Integrated Crop Management News

Soybean aphid is still the most important insect pest of soybean in Iowa, despite low populations throughout the state in recent years. This summer, we have seen high populations throughout Iowa, with hundreds of aphids per plant, honeydew, and sooty mold development on leaves. We have also heard various reports about performance issues with pyrethroid applications. This has prompted many questions about when to spray soybean aphids and which insecticides to use.

Corn earworm is a pest that causes direct injury to corn ears. Corn earworms do not survive winters above the 40^th parallel but some migrate north to the Corn Belt every year. Economic injury in field corn is uncommon due to the high adoption rate of Bt traits in Iowa (e.g. Cry1Ab, Cry1F, Cry1A.105+Cry2Ab2, Vip3A). However, non-Bt sweet corn and popcorn is at risk every growing season, and the financial impact in these specialty crops is especially important.

Weed communities in three cropping systems suitable for the Midwestern USA were studied from 2017 through 2020 to examine how crop diversification and the intensity of herbicide use affected weed stand density and aboveground mass. A baseline 2-year cropping system with corn and soybean grown in alternate years was diversified with cool-season crops, namely oat and red clover in a 3-year system, and with oat and alfalfa in a 4-year system. Herbicides were not used in the cool-season crops.

Farm fields that have been covered with flood waters may need structural (physical) repair before returning to full production. Flood debris, sand, silt, erosion, and loss of soil structure may all result as residual effects of flooding.

Before You Begin

Grasshopper activity in field crops has picked up recently, and these jumpy insects and their defoliation have caught the attention of crop scouts and agronomists across the state. Grasshoppers tend to thrive under dry conditions, and although most areas have received adequate moisture in 2024, consecutive drought years have likely led to higher than usual populations. This article discusses identification, scouting and management of grasshoppers in corn and soybeans.

Those looking for any bit of good news among all the rain-soaked suffering we have endured this growing season have asked if the overabundance of moisture has drowned SCN. Unfortunately, the answer is no.

AMES, Iowa – Extreme rains in northwest Iowa have caused instances of stored grain being covered with floodwater. According to current Food and Drug Administration policy, grain inundated by uncontrolled river or stream water is considered adulterated and must be destroyed. The current situation is one of river water flooding rather than of rain-driven pooled water in low ground, for which there are salvage options. River-based floodwaters can bring in many hazards and rapid spoilage.

The spring has certainly looked a little different than previous years. What does it mean for disease development? With some of our more destructive diseases – sudden death syndrome (SDS) and white mold – the rains have certainly increased the chances of disease developing. Each season these diseases have two hurdles to clear: early season conditions that set up the disease, and mid to late-season conditions that make a disease situation worse.

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). Most areas within Iowa have reached peak egg hatch for corn rootworm (Figure 1), and we have heard several reports of larvae in cornfields.

Japanese beetle development seems to be a bit ahead of schedule this year, which is not surprising with the warm temperatures this 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.

Continued above average rainfall from April through May has led to flooded fields and conditions that are too wet to plant or do field work in parts of Iowa. Early June planting decisions surrounding your delayed and prevented planting provision should involve a conversation with your crop insurance provider. The Ag Decision Maker File A1-57 talks about the insurance provision implications related to late planting, prevent planting, and replanting decisions in Iowa.

Many fields are flooded or too wet to continue planting in many parts of Iowa. Delayed and prevented planting crop insurance dates are fast approaching with an unfavorable weather forecast. Decisions surrounding delayed and prevented planting provision need to involve a conversation with your crop insurance provider. There is a nice article available on the Ag Decision Maker website that talks about the insurance provision implications.

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.

As of this spring, we’ve identified Asian copperleaf (Acalypha australis) in crop fields in six counties, and it's likely in more. As we find more populations, it is easier to monitor their development through the growing season. Field agronomists have been monitoring two of the infestations this spring and have observed many emerged seedlings in Boone and Franklin counties.