Integrated Crop Management News

In addition to checking alfalfa stands for winter injury, it is time to start thinking about scouting for alfalfa weevil. Despite recent warm temperatures, alfalfa weevil development is slightly behind last year. However, it is likely adults have emerged from their overwintering sites to lay eggs in alfalfa stems in southern Iowa.

Spring has arrived and many fields are full of activity. April is a great time to seed alfalfa whenever the soil is fit. Shallow-seeded forages will germinate and grow very quickly with adequate soil moisture and just a few warm days. The key to getting a great alfalfa stand is proper soil preparation and timing of the seeding.

Seedcorn maggot larvae feed on germinating seeds or seedlings of corn and soybean (Photo 1). Feeding can delay development or kill the plant, and plant injury is especially prevalent during cool, wet springs when plants grow slowly. Even with variable weather so far this spring, seedcorn maggot development is on track with previous years. Forecasted temperatures suggest that seedcorn maggot will likely develop quickly in the next few weeks.

While row crops are generally the focus of attention this time of year, spring is a great time to scout for winter injury in alfalfa fields and assess stand health. This is especially true if stands did not have adequate snow cover or were covered by sheets of ice during the winter. Several other factors may contribute to alfalfa winter injury, including soil moisture, 4-inch soil temperatures, and other stresses like soil fertility, stubble height, as well as the age of the stand.

Prepare for a safe pesticide application season by checking the FieldWatch® registry before making pesticide applications. The FieldWatch® registry provides easy-to-use, accurate, and secure online tools to enhance communications and awareness between crop producers, beekeepers, and pesticide applicators.

Pesticide residues can be carried on your clothing even if you wear personal protective equipment (PPE) over your own work clothes. Therefore, it is important to properly clean your clothes after working with and around pesticides. Many pesticide labels provide limited instructions for cleaning work clothes. In situations where no instructions are provided, follow these guidelines for washing contaminated clothing. 

Guidelines for soil-test phosphorus (P) and potassium (K) interpretations and application rates were last updated in 2013. Since then, significant field research was conducted to assure that nutrient management guidelines are kept current.

With harvest winding down, one weed that made harvest more frustrating for some is burcucumber. Consequently, there have been many questions on how to better manage this weed to prevent those frustrations.

With harvest in full swing and while conditions have generally been good for in-field drying this fall there are still some corn fields in areas of the state with moisture levels in the low to mid 20s.

October began dry across most of Iowa except for some areas in southern and southeast Iowa. These conditions are allowing for rapid harvest progress. The outlook for the rest of the month calls for lower than normal rainfall. Below normal rainfall since August until the soil sampling time may result in lower than expected soil test results for phosphorus (P), potassium (K), and pH. Therefore, farmers and crop consultants should interpret those soil test results with caution.

While Iowa weed communities change constantly, it is rare that a species new to the region is discovered. Asian copperleaf (Acalypha australis) was first discovered in Iowa in 2016 in a corn field near Cedar Falls. Prior to this discovery, the only documented infestation in North America was within New York City. The plant was recently found in a soybean field in Grundy County, nearly 30 miles from the original infestation (Figure 1).

Recent rainfalls are likely to result in the establishment of winter annual weeds. Many fields may have dense stands of these weeds going into winter (Figure 1). It is often difficult to achieve timely burndown of these species in the spring, so farmers with persistent problems should consider making a fall burndown application to control winter annuals.

Fall is one of the best times for managing perennial and biennial weeds found in pastures or other areas maintained in perennial grass. As perennials prepare for the upcoming winter, they move energy reserves from shoots to their perennial vegetative reproductive structures (e.g. rhizomes, perennial rootstocks).

When heading to the field for harvest, it’s important to make sure your monitors, sensors and scales are getting accurate numbers. Taking the time to calibrate your combine yield monitor is the first step in making sure you are using high quality yield data to make decisions in your operation.

Sap beetles are a relatively common insect in cornfields, typically seen each year around harvest. People usually notice sap beetles (and other ear-feeding pests) while doing pre-harvest yield checks. Adult sap beetles are usually less than ¼ inch long and oval. Most are dark colored and sometimes have orange or yellow spots (Photo 1). Sap beetles can be distinguished from other beetles in corn by their antennae, which have a knob at the end. Larvae may also be found on corn ears.

Plant-parasitic nematodes that feed on corn are relatively common in Iowa fields. One or more species of these nematodes were found in 92% of samples submitted to the Iowa State University Plant and Insect Diagnostic Clinic from 2000-2010 (ICM News summary article).

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. Even with recent warm temperatures, hatching is a bit delayed this year due to cool spring temperatures. 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).