Hodgson Laboratory

In March, I predicted low overwintering mortality based on our mild winter. You may have noticed adults become active in alfalfa starting in April. Some soybean research plots around southern and central Iowa have decent numbers feeding on unifoliates. Read more about early-season management of bean leaf beetle here.

 Soybean can compensate for early-season defoliation by bean leaf beetle. Photo by Erin Hodgson (17 May 2012 near Ames, IA).
Circular-shaped defoliation on leaves is an indicator of bean leaf beetle feeding, even if you don't see the beetles. Photo by Erin Hodgson (17 May 2012 near Ames, IA).

In May, reports from around the state have indicated leafhoppers are rising in numbers. The species we are most familiar with in Iowa is potato leafhopper. They are small, bright green and have white eyes. Note the spiny legs and clear wings that extend well past the end of the abdomen. Treatment thresholds for alfalfa can be found here. Consider reducing this threshold for high-quality dairy hay.

Potato leafhopper adults are about 1/8 inches (3 mm) long. Photo by Marlin E. Rice.
A few places in Iowa, Nebraska and the Dakotas have reported another species, aster leafhopper, in fields this year. They are a little bigger and have an olive green or brown body. Aster leafhoppers have a wide host range and are can be a pest of vegetables, field crops, and ornamentals. A treatment threshold for alfalfa and other field crops isn't well defined. That is partly because they can vector a plant disease called aster yellows. Cost-effective treatment decisions would be dependant on disease severity in combination with leafhopper density. Aster yellows has similar visual symptoms to barley yellow dwarf virus in small grains. So consider an insecticide application when symptoms first appear (e.g., yellow or mottled leaves) or if clouds of leafhoppers are disturbed when walking through fields. Pyrethroids are generally effective but may need to be reapplied if migratory populations reinfest fields.

Aster leafhopper are about 5/32 inches (4 mm) long and have a wedge-like body. Photo by Whitney Cranshaw, www.ipmimages.org.

Iowa has been steadily accumulating degree days ahead of schedule in 2012. Over the weekend, some parts of southern Iowa hit an important degree day benchmark for common stalk borer. About 10 percent of stalk borer larvae can begin moving to corn after accumulating 1,300 to 1,400 degree days. Part of southwestern and southeastern Iowa have reached that threshold and we recommend starting to scout this week in corn. Central and northern Iowa should start scouting May 12 to May 18, if warm temperatures continue. This is about three weeks earlier than last year. 

 Growing degree days accumulated (base 41°F) for stalk borer larval movement in Iowa for 2012. Begin scouting around 1,300 to 1,400 degree days. Map courtesy of Iowa Environmental Mesonet, ISU Agronomy. 
For the full ICM News article about stalk borer management, click here.

Each year, the ISU Entomology Department produces a few Yellow Books that evaluate insecticide efficacy and PIPs (plant-incorporated protectants). My lab produces one for soybean insects, but mainly focuses on soybean aphid. Aaron Gassmann produces one for corn insects, with the majority of the report on corn rootworm.

Both are available (FREE!) as a pdf on our departmental website.

View the 2011 Corn Pests Yellow Book.

View the 2011 Soybean Pests Yellow Book.

Last week, I had several people ask me about painted lady butterflies in Iowa. They reported seeing high numbers and were wondering if this was an insect we should keep an eye on this summer. The last time I remember seeing high populations was in 2003 (while I was a grad student up in St. Paul, MN). Of course the adults are beautiful butterflies, but farmers care about the larvae (called thistle caterpillars) that are defoliators in soybean.




Thistle caterpillars are unique-looking defoliators. They have dark bodies with yellow strips, and short spines. Photo by Marlin E. Rice.
Thistle caterpillars do not overwinter in Iowa and must migrate here every year. The first generation larvae can cause the most injury during V3-V4. The last two instars eat about 97% of the soybean tissue consumed.
  Thistle caterpillars often web together leaves for protection. Photo by Marlin E. Rice.  
Although the females lay single eggs on leaves, populations tend to be aggregated at field edges. Rarely do thistle caterpillars reach economic thresholds in Iowa. You would have to see larvae on every plant and have overall defoliation reach 20% to justify an insecticidal treatment. Since most damage is found at field edges, consider a spot treatment to save on application costs if defoliation exceeds 20%. 
You may be wondering what the adults are larvae feed on besides soybean. Painted lady butterflies feed on nectar from composite plants like thistles, asters and milkweed. The caterpillar can feed on over 100 species of plants, including: Canada thistle, soybean, vegetables and ornamentals. So they have many other food choices besides soybean and not considered a regular pest. Bottom line is you might see more adults and larvae this summer, but I don't expect them to cause widespread outbreaks in beans this year. 
 Painted lady butterfly. Photo by Whitney Cranshaw.

Recently, Christian Krupke (field crops extension entomologist at Purdue University) published a paper on how honey bees may be getting exposed to a class of insecticides most commonly used in seed treatments. The authors found neonicotinoids in soil, dandelions, and pollen. Dead and dying bees collected from aparies near agricultural fields had traces of neonicotinoids.

He recommends the following to minimize exposure to honey bees during planting:

1. Farmers should be in communication about planting timing with local beekeepers.
2. Beekeepers should move hives during planting if possible.
3. Use the appropriate amount of talc to plant treated seed.
4. Do not clean planter equipment near fields.

 For more information, read this recent ICM News article.

 Honey bees exhibit neurotoxic symptoms when dosed with neonicotinoids. Dying bees have trouble flying, collecting food and getting back into the hive. Photo by John Obermeyer, Purdue Extension Entomology.

Iowa has steadily accumulated growing degree days (DD) all through March. One of the first insects to hatch is alfalfa weevil. In general, we can expect egg hatch around 200 DD south of I-80 and around 250 DD north of I-80. Most of the state has already hit those benchmarks.

 
Accumulated growing degree days (base 48F) in Iowa form 1 January - 2 April 2012. This map is updated daily (click here). Map courtesy of Iowa Environmental Mesonet, ISU Department of Agronomy. 
 Alfalfa weevil is an important defoliator because adult and larval feeding can reduce tonnage and forage quality. If plants are greater than six inches, use a sweep net to initially sample. Insecticidal treatments are based on crop value and plant height. Read this recent ICM News Article for management guidelines.

Alfalfa weevil adults are brown and hairy, have elongated snouts and elbowed antennae. Photo by Joseph Berger, ipmimages.org.

On March 20, we confirmed the first black cutworm moth trapped in Muscatine County, Iowa. Since then, several counties have also reported captures. Adults were trapped in Lucas County (30 March), Des Moines County (30 March), Marion County (29 March), and Story County (31 March). We use these captures to start estimating growing degree days for predicted cutting dates in corn. Normally predicted cutting dates happen in mid-May, but they may be slightly earlier this year. Look for our 2012 predicted cutting dates later this month.

Black cutworm larvae typically damage corn, but can also feed on soybean. Certain fields may be at a higher risk for black cutworm damage than others; low lying and poorly drained, next to areas of natural vegetation, weedy, and other characteristics should be scouted first.
 


Cutworms are normally noctural feeders and curl up with disturbed. Look for wilted, dead or missing plants. Top photo by Steph Marlay, bottom photo by Tracy Cameron.

About two weeks ago, we sent out a general request looking for cooperators to trap black cutworm moths in Iowa. We use the adult captures to help us predict larval cutting dates in corn. Last night, the first moth was captured in a trap in Muscatine County, Iowa. This is very early to see migratory moths moving up north. I am not sure what this means for spring populations, but last year had higher-than normal trap numbers. As a result, we saw more damaged corn and soybean during establishment. I will keep you updated on trap numbers for 2012 and predicted cutting dates later this spring. 

Black cutworm moth. Photo by Marlin E. Rice.

Have you heard about a peer-reviewed extension publication called the Journal of Integrated Pest Management? It's an open-access journal (free for anyone to read and save files!). You can now access research-based management recommendations on all pests - not just insects and not just field crops. The Editors-in-Chief of JIPM are Marlin E. Rice of Pioneer Hi-Bred International (formerly with Iowa State University) and Kevin L. Steffey of Dow Agrosciences (formerly with the University of Illinois).

This new journal will offer a wide scope of peer-reviewed articles, including entomology, plant pathology and weeds. The intended readership for JIPM will be professionals who are engaged in any aspect of integrated pest management, especially those individuals working in crop protection, retailers, manufacturers and suppliers of pest management products, educators and pest control operators. The firs issue was released in October 2010.  and included articles about stalk borers and western bean cutworm. 

Three recently posted articles may be of particular interest to you. Click on the links to access pdf files:

1. Biology of the soybean aphid
2. Management of soybean aphid
3. Biology and management of bean leaf beetle and bean pod mottle virus


Alate (winged) soybean aphid and a few nymphs. Photo by Erin Hodgson

Host plant resistance for soybean aphid is the newest management tool for farmers. In small plot evaluations of the Rag1 gene, there was a dramatic decrease in the seasonal accumulation of soybean aphid compared to susceptible varieties. The entomology department at Iowa State University recently released a new publication, Soybean aphid-resistant varieties for Iowa, that lists currently available soybean seed with resistance to soybean aphid. The list is intended to assist farmers wanting to adopt this new management tactic for soybean aphid.

The publication also contains Iowa State University recommendations for considering soybean aphid-resistant varieties. For more information on soybean aphid management consult: Soybean Aphid Management Field Guide 2nd edition. Additional information about insecticides is found in the most recent soybean aphid insecticide efficacy evaluation.


Small plot research shows the benefit of host plant resistance. Note susceptible plants (right) are covered with sooty mold that developed on aphid honeydew.
Host plant resistance for soybean aphid can dramatically decrease aphid growth over the summer, and often prevent the economic threshold from being reached. Ultimately, this new tool will help reduce production costs by reducing the number of foliar insecticides being applied to soybean.

Yesterday I was sitting in my deck enjoying a nice evening. I noticed a few aphids landed on one of my dogs! Of course I got excited seeing the first winged aphid of the season (I know that only a few people in the world get a thrill from seeing aphids!). I have no idea what the species was, but I know it WASN'T soybean aphid. So I used my phone camera to take a few pics of the aphid and a few other insects flying around the yard. I noticed a multicolored Asian lady beetle, a few brown lacewings and a ton of flies. I did think it was interesting two of these insects are considered predatory as larvae and adults. I wonder if they were finding enough food? 

Iowa's warm winter and lack of moisture has generated a lot of talk about corn and soybean production lately. Some of the discussion is centered around insect survival and what a mild winter may mean for increased numbers this summer. I addressed some of these issues in a recent ICM News article with Laura Jesse, but specifically talked about bean leaf beetles in an article released today.

In general, overwintering bean leaf beetle adults are susceptible to cold temperatures and are more likely to survive a warm winter. Predicted mortality around the state is low compared to most years, ranging from 30-53%. But lack of insulating snow cover may actually increase mortality. With those factors in mind, I am estimating overwintering beetles may be out in greater numbers compared to the last few years. Early-planted fields should be scouted for adults, especially food-grade soybean.

Predicted overwintering mortality of bean leaf beetle based on accumulated subfreezing temperatures during the 2011-2012 winter.

The Department of Entomology produces an annual newsletter to help our friends and alumni keep in touch with current faculty, staff and students. Our newsletter highlights awards, graduations and research findings. I am currently the editor of the Newsletter Committee and arrange the layout.

Click on this link to see a free full-color copy. Also consider "liking" our departmental Facebook page to stay in the loop with current events.

Articles in this 2012 issue include:

Coats awarded Distinguished Professor
Blodgett is New Department Chair
Gassmann named DuPont Young Professor
Rootworm Resistance to Bt
Photos from the 2011 ISU Mixer at ESA - Reno

Most of you probably have seen the spiral-bound field guides produced by Iowa State University Extension. They have been very popular resources for farmers and ag professionals, and convenient for management in corn and soybean. Now there is a new full-size publication that is focused on insects available at the ISU Extension Online Store (CSI 0014) for $5! The guide can also be viewed online.

In January 2012, Iowa State University and the Iowa Soybean Association released a collaborative publication, Field Crop Insects, the latest in a series of practical and valuable reference tools for farmers. This publication is a comprehensive resource to help with identification and management of common corn and soybean pests. The 74-page publication is filled with vivid, full-color images and descriptions of insect pests and the damage they cause to soybean and corn. Management options are provided as well as Web addresses for access to more detailed insect control recommendations.