In 2016, the record-breaking precipitation in the fall and winter prompted flushes of winter weeds to germinate. Experts agree this weather shift may have caught growers off-guard and ill-prepared to deal with weed growth. Mick Canevari, farm advisor emeritus at the University of California, Davis, says, “Growers had experienced fewer winter weeds in recent years due to lack of moisture, so they may have become complacent on timing weed control.” In 2016, the record-breaking precipitation in the fall and winter prompted flushes of winter weeds to germinate. Experts agree this weather shift may have caught growers off-guard and ill-prepared to deal with weed growth. Mick Canevari, farm advisor emeritus at the University of California, Davis, says, “Growers had experienced fewer winter weeds in recent years due to lack of moisture, so they may have become complacent on timing weed control.”
While seasonal weather patterns have become less predictable on the West Coast, the one thing you can count on when winter rains arrive is the weeds will quickly follow. Most orchards are plagued by a healthy crop of young weeds when winter moisture is plentiful and soils begin to warm in the spring. Stopping weeds before they emerge is key to staying ahead of weeds throughout the year.
Aim for Season-Long Control
A two-application herbicide program has become the norm for most tree nut growers. This practice helps manage a broad spectrum of weeds and extends the window of control.
Ideally, a winter herbicide application should be made between November and January to control marestail, fleabane and malva. A second application between late February and April can take advantage of rainfall for better activation and residual control. Grasses like junglerice, barnyardgrass and crabgrass, which tend to be a problem in the spring and summer, are managed with the second herbicide application.
DuPont™ Matrix® SG, used in sequential winter and spring applications with tank mix partners, is a good choice for preemergence and early postemergence control of grass and broadleaf weeds in tree nut orchards.
Resistant Weeds on the Rise
While planning herbicide applications, follow best management practices to control the spread of resistant weed populations.
“Glyphosate-resistant weeds are spreading each year, primarily because many herbicide applications for trees and vines include only glyphosate,” says Canevari. “Tank-mix partners with different modes of action are really important for the management of resistant biotypes.”
Matrix® SG herbicide is a good tank-mix partner and controls glyphosate-resistant fleabane and marestail. Combining diverse modes of action in a tank mix helps prevent weeds from developing resistance.
Tips for Effective Weed Control
Canevari offers the following tips for growers heading into spring:
• Know your weeds and use weeds identified in the previous year to set expectations for pressure next season.
• Use timely herbicide applications for cost-effective control. Small weeds are easier to control, making herbicides more effective.
• Don’t rely on a single herbicide to control weeds. Canevari explains that weed control is too complex and there are too many variables for one product to successfully manage the broad spectrum of weeds. “In the long run, it’s going to cost more to rely on one herbicide. It’s more beneficial to tank-mix different modes of action. There will be less spraying and less opportunity for weed shifts and resistance issues.”
Always read and follow all label directions and precautions for use.
DuPont™ Matrix® SG herbicide is not registered for use in all states. Contact your local DuPont sales representative for details and availability.
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