Integrated Crop Management News

Across Iowa, grain harvest is ramping up. A challenge this harvest season will be dealing with variable grain moistures from field to field as well as within individual fields. Additionally, drought conditions that have persisted all year and rapid accumulation of growing degree days are leading to grain that quickly became overly dry. Follow the below set of tips to limit yield loss this fall.

Decisions for phosphorus (P) and potassium (K) fertilization should consider slightly lower but still fluctuating crop and fertilizer prices compared with last year and very variable rainfall across the state. The current or expected crop and fertilizer prices after harvest and the yield level this harvest have a major impact on producers' fertilization decisions.

Soil-test P and K interpretations were updated last winter

While the registration of 2,4-D and dicamba products for over-the-top use in resistant-varieties has improved waterhemp control for many farmers, weed scientists warned that these herbicides would eventually select for resistant waterhemp populations. Bayer recently reported the discovery of two likely dicamba-resistant waterhemp populations in Iowa, which warrants a discussion on best management practices to slow the evolution of resistant waterhemp populations.

This is a great time of year to scout 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 slowed since the widespread introductions on non-crop acres in 2016.

Since 2010, aphids have been colonizing corn later in the summer and can build up to surprising levels in Iowa. They can be found at the base of the stalk, around the ear and sometimes above the ear leaf. Aphids have been sighted in corn again this summer.

Soybean aphids have been quiet the last few growing seasons in Iowa. This year there have been isolated fields in northern counties that exceeded the economic threshold, but most fields have not warranted insecticides. However, many scouting reports and our observations in northern Iowa counties for the last two weeks show soybean aphids are established. We strongly encourage sampling soybean now to gauge the pressure and make timely treatment decisions.

The Ag Container Recycling Council (ACRC) works with private and state contractors across the United States to collect and recycle 55-gallon or smaller containers. In 2022, over 900,000 pounds of pesticide containers were collected and recycled in Iowa.

When it comes to soybean, one of the most common types of injury is defoliation from insects. This damage can be easily detected in the canopy by observing holes in the leaves or along leaf margins as insects with chewing mouthparts consume leaf tissue. The insects most responsible for defoliation are bean leaf beetles, Japanese beetles, and grasshoppers.

Corn rootworm egg hatch in Iowa typically occurs from late May to the middle of June, with an average peak hatching date of June 6 in central Iowa. Development is driven by soil temperature and measured by growing degree days (GDDs). Research suggests about 50% of egg hatch occurs between 684-767 accumulated GDDs (since January 1; base 52°F, soil).

Japanese beetle development seems to be a bit ahead of schedule this year, much like other pests we track each spring. Japanese beetle adults begin emergence when approximately 1,030 growing degree days (GDD; base 50°F) have accumulated since January 1 and will continue emerging until 2,150 GDD have accumulated. Japanese beetle adults likely began emerging in the southern portion of the state last week, and emergence will likely occur within the next two weeks in northern Iowa (Figure 1).

Variable rainfall and soil temperatures across Iowa since April have resulted in variable planting dates and early crop growth. As of today, June 12, upper soil moisture ranges from deficient to about normal. Some producers and consultants are wondering if the dry conditions are affecting the normal crop uptake of soil nutrients and plant tissue-test results.

Two male adult soybean gall midges were found in emergence cages at the Northwest Research and Demonstration Farm near Sutherland on June 6. This is about one week earlier than previous first captures in Iowa since we started monitoring emergence in 2019. The first Midwest report of soybean gall midge emergence in 2023 was May 31 near Mead, Nebraska. You can keep up with soybean gall midge emergence at soybeangallmidge.org/.

Stalk borer is an occasional pest of corn, but it can be persistent in some fields, especially those fields near perennial grasses that serve as overwintering sites (fence rows, terraces, and waterways are typical sources). Tracking degree days is a useful way to estimate when common stalk borer larvae begin moving into cornfields from their overwintering hosts. Foliar insecticide applications are only effective when larvae are migrating and exposed to the insecticide.

Last fall, we identified yet another field with an infestation of Asian copperleaf (Acalypha australis). For more background, check out this ICM News article from last fall.

In late April, the Environmental Protection Agency (EPA) authorized product registrants, Corteva Agriscience and Adama US, to proceed with accepting return shipments of certain cancelled products containing the active ingredient, chlorpyrifos.

Alfalfa growth has been slow this spring due to cooler than normal weather. This is a good reminder that using a calendar date to determine when to harvest the first crop of alfalfa may not be the best method. A better way to make harvest decisions is the PEAQ method (Predictive Equations for Alfalfa Quality) which takes several factors into account to roughly estimate the relative feed value (RFV) of standing alfalfa in the field.

Black cutworm (BCW) is a migratory pest that arrives in Iowa with spring storms each year. Black cutworm moths lay eggs in and near crop fields, and larvae can feed on leaves or cut corn seedlings. Larvae must attain a certain size (4^th instar) to be large enough to cut corn plants, and cutting can occur until plants reach the V5 stage.

Iowa’s most significant soybean insect pest, the soybean aphid, alternates between two hosts to complete its development. The primary host of soybean aphid is buckthorn, an invasive shrub often found in hedgerows and roadside ditches, and its secondary host is soybean. For most of the year, soybean aphids exist as cold-hardy eggs on buckthorn branches near leaf buds. For many aphids that overwinter as an egg, hatching happens when the host resumes spring growth.