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2/13/2012 - 2/19/2012

What Does This Warm Winter Mean for Insects?

Erin Hodgson, Department of Entomology and and Laura Jesse, Plant and Insect Diagnostic Clinic

Iowa has experienced a mild winter. In fact, Des Moines has yet to experience a temperature of zero degrees this winter. This is a record for the latest winter date. In addition to warmer temperatures, the total snowfall for our state has been low (Fig. 1) and below average compared to a normal year (Fig. 2). As a result, many are predicting dry planting conditions for 2012.


Figure 1. Estimated total snowfall for Iowa (Nov. 1, 2011 – Feb. 6, 2012).
Map generated by Daryl Harzmann, Iowa Environmental Mesonet. 


Figure 2. Estimated total snowfall departure from average for Iowa (Oct. 1, 2011 – Feb. 16, 2012).
Map generated by Daryl Harzmann, Iowa Environmental Mesonet. 

With that weather data in mind, how does a dry and mild winter affect overwintering insects? Some might think warmer temperatures would increase the chances of insect survival. Perhaps that is true. But there are many factors that influence successful overwintering and are worth strong consideration. Some winter survivorship factors are highlighted here:

  1. Insects that overwinter above ground (e.g., bean leaf beetle adults) may be more likely to survive with fewer cold days. But a lack of snow cover can expose insects to those days with below-freezing temperatures, and could increase mortality compared to year with insulating snow.
  2. Insects that overwinter below ground (e.g., Japanese beetle grubs) will not likely be affected by a mild winter because soil temperatures are more constant. However, there could be more survivors than normal if the frost layer is shallow.
  3. All insects develop based on temperature. A warm winter day could cause insects to become active (e.g., woolly bear caterpillars) when they normally would be dormant. Activity uses up stored fats they depend on to survive until the spring. Without access to food, these active insects could starve to death before food becomes available.
  4. Most insects adapt to cold winters by slowly preparing in the fall and staying dormant until the spring. Therefore, large temperature swings can be detrimental to insects; the body can be injured or death can occur. We would expect some insect mortality due to cold intolerance when temperatures regularly fluctuate from 0-50 degrees.

Also, there are other factors to understand before we can predict how successful insects will be in the spring and summer. The same survival factors outlined above also apply to beneficial insects, like predators and parasitoids, and insect-killing pathogens. So ultimately it might not matter too much if more pests survive in a mild winter, because more beneficial insects will likely survive and help regulate spring populations. The uncertainty of insect survival in the winter can make predicting pest populations very difficult. 

Lastly, there have been questions about how to calculate degree days with winter days that exceed the lower developmental temperatures (i.e., 50 degrees for most insects). In other words, should we include those warm days in estimating insect development? This is a difficult question to answer, given we do not have a lot of experience with predicting insect development with an especially warm winter. Our educated guess is to calculate accumulating degree days from Jan. 1, 2012. As we observe actual insect development this spring and summer, we will see if temperature models are accurate or need to be slightly modified.


Erin Hodgson is an assistant professor of entomology with extension and research responsibilities; contact at or phone 515-294-2847. Laura Jesse is an entomologist with the Iowa State University Extension Plant and Insect Diagnostic Clinic; contact at or by phone 515-294-5374.

Southern Iowa Biomass Crop Workshop

By Emily Heaton, Department of Agronomy and Rick Sprague, Natural Resources Conservation and Service

There is increasing interest in biomass crops for energy in Iowa. Initially, it was thought that strong commodity prices would limit the interest of growers in planting perennials for bioenergy, but that doesn’t seem to be the case. A Biomass Crop Production workshop Thursday, March 8, at Southwestern Community College in Creston, Iowa will explore why interest is increasing. The program will start at 8:45 a.m. and conclude at 2:15 p.m.

Workshop participants will learn about opportunities to grow and market profitable biomass crops that are adapted to southern Iowa soils and climate. The Southern Iowa Resource Conservation and Development Area has been working with Iowa State University and the Iowa Farm Energy Working Group to evaluate biomass crops, including giant Miscanthus and warm season grasses that can be used to produce renewable energy feedstocks. Two companies are cooperating in this joint venture, with plans to create businesses that convert biomass to anhydrous ammonia and energy pellets. Collectively, these renewable energy enterprises would consume 54,000 acres of energy crops and create over 50 new jobs.

Based on feedback from the 2011 Workshop, this year’s event has been structured with more time for participants to interact with speakers.  The morning session will feature three speakers.  Steve Flick of ShowMe Energy with an update on his company’s activities since they received funding from the Biomass Crop Assistance Program (BCAP) in Missouri.  John Caveny , the second speaker, will focus on Miscanthus production.  He has been growing  Miscanthus longer than any farmer in the United States and will share his experiences and offer advice on growing Miscanthus as an energy crop.  The final speaker, Allen Powell of the Farm Service Agency in Columbia, Mo., will tell how BCAP is working on the ground. 

Guided small group discussions and networking opportunities will make up the afternoon activities. Discussion will focus on identifying strengths and needs in developing a strong supply chain in Southern Iowa.

Pre-registration is $20 until midnight, March 2. After that registration is $30. Registration can be completed online with a credit card (MasterCard or VISA only) at Registrations may also be faxed with a credit card to 515- 294-1311 or be mailed along with a check or credit card information to: ANR Program Services, 2101 Agronomy Hall, Ames, Iowa, 50011-1010. Registration includes refreshments, lunch and class materials. A student discount is available.

Registrations will be accepted the day of the workshop with registration opening at 8 a.m. on March 8.  For more information, call (515) 294-6429 or email

This program is sponsored by ISU Extension, USDA-NRCS, Southern Iowa Resource Conservation and Development Area and SynGest.


Emily Heaton is an Iowa State University Extension production biomass specialist. She can be contacted at 515-294-1310 or Rick Sprague is the Natural Resources Conservation Service (NRCS) Grassland Specialist for Southwest Iowa.  He can be reached at 641-782-4218  or

Strip-tillage Concept and Management

By Mahdi Al-Kaisi, Department of Agronomy

Where does strip-tillage fit? Where does no-till work best? Will strip-tillage out yield no-till on my farm? Those are several of the questions that I have received from farmers at meetings this winter. Here are some thoughts about strip-tillage in answer to these questions.

Strip-tillage, which creates a soil environment that enhances seed germination, is an alternative to no-till in areas where poorly drained soils are dominant. Where soil moisture conditions are suitable, strip-tillage – traditionally in the fall – creates narrow-width tilled strips to increase early spring soil evaporation and soil temperature in the top two inches.

This is particularly effective in poorly drained wet soils, where slightly raised soil strips are created by farm equipment such as anhydrous knives, disks, coulters, tool bars or manure injection equipment. Both fertilizer application and strip-tillage can be performed in one operation.

The basic requirements for strip-tillage to be effective are accuracy in matching tillage equipment on the tool bar with the planter and placement of seeds in the tilled zone.

Improving plant emergence
Faster and more uniform emergence of corn plants are two of the key goals of strip-tillage. In the fall, anhydrous ammonia injection knives, fluted coulters or other tool attachments are used to create residue-free strips and tilled zones that are approximately 6 to 8 inches wide and 6 to 8 inches deep. In the spring, seeds are planted directly in the same strips. Fertilizers may be incorporated while tilling these strips.

This concept is similar to another system, zone-tillage, with one exception. In zone-tillage, multiple fluted coulters create a zone that is approximately 1 to 2 inches deep and 8 inches wide and free of residue. These coulters operate at shallow depths to avoid creating void pockets below the seed. Another variation involves making a deep vertical slit with a thin profile knife centered in the middle of an 8-inch tilled zone.

Zone tillage can be achieved by using a planter equipped with fluted coulters as well. Coulters may be operated 2 or 3 inches to 6 inches deep if the soil is dry.

Farmers in southeastern states with particularly compacted soils have used in-row subsoiling with planter-mounted shanks in each row to create a tilled zone 12 inches deep. Seeds are then planted in the disturbed zone directly behind the shanks. This system is different from the two systems previously mentioned (zone tillage and strip-tillage) in that it is often used with a full width conventional tillage system.

Effect on soil temperature
Studies have shown corn is more susceptible to delayed germination or disease in cool soil temperatures when soil is poorly drained and there is high no-till residue cover. Other studies show that by removing residue over the row or disturbing a narrow zone (6 to 8 inches wide) the seedbed warms up more rapidly. This can help corn in the early part of the growing season; in some cases corn grain yield improved over no-till simply due to improved soil temperature.

Recently it was found that removing residue or strip-tilling to create a residue free zone improves corn germination due to increased soil temperature at the top two inches. You can use planter attachments that move no-till residue away from the row during planting. This assists in more rapid warming of the soil and combats slow germination caused by cold and residue-covered soils.

Topography is important to consider before using strip-tillage. In areas where the soil slope is steep or on highly erodible land (HEL), strip-tillage may not be the best choice. The disturbance of soil and removal of crop residue can create a significant water erosion problem in the row on steep slopes. It is recommended that after soybeans, at least 70 percent residue cover should be on the surface before strip-tilling. Strip-tillage is recommended on relatively flat land with poorly drained soils, where soil temperatures tend to be cold.

Key Points

  • Strip-tillage leads to warm up of soil temperature and improvement of plant emergence.
  • Strip-tillage has a yield advantage over no-till in wet, poorly drained soils.
  • Strip-tillage minimizes soil disturbance and keeps 75 percent of residue on soil surface.

For more information, read the publication Consider the strip tillage alternative.


Mahdi Al-Kaisi is an associate professor in agronomy with research and extension responsibilities in soil management and environmental soil science. He can be reached at or (515) 294-8304.

This article was published originally on 2/20/2012 The information contained within the article may or may not be up to date depending on when you are accessing the information.

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