This spring, we have had several reports of fields with high numbers of grubs from field agronomists in central Iowa. There are multiple species of white grubs in Iowa, including the Japanese beetle. Recent warm temperatures are accelerating insect development, and with forecasted temperatures, Japanese beetle emergence could begin in southern Iowa counties this week (Figure 1). Japanese beetle adults will 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.
Integrated Crop Management News
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Plant-parasitic nematodes that feed on corn are relatively common in Iowa, but their presence in fields does not mean that damage and yield loss are occurring. The number of nematodes necessary to damage corn varies greatly among nematode species, and the potential for yield loss can only be established by determining the types and numbers of nematodes present in a field. This article explains the “why” and “how” of sampling corn fields to determine if nematodes are causing damage and are likely to reduce corn yields. Management options for nematodes on corn also are listed in the article.
Stalk borer is an occasional pest of corn, but it can be persistent in some fields, especially those fields near fence rows, terraces, and waterways that serve as overwintering sites. Tracking degree days is a useful tool 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. Start scouting corn for larvae when 1,300-1,400 degree days (base 41°F) have accumulated.
ISU Extension and Outreach Field Agronomists recently highlighted a significant number of phone calls related to fomesafen carryover injury to corn rotated from 2020 soybeans.
“How much nitrogen (N) has been lost?” is a question we get this time of year, particularly in areas that have received more rainfall. Although most of the state is dry, the southeast part of the state has received above normal rainfall, and there are valid concerns that some N has been lost and additional N could be needed.
While we cannot specifically answer the question of how much N has been lost due to the complexity of the N cycle; below are some approaches we can use in making estimates on the status of N and the potential need for additional N during the growing season.
Canada thistle has been a consistent threat to crop production and perennial habitats since its introduction to the state in the late 1800s. Canada thistle is commonly found in crop fields, pastures, hayfields, CRP, and other full sun habitats. While fall is typically the best time to manage this weed species, late spring, when Canada thistle plants are in the bud or early bloom stage, is a close second for providing consistent herbicidal control. Now is time to be treating Canada thistle in pastures, hayfields, and other non-crop areas if you don’t want to wait for fall.
Multiflora rose (MFR) is a common weed in pastures, CRP, timber and other areas that are not annually disturbed. Now is an appropriate time for treatment of these weeds in pastures and other areas they invade.
Iowa’s most significant soybean insect pest, 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 the majority of the year, soybean aphids exist as cold-hardy eggs on buckthorn branches near leaf buds. As spring temperatures increase, the eggs hatch and a few generations are produced on buckthorn before moving to soybean. In the summer, soybean aphid has multiple, overlapping generations on soybean. During the fall, soybean aphids return to buckthorn.
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. Since much of the corn planting around the state is complete and many fields have emerged, now is a good time to begin scouting for larvae.
Performance of preemergence herbicides in many areas of the state may be less effective than normal due to limited rain following application. Although weed emergence following planting was reduced by dry soils and cool temperatures, it is likely that most fields will have some weeds that emerged during this period. Systematic scouting of fields, beginning shortly after crop emergence, will be essential to determine how best to manage weeds throughout the remainder of the season