Letters from the Inbox

Q&A

Q.

Dear Longleaf Alliance,

I sprayed Spyder (generic Oust®) over my newly planted (January 2021) longleaf in April. It controlled the weeds. But with such a rainy summer, they came back with a vengeance in late summer. Is it safe to spray Spyder over them again this spring, the beginning of their second growing season?

Angry Weeds in Georgia

Dear Angry Weeds,

Thanks for reaching out with your question regarding sulfometuron (the active ingredient in herbicides Oust® or Spyder) application in successive years. Sulfometuron is a useful herbicide for controlling broadleaves and annual weeds, especially when converting former agricultural sites back to longleaf. Specific targets include weeds like dog fennel, goldenrod, ragweed, crabgrass, and horseweed. Perennial grasses, croton, and all trees are less susceptible, which can be useful in promoting fuel recovery for earlier burning.

The label for Spyder allows repeat applications and goes on to say do not exceed more than 3.75 oz. per acre per year. A little goes a long way, and usually, we are talking about 2 oz. per acre. Earlier applications would be more effective because Oust® has both pre-and post-emergent activity on the target species, which are more effectively controlled at the early stages of growth (< 6” tall). Waiting until you have a rank infestation of ag weeds is too late for best control.

For any herbicide treatment, always begin with an assessment of the site to determine the problematic species, the extent, and with an eye also to what desirable species are also returning. This applies to the initial application and even more to any second-year repeat application. We want to use the right tool for the job, the right timing, minimize collateral damage and expense, and be more able to introduce fire before the trees initiate height growth. Put another way, if the first-year application was not that effective, was it the right herbicide choice, a timing issue, or just overwhelmed by an extremely wet season? Could another tool better interrupt seed-setting in the problem species? We can help with this evaluation, and the next steps might be to send some photos of the typical problem species on site, sharp and clear enough for identification. We have some time to sort out the best next steps before early spring.

For anyone considering a release application of sulfometuron be sure to keep the following in mind: • For release treatments (applied after planting to

“release” the seedlings from weedy competition), do not use any surfactant when going over the top of seedlings.

Note - there are exceptions with certain grass herbicides. • Dig before you spray! Oust® functions as a root inhibitor and should only be applied over seedlings that have initiated 6+ new roots at least 2" long in the first year following planting. The visual check is much more certain than any arbitrary waiting period and might allow an earlier application. • Test the soil to ensure the soil pH is 6.2 or below. • Make sure you are not using the “Extra” version of a product; that "Extra" component is usually metsulfuron (Escort®), which can be lethal to longleaf seedlings even with very low application rates. • Repeated applications of herbicides can get expensive and may create new challenges as species that are tolerant of the treatment increase or target species become resistant.

A.

Always keep detailed records of any herbicides applied. Memory can be tricky, and management actions and expenses should be detailed both in your plan binder and for any reforestation benefit on your taxes.

Sincerely, The Longleaf Alliance