Skip Navigation

7/12/2010 - 7/18/2010

Green Cloverworms Appear in Soybean

By Michael McCarville, Erin Hodgson and Matt O’Neal, Department of Entomology

Iowa State University researchers are seeing green cloverworm defoliating soybean in central Iowa (Fig. 1). The caterpillars are a rare pest of soybean in Iowa, but researchers have reported higher than normal populations this year. These moths migrate into Iowa from southern states each year. The last major outbreaks occurred in the 1970s (Fig. 2).
 
green cutworm defoliation

Fig. 1.Sub-economic defoliation caused by green cloverworm
 

green cloverworm defoliation

Fig. 2. Economically damaging levels of green cloverworm were last seen in Iowa forty years ago.

The larvae appear pale green with one or two white stripes along their sides.  Their three pairs of abdominal prolegs distinguish them from other similar caterpillars. For example, armyworms and cutworms have four pairs of prologs; loopers only have two pairs of prolegs. Green cloverworm adults are black and gray moths with a obvious snout-like mouth, and can be distinguished from other moths using a chart published in the June 2001 ICM News. 


green cloverworm

Fig. 3. Green cloverworm larvae have a horizontal white stripe and three pairs of abdominal prolegs.
 

In Iowa there are three generations a year, with the first typically seen in alfalfa. The second generation is capable of reaching economic levels in soybean in July; however, the third generation is normally kept below outbreak levels in August by natural occurring fungi that infect the caterpillars.

Larry Pedigo, research entomologist at Iowa State, developed economic thresholds based on his research in the 1970s and 1980s. Management recommendations from his work (Ostlie and Pedigo 1985) appear in the table below with thresholds adapted for today’s management costs and crop value.

Table 1. Economic thresholds for green cloverworm in soybean

 

Recommendations are based on sampling with a drop cloth. Sweep net sampling based recommendations do not exist. Below is a description of how to sample with a drop cloth. Remember to scout each field and each variety separately.

Drop cloth technique
• Walk 100 feet in from the field edge.
• Place a 1-foot-long strip of cloth on ground between the rows.
• Bend the plants of one row over the cloth, and shake them vigorously.
• Count the number of larvae on the cloth.
• Repeat the procedure four times for each 20 acres of the field.
• Determine the average number of larvae per foot of row.
• See Table 1 for the number of larvae per foot of row necessary to justify insecticide treatment for green cloverworm.
• If the number of larvae is below the economic threshold, sample your fields again the following week, or a third week if necessary.

Other insects  are capable of defoliating soybean (e.g., bean leaf beetle, armyworms, etc.). Even if green cloverworms are below treatment levels, fields may still warrant treatment if the combined defoliation of multiple pests approaches 20 percent. People tend to overestimate percent defoliation, so use Figure 5 as a reference showing a gradient of defoliation levels.
 

Fig. 5. Visual estimations of percent defoliation in soybean

 

Michael McCarville is a Department of Entomology graduate student; he can be reached at 515-294-8663 or by email at mikemcc@iastate.edu. Erin Hodgson is an assistant professor of entomology with extension and research responsibilities. She can be contacted by email at ewh@iastate.edu or phone 515-294-2847.  Matt O'Neal is an assistant professor of entomology with teaching and research responsibilities. He can be reached at oneal@iastate.edu or at 515-294-8622.

Western Bean Cutworm Scouting Update

By Adam Sisson, Corn and Soybean Initiative and Laura Jesse, Plant and Insect Diagnostic Clinic

Western bean cutworm (WBC) moths have been reported in several Iowa counties. The first moth was captured in Adams County, located in the southeast part of the state, on June 16. Iowa State University trap data can be viewed by county. The presence of adult moths in traps indicates only that scouting efforts should begin in an area.

Adult emergence can also be predicted by combining a degree day (DD) model developed in Nebraska with actual trap captures. The DD model is based on the accumulation of DDs (base 50 F) from May 1. Corn field scouting should begin when 1,319 DDs (base 50 F) have accrued, as this is when 25 percent of adult moths have emerged. The following map (Figure 1) displays the accumulated DDs for Iowa.

According to the combined DD and trap capture data, growers should be scouting corn fields now for WBC throughout Iowa.
 

Figure 1. Base 50 F degree days (DD) in Iowa since May 1. Scouting for WBC should begin when 1,319 DDs accumulate. However, when this information is combined with trap capture data, it indicates that corn growers should be scouting throughout the state for WBC. Map courtesy of Iowa Environmental Mesonet, ISU Department of Agronomy.

 

When scouting corn for WBC, examine 20 successive plants in five different areas of a field. On these plants, check for the presence of eggs or young larvae on the top three to four leaves. (See Figures 2 and 3.) Thresholds, management options and descriptions of WBC are outlined in a previous ICM News article.  


Figure 2. Western bean cutworm eggs
 

Figure 3. Western bean cutworm larvae that have just hatched

 

 

Adam Sisson is a program assistant with responsibilities with the Corn and Soybean Initiative. Sisson can be contacted by email at ajsisson@iastate.edu or by calling 515-294-5899. Laura Jesse is an entomologist with the Iowa State University Extension Plant and Insect Diagnostic Clinic. She can be reached by email at ljesse@iastate.edu or by phone 515-294-5374.

Grain Producers Need to Consider Crop Insurance Options for Late Planting and Replanting

By William Edwards, Department of Economics

 

The frequent rains that have soaked Iowa this year have left many corn and soybean fields with areas where little or no production will be realized.  Many producers are wondering what options they have under their multiple peril crop insurance policies.

 

For crops already planted, excess moisture is an insured event. The size of payment received will depend on the final quantity and quality of the grain harvested. Indemnity prices for revenue insurance policies this year are $3.99 per bushel for corn and $9.23 per bushel for soybeans. Payments are based on actual production over the whole insurance unit, however, not just on the damaged areas. If corn is harvested as silage, a check strip should be left so the insurance adjustor can estimate the grain yield.

 

Insured producers may be able to receive a payment to help offset the cost of replanting crops. Affected areas must be at least 20 acres in size or 20 percent of the insured acres, whichever is smaller, and the same crop must be replanted. If a different crop is planted, the producer can choose to insure the second crop if it was included on the original policy, and take a partial payment for damage to the first crop. If the second crop is not insured, a full payment can be received for the first crop based on the level of guarantee purchased and the appraised loss on the crop. The insurance company’s agent should be contacted before replanting is done.

 

Some fields were not able to be planted at all. They may be eligible for a prevented planting payment equal to 60 percent of the original insurance guarantee. No other crop can be planted, except a cover crop. Prevented planting acres cannot be harvested or grazed before November 1.

 

More details can be found in the publication “Delayed and Prevented Planting Provisions,” file A1-57 on the Iowa State University Extension Ag Decision Maker website at www.extension.iastate.edu/agdm/. Producers should communicate with their crop insurance agent before making decisions about replanting or abandoning acres.

 

 

 

William Edwards is a professor of economics with extension responsibilities in farm business management. Edwards can be contacted at (515) 294-6161 or by emailing wedwards@iastate.edu.


 




This article was published originally on 7/19/2010 The information contained within the article may or may not be up to date depending on when you are accessing the information.


Links to this material are strongly encouraged. This article may be republished without further permission if it is published as written and includes credit to the author, Integrated Crop Management News and Iowa State University Extension. Prior permission from the author is required if this article is republished in any other manner.