Marestail is one of the most difficult weeds to manage in no- till soybeans. Harvest has begun and as you drive down the roads more and more soybean fields are being harvest and are now susceptible to weeds. Marestail is classified as a winter annual, but also emerges in both early fall and in the spring. Attempting to control the populations at the time of planting often results in failures as the plant is already too large to be controlled.
When running into this problem you should consider fall or early spring herbicide applications; however most of the time weather conditions prevent us from getting into the field for an early spring application. This will also allow Marestail to emerge in the fall and get to large for consistent control. For this reason, fall application is the way to go. Marestail is generally glyphosate-resistant across Iowa, therefore, 2,4-D is recommended for a base of Marestail burndown. However, putting Glyphosate and other products in the tank mix can help with winter annuals and other perennial weeds. It is not recommended to include residual herbicides in fall application because it will have little benefit on managing weeds in the spring.
With high amounts of rain during September to promote winter annuals, a fall herbicide application and scouting the fields prior and after harvest is recommended for no-till fields. Applications should be made with temperatures are in the mid-50s.
Fall applications are unlikely to eliminate the need for burndown treatments at planting but will help with the control and height of them. Rye cover crops are effective is suppressing the establishment of winter annuls and are another possibility to a fall application.
