By Mark Loux, Ohio State University Extension herbicide specialist
We don’t usually run articles about fall herbicide application this late in the season, since most everyone is done applying by now. We’ve run several articles on this subject within the past couple months but here’s another one anyway, even if it makes us look pushy and obnoxious. Here’s why.
The consensus of a bunch of competent field people seems to be that fall herbicide treatments are more important than usual this year, due to the product shortages and price increases that could really mess with spring burndowns. We are all used to a plentiful supply of cheap glyphosate and 2,4-D, which may not occur again for a while. Fall treatments result in fields that are almost weed-free well into spring, so that an early May burndown has to control primarily a few spring-emerging broadleaf weeds (see photos). Benefits are numerous, but a primary one is that fall treatments create a spring burndown situation requiring a less aggressive burndown mixture. So, where shortages or high prices cause a reduction in application rates and complexity in spring burndowns, things are likely to go way better where fall herbicides were applied.
Here’s another reason. The current forecast is for a warm and wet winter. The thinking of some weather experts is that the wet may persist into spring planting season. Wet spring means delay in herbicide applications, and burndown situations that will get tougher as we move into May and June without weather that allows application, leaving us to contemplate the less than ideal combination of big weeds and herbicide shortages. Hence our one final pitch to get something applied this fall yet. We have applied herbicide into December following very cold conditions and still killed weeds, albeit slowly, so our recommendation is to keep spraying.
On a final note, we have applied a fair amount of rimsulfuron-containing products (e.g. Basis Blend) in the fall prior to soybeans in our research, and have not observed any crop injury the following spring. Other Ohio users of these products seem to have had the same experience. Apparently, there have been some instances in other states where fall application of rimsulfuron has persisted into spring at levels that can cause injury to soybeans. Rimsulfuron is one of the few herbicides with decent activity on bluegrass in the fall, as well as broadleaf weeds so it definitely has utility. Be sure to follow label guidelines regarding rate and timing of application for rimsulfuron products where soybeans will be planted. Relevant information for several rimsulfuron products can be found on page 35 of the Weed Control Guide and is presented here:
“Basis Blend can be applied in the fall or early spring prior to soybean planting with the following guidelines: 0.825 oz—at least 15 days before planting; 1.25 oz—at least 60 days before planting. These guidelines assume that at least one of the following conditions has been met (if not then soybeans should not be planted for 10 months after Basis Blend application): the soil temperature is above 50 F for at least 10 days between application and planting; the field is tilled; or the soybean variety used has high tolerance to sulfonylurea herbicides. Crusher can be applied at rates up to 1.3 oz/A in fall or early spring, at least 30 (1 oz) or 60 days (1.3 oz) days before soybean planting. Leopard can be applied at rates up to 2 oz/A in fall or early spring, at least 30 (1.5 oz) or 60 days (2 oz) days before soybean planting.”
If the rimsulfuron needs 10 days of 50 degree weather prior to planting, it seems like the worst case would be something like a late fall application followed by a relatively early-spring soybean planting. Or late fall application followed by a really cold spring prior to soybean planting. The labels for Crusher and Leopard do not contain the same statements about temperature and tillage that are on the Basis Blend labels, but do have statements about possible injury.