Fall Pre-Emergent Herbicide Reminders

Mike Basedow and Janet van Zoeren

As harvest season is winding down, we wanted to recommend you consider a fall pre-emergent herbicide application. From our multi-year ARDP-funded pre-emergent herbicide timing trials, we found fall applications of either Chateau + Prowl or Alion controlled weeds as well or better than applications made during the spring when integrated into a season-long weed management program, and that any timing of a pre-emergent is better than relying only on burndown materials.

Previous work by Deborah Breth, Dan Donahue, and Anna Wallis also found good efficacy from fall applications with the following materials/combination of materials.

• Chateau (mostly annual broadleaves and some grasses) + Prowl (mostly annual grasses)
• Alion (annual broadleaves and grasses)
• Sandea (annual broadleaves and sedges) + Prowl (mostly annual grasses)
• Goaltender (annual broadleaves and some grasses)
• Simazine (mostly broadleaves) + Diuron (broadleaves and grasses)
• Sinbar (annual broadleaves)
• Casoron (annual broadleaves and grasses)
• Matrix (annual broadleaves and grasses)

We generally recommend making fall applications of pre-emergent herbicides where your herbicide strips are clean enough and weather conditions are favorable. If your strips are weedy heading into the fall, you could tank mix with a burndown material. Even more effective would be to get the burndown on a week or two ahead of your pre-emergent application, but you will need to weigh the time and labor costs associated with two separate fall herbicide applications.  Applications should be made prior to ground freeze up, which may be difficult in years with an early cold snap.

Here are a few suggestions if you would like to apply pre-emergent herbicides this fall:

• Choose materials that fit your weed species composition – different materials work better on different weed species. Scout your orchards and see what your most problematic weeds are when deciding on which materials to apply. Our herbicide lookup table can help you select which materials to use.
• Tank mix materials to get the full spectrum of control that you need, as few products will likely control all your weed species present.
• Adjust your rates by your soil textures – product efficacy is going to be impacted by your soil textures. Many products contain a range of rates by soil texture, follow this closely to maximize efficacy and to reduce the risk of negative impacts to your trees.
• Apply to as clean of a strip as possible – Many pre-emergent materials need to reach the soil surface, so applying them on top of a weedy strip is going to greatly reduce your control. In Peru, we went through two weeks ahead of our Alion application with paraquat to burn down the vegetation that had come up during harvest. We applied the Alion two weeks later, after the vegetation had time to burn back and expose the soil surface.
• Pay close attention to weather requirements – Pre-emergent herbicides are finicky materials. Most need to go on prior to soil freeze up. Treatments should receive enough water (at least 0.5”) within 7 to 10 days after application so that herbicide can be “activated” (penetrate into the ground and dissolved into the soil solution) and protected from photo-degradation or volatilization. Check the labels closely to make sure you are applying them under (as close to) ideal conditions as possible.
• Apply with a “conventional” fixed-boom sprayer calibrated to accurately deliver 40 to 60 gals. of water/A using flat fan nozzles and 30 to 40 psi, unless otherwise stated.
• Don’t rely on one application to give season long control – Like any IPM program, the best control is going to be gained by using multiple tools from the tool box. Use a variety of tactics (pre-emergent materials, timely burndown applications, well-timed systemic materials) to manage your weeds season-long.

Fall weed control has the potential to relieve time sensitive work in the spring, while providing similar levels of weed control to applications made in the spring. Like many chemical applications though, the best efficacy will be from following the label closely, paying close attention to the weather ahead of the application, and applying them to a clean herbicide strip in the fall. Rather than relying on the fewest applications possible, manage your weeds throughout the growing season with multiple tactics to keep your problematic weeds in check.

 

Changes in pesticide registrations occur constantly and human errors are possible. Read the label before applying any pesticide. The label is the law. No endorsement of companies is made or implied.