Insect Trapping Update:Week Ending May 11, 2018

Black cutworm

Black cutworm moth flights continue across much of Illinois. Several counties reported second -and even third- significant moth flights (Madison, Champaign, and Lee). Several counties had near significant flights (Piatt and Coles). It is important to remember that lack of a reported significant flight and subsequent projected cutting dates does not take black cutworm out of the equation in your area. I have had reported of 1st-2nd instar feeding and even a report of 3rd-4th instar cutting in a couple areas of the state. These reports have been isolated, and under recommended thresholds for rescue treatments.

Black cutworm projected cutting dates.

True Armyworm

While spring storms and southern winds brought black cutworm moths to many areas of Illinois, that is not the case for true armyworm. Trap counts remained low across the state for a second week in a row.  

 

Weekly Moth Total

(May 5-May 11)

Northern (Lee County) 2
West Central (Warren County) 4
East Central (Champaign County) 5
Southern (Madison) 0

 

Corn Rootworm

We remain several weeks from corn rootworm hatch in Illinois. Soil temperatures are warm and degree-day accumulations reflect totals that are slightly ahead of the historical average. We will continue to monitor degree-days and egg hatch.

Alfalfa Weevil

No reports of alfalfa weevil feeding have made their way to the office this week, but varying life stages are possible across the state. A quick refresher on biology, injury and management can be found on the alfalfa weevil factsheet.

Corn Earworm

While we won’t begin trapping for corn earworm for a couple of weeks, Purdue University reports the first 2018 moth catch of the year in Indiana. At this time of year, the catch has little significance on field crops, but is a reminder that spring is truly here and we will be transitioning for our early season insect pests to summer insect pests soon.

 


Managing Corn Rootworm Populations in Illinois: Considerations for 2018

 

Authors: Nick Seiter, Joe Spencer, and Kelly Estes

Rootworm management is a yearly consideration for most corn producers in central and northern Illinois. Western corn rootworm (Fig. 1) is the primary pest species throughout most of the state, but areas in northern IL can experience pest pressure from the northern corn rootworm (Fig. 2) as well. Adult population densities have been low in recent years compared with historical averages, although they did creep up a bit in 2017. The overall reduction in corn rootworm pressure is likely due to a combination of unfavorable weather (or at least unfavorable to rootworm larvae) and widespread adoption of corn hybrids expressing combinations of Bt toxins for rootworm control.

Fig. 1. Western corn rootworm adult. Photo: J. Spencer

Over the last few years, western corn rootworm populations with resistance to Cry3Bb1 and mCry3A (two commonly expressed toxins in Bt corn hybrids) have been documented in Illinois. Research published in 2016 on Iowa1 and Minnesota2 western corn rootworm populations showed that resistance to these toxins also confers resistance to the structurally-similar eCry3.1Ab toxin.  Cross-resistance among these “Cry3” Bt toxins should be expected for Illinois western corn rootworm populations.  Resistance to pest control practices in the western corn rootworm is nothing new; this insect is notorious for developing resistance to control tactics such as insecticides and crop rotation. Part of the concern with these recent developments is that there are relatively few Bt toxins available to combat corn rootworm. Furthermore, all available hybrids with pyramided traits for corn rootworm use either Cry3Bb1 or mCry3A in combination with a second toxin (either Cry34/35Ab1 or eCry3.1Ab). This means that, where resistance is present in the population, there might in fact be at best only one effective toxin at work. (If you have trouble keeping all of these toxins straight, a good resource is the “Handy Bt Trait Table” produced by Dr. Chris DiFonzo at Michigan State University: https://www.texasinsects.org/bt-corn-trait-table.html).

Fig. 2. Northern corn rootworm adult. Photo: J. Spencer.

There are steps producers can take to manage corn rootworm and hopefully slow the further development of resistance. The best way to delay resistance to any control tactic is to reduce exposure of the target insect to that tactic in the environment. Specific ways to accomplish this with Bt toxins include:

  • Apply rootworm control (whether in the form of a Bt hybrid or a soil insecticide) only where it is economically justified based on sampling rootworm adults the previous year. If you monitor using a yellow sticky trap, the economic threshold is 2 rootworm beetles per trap per day in corn following corn. For rotated corn, the economic threshold is 1.5 western corn rootworm beetles per trap per day in soybean3. (These thresholds are based on a recent study in Iowa, which recalculated economic thresholds for corn rootworm based on updated crop values and control costs3).
  • Rotating corn with soybean or another non-host crop remains an effective management strategy in the southern portion of the state. While crop rotation is no longer a reliable method to protect first-year corn from western corn rootworm damage in central and northern Illinois, all larvae that hatch into soybean still die, and every acre planted to soybean is an acre where larvae are not being exposed to Bt toxins or soil insecticides.
  • Where monitoring indicates that control is justified in corn, rotate the control measures used from year to year. This means rotating among Bt hybrids with different trait combinations and non-Bt hybrids treated with a soil insecticide.
  • Follow all refuge requirements for any Bt corn hybrids you plant. In many cases, the “refuge in a bag” or “RIB” approach is now used, but check with your seed distributor on specific requirements for your hybrids.

Finally, an important step is to monitor the performance of your control methods. While lodging is often the cue we look out for to identify rootworm damage, keep in mind that (1) corn can take a lot of damage without lodging depending on soil type and weather conditions and (2) plenty of factors other than rootworm damage can lead plants to lodge. The best approach to evaluating rootworm damage is to dig a representative sample of roots in late July and evaluate them for feeding damage: unpleasant work, but necessary if we want to understand the true extent of the damage.  Consider planting a small area or a portion of a row with a non-Bt/untreated hybrid as a check strip. Having an untreated patch in your field will allow you to compare the efficacy of your management tactic vs. the background level of damage where no rootworm protection was used. Finally, if you experience greater damage than expected in Bt corn hybrids in 2018, please let us know at the email address below; your reports will help us to document the status of resistance in Illinois and provide updated information to producers.

Correspondence:

Nick Seiter: nseiter@illinois.edu Research Assistant Professor, Field Crop Entomologist,University of Illinois Department of Crop Sciences

Joe Spencer: spencer1@illinois.edu Principal Research Scientist and Research Program Leader in Insect Behavior, University of Illinois, Illinois Natural History Survey
1Jakka, S.R.K., et al. Scientific Reports 6: 27860. DOI: 10.1038/srep27860

2Zukoff, S. N. et al. 2016. Journal of Economic Entomology 109: 1387-1398. DOI: 10.1093/jee/tow073

3Dunbar, M. W. and Gassmann, A. J. 2013. Journal of Economic Entomology 106: 168-180. DOI: 10.1603/EC11291


Insect Briefs – June 30

Japanese Beetles

Japanese beetles are back. Reports statewide indicate Japanese beetles are here (and in some locations, in very high numbers.) With corn starting to tassel and getting close to tassel, it’s important to remember, even though densities may appear to be extremely high, the average density of beetles across the field may be below levels of economic concern. An insecticidal treatment should be considered during silking if:

  • There are 3 or more beetles per ear,
  • Silks have been clipped to less than ½ inch, AND
  • Pollination is less than 50% complete.

Also remember, that there are usually clusters of Japanese beetles near field edges and if those are the only locations sampled, it will skew the numbers.

1 2

After with reports of thistle caterpillar in soybeans the past two weeks, the concern now seems to be focused on other defoliating pests like Japanese beetles.  It’s important to scout flowering soybean fields for the presence of Japanese beetles. Insecticidal treatments should be considered when defoliation reaches 30% before bloom and 20% between bloom and pod fill.

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Grape Colaspis

Another pest starting to make a stir is grape Colaspis. Grape Colaspis has been a sporadic pest in Illinois. We often focus on the injury caused by grape colaspis larvae in corn. The larvae feed on root hairs and eat narrow strips from the roots. We did see quite a few adults in our 2016 statewide survey and there are some early indications that high numbers have returned to some areas this year. Foliage feeding by adults is usually insignificant but scouting will be important in areas where there are several defoliators at work.

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Western Corn Rootworm

Western corn rootworm emergence has begun.  Emergence is still in its early stages, but as we move into the July 4th holiday, reports will be more frequent.

5

 

Corn Earworm

Corn earworm flights have been steady for 2 weeks with several locations peaking 6/15-6/20. Moths will lay eggs in the evening and with hatch in 3-4 days at 77F. Larvae feed on whorl stage corn and other host plants for a period of 3 to 4 weeks before burrowing into the soil to pupate. We expect a second generation of larvae and moths to peak in late summer.

 

European Corn Borer

Corn borer flights have been very low, but that doesn’t mean ECB isn’t present. Be sure to scout for corn borer feeding on conventional corn.

 

Fall Armyworm

Flights of fall armyworm have also been low, but consistent. There is a good chance we may still see these numbers pick up. Fall armyworm will feed during the day and night unlike the night-feeding armyworm. Early symptoms may be similar to corn borer feeding (small holes and window-pane feeding in the leaves.) As larvae get larger, they will consume more leaf tissue before moving to the ear as plants begin to tassel.

Western Bean Cutworm

Western bean cutworm trapping is underway. Numbers have been very low with only a few locations reporting a couple of moths. Purdue is reporting very large numbers the first week of trapping with the peak expected in 2-3 weeks. Wisconsin has reported WBC emergence. High risk areas include those with high moth flights and WBC history and sandy soils. We encourage scouting during the growing season as evidence at harvest does not necessarily confirm WBC presence. The latest Purdue Pest & Crop Newsletter has a fantastic article with WBC information and a video for scouting.

 

“Scouting should begin once moths are being captured nightly. In five different areas of a field, inspect 20 consecutive plants for egg masses which are laid on the upper surface of the top leaves of corn and/or larvae that may have hatched and crawled to the whorl and begun to feed. Usually the newest, vertical leaf is the best place to look for egg masses. Young larvae need pollen to survive, and female moths are most attracted to cornfields that are just about to pollinate. Moths will lay eggs on whorl stage corn when pre-tassel/pollinating corn is not available. Larvae may initially be found in leaf axils, feeding on pollen that has accumulated there. Later damage from larvae, as they feed deep in the whorl (attacking the tassel to get at pollen), will resemble corn borer or fall armyworm damage. Initially the damage will be subtle and not economically important (or even noticeable). Later stage larvae enter the ear and feed on corn kernels and can cause economic damage, and also can exacerbate ear rots, including Gibberella ear rot.”

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Brown Marmorated Stink Bug

We continue to monitor the spread of brown marmorated stink bug in Illinois. Populations continue to grow. Most issues stem around it being a nuisance pest in homes, though we expect to see injury in agricultural and specialty crops in the near future. While we will be including BMSB in our summer surveys, I did receive my first garden report this week. Gardeners in areas with high populations should keep an eye on home gardens.

20170630_121655

Spotted Wing Drosophila

Spotted wing drosophila has become a serious pest for both specialty crop growers as well as home gardeners. This invasive fruit fly will insert eggs into healthy fruit, leading to the immature stages (maggots) that feed on the fruit flesh causing decay and reduction of quality. Often times, there is no outward indication of an infestation. While populations are low in the spring, they will gradually increase throughout the summer and later season fruit tend to have more damage. In our 2017 orchard survey, SWD has been confirmed in Pope, Champaign, and DeKalb counties in the last two weeks.

 

5444194-SMPT DrosophilasuzukiiphotoMcEvey

 

 

 


Insect Snapshots from the Field

Just a quick overview of some insect issues presenting themselves recently.

True Armyworm

Lots of reports of armyworm being found in wheat and corn. With reports of wheat harvest starting/getting close, reports of armyworm in corn seem to be taking over. I’ve seen a range of larvae stages from 2nd-4th instars. Injury to the whorl and ragged leaf margins is usually noticed around field margins first.  Armyworm larvae are night feeders and will usually spend the day in soil cracks, under dirt clods, or in the whorl. Control may be justified when 25% of the plants are being damaged. Things to consider: hot spots in the field and also size of the larvae. Larvae greater than 1 ¼” will have completed most of their feeding.

IMG_5699a

Armyworm larvae (Photo courtesy of Stephanie Porter)

 

Corn Rootworm

Reports of lightning bugs in the central part of the state along with degree day accumulations suggest rootworm hatch is underway.

CRW June 9

Corn Earworm

We picked up our first corn earworm moth last week. To date, we’ve trapped a total of 10 moths in Champaign. We expect those numbers to slowly pick up over the next couple of weeks.

 

Corn earworm moth (Photo courtesy of University of Maine)

Corn earworm moth
(Photo courtesy of University of Maine)

Fall Armyworm

A few fall armyworm moths have been picked up in our traps here in Champaign. We expect those numbers to increase in the next few weeks as well.

 

European Corn Borer

We have yet to pick up any moths in our trap in Champaign. We also have been sampling action sites (dense stands of tall grasses along roadsides ditches or waterways) by making 100 sweeps with a standard insect sweep net. To date, no moths have been recovered in any of the samples statewide.

 

European corn borer  (Photo courtesy of Marlin Rice)

European corn borer
(Photo courtesy of Marlin Rice)

Stalk Borer

A few reports of stalk borer in corn. These younger larvae did not have the distinct purple “saddle” that we often use to ID these insects. Young larvae will be light brown with a narrow white stripe running down its back from head to tail. There will be a similar white stripe on each side of the body that is interrupted by a purplish-brown band that circles the front third of the body. As larvae get bigger they move from the grass hosts they are quickly outgrowing to larger hosts, such as corn.

Stalk borers will attack corn in 2 different ways:

  • Burrow into stalks at ground level and chew upwards through the center of the plant. Wilted leaves will be the first obvious symptom with this injury along with the potential for some plants to buckle at ground level.
  • Some larvae may crawl to the top and feed down through the rolled leaves into the stalks. Ragged leaves, along with frass on the leaves may allude to this type of feeding which may also cause wilting of the top half of the plant.

 

Stink Bugs

I’ve also gotten reports of stink bug injury in southeast Illinois. Stink bug can cause three different types of injury – tillering, stunted plants, and may even kill small seedlings. Signs of stink bug injury will include oval holes where they have inserted their needlelike mouthparts.  The stink bug sticks the base of the plant or their leaves with their small needle-like mouth. When they do this, they are causing these plants to die as a small seedling, produce stunted plants- such as misshapen ears instead of tassels- or suckering- the production of tillers form the base of damaged plants. Most often, you see this pest in fields that are no-tillage, near wooded areas, or conventional fields as well as along field edges.

 

Slugs

Slug injury has been reported across much of southeast Illinois as well and as far north at Livingston county in both corn and soybeans. Slugs are generally a problem in no-till fields; especially if they are late-planted. Slugs take advantage of the smaller plants and as the plants grow, they quickly outpace the slugs. Feeding generally occurs on the lower parts of the plants. Symptoms may resemble that of the corn flea beetle (narrow, irregular tracks or scarring), but the presence of a slime trail will be indicative of the presence of slugs.

 

Black Cutworm

Once again, we received sustained flights across much of Illinois. Several counties saw repeated significant flights. This map gives you a good indication of projected cutting dates, but several counties like Champaign and Lee saw 4-5 significant flights, so the bottom line is that some of this late planted corn will still be susceptible for BCW injury. Speaking of BCW injury, I have had a few reports of feeding around the state. No indication of anyone area being more severe than another. There is still a lot of small corn across the state that could be susceptible.

BCW May 26

Centipedes/Millipedes

I’ve also fielded a few call on centipedes and millipedes last week, though with the warm, dry weather, I don’t suspect to hear much more about these.

 

 

Information compiled with the assistance of Kaela Miller, University of Illinois Agriculture Communications.