By Matt Reese
As problem weeds like winter annuals, dandelions and marestail have been a growing challenge, more farmers have been relying on fall herbicide applications for better control.
Morrow County farmer Anthony Bush has seen a particular problem with marestail and has found that the only way to get good control is a total herbicide program approach, which usually includes a fall application. Unfortunately, as harvest continues to drag on, there have been few, if any, opportunities to get fall herbicides applied.
“I personally like doing it in the fall, but if I have to do it in the spring I will,” Bush said. “I definitely would say that marestail is a problem in the area. When people don’t take care of it in the beginning with a burndown pass, it makes a mess that is obvious in the fall. My approach to controlling marestail is an overall approach. It is your entire chemical program across all of your crops that takes care of marestail. You have to get your 2,4-D in the program, get your wheat stubble sprayed when you need to and keep atrazine in the program. And whenever possible, I really like spraying in the fall when the weeds are little and you have a lot better chance of controlling the problem.”
But by late October, Bush still had a quite of bit of harvesting ahead of him. How crucial is a fall application for controlling maretail and other problem weeds?
“Fields not treated in the fall can require a more aggressive spring burndown program, compared with those treated in the fall,” said Mark Loux, Ohio State University Extension specialist. “It’s not a huge problem except in those fields loaded with winter annual weeds in the fall, since the mat of weeds can keep fields from drying out in spring and interfere with spring tillage.”
In general, herbicides are applied in the fall primarily for control of an existing infestation of winter annuals or marestail, volunteer wheat, biennials (wild carrot, poison hemlock), or cool-season perennials (dandelion, quackgrass, Canada thistle) that are most susceptible to herbicides in the fall, Loux said.
“We consider the fall herbicide application to be an essential component of an effective marestail management program, although fall is not where the majority of the money should be spent on managing this weed. Even where the herbicides lack residual, the fall treatment seems to enable more effective control of marestail the following season,” he said. “In some cases, it’s probable that you don’t even know how much the fall treatment helps out, but our research shows that more often than not it does. For most other weeds, a field that appears fairly weed free following corn or soybean harvest may not require fall treatment, especially given how late harvest is this year.”
It is also important to note that there is still time to spray weeds this year.
“In our research, herbicides seem to be effective for control of winter annuals and biennials well into December. The rate of plant death can slow considerably, but this is not a problem since weeds just have to die by early spring,” Loux said. “Control of perennials typically declines in late November or early December though, depending upon weather.”
In a recent CORN Newsletter article, Loux highlighted a core group of herbicide treatments that make sense to use in the fall based on their effectiveness and cost.
Glyphosate + 2,4-D can be used in the fall prior to any spring crop. It is the most effective of the treatments for grasses, biennials, and perennials. The combination of 0.38 lb acid equivalaent per acre of glyphosate plus 0.5 pounds of 2,4-D ester is effective for most winter annuals, and rates of both herbicides can be increased for perennials and biennials or large weeds.
2,4-D + dicamba (premixes such as Weedmaster, Brash, etc) can be used prior to corn or soybeans. This combination controls most broadleaf weeds, but is not as effective as glyphosate-based treatments on dandelion or Canada thistle. In OSU research, application of dicamba alone has not typically provided adequate control when applied in November, but the combination of the two herbicides seems to work.
Canopy EX or DF + 2,4-D can be used prior to soybeans. The only one of the treatments listed here that provides residual control into the following spring/early summer. The lower labeled rates of Canopy are adequate for control of emerged winter annual weeds. Canopy DF may not adequately control chickweed unless mixed with glyphosate, metribuzin, or Express. Canopy treatments have been the most effective for control of dandelion.
Metribuzin + 2,4-D can be used prior to corn or soybeans. This mixture controls winter annual weeds only. The metribuzin can provide some residual weed control into later fall, but residual control does not persist into the spring.
Basis + 2,4-D can be used prior to corn, and also prior to soybeans south of I-70 at rates up to 0.5 ounces per acre. This combination is effective on winter annuals and dandelion, with some activity on biennials.
Simazine + 2,4-D can be used prior to corn. It controls winter annuals only. While simazine is a fairly persistent herbicide, it provides little residual control into the spring.
Autumn + 2,4-D or glyphosate can be used prior to corn or soybeans. This controls winter annual weeds and can suppress dandelions, but overall is not as effective as Basis or Canopy treatments. The 2,4-D or glyphosate carries more of the load for this treatment compared with the others shown here, so higher rates of these herbicides may be required.
Express + 2,4-D can be used prior to corn or soybeans and controls winter annual weeds and dandelion, but is less effective than Basis or Canopy treatments on the latter.