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Agronomic Crops Network

Ohio State University Extension


Weed Management in Dry Conditions

This article is written with the hopes that relaying some information about management in a dry pattern will bring on some rain. If that doesn’t work, below are some reminders and considerations for weed control in dry conditions.

  • To wait or not to wait – one consideration is whether it’s better to apply POST herbicides when weeds are small or to hold out for some rain. Weeds are most effectively controlled when actively growing and drought stress can impede control to some degree. However, large weeds are more difficult to control especially if the stress-inducing conditions persist. For this reason, and the fact that herbicides generally work across a range of conditions, it might be best to go ahead and spray when weeds are small unless there is some definite rain in the forecast.
  • Weed emergence – dry conditions can delay the later emergence of weeds, especially those that are in the upper portion of the soil and have small seeds. The emergence of large-seeded species and those at lower depths will be less affected. Weed emergence flushes can occur periodically following rainfall events.
  • Residuals – residual herbicides will not be properly incorporated, and thus not available for uptake by weeds, to help control those that do emerge before we receive a decent rain. Mark Loux talked about this and the use of a rotary hoe in an article a couple of weeks ago, which can be read here. A layered residual strategy for control of waterhemp is still recommended, especially where crops were planted early. Rain will still be needed to incorporate later-applied residual herbicides into the soil profile.
  • POST applications – plants respond to drought stress in part by increasing cuticle thickness to preserve water. This can decrease herbicide absorption, and translocation within the plant is also affected. Optimizing the use of adjuvants can help to increase absorption by improving coverage and uptake. Follow the label and herbicide/adjuvant manufacturer recommendations to determine the best type and rate. Also, be aware that an increase in activity can lead to crop injury in some instances, and that applications early or late in the day may reduce the risk of injury.
  • Antagonism – dry conditions can exacerbate antagonism issues, especially when using POST grass and broadleaf herbicides together. Control can be reduced especially for larger grasses with substandard root systems (hanging on by a few roots). Sequential applications can help overcome this antagonism. Wait seven days between applications when the broadleaf herbicide is applied first, and about one day when the grass herbicide is applied first.

For more information on weed control in a variety of conditions, check out the Weed Control Guide for OH, IN, IL, and MO available for purchase here.

Crop Observation and Recommendation Network

C.O.R.N. Newsletter is a summary of crop observations, related information, and appropriate recommendations for Ohio crop producers and industry. C.O.R.N. Newsletter is produced by the Ohio State University Extension Agronomy Team, state specialists at The Ohio State University and the Ohio Agricultural Research and Development Center (OARDC). C.O.R.N. Newsletter questions are directed to Extension and OARDC state specialists and associates at Ohio State.