rice yields, the big yield losses come from larval feeding on the roots. However, in the two untreated fields, plants were significantly stunted and the amount of defoliation seemed to be holding the plants back significantly compared to adjacent rice with a seed treatment.  We have taken cores from several fields across the Delta and most samples are running in the high range in terms of larval densities. However, Nathan brought us some cores from one of his trials and weevil numbers were fairly low. Based on what we have seen so far, the high weevil populations appear to be widespread, but somewhat scattered. In general, adult feeding will not negatively impact yields once the rice is flooded. The seed treatments seem to be doing their job on the fields that we have sampled, but if adult feeding gets too bad an insecticide application may be waranted. We have seen that none of the insecticide seed treatments are bullet proof in terms of eliminating larval densities, so a well timed pyrethroid application may help to take some pressure off of the seed treatments.  Again, it is not that the seed treatments are not doing what they are supposed to do because they are. It is just a case of sheer numbers we are seeing in some fields this year. If not for the seed treatments, we would likely see some significant yield losses in many fields this year even with foliar insecticide application. 

In terms of rice stink bugs, we have a graduate student that is monitoring rice stink bug populations in wild hosts. As of right now, rice stink bug populations appear to be about 10 times higher than they were last year at this time on grasses that are heading. Last week he was averaging over 100 stink bugs per 10 sweeps in wild grasses. He is collecting high numbers on all grasses that are heading as well as pigweed that is flowering.  I would urge growers to keep the grasses mowed around their rice fields before the rice begins to head. This likely won’t eliminate rice stink bug problems later, but it will help to reduce the populations some before they move into the rice.

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Jeff Gore, Research and Extension Entomologist
By Jeff Gore, Research and Extension Entomologist June 17, 2011 07:00
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