Last year, heavy October rains in northern California wine valleys, along with above-normal fall temperatures, created the ideal growing environment for weeds. By winter, weeds were visible in vineyards, many becoming too big to control with a pre-bud-break herbicide application in late January or early February. Farmers are advised to control-late season weeds now to avoid these same weed issue this year. Last year, heavy October rains in northern California wine valleys, along with above-normal fall temperatures, created the ideal growing environment for weeds. By winter, weeds were visible in vineyards, many becoming too big to control with a pre-bud-break herbicide application in late January or early February. Farmers are advised to control-late season weeds now to avoid these same weed issue this year.
Now is the time to take out these weeds, many of which germinated in late summer, says John Roncoroni, weed science farm advisor, University of California Cooperative Extension, Napa County. “You can’t afford to give them another month or two of growth before making an herbicide application because by that time they will be too big for effective control. It’s even more important if you’re dealing with herbicide-resistant species.”
Roncoroni reminds grape growers it’s worth taking a three-year approach to budgeting for weed control. “The first year may be more expensive and require an additional application or two, but the end result is better control and often reduced costs in years two and three.”
Control late-season weeds now
If late-season weeds have emerged, apply a contact herbicide after grape leaves have dropped, making sure you remove the leaves from below the vines first, says Roncoroni. “Using a sweeper or blower works well to remove leaves, which is necessary in order to get good herbicide coverage of weeds and thorough soil coverage when using a preemergence herbicide in a tank mix.”
Removing dropped leaves doesn’t have to require an extra pass, he adds. “I’ve seen efficient use of a leaf blower strapped to the front of an ATV in order to remove leaves just ahead of the herbicide application.”
For control of herbicide-resistant weed species, such as glyphosate-resistant horseweed and hairy fleabane, use a tank mix of herbicides with different modes of action. “For example, DuPont™ Matrix® SG herbicide is a good tank-mix partner with glyphosate, providing a second mode of action and residual control.”
Know your major weed issues and watch for new species, says Roncoroni. “The major species germinating in fall and early winter are sharppoint fluvellin, horseweed (marestail), cheeseweed (malva), whitestem filaree and annual ryegrass. We’re now seeing ryegrass that’s showing resistance to glyphosate and at least two other herbicide classes, which makes herbicide rotation and the use of a tank mix essential.”
Maximize spring residual control
The pre-bud-break herbicide application is really the backbone of weed control for the season. Using the right herbicide tank mix at the right time can help maximize residual control through spring and even into summer.
“Typically, we expect to get at least four months of weed control from a good late- January application,” says Roncoroni. “Under the right conditions that can stretch to six or even eight months. Then you have the flexibility to make a postemergence summer application before July, if needed.”
Problems occur when growers can’t make a pre-bud-break application, he adds. “If time or weather don’t allow a preemergence application in February or March, you’ll likely be dealing with summer grasses such as barnyardgrass and jungle rice in many areas. If that’s the case, you could need to make a postemergence application in May.”
Tailor your weed control
It’s important to choose the right herbicides to fit application timing and weed spectrum. DuPont™ Matrix® SG fits well into most vineyard weed control programs as a foundation combination preemergence herbicide that provides consistent control of problem weeds such as filaree, horseweed (marestail), fleabane, Italian ryegrass, panicle willowweed, and suppression of yellow nutsedge.
Matrix® SG offers flexibility to fit several application scenarios:
• Fall/early winter – To control tough winter annual weeds such as horseweed (marestail), filaree or panicle willowweed, an application of Matrix® SG at 4 ounces per acre in an approved tank mix, provides excellent residual control.
• Late winter/early spring – A 4-ounces-peracre application of Matrix® SG (used with other herbicides registered for grapes, such as Alion SC or Prowl H2O with activating rain or irrigation) extends control of summer annual broadleaf weeds and grasses into the summer months and reduces the need for a preharvest foliar herbicide application.
• Two banded applications – Where 50 percent or less of the vineyard floor is treated in a herbicide band, Matrix® SG can be applied twice a year at the 4-ounce rate.* Growers can use a sequential weed management strategy that combines a late-fall to early-winter Matrix® SG application with a late-winter to early-spring application to maximize year-long residual control.
*Do not apply more than 4 ounces of product per acre per year on a broadcast application basis.
Always read and follow all label directions and precautions for use. DuPont™ Matrix® is not registered in all states. Contact your DuPont representative for details and availability in your state.
®™ Trademark of The Dow Chemical Company (“Dow”) or E. I. du Pont de Nemours and Company (“DuPont”) or affiliated companies of Dow or DuPont.
Alion® (Bayer); Prowl® (BASF).