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True armyworm is a migratory pest from the southern U.S. Each spring, volunteers help us monitor for true armyworm moths during April and May and weekly updates are posted on the ICM Blog. Although a trapping threshold does not exist to indicate whether a certain area might be at high risk for true armyworm feeding, we can use information from the trapping network to guide scouting efforts.
Scouringrush (Equisetum arvense) and field horsetail (Equisetum hymale) are two species of the Equisetum genus found in Iowa. There are 15 Equisetum species worldwide. They are primitive perennials that produce spores rather than seeds and spread primarily by rhizomes (underground stems). These two weeds are commonly found in roadside ditches, preferring poorly drained soils. More information about scouringrush, its lifecycle and its history can be found here.
Aphids are common insects to see in field crops, especially in alfalfa. In Iowa, there are at least four aphid species that colonize this crop. A quick scouting bout in central Iowa yesterday (May 17) revealed at least two species feeding within the same field. Learning to distinguish aphids in alfalfa takes a little practice, but is worth knowing for making sound treatment decisions.
Black cutworm (BCW) is a migratory pest that arrives in Iowa with spring storms each year. It is sporadic and unpredictable, making it essential to scout to determine whether BCW larvae are present in a field and management is required. Because BCW is sporadic, it is usually not economical to use preventative insecticide applications; however, rescue treatments can be very effective if scouting reveals larvae are present.
Iowa’s most significant soybean insect pest, the soybean aphid, has host-alternating biology. Its primary host 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 often happens when the host resumes spring growth. This makes biological sense because the aphids feed on phloem from actively growing tissue. If egg hatch happens too soon, they can suffer mortality from starvation.
With the cool and wet spring in 2022, there haven’t been many opportunities to seed forages. Looking at the calendar date, is it getting too late to plant forages? The short answer is that there is still some time to seed forages this spring. While the typical planting window is late February (frost seeding) through late April, planting forages in May can still be successful. For areas south of I-80, agronomists suggest seeding by the middle of May, whereas north of I-80 could get by seeding even a little later in May.
Alfalfa growth and development is affected by many factors, including temperature, soil moisture, stand age and even cultivar. Alfalfa growth has been slow this spring due to cooler than normal weather. This is a reminder that using the calendar date to determine when to harvest the first crop of alfalfa may not be the best method. In order to accurately predict the optimal time for the first cutting, the University of Wisconsin developed the Predictive Equations for Alfalfa Quality (PEAQ) method.
The weather forecast for the rest of April suggests below average temperatures will be likely, which may result in corn planting on soils colder than optimum, which requires careful consideration (see recent ICM News article). Also, fertilizer prices continue to be higher than normal. Therefore, starter fertilization can be useful to complement primary preplant fertilization for corn.
Bean leaf beetle adults (Photo 1) are susceptible to cold weather, and most will die if exposed to air temperatures below 14°F. However, they avoid harsh temperatures by burrowing under plant debris and loose soil. Each spring, adult beetles emerge from their overwintering habitat and migrate to available hosts, such as alfalfa, tick trefoil, and various clovers. As the season progresses, bean leaf beetles move to preferred hosts, like soybean. While initial adult activity can begin before soybean emergence, peak abundance often coincides with early-vegetative soybean.
In addition to checking alfalfa stands for winter injury, it is time to start thinking about scouting for alfalfa weevil. Even with recent cool temperatures, overwintering alfalfa weevil adults have become active, made their way to alfalfa fields, and have likely begun laying eggs in stems. Alfalfa weevil is a cool-season pest and is able to survive less than ideal temperatures by moving under residue or near the crown.
