As growers across the Eastern Corn Belt prepare for the 2017 growing season, one major issue that continues to be a challenge is weed control. Now is an appropriate time to make plans for control of weeds, especially aggressive, herbicide resistant species. Palmer amaranth is an aggressive plant that thrives in drought, can grow more than 2 inches a day, is resistant to multiple herbicide modes of action, and produces 100,000 or more seeds per plant. Many populations of this weed are resistant to multiple herbicide modes of action. Palmer amaranth has been observed to emerge from May through September. The key to keeping Palmer Amaranth from establishing itself is implementing management practices to effectively eliminate seed production and hinder its ability to spread.
Tips for controlling Palmer amaranth
1. Scout for and identify problem weeds early. Palmer Amaranth is a pigweed species and can easily be confused with other pigweeds, such as redroot pigweed, during early growth stages. It is critical to identify weeds correctly in order to keep them from spreading. Universities such as Ohio State, Purdue, and Michigan State have excellent fact sheets with pictures to aid in weed identification.
2. Start with a weed-free seedbed. Effective burndowns or deep tillage will help control Palmer Amaranth and will allow growers to begin the season with a weed-free seedbed. Apply herbicides when the seedlings are less than 4 inches tall.
3. Use residual herbicides. Use of residual herbicides will control seedlings at emergence and limit the number of plants that will need to be controlled by post-emergence applications. This is especially critical in soybean fields, where effective post-emergence options are very limited
4. Crop Rotation. Rotation from soybeans to corn will allow for the use of additional herbicide modes of action (herbicides used in corn) that are effective at controlling Palmer Amaranth.
5. Hand Weeding. If plants escape normal management practices, removal before they produce seeds is essential. If a seed head has formed, place a trash bag over the seed head before removing the plant from the field to eliminate the spread of seeds across the field.
6. Manage drainage ditches, field borders, etc. Regularly mowing ditches, waterways, field borders, etc. will help control the spread of this weed. Although weeds growing in ditches do not directly compete with field crops, they will produce seeds and promote the spread of Palmer Amaranth.