By Nick Bateman, Gus Lorenz, and Ben Thrash, Extension Entomologists
Rice stink bugs have been relatively quite so far this year. We are still seeing a large amount of rice stink bugs, although mainly nymphs, on turn rows feeding on native grasses. We have heard of a handful of fields that were either right at threshold or slightly above and were treated, but this has been the minority. While our earliest rice may not be hit hard by rice stink bugs like we see in most years, our later planted rice will most likely deal with high rice stink bug pressure.
When sampling for rice stink bug, time of day and sweeping technique is critical. Rice stink bugs become very flighty and in some cases will leave rice fields during the heat of the day. The best times to sample for rice stink bug are from daylight until 11:00 am as well as 5:00 pm until sunset. They will be higher in the canopy and are not as prone to fly during these time periods. If sampling must be done during the day, be aware you may only be catching 60% of the rice stink bugs that are actually present.
Sweeping technique is a major factor in monitoring rice stink bug populations. We have changed our recommendation on how to sweep for rice stink bugs from doing 180 degree sweeps to 6 foot sweeps. A 6 foot sweep is easier and more consistent than a 180 degree sweep. When sweeping heading rice, it is important to keep the sweep net level with the top of the canopy where the heads are present. Move at brisk pace with multiple steps in between sweeps. When counting rice stink bugs, we combine both nymphs and adults for a total count.
The current threshold for rice stink bug in Arkansas is 5 rice stink bugs per 10 sweeps during the first two weeks of heading and 10 per 10 sweeps during the second two weeks of heading. The first threshold is to protect from yield loss while the second threshold is to protect growers from peck. We have reevaluated this threshold for rice stink bug extensively over the past 5 years. We started this work when surrounding states lowered their early season thresholds. Our work suggest that our current threshold is correct.
Multiple products are labeled for control of rice stink bugs. Our recommendation is to use the cheapest Lambda-cyhalothrin product that growers can find. Other products like Tenchu (dinotefuran), Sevin (Carbaryl), and Malathion do provide control of rice stink bug, but it does come at a major increase in cost to the grower. Applications should only be made once threshold level rice stink bugs are present in the field. Over the past several years, we have heard about insecticide applications going out with a fungicide application when the rice is booting. We have done several studies exploring this timing, and we see no benefit at this timing. In most cases this can increase rice stink bug numbers by eliminating natural enemies in the field. Applications can be terminated at 60% hard dough (straw colored kernels). Our work shows that after 60% hard dough no more yield loss or peck can be caused by rice stink bugs.