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.

 


A Mixed Bag of Insect Densities in 2016 Corn and Soybean Surveys

Once again, statewide surveys of insects in corn and soybean fields were conducted during the summer of 2016.  A total of 33 counties were surveyed this year. The surveys were performed during the first week of August by sampling five corn and five soybean fields per county. For the past several years (2011, 2013–2016), surveys in corn and soybean fields have been conducted with the goal of estimating densities of common insect pests. Densities are reported for the various USDA crop reporting districts of Illinois to highlight portions of the state where the risk of economic insect damage is greatest. 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.

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. Much like 2015, the number of western corn rootworm adults in corn was very low throughout the state (Table 1).

Table 1  ∙  Mean number of western corn rootworm beetles per plant in corn by crop reporting district and year
District 2011 2013 2014 2015 2016
Northwest 0.26 0.33 0.05 0.02 0.02
Northeast 0.15 0.20 0.02 0.00 0.02
West 0.01 0.10 0.01 0.01 0.00
Central 0.35 0.37 0.74 0.02 0.05
East 0.31 0.81 0.51 0.01 0.01
West-southwest 0.01 0.20 0.06 0.00 0.01
East-southeast 0.02 0.01 0.00 0.00 0.00
Southwest 0.00 0.00 0.00 0.01 0.01
Southeast 0.00 0.03 0.01 0.00 0.02
Means were determined by counting the number of beetles on 20 consecutive plants for between 15 and 50 fields per district.

 

Within an adjacent soybean field, 50 or 100 sweeps were performed 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. Depending on the year, five or ten pairs of corn and soybean fields were sampled at random in each county visited. The number of western corn rootworm adults in soybean fields throughout the state was very 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.)

Table 2  ∙  Mean number of various insect pests per 100 sweeps in soybean by crop reporting district and year

District

Year Bean leafbeetles Japanesebeetles Western cornrootworm beetles Grasshoppers Greencloverworms Soybeanloopers

Stink bugs

Northwest 2011 0.0 31.7 0.3 0.2 0.2 0.0 0.2
2013 0.3 28.3 1.0 0.4 0.0 0.0 0.1
2014 0.3 14.5 1.0 0.7 0.9 0.2 0.5
2015 1.1 13.4 0.0 1.6 1.9 0.1 0.5
2016 1.1 21.8 0 3.2 2.0 0.0 0.8
Northeast 2011 1.4 13.0 0.3 0.1 0.1 0.0 0.1
2013 0.5 13.8 10.0 0.5 0.2 0.1 0.0
2014 0.2 18.3 3.0 0.3 0.6 0.1 0.6
2015 0.7 12.9 0.1 1.7 2.3 0.0 0.6
2016 8.3 1.3 0.0 5.9 2.9 0.0 0.0
West 2011 0.7 9.5 0.1 0.6 0.7 0.0 0.2
2013 1.0 5.0 0.4 0.3 0.3 0.0 0.2
2014 11.7 2.1 0.2 1.2 0.4 0.2 1.5
2015 1.6 17.5 0.0 2.8 1.3 0.1 0.5
2016 0.9 89.4 0.7 1.5 6.6 1.4 0.2
Central 2011 3.3 24.1 0.9 0.5 0.1 0.0 0.1
2013 0.5 0.9 6.4 0.3 0.4 0.1 0.2
2014 2.4 0.7 18.9 0.6 2.6 0.3 0.7
2015 5.8 2.7 0.2 4.0 0.5 0.0 0.7
2016 16.8 2.0 5.2 4.0 10.0 0.0 0.0
East 2011 17.0 5.3 7.0 1.1 5.4 0.0 0.3
2013 1.4 2.2 9.8 1.0 1.4 0.0 0.1
2014 1.9 0.4 10.2 0.7 3.0 0.0 0.7
2015 5.5 2.0 0.1 3.8 2.3 0.0 0.8
2016 13.4 0.8 0.13 2.3 11.3 0 0.0
West-southwest 2011 1.4 7.0 0.0 1.3 6.1 0.0 0.5
2013 1.3 2.4 1.5 0.5 1.4 0.0 0.1
2014 1.8 7.3 0.4 0.4 0.9 0.3 1.9
2015 5.4 22.2 0.0 5.8 1.5 0.1 1.7
2016 4.0 10.5 0.3 5.2 12.8 0 0.6
East-southeast 2011 4.1 2.0 0.4 1.3 23.8 0.0 0.1
2013 1.1 0.5 0.1 0.4 1.6 0.0 0.0
2014 1.7 0.4 0.0 0.5 2.7 0.0 0.7
2015 0.9 2.7 0.0 1.7 3.4 0.5 2.1
2016 0.8 2.0 0.0 2.2 7.0 0.0 0.1
Southwest 2011 2.6 2.7 0.0 1.0 4.4 0.0 0.4
2013 1.2 0.4 0.1 0.3 3.4 0.0 0.2
2014 8.4 0.2 0.0 0.6 6.1 0.1 1.3
2015 0.8 2.1 0.0 1.1 2.7 0.0 0.3
2016 1.2 12.0 0.0 4.0 13.2 0.0 0.1
Southeast 2011 1.9 2.5 0.0 0.9 9.7 0.0 0.3
2013 0.5 0.5 1.5 0.1 2.4 0.2 0.3
2014 2.4 0.8 0.1 0.4 2.2 0.2 1.2
2015 0.2 2.5 0.0 1.1 3.3 0.1 0.3
2016 1.9 7.7 0.53 1.1 6.1 0 0.6
Means were determined by counting the number of insects in a 50- or 100-sweep sample for between 15 and 50 fields per district. The stink bug species reported here are the green stink bug and the brown stink bug.

 

Increased densities of some of the defoliating insect species were observed in several districts. Samples were screened for bean leaf beetles, Japanese beetles, grasshoppers, green cloverworm, soybean loopers, and stink bugs. As with many years, Japanese beetles “hot spots” were observed around the state. The western part of the state yielded the most impressive numbers (89.4 per 100 sweep average), with 240 per 100 sweeps and 108 per 100 sweeps recorded in Pike and Warren counties, respectively.  Interestingly, we had higher numbers across the board for green cloverworm in 2016. A few counties had noticeable bean leaf beetles in the samples (Central – 16.8 bean leaf beetles per 100 sweeps and East 13.4 bean leaf beetles per 100 sweeps). No brown marmorated stink bugs were detected in any of the soybean or cornfields that were sampled, though this species has been confirmed in many Illinois counties (Figure 1).

BMSB August 2016

Funding for survey activities was provided by the USDA National Institute of Food and Agriculture and the Illinois Soybean Association. 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, Colleen Musson, Ryan Pavolka, Emma Sementi, and Jacob Styan as well as Department of Crop Science interns Lacie Butler and Sarah Luce.