Integrated Crop Management News

A monitoring network was established this year to monitor corn rootworm adults in Iowa cornfields, similar to the moth trapping network we manage in the spring each year. The goal was to help farmers and agronomic professionals monitor populations of northern corn rootworm (NCR) and western corn rootworm (WCR) in their fields and assess management decisions. A secondary goal was to estimate the ratio of NCR to WCR throughout the state and describe changing ratios into the future.

The August 10 derecho left portions of Iowa with broken, uprooted, and damaged corn across a significant portion of the state.

The majority of Iowa is currently in moderate to severe drought, with west central Iowa under the most extreme drought. As if drought were not enough, we were dealt another blow with extreme and widespread wind damage on August 10, some of which overlapped the drought area. With these events come an increased risk for ear rots and associated mycotoxins.

The Derecho storm on August 10 left fields with varying degrees of downed corn. In the weeks following the storm, the condition of the corn plants has worsened and the quality of the corn grain appears to be deteriorating. This deterioration in quality is expected to increase with time. 

The dry conditions throughout large areas of Iowa during 2020 reminds us of Iowa’s last significant drought in 2012 and the subsequent impacts on nitrate-N levels in subsurface drainage the following spring. This article will address concerns for water quality in drought conditions and opportunities to reduce nutrient losses from fields this fall.

Many fields have been ravaged by adverse weather this year in Iowa. On top of drought and hail we had a devastating derecho steam-roll a wide swath of Iowa starting in Sac County and progressing eastward along Highway 30. Along with the decision of how to handle this year’s crop, consideration for protecting the soil and preparing for next year’s crop should include cover crops.

Extreme weather events may lead to a decision to make corn silage rather than harvest corn for grain, or to harvest acres that will exceed current silage storage capacity. Before harvesting for silage, make sure you have a market for the silage or a sufficient number of livestock to feed it to. It may be difficult to harvest good quality corn silage if the crop has weather damage and the economic value of the silage will likely be lower than silage from non-damaged fields.

The decision to chop corn for silage should be made when there is no further potential to increase grain dry matter and whole plant moisture is in the proper range for the storage structure. The proper harvest moisture content is the same for drought stressed and normal corn. Recommended whole plant moisture contents are 65-70% in horizontal silos (trenches and bunkers), 60-70% for bags, 60-65% for upright stave silos, and 50-60% for upright oxygen limiting silos.

The August 10, 2020 high winds (derecho) caused lodged or flattened corn in many Iowa fields. The corn development ranged mainly from stages R3 (milk) to R5 (dent). Some fields may not be harvested, some chopped for silage, and some harvested for grain. Nutrients such as nitrogen (N), phosphorus (P), and potassium (K) remaining in the field may be different than with normal harvest due to partial plant removal, grain harvest, or grazing.

Derecho. Another of those words we wished we hadn’t heard in 2020 but are quite certain we won’t forget about the results from its occurrence. Millions of corn acres were damaged, and there are many questions about the lasting impact.

In cornfields, what did it leave behind? The damage varies considerably, but for this article, let’s break injury into three categories:

Waterhemp control is an increasing challenge for soybean producers due to the evolution of multiple herbicide-resistant populations. With dwindling herbicide resources, there is a need to integrate non-chemical strategies into current weed management programs in soybean. Cereal rye is the most common cover crop grown in the Midwest due to its winter hardiness and short life cycle.

This is the time of year to begin scouting for Palmer amaranth (Amaranthus palmeri) in Iowa crop fields. While Palmer amaranth has been identified in more than half of Iowa’s counties, new identifications have waned since the widespread introductions in 2016. Palmer amaranth is still a species to watch out for in every Iowa crop field. Minnesota recently reported finding the weed in a county previously not known to have infestations – thus the weed is still on the move.

Most people are probably aware of the unsolicited mailing of seed packets from China and other countries. The Iowa Department of Agriculture and Land Stewardship (IDALS) has issued guidelines on how to deal with the situation if you should receive one of these packages.  The following statement was made by IDALS.

Why do we care?

Late summer can provide a window of opportunity to seed perennial forage legumes and grasses, whether you want to establish a new forage crop or need to fill in bare and thin spots in an existing forage stand. To help improve the chances for a successful late summer seeding of forages, consider the following.

Field preparation prior to seeding

As parts of Iowa enter severe drought on July 14 (D2, US Drought Monitor), I encourage you to scout for twospotted spider mites in crops. Twospotted spider mites can increase whenever temperatures are greater than 85°F, humidity is less than 90 percent, and moisture levels are low. These are ideal conditions for the twospotted spider mite and populations are capable of increasing very rapidly.

Scouting

This year we have received many inquiries about potato leafhopper (Photo 1) in soybean and alfalfa. Although they are present in Iowa every year, populations are higher than in 2018 and 2019. Usually, potato leafhoppers are only considered a pest of alfalfa in Iowa, but they do feed on soybean, too. Potato leafhoppers prefer smooth leaves and are usually repelled by varieties with pubescence (hairs).

An ongoing public concern is the loss of nutrients from agricultural land in the corn belt. In Iowa, nitrogen and phosphorus losses from farm fields are driven by a variety of factors. Since the mid-twentieth century, statewide corn and soybean acres have increased as extended rotations, hay, and pasture declined. Compared to perennial crops and small grain rotations, corn-soybean and continuous corn rotations are leaky systems.

The Ag Container Recycling Council (ACRC) sponsors a free program to recycle clean triple-rinsed or pressure-rinsed pesticide containers up to 55 gallons in size. Refer to the ACRC Container Preparation Checklist for more information on preparing containers. Under the ACRC program, G. Phillips and Sons, LLC, located in Stanwood, IA collects and recycles containers in Iowa. For more information, visit G. Phillips and Sons, LLC. To set up a pickup, call G.

Soybean gall midge was confirmed as an economic pest of soybean in 2018. Worldwide, it is only known to occur in five states in the Midwestern US (Figure 1). Research began in 2019 to monitor the emergence of adults and incidence of larval feeding, as well as management options for the pest. This year, soybean gall midge adults were first collected on June 12 and larvae were detected in soybean on June 23.

Farmers have enjoyed the benefits of Bt corn since its introduction in 1996, particularly “in the bag” transgenic protection from insect pests and the yield loss they inflict. European corn borer (ECB), Ostrinia nubilalis, was particularly challenging and the target of the first Bt hybrids. The adoption of Bt corn in the U.S. prompted a widespread suppression of ECB. Even so, ECB still shows up in conventional cornfields in Iowa and can be a devastating pest.