Fighting winter annuals

By John Brien, CCA, AgriGold regional agronomist


The Eastern Corn Belt is experiencing one of the warmest winters on record. Temperatures have consistently been 5-10 degrees Fahrenheit above normal for most of the winter months, with some locations recording 60+ degree temperatures in the month of February. The warm weather throughout the winter could lead to a lot of unwanted situations in 2012. One of the unintended situations caused by warmer than normal temperatures is the potential for high infestations of winter annuals.

Winter annuals are unique in that they grow during the cool times of the year when other annual weeds become dormant. The life cycle of winter annuals begin anytime between late summer and early spring. The newly sprouted weeds overwinter as small seedlings and then when the weather begins to warm in the spring they continue to grow, flower, put on seeds and then die. Winter annuals typically grow close to the ground for protection against cold winter days. The young plants are very cold hardy and often stay green late into fall and are often the first plants to grow in the spring.

Two main factors dictate the severity of a winter annual infestations. The first factor is favorable conditions during the early to mid-fall time frame. The favorable conditions would include cool weather with favorable moisture. The second factor is a mild winter that allows for continued growth throughout the winter months. The current winter has met and exceeded all the requirements for a heavy flush of winter annuals in 2012.

Winter annuals do not have a direct impact on corn production, but do have an indirect impact on growing corn in fields with moderate to high levels of winter annuals. There are really three indirect ways winter annuals interfere with corn production:


  1. Dense populations of winter annuals can form a “mat” in the field. The mat can slow soil drying and warming which in turn interferes with planting and tillage applications in the spring. Most growers that have attempted tillage to extremely dense winter annual fields walk away extremely frustrated with the quality of their work and have left the soil surface uneven and difficult to plant into. A uniform seedbed is extremely important in achieving adequate emergence.
  2. Winter annuals will harbor insects in the spring. Black cutworm is one of these insects. Black cutworm moths migrate to the Corn Belt from coastal areas of the Gulf of Mexico early in the spring. They deposit their eggs in fields with low, dense vegetation, such as chickweed, henbit and curly dock. Fields that have dense early spring weed cover are much more likely to attract black cutworm moths.
  3. Purple deadnettle and several other winter annual species appear to serve as alternate hosts for soybean cyst nematode.

The next step is to begin scouting the fields that will be planted to corn in 2012. Fields with uniform infestations of winter annuals may benefit from burndown or tillage treatments made well ahead of planting. The earlier the treatment, the easier the weeds should be to control and the less biomass developed. If planting is delayed due to a wet spring, there will be large benefits to early control. In early March growers need to assess their fields, determine weed size and density, and if fields are dry enough for applications. If these conditions are observed they may need to get burndown or tillage treatments performed earlier than normal. 2012 is not a year to let these weeds get away.

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