Increased Insect Densities Reflected in Annual Corn and Soybean Survey

 

Thirty-six counties representing the nine crop reporting districts were surveyed at the end of July/beginning of August as part of our annual statewide corn and soybean survey. The surveys were performed by sampling five corn and five soybean fields per county. For the past several years (2011, 2013–2017), surveys in corn and soybean fields have been conducted with the goal of estimating densities of common insect pests. The estimates provided in this article should not be considered a substitute for scouting individual fields and making informed pest management decisions—even areas of the state that appear to be at low risk could have contained fields with high densities of a given insect pest.

Crop Reporting Districts

Figure 1. Illinois crop reporting districts surveyed during 2017 annual corn and soybean insect survey.

 

Western corn rootworm beetles were sampled in cornfields by counting the number of beetles on 20 consecutive plants beyond the end rows of a given field—a beetle per plant average was calculated for each field. A mild winter followed by favorable conditions at egg hatch and adult emergence helped the small populations from 2016 gain some traction in 2017 (Table 1). Per plant averages are up compared to recent years, though looking at the big picture, these numbers are still considered low. The district average from the northeast (1.95 beetles per plant), was affected by a single field in LaSalle county that average 7 beetles per plant which leads to a very important point to consider with this survey. Fields are randomly selected. We have no knowledge of insect management strategies that are used – soil insecticides, transgenics, or foliar applications.

Table1

Within an adjacent soybean field, 50 or 100 sweeps were performed on both the exterior of the field (outer 2 rows) and interior (at least 12 rows beyond the field edge) using a 38-cm diameter sweep net. The insects collected in sweep samples were identified and counted to provide an estimate of the number of insects per 100 sweeps (Tables 2 and 3).

Table2

 

Table3

The number of western corn rootworm adults in soybean fields throughout the state was low as well. The greatest number of beetles in soybeans occurred in McLean County, 8.00 beetles per 100 sweeps. All other counties sampled had fewer than 5 beetles per 100 sweeps (range of 0 to 2.4 per 100 sweeps).

Japanese beetles continued to increase in number from 2016 in the western part of Illinois. Both Fulton and McDonough counties recorded over 200 beetles per 100 sweeps in several fields, with their county averages of 525 and 340 beetles per 100 interior sweeps, respectively. Undoubtedly some of the highest numbers I’ve seen in this survey.

Overall, grape colaspis numbers were higher in several districts. This follows earlier reports during the growing season of grape colaspis feeding in soybeans. Unfortunately, there is no direct correlation between grape colaspis presence in soybeans and potential for larval injury in corn the following year. Numbers continue to be variable for this insect, but were high in the east southeast counties and should bear watching in 2018.

Stink bug injury in soybeans continues to make news in the southern states. We saw little damage caused by stink bugs in this survey, though numbers were slightly higher than past years. We continue to monitor for potential spread of not only the southern species like red banded and redshouldered stink bugs, but also the spread of brown marmorated stink bug as it gets its foothold here in Illinois.

Funding for survey activities was provided by the USDA National Institute of Food and Agriculture. This survey would not be possible without the hard work and contributions of many people. I would like to thank Illinois Cooperative Agriculture Pest Survey Program interns Evan Cropek, Ryan Pavolka, Emma Sementi, Jacob Styan and Hannah Hires as well as Department of Crop Science interns Lacie Butler, Kaela Miller, and Matt Mote.


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.

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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.

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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.

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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.

 

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