By Jeff Gore, research entomologist and Don Cook, research entomologist, Mississippi State University
I know it is a little early in the year, and very little if any rice is heading at this time. However, it is not too early to start thinking about rice stink bugs. We have seen both extremes over the last two years in terms of rice stink bug numbers. If you remember, 2011 was one of the worst rice stink bug years we have seen in a long time. Last year, they were almost non-existent. Based on what we are seeing this year, we are somewhere in the middle.
We swept wild hosts around Washington and Bolivar counties this week. Numbers ranged anywhere from 0 rice stink bug per 10 sweeps up to 11 per 10 sweeps. Those numbers may not seem too bad, but we had very few samples that didn’t catch any stink bugs. The majority of samples ranged from 2 to 6 per 10 sweeps.
Again, those numbers may not seem too high, but when you consider the vast areas of grasses along roadsides and other fallow areas, the fact that stink bugs seem to be scattered all across the landscape, and the low rice acreage this year, some fields are likely to be exposed to high stink bug numbers once the rice begins to head.
The main thing that can be done now is try to eliminate as many heading grasses as possible on the farm. Once they move into rice, insecticides are our only management option for rice stink bug. The threshold in the insect control guide for rice stink bug in rice is 5 per 10 sweeps during the first 2 weeks of heading and 10 per 10 sweeps after that point. We recently had a graduate student , Mr. George Awuni, who did his research on rice stink bug injury in rice.
Based on his research, I believe that the threshold of 5 stink bugs per 10 sweeps should be extend at least until the majority of the crop has reached the hard dough stage. George’s research showed that rice stink bug causes similar levels of injury or peck at the milk and soft dough stages. In most situations, it is going to take longer than two weeks for the majority of the crop to reach the hard dough stage, especially in rice with lower seeding rates (i.e. Clearfield or Hybrid rice).
We are currently doing research to determine if hybrid rice is going to be susceptible to peck for a longer period of time than conventional varieties. It seems logical that hybrid rice would be susceptible for a longer period of time because of the increased number of tillers, and differences in maturation of those tillers.
Until we can determine if this is the case or not, I would suggest being a little more cautious on hybrid rice to minimize quality losses from rice stink bug. It is because of these issues that I am leaning more toward thresholds based on grain maturity rather than weeks of heading and those changes will be reflected in the insect control guide next year.
Now for the important part: What do we use to control stink bugs once they are in rice? The pyrethroids have continued to work well throughout Mississippi, but rates at the upper end of the range should be used for high populations. All of the insecticides labeled for rice stink bug in rice should work well, but multiple applications may be needed in many situations.