Field & Feedlot

Field & Feedlot is a monthly newsletter of current educational topics written by Agriculture and Natural Resources Extension and Outreach specialists in Northwest Iowa.

August 2021

Protecting Yourself from Summer Heat Stress by Fred Hall, Dairy Specialist

Corn Rootworm Review by Joel DeJong, Field Agronomist

Feed Efficiency and High Feed Costs by Dave Stender, Swine Specialist

Swine Building Maintenance Workshop Offered in August by Kris Kohl, Ag Engineering Specialist


Protecting Yourself from Summer Heat Stress

Fred Hall, Dairy Specialist

Exposure to heat can cause illness and death. Agriculture workers are often in hot environments as part of their jobs. Knowing how to identify heat stress and avoid it is important for worker health in the summer. The Occupational Safety and Health Administration has put together this information for worker safety.

The most serious heat illness is heat stroke. Other heat illnesses, such as heat exhaustion, heat cramps and heat rash, should also be avoided. There are precautions that can be taken any time temperatures are high and the job involves physical work.

Risk Factors for Heat Illness

  • High temperature and humidity, direct sun exposure, no breeze or wind
  • Heavy physical labor 
  • No recent exposure to hot workplaces 
  • Low liquid intake
  • Waterproof clothing

Symptoms of Heat Exhaustion

  • Headache, dizziness, or fainting
  • Weakness and wet skin
  • Irritability or confusion
  • Thirst, nausea, or vomiting

Symptoms of Heat Stroke

  • May be confused, unable to think clearly, pass out, collapse, or have seizures
  • May stop sweating

Protect Yourself and the People Around You

  • Know the signs/symptoms of heat illnesses. Monitor yourself and use a buddy system.
  • Block out direct sun and other heat sources.
  • Drink plenty of fluids. Drink often and BEFORE you are thirsty. Drink water every 15 minutes.
  • Avoid beverages containing alcohol or caffeine.
  • Wear lightweight, light colored, loose fitting clothes.

What to Do When a Worker is Ill from the Heat

  • Call a supervisor for help. If the supervisor is not available, call 911.
  • Have someone stay with the worker until help arrives.
  • Move the worker to a cooler/shaded area.
  • Remove outer clothing.
  • Fan and mist the worker with water; apply ice (ice bags or ice towels).
  • Provide cool drinking water, if able to drink.

A “Quick Card” that can be posted on the wall is available at:

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Corn Rootworm Review

Joel DeJong, Field Agronomist

I have received several calls recently about rootworm injury on corn. Almost all discussions have revolved around corn-on-corn acres, and most fields seem to have more than one corn rootworm Bt trait. ISU rootworm researcher, Aaron Gassmann, has confirmed western corn rootworm has developed resistance to all four Bt traits in Iowa. Rotation really helps – but many refuse to do so, creating a bigger problem.

This is the time of year to assess root injury in your cornfields – in particular, corn-on-corn acres. Corn rootworm larvae feed on corn roots and can potentially cause severe economic loss. For every node of roots pruned by larvae, expect a 15 percent yield loss on average. Evaluate root injury in every cornfield to better understand the efficacy of your management strategy. Get into fields, dig several roots from different locations, haul them to a water source, wash the soil off, and evaluate for larval feeding injury. The Iowa State node-injury scale ranges from 0-3 and is directly related to yield loss. Learn more about the scale at Root injury that exceeds 0.25 can experience economic loss.

Corn rootworm variants. The typical life cycle for northern corn rootworm and western corn rootworm consists of one generation per year, with females laying eggs in cornfields to overwinter and hatch the following year. However, these highly adaptable pests have developed population variants to overcome crop rotation. To confirm variants of either species, check for larval root injury in first-year corn and whether adult western corn rootworm or northern corn rootworm are present in the field.

The northern corn rootworm has resistance to crop rotation through extended diapause. Instead of overwintering eggs hatching the following spring, it may be two or three years before larvae hatch. Female northern corn rootworms only lay eggs in corn, regardless if it is from a variant or normal population. Larval injury is possible to first-year corn if a significant extended diapause population of this northern corn rootworm is in the field. Although northern corn rootworm often leave cornfields to feed on pollen and leaf tissue of weeds and soybeans, we have no evidence this species does not lay eggs outside of cornfields.

By contrast, western corn rootworms have not shown the extended diapause trait – they hatch the next year in fields but will starve if corn isn’t planted in that field. That is why rotation helps reduce this problem! So far, when we see resistance to Bt rootworm traits in Iowa, it has always been the western corn rootworms. We have not documented Bt trait resistance with northern corn rootworms, so at this time I expect all Bt traits to work on the northerns.

An effective way to manage fields with Bt trait resistance from western corn rootworms is to rotate fields out of corn production to break up the life cycle of this pest. This remains an extremely effective way to manage corn rootworm in Iowa. However, in cornfields where large populations of northern corn rootworm are observed, and where the presence of rotation resistance is suspected, farmers should protect first-year corn against northern corn rootworm larvae. That is why it is important to not only monitor root injury in fields, but also monitor which type of adult rootworm beetles are present in your fields.

Do not forget, soil-applied insecticides may be used at planting to protect from larval corn rootworm injury. You can find management information, along with all the basics to help you understand corn rootworms, on the new Corn Rootworm IPM Regional Working Group website, found here: It is worth spending some time there to learn more about this pest we are fighting.

To successfully manage corn rootworm, develop a long-term strategy that rotates among a variety of management approaches over multiple seasons. This is the best way to guard against the build-up of large populations and the development of resistance.

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Feed Efficiency and High Feed Costs

Dave Stender, Swine Specialist

Swine producers are paying more attention to feed efficiency to reduce the impact of high feed cost.

Feed costs are high because the price of both corn and soybean meal have increased dramatically. A few years ago, Iowa State University was part of a multi-state research project that studied various influencing management issues that can improve feed efficiency. One of the outcomes of that research project was a list of publication fact sheets that discuss ways to enhance feed efficiency. The fact sheets can be found at

The first paper on the list, written by Dr. John Patience, gives a great overview of how complicated feed efficiency can be and examples of areas to manage more diligently during times when feed prices are high. Dr. Patience states, “The value of one feed conversion point varies between 30 and 50 cents. At an average feed cost of $350/ton, it is worth 46 cents per pig. As feed cost changes, so too does the economic value of feed efficiency.” He continues “All other factors being equal, the best feed efficiency may lead to the best net income” as he points out that many factors are not equal when comparing one closeout to another. Patience elaborates that although feed efficiency is commonly used in decision making, mistakes can be made because interpreting feed efficiency can be over-simplified.

There are many variables that influence feed efficiency. Patience continues to explain the physical and social environment in the barn regarding the pig’s comfort zone. Additionally, pig factors such as entry/exit weight, health, growth rate, lean yield, genetics, and mortality can influence feed efficiency. For example, mortality will lower feed efficiency more if the deaths happen late in the finishing period.

During this time of high feed cost, various technologies that impact feed efficiency should be re-evaluated for cost return analysis. The Iowa Pork Industry Center has fact sheets available to help producers evaluate possible changes. Consider genetic impact, particle size of feed, pelleting, temperature comfort zone, target market weight, feeder management, amino acids, and sow farm feed efficiency as the major considerations.  

Check out the web site at click ‘Fact Sheets’ or call and discuss options with me (712-225-6196).

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Swine Building Maintenance Workshop offered in August

Kris Kohl, Ag Engineering Specialist

Swine producers and anyone involved with swine building maintenance can attend an upcoming workshop on building maintenance and repair. The workshop will be hosted Aug. 17, from 9 a.m. to 3 p.m., at the ISU Extension and Outreach Plymouth County office in Le Mars. It will focus on concrete pit maintenance and construction, truss management, roof and moisture management and other repair and maintenance issues that can help protect the building and extend its life.

Participants will also learn about unique ways to allow clean air into the attic space and minimize pit-ventilated gases from entering the attic during periods of minimum ventilation during winter months, helping to reduce roof corrosion. Ways to maintain concrete slats including their repair, to help enhance their usable life, will also be discussed.

The workshop is geared toward livestock producers, livestock building owners and contractors, facility managers, maintenance crew members, engineers, designers and others interested in swine building maintenance.

Registration is $20 and includes all materials and lunch. Pre-register at least two days before the workshop by calling 712-546-7835.

This workshop is being offered across the state in collaboration with the Iowa Department of Natural Resources and sponsored by the Iowa Pork Producers Association, Hog Slat, Pinnacle, AgVice, Premier Ag Systems, FarmTek, Ag Property Solutions, Manure Magic, Hills Bank, and Washington State Bank.

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Other resources:

Iowa Concern, offered by ISU Extension and Outreach, provides confidential access to stress counselors and an attorney for legal education, as well as information and referral services for a wide variety of topics. With a toll-free phone number, live chat capabilities and a website, Iowa Concern services are available 24 hours a day, seven days per week at no charge. To reach Iowa Concern, call 800-447-1985; language interpretation services are available. Or, email an expert regarding legal, finance, stress, or crisis and disaster issues. Or, visit to live chat with a stress counselor one-on-one in a secure environment.

COVID Recovery Iowa offers a variety of services to anyone affected by the COVID-19 pandemic. Virtual counselors and consultants provide counseling, family finance consultation, farm financial consultation, referral information and help finding resources for any Iowan seeking personal support. Iowans of all ages may join groups online for activities and learn creative strategies for coping with the effects of the pandemic. COVID Recovery Iowa will announce upcoming programs on the website and via all social media to help Iowans build coping skills, resilience and emotional support. To request support, go to

Finding Answers Now. As Iowans deal with disruptions to their families and communities, Finding Answers Now provides information to help you cope with concerns about stress and relationships, personal finance, and nutrition and wellness. Visit the website at

211 is a free, comprehensive information and referral line linking Iowa residents to health and human service programs, community services, disaster services and governmental programs. This service is collaborating with the Iowa Department of Public Health to provide confidential assistance, stress counseling, education and referral services related to COVID-19 concerns.

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