Month: June 2023

Weed Management in Dry Conditions

Source: Dr. Alyssa Essman

Finally, some much needed rain.  It looks like most of the County received around .5 inches Sunday night.  A welcome relief, but more is needed.  Hopefully that happens tomorrow and Wednesday.

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.

Meet Your New Weed Science Extension State Specialist- Dr. Alyssa Essman

Currently, Alyssa is a Visiting Assistant Professor in Weed Science with responsibilities in research, teaching, and Extension on a two-year appointment. We are happy to announce that Alyssa will be continuing in the Department of Horticulture and Crop Science as a tenure-track Assistant Professor on August 15. She will have responsibilities in Extension as the Weed Science State Specialist and will be conducting applied research in weed management.

Alyssa’s time in weed science dates to April 2014 when she worked as an undergraduate student for Dr. Mark Loux’s weed science program. She received her MS in Weed Science in 2018 followed by her PhD in 2022. Congratulations to Alyssa on this major accomplishment, and we are excited to have you as a permanent AgCrops Team member!

Consideration for Corn N Management under Dry Soil Conditions

Source: C.O.R.N. Newsletter

Sidedress applications of nitrogen have begun and many more fields will receive applications in the upcoming week.  The information below from the C.O.R.N. Newsletter maybe of some interest.

When considering adjusting your corn nitrogen program for dry weather conditions, consider how N gets to the root system for uptake. Mass flow is the primary mechanism for nitrogen (also sulfur, magnesium, and calcium). Mass flow is where nutrients in soil solution move toward the root as the plant takes up and transpires water through the crop canopy. Also, consider how dry weather affects the plant root system. Root growth will slow in dry soils, the situation we are now experiencing in the upper soil depths. Fortunately, root growth will re-establish, and the mass flow of nitrogen will quickly improve with rainfall. Here are a few considerations for managing N applications.

Nitrogen placement is one area to consider changes within the limitation of equipment available. The nodal root system originating from the lowermost nodes will take up nearly all N. Normally we discourage surface applications of nitrogen due to potential volatilization losses of N in urea form found in UAN or urea. Under dry weather conditions, we have limited opportunities for rainfall to move N into position for uptake. The goal should be to have nitrogen close to the root system and close to roots actively taking up water. So, moving UAN placement closer to the row and a little deeper will improve plant access. Anhydrous application is already deep enough and moving closer to the row increases root injury potential, so no adjustment is needed.

Nitrogen rate is another consideration. Looking at our N yield response data from 1998-2022 does not show that lower yields usually require less fertilizer N than higher yields. We think that’s because the causes of lower yields, which are typically stress from having less available water at critical times, often affect root growth, and so may make it harder for plants to take up the N that is in the soil. If your plan was to apply a rate based on the Corn Nitrogen Rate Calculator (https://www.cornnratecalc.org) which is for corn after soybean and a N:Corn Price between 0.1 and 0.15, the rate is 160 to 181 pounds of N per acre then stay with that amount. If the plan was to apply more than that, then cutting back would be reasonable.

A final consideration is timing. Application systems that make late-season applications possible have become more common. Putting down a reasonable side-dress rate and then basing a later application on rainfall could be a reasonable strategy.

Cover crops would also be something to start looking at now. We know if the yield falls short of normal, we will have excess soil nitrogen left after the growing season. The edge of field studies conducted by USDA-ARS has shown we can recover a substantial amount of this residual N through a cover crop. Exploring available cost-share programs with NRCS and SWCD would be a reasonable way to retain that valuable N on your field for a future crop.