Arkansas Rice: Beginning Push to Heading; Dealing with Armyworms, Stink Bugs

Armyworm damage in rice. Photo: Kevin Lawson, University of Arkansas

The 2021 rice crop finally appears to be taking shape.  We’re entering the major push to heading for the majority of the crop over the next couple of weeks.  The overall outlook for upcoming conditions is positive at this point with average temperatures day and night along with some continued rain chances including today.

Today and the next few days carry decent rain chances that should help us with irrigation efforts.  Rice that has begun to head and flower we hope to avoid mid-day showers that could disrupt pollination.  Any strong winds that accompany storms may also lead to blanking of kernels and sections of panicles from physical damage (heads hitting other plant parts damaging flowering kernels).

High humidity and regular rainfall events could also exaggerate disease situations, so be diligent in scouting for sheath blight.  Also be mindful of possible blast development on susceptible cultivars.  As heading begins so too does stink bug pressure.  Scout, scout, scout for insects and disease.  One other big insect item covered in detail in the update this week is armyworms hitting rice fields – keep your eyes peeled!

NOAA 7 day precipitation forecast

Fig. 1.  NOAA 7-day Precipitation Forecast. Click Image to Enlarge

Armyworms and Stink Bugs in Rice

Armyworm calls have picked up big time this week.  A majority of the fields with armyworms in them is row rice at various stage, spanning from early tiller all the way up to half-inch joint movement.  Some of these fields have high numbers of worms in them, 2-4 per plant, and a large amount of defoliation occurring.

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Our threshold for defoliation in rice is: No treatment is warranted for rice between the seedling and 2-3 tiller growth stages unless armyworms are able to feed on the growing point.  For May and June plantings, armyworms should be treated when defoliation exceeds 40% at 5-6 tiller and 20% at green ring.  During heading, treat if head clipping is occurring and armyworms are present.

Our work over the past 4 years has shown that the later we plant the worse yield is impacted from defoliation (Table 1).  Armyworms have the potential to do large amounts of defoliation in a short amount of time.  Fields with armyworms in them should be monitored closely to ensure we do not exceed these defoliation thresholds.

If applications are warranted, we are recommending lambda-cyhalothrin (Warrior II, Lambda-Cy, ect.) plus Dimilin 2 L.  We have seen a lack of control in some cases with straight lambda.  The Dimilin will also provide some residual.

Yield and maturity delays from defoliation at green ring

Table 1. Yield and maturity delays caused by defoliation at green ring. Click Image to Enlarge

Now that we have rice reaching 50-75% heading we are starting to spray for rice stink bugs.  Numbers have ranged from right at threshold to 30-40 on 10 sweeps.  Based on our assays from this year (Table 2), we are getting adequate control from lambda.  With that being said, we need to follow up these applications within 3-4 days to determine the efficacy.

It is common to see adults shortly behind an application and this is typically new stink bugs moving in.  If nymphs are found shortly behind an application, that is a sign of potential resistance issues.  We have seen some issues with lambda late in the heading season (late August through September) but none during July and August.

If you have concerns that you missed stink bugs with lambda, please contact one of us so we can conduct assays.

Control of rice stink bug with lambda-cyhalothrin

Table 2. Control of rice stink bug with lambda-cyhalothrin.

Armyworms defoliating rice

Fig. 2.  Armyworms defoliating rice.

Armywroms sampled in rice

Fig. 3.  Armyworms sampled from rice field.




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