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OSU Extension

College of Food, Agricultural, and Environmental Sciences

October 25, 2023 - 9:00am --

Harvest is upon us and in some areas, actively ongoing. As crops mature and we get to see a little deeper into the fields, you may be able to better see a few of the weed escapees that have been hiding among the crops all season long. Fall is a great time to evaluate the efficacy of your weed control methods, identify issues and prepare your integrated weed management plan for next year.

Although the view from the combine seat is a great bird’s eye view of the field, fall scouting for weeds is best done when you are able to take a few moments and walk out into the field and get an up-close look at the weeds that are present. Being able to correctly identify these weeds and getting a true understanding of their population density in the field will help you make appropriate management decisions. Without correct identification of species, management can be extremely difficult and result in wasted resources. It is also important to recognize the different growth habits and life cycles that may be present in the fields. Maturing summer annuals such as bur cucumber, rag weeds, amaranth species or velvet leaf are likely to be found as large, mature plants with seeds maturing or already being dispersed. Mature annual grasses like fall panicum or foxtails are also easily detected. Perennials like pokeweed, curly dock and Canada thistle are commonly seen, especially in soybean fields. The weeds that require closer scouting are first year biennials and winter annuals, both of which are going to be observed as young plants that are low to the ground, either as a recently germinated plant or as a rosette stage, which is a low-lying foliar stage of most biennials. Winter annuals such as purple deadnettle, henbit or marestail are common weeds to scout for. Biennial weeds such as burdock and poison hemlock would be weeds to look for that would currently be observed as a rosette.

What to do if herbicide is warrented

Based on your scouting, you may determine that a fall herbicide application is desired. In the most recent Agronomic Crops Newsletter, Alyssa Essman, Ohio State University Weed Science State Specialist shares these reminders:

  • Evaluate weed emergence and growth post-harvest to help determine if an application is necessary.
  • Fall-applied herbicides should primarily target weeds that are emerged at the time of application.
  • Species present in large quantities late-season that would necessitate the application of an herbicide include (but are not limited to): marestail, dandelion, wild carrot, poison hemlock, common chickweed, purple deadnettle, henbit, annual bluegrass, and cressleaf groundsel.
  • OSU research has not found much of a benefit from adding metribuzin or other residual products late in the fall. The exception to this is chlorimuron, which can persist into the spring. The recommendation here has generally been to keep costs low in the fall and save those products for spring when you will get more bang for your buck.
  • Herbicides generally work across a range of conditions, though activity can be slower as temperatures drop. Foliar products are most effective when daytime temperatures are in the 50s or higher and nighttime temperatures remain above 40.

Keep in mind that your integrated weed management plan should not rely solely on herbicide use. Utilizing best management practices, timely mowing, crop rotation, tillage, and a variety of other preventative, cultural, mechanical, biological, and chemical methods help diversify our angle of attack on weeds. Practicing integrated weed management over time will help to draw down your soil seed bank and reduce the impact of weeds on your farm.

As always, we wish everyone a safe and bountiful harvest!

Frank Becker is the Agriculture and Natural Resources Extension Educator with Ohio State University Extension – Wayne County, and a Certified Crop Adviser, and may be reached at 330-264-8722 or
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This article was previously published in The Daily Record.