7/26/2011 8:54:30 PM
Originally posted June 17, 2011 by Natalie Hummel on Louisiana Rice Insects
It’s funny how when you work a field crop, life eventually moves in a pretty predictable cycle. Well, it’s that time of year again. Time to start scouting for rice stink bugs (Picture 1) in headed rice, although it does seem to be coming a little bit earlier than usual. This is probably a result of very early planting of rice in some parts of South Louisiana. Unfortunately, field conditions are favoring a bad year for stink bugs. The drought conditions have killed off grasses that would normally serve as a host/reservoir for stink bugs, so there is a chance they will move more readily into heading rice. Recent reports from Arkansas and Mississippi indicate that large populations of rice stink bugs are present in the mid-south. We are already finding them in headed rice fields at the rice research station in Crowley, La.
Last Friday, Johnny Saichuk and I scouted a variety trial in Vermilion Parish where the CL111 was heading first and was already infested with rice stink bugs. I received a call about the field because they noticed quite a bit of blanking in the panicles. They also found a high population of grasshoppers (Picture 2) and suspected they may have been causing injury. When we assessed the situation, Johnny determined that the blanking was most likely physiological, some sort of effect of weather conditions when the rice was at panicle development (pd). You can read more about it in his field notes. If you don’t receive Johnny Saichuk’s Field Notes via e-mail, please send Johnny an e-mail to be added to his list: firstname.lastname@example.org. As we examined the grasshopper situation, we found that the grasshoppers were long-horned grasshoppers, which are typically predators. We would not recommend treating for grasshoppers unless they are causing excessive defoliation. Click here to read more about long-horned grasshoppers in rice. Odds are that they were attracted by the rice stink bugs, which we did find to be abundant in the field. We advised holding off on an insecticide application until the rice reached 50% heading. It is very tempting to put out a pyrethroid with the fungicide application at early-heading, but research has shown that this is too early to prevent injury. Putting out an early application will probably just add to the number of times you need to spray the field, while not providing any additional protection. To learn more about rice stink bug management click here.
We have a graduate student, Bryce Blackman, who is currently studying rice stink bugs for his dissertation research. One aspect of his work is to re-evaluate treatment thresholds. At the moment, we continue to use the standard recommendations. To scout for rice stink bugs in the field, use a 15-inch diameter sweep net, take 10 sweeps at 10 different areas around each field. Count the number of bugs collected after every 10 sweeps. In the first two weeks of heading, treat fields when there are 30 or more bugs per 100 sweeps. Pesticides that can be used include malathion, methyl parathion and a variety of pyrethroids including Declare, Karate Z, Mustang Max, Prolex and a number of generics. From the dough stage until two weeks before harvest, treat fields when there are 100 bugs per 100 sweeps. When approaching two weeks before harvest, you can treat with any of the chemicals listed above with the exception of Karate Z and Prolex, which have 21 day pre-harvest intervals. You can learn more about rice stink bug biology by clicking here.
Resistance to pyrethroids has been increasing in Texas, and there is a chance that we could have some issues with resistance developing in Louisiana also. If you have a field where you are finding it particularly difficult to control the rice stink bugs with your traditional control strategies, please contact me so we can sample the insect population. If you have further questions about rice stink bug management, please contact your local County Agent.