Fall Orchard Herbicide Reminders

Posted on by mrb254

Fall Orchard Herbicide Reminders

Mike Basedow and Janet van Zoeren

As harvest season is winding down, we want to recommend that you consider a fall herbicide application (if the weather remains favorable postharvest).

Fall Pre-Emergent Herbicide Recommendations

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, and that any timing of a pre-emergent is better than relying only on burndown materials. It is important to point out that these pre-emergent applications were integrated into a season-long weed management program.

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 when your herbicide strips are mostly clean 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. If you are unsure how to differentiate lookalike weed species, feel free to contact Mike at mrb254@cornell.edu – I’d be happy to visit and/or look at pictures to help ID weeds. Once you identify your weed complex, 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 (and potential for phytotoxicity) 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 the 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.

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. Use a variety of tactics (pre-emergent materials, timely burndown applications, well-timed systemic materials) to manage your weeds season-long.

Fall Applications of Systemic Materials

Following our 2023 and 2024 ARDP trials, we have a few tentative recommendations for fall applications of the systemic materials Stinger and 2,4-D.  While we are still conducting our final data analysis, we were generally very pleased with our results of fall applications of full rates of stinger post-harvest for controlling Canada Thistle in the following season.  This application should be made post-harvest, but prior to a hard frost, as this will likely reduce the overall absorption of the herbicide, ultimately reducing efficacy.  In our trial, we found a fall application post-harvest, paired with a follow up application after petal fall in the spring, gave very good season long control of the Canada thistle.  Note that you can only use one full rate of Stinger per growing season, so after this fall application, we recommend making follow up applications annually shortly after petal fall as the thistle begins to bolt.

We also trialed post-harvest applications of Unison, tank mixed with Stinger across the entire orchard floor to control creeping perennials like bindweed.  This application gave very little control of hedge bindweed at both of our sites. However, this application did give very nice control of other broadleaf perennial species like clover, dandelion, and broadleaf plantain within the row middles.  Similar to the Stinger application, best efficacy will likely be achieved if you make your applications prior to a frost while weeds are still actively growing.

Below are photos from our 2023 Canada Thistle Stinger Trial.  The top photos shows the plot in August 2023 prior to Stinger application.  The bottom shows the same plot in August 2024, after receiving Stinger applications post harvest in 2023 and after petal fall in 2024, along with the grower’s standard herbicide program. 

 

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