COLUMBUS, Ohio — Now that Ohio has experienced its first frost of the season, growers should be conducting fall herbicide treatments in preparation for spring planting.
Jeff Stachler, an Ohio State University Extension weed specialist, said that attacking winter annuals and simple perennials and biennials in the fall, rather than waiting until spring, is the most effective way to control these weeds.
"You will get a better kill with a fall program," said Stachler. "With winter annuals, it's easier to kill them in the fall when they are young and smaller than when they are much bigger in the spring and stressed from the winter weather. And with biennials and simple perennials, any translocating product will go with the nutrients down to the root systems and kill the plant."
Winter annuals, such as purple deadnettle, common chickweed, and marestail or horseweed, pop up in August and grow until June — with the exception of marestail which grows until October. Simple perennials, such as dandelion and curly dock, and biennials, like wild carrot and poison hemlock, can survive during winter by redirecting nutrients to the roots before cold weather sets in.
Stachler said that a fall treatment of such weeds is effective for several reasons:
• Weeds such as marestail and dandelion are much harder to kill in the spring than in the fall. And fall treatments require less of an herbicide rate because the overall size of the weed can be much smaller.
• Some weeds, like shepherd's-purse, can be effectively killed in the spring, but they must be controlled before setting seed. By treating in the fall, a grower can reduce the amount of seed production of winter annuals.
• A fall treatment affords a grower bare soil in the spring. Bare soil allows for more sunlight, which results in higher soil temperatures, faster drying times and an earlier planting date.
• Some weeds are host for insects. Purple deadnettle, for example, is host for soybean cyst nematode (SCN). "Purple deadnettle has come in early enough already this fall to help create another generation of nematodes," said Stachler. "So with that alone, nematode populations could increase." Chickweed is a good host for cutworm moth, which can reduce corn stands in the spring.
Stachler said that fall herbicide treatments are most effective under no-till production, but growers who till their fields may also benefit from the practice. "I've seen some growers who have built up their seed banks so much that they could not till the soil properly in the spring," he said. "So even if you are practicing tillage, there may be a need to apply fall herbicides."
And the steps a grower takes to treat weeds depend on what weeds are being targeted. "If a grower is targeting biennials, simple perennials and winter annuals, then a base program of 2,4-D is needed," said Stachler. "The remainder of the treatments can be based on two approaches."
One is a treatment that leaves no residual effects, such as using 2,4-D then adding glyphosate (at least at 0.75 pounds acid equivalent per acre) into the mix. "The one drawback with that approach is it's not going to give you any more help if anything germinates after the treatment, including in the spring," said Stachler. "However, this is the most broad-spectrum fall herbicide program, especially for perennials and biennials."
The second approach is to look at residual treatment programs mixed with 2,4-D, the best of which include Canopy XL. "Those programs are going to give you residual control for winter annuals and residual control in the spring for such summer annuals as lambsquarters and ragweeds," said Stachler. "Doing something with almost any herbicide program that is marketable for the fall will be more beneficial than doing nothing."