Winter annual weeds are species that begin growth during the late summer and fall, survive the winter and flower and produce seed in the spring. Common winter annual weed species in Michigan include common chickweed, purple deadnettle, and henbit. Excessive growth of these species often create dense mats of vegetation that can cause challenges with spring tillage operations, reduced seed to soil contact at planting time and can keep the soil from warming and drying in early spring.

Fields infested with winter annual weeds may also increase the risk of damage from several field crop insect pests.

Black cutworms

Black cutworms overwinter in the southern states; moths are carried to the state by warm air currents or storm fronts each spring. Black cutworm moths lay eggs in fields that have significant weed growth or cover crops at the time of their arrival. In 2011, we saw severe damage from black cutworm larval feeding in corn fields scattered across Michigan. Incidence of black cutworm damage varies each year, depending on populations of black cutworms to our south.

White grubs (various species)

White grubs are the larval stages of several beetle pests in Michigan. They can often be found near the soil surface early in the season feeding on the roots of winter annual weed species in southwest Michigan. It is likely that the roots of winter annual weeds help provide food for the larvae until the crop develops. In cases where white grub numbers are high (around one beetle per foot), we are seeing damage despite the 250 level of seed treatment in fields in southwest Michigan, especially from Asiatic garden beetles.

Application of soil insecticides at planting time, or perhaps the use of stronger seed insecticide treatments (1250 level), is important in controlling these pests. There are no effective rescue treatments for white grubs, so early detection of fields with high numbers of grubs is critical in protecting corn stands.

Seed corn maggots

Seed corn maggots are the larvae from a small species of fly that can sometimes reduce stands and seedling vigor in fields. Adult seed corn maggot females are attracted to rotting organic material at or near the soil surface. Decomposing winter annual weeds following tillage with incomplete coverage is often associated with challenges with seed corn maggots. Since virtually all commercial corn seed is treated at the 250 level with a seed insecticide, there should be less incidence of stand loss due to damage from seed corn maggots in corn than in the past. However, soybeans are also vulnerable to seed corn maggot feeding. Conditions that slow germination and seedling growth increase the risk of seed corn maggot injury.

View MSU Extension’s Insect Control Guide for Field and Forage Crops (near the bottom of the webpage). For more information on field crops insects, their biology and options for control, visit MSU entomologist Chris DiFonzo’s website.

Soybean cyst nematodes

Purple deadnettle and henbit have also been found to be alternate hosts for soybean cyst nematodes. We continue to see increases in numbers of soybean cyst nematodes in soybean production fields across Michigan. These winter annual weed species may be part of that equation.

Controlling winter annual weeds

Tillage operations and herbicide applications are the main options for keeping winter annual weed growth in check. Fall and early spring tillage, when soil moisture conditions are dry enough for tillage, can reduce the potential for negative impacts from these weeds. Timing of chemical control is important in the spring. Read an article written by MSU’s Christy Sprague discussing timing of application and herbicides to consider when making herbicide applications to no-till fields in the spring.  Information on the effectiveness of herbicides for spring burndown in corn is listed in Table 1J in the 2012 MSU E-434 Bulletin “Weed Control Guide for Field Crops.” Weed management options for no-till soybeans are listed Table 2N in this publication.

This article was published on MSU Extension News. For more information from MSU Extension, visit http://news.msue.msu.edu.