Moderate to exceptional drought conditions (D1-D4) are being experienced in much of Ohio. Conditions are worse in the south and southeast regions of the state. Crop plants are maturing rapidly, and harvest is either underway or expected to be early in many areas, especially these harder hit regions. Between tough growing conditions this season and low commodity prices, it’s a fair question to ask if it’s worth investing in a fall herbicide application this year. One consideration is the likelihood of an earlier than average harvest, which means that the window for fall applications may be longer than normal. The potential benefit from including this application in a no-till production system is dependent on field history and the presence or lack of some species that are most easily controlled in the fall. The goal for these applications is to target emerged weeds, especially troublesome winter annual, biennial, and perennial species such as marestail, annual ryegrass, wild carrot, and dandelion. Populations of waterhemp, giant ragweed, and other summer annual species will not be influenced by a fall application.
The dry pattern may reduce winter annual weed emergence some, especially if there are no considerable precipitation events between now and the first frost. Whether or not a fall application will be necessary may depend on rainfall and weed emergence patterns through the end of the application window in late-fall. Scouting to monitor weed emergence and growth after harvest will help determine if an application is necessary. A relatively inexpensive but effective application provides the most value, especially in years like this year when prices are low, and conditions have been tough. Glyphosate + 2,4-D is an effective combination for most of the target weeds at this application timing and can be applied ahead of corn or soybeans. Some other effective fall application programs include:
Corn or soybeans next spring
Glyphosate + 2,4-D
Metribuzin + 2,4-D
Dicamba + 2,4-D
2,4-D + tribenuron and/or rimsulfuron (Basis, Nimble, Audit, Express, Victory, Crusher, Leopard, etc.)
Soybeans next spring
Canopy EX/Cloak EX/Fallout + 2,4-D
Canopy/Cloak DF + 2,4-D
Corn next spring
Simazine + 2,4-D
In trials conducted at Ohio State in years past, there was no benefit of adding metribuzin or other residual herbicides when applications are made late in the fall. Chlorimuron (Classic, Canopy, Cloak, etc.) is one active ingredient that can persist into the spring; however, it’s often a better strategy to prioritize spending on residual products for use in the spring when more benefits will be realized. The main deciding factor in whether to include a fall herbicide as part of your program should be the presence or lack of overwintering weed species (winter annuals, biennials, and perennials) that are most effectively controlled in the fall. Although the death of plants is slower, herbicides applied into December are still effective, so the decision about whether to make an application can be determined later in the year depending on weather and weed emergence patterns. As a general reminder, foliar herbicides are more effective when daytime temperatures are 50°F or higher, and nighttime temperatures are above 40°F. Herbicides applied in cooler temperatures can result in a slower kill or poor control. Using appropriate adjuvants according to label guidelines can ensure better performance in these tough conditions, and where weeds are weathered and stressed. Check herbicide labels prior to selecting rates as the herbicide rate used may influence crop rotation intervals.
The need for a fall application will likely depend on conditions in a given region and may differ from field to field within an operation. Repeated scouting from now through December to assess weed emergence and growth, especially following precipitation or frost events, can be helpful in making this decision. As always, reach out if you have questions at Essman.42@osu.edu.
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