Friday, September 24, 2021

Get geared up for rice stink bugs

• By Nick Bateman, Gus Lorenz and Ben Thrash •

rice stink bug adultv
Rice stink bug adult — photo by Vicky Boyd

We have been observing large numbers of rice stink bugs (RSB) in native grasses along ditch banks and turn rows over the past several weeks. I know, I know, we say this every year. We saw similar populations this time last year, and we sprayed very little until mid-August for RSB.

We just wanted everyone to be aware that there is potential for some of this early planted rice that will be heading in the next two weeks to be infested with some high populations of RSB.

We have been conducting assays on RSB for the past couple of years to test for resistance to lambda-cyhalothrin (Warrior II, Lambda-Cy, etc.). Our assays so far this year have shown between 90% and 100% control with a 1X rate of lambda.

This has been the case for the past two years until we get into late August and September. We have seen some slippage during that time. We are recommending to start out with lambda and to scout those fields within three to four days after application.

If nymphs are found shortly after an application is made, then that is a sign of a failure, and it’s time to swap to Tenchu, which is the only non-pyrethroid option for RSB control. If only adults are found, it is more likely that a new flush of RSB has moved into the field.

Just as a reminder our thresholds is 5 RSB (nymphs plus adults) per 10 sweeps during the first two weeks of heading, and 10 RSB per 10 sweeps during the second two weeks of heading.

The last thing we want to cover is adding lambda in with a fungicide application. You know we are big proponents of integrated pest management and only spraying when we reach a threshold for an insect pest.

We have tried spraying lambda prior to heading, and our data doesn’t support doing this (Fig. 6). We hear all the time that it’s only a dollar, and I don’t want to ask the grower to turn around and spray a week later for RSB.

insecticide application timing for RSB
Click on image to enlarge

Rice stink bugs are seed feeders, and rice has to be blooming with some kernels moving into milk to really be a host for them. This is why we don’t recommend scouting for RSB until we are 75% headed.

When we make applications of lambda prior to this point we consistently see higher populations of RSB than if we wait until at least 75% heading. We also feel like this could be part of the problem with the failures we have seen late in the season.

**NOTE: If you are spraying a fungicide at the proper timing for smut prevention, then you are well in advance of having heading rice where RSB pressure would be present to justify an insecticide application.

If you delay the fungicide application until right at heading when you might have more RSB entering the field to justify an insecticide application, then you are too late for the fungicide to have much effect.

There is NOT a situation where spraying a late fungicide and an insecticide together lines up for management of both – you will be too early or too late on one of the products going out.**

Hopefully this year will be like last, and RSB will be a nonissue on a bulk of our acres. Let us know if you have any questions or need anything. Also please contact us if you see a failure with lambda so we can make a collection to conduct resistance assays.

Drs. Nick Bateman, Gus Lorenz and Ben Thrash are University of Arkansas Extension entomologists.

 

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