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How to deal with weed management in late fall
CROPS & WATER

How to deal with weed management in late fall

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Fall weed management is a great tool, but it’s important to know which weeds are present and if a pesticide application will be beneficial this late in the season.

Scout your fields first to determine if there’s enough weed pressure to warrant an herbicide application. Recent snowfalls and cooler temperatures raise the question if fall herbicide applications are still effective for weed management.

According to Amit Jhala, University of Nebraska-Lincoln Extension weed specialist, the ideal temperature to manage weeds using a post-emergence herbicide is between 65 and 85 degrees F. Herbicides can be applied when temperatures range from 40 to 60 degrees F, but it might take longer for the weeds to die, especially if it’s overcast.

In colder temperatures and overcast conditions, weeds are not able to translocate or metabolize herbicides as quickly. They might also have frost injury, making herbicide uptake difficult. After a cold snap, it’s best to wait a few days when temperatures are consistently above 45°F-50°F before continuing with fall weed management.

Looking at the forecast in the coming weeks will help producers determine if a fall herbicide application is worth the investment. Research at UNL has shown that up to 95% of marestail germinates this time of year, making fall management a good option for reducing weed pressure and competition next spring. T

here are plenty of products available to manage winter annuals this time of year and many of them include 2,4-D or dicamba. Understanding pesticide labels will also be important as the addition of certain adjuvants may help herbicide coverage and uptake in cooler temperatures.

If you plan to make herbicide applications yet this fall, be sure to read and follow all label instructions, especially if you intend to graze cattle. Follow the grazing restrictions, or at least the pre-harvest interval, to avoid detrimental effects on your cattle this winter.

Information on fall herbicide applications and grazing restrictions can be found in the 2020 Weed Guide: https://extensionpubs.unl.edu/publication/9000016794277/2020-guide-for-weed-disease-and-insect-management-in-nebraska/.

Winterizing spray equipment

Winterizing spray equipment can be tedious work but taking a little time this fall can save a lot of headaches next spring.

The first thing you want to do is to consult the pesticide label and determine the proper PPE to wear. Once you are properly equipped, drain the tank and fill it up to about 15-20% total tank volume with clean water. Circulate clean water through the system and dispose of any rinsate collected according to label instructions. Triple rinsing the system ensures the removal of residual chemicals but adding a cleaning agent can be helpful when cleaning out the sprayer.

When filling up the tank the second time, it’s a good practice to add a cleaning agent. You will want to consult the label of any pesticides used in the tank to ensure the cleaning agent is compatible and appropriate for the tank. Depending on the quality of the sprayer, certain pesticides may hold on longer in the system by getting caught in any pitting in the tank or hoses. A cleaning agent can help strip these residual chemicals out of the system and avoid carryover issues next spring.

After the cleaning agent sits in the system for an appropriate amount of time (see label for directions), rinse the system for a third time with clean water. You will also want to remove any additional sprayer parts (nozzles, screens, filters, sprayer tips, end caps, etc.) to allow for proper drainage. These parts need to be thoroughly cleaned before putting them back on the sprayer. It’s also important to clean the exterior of the tank, sprayer, or tractor used to pull the sprayer (if applicable).

Make sure everything on the system is drained and completely dry before doing your final inspection. Look for cracks, leaks, corrosion, or hidden damage and replace anything that needs to be fixed.

Follow manufacture recommendations and add antifreeze or oil (if necessary), check the tires and the battery, and store in a dry, well maintained building that is protected from the winter elements.

More information on cleaning and winterizing your sprayer can be found at UNL’s Pesticide Application Technology Website (https://pat.unl.edu/) or by listening to this Podcast with Greg Kruger, UNL weed scientist: https://cropwatch.s3.us-east-2.amazonaws.com/Podcast/CW-20-10-14-pestidice-tank-cleanout.mp3.

Sarah Sivits is the Dawson County Extension educator in crops and water, and serves Dawson, Buffalo and Hall counties. Contact her at 308-324-5501 or by email at ssivits@unl.edu.

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