How to get good coverage on vertical weeds.
Spraying grassy weeds is a little tricky in terms of optimizing herbicide performance. To get good coverage on a vertical spray target, you’ll need to get your water volume, nozzle selection, spray pressure and timing all working for you.
“In most cases, you want to control grassy weeds as early as possible,” says Eric Johnson, weed biologist at the Scott Research Station with Agriculture and Agri-Food Canada (AAFC) in Saskatchewan. “Although early is important, the weeds must be emerged to be controlled.”
If you’re working in a less competitive crop such as flax, a herbicide application applied too early may not result in enough spray retention to give you the control you want. “We found that in some situations where the grass weeds were just emerging or in the 1-leaf stage, we didn’t get adequate levels of control. It didn’t make much difference in a competitive crop such as barley, however, in a non-competitive crop like flax, there was a benefit to applying a bit later between the 2- and 4-leaf stage of the weed.”
Start good control by correctly identifying the weeds. For example, in Saskatchewan the dominant foxtail species is green foxtail. Manitoba has yellow foxtail as well as other foxtail types. “Weeds should be actively growing at the time of application,” Johnson says. “This enhances their ability to take up and translocate the herbicides.”
Grassy weeds have more vertical leaves, making them harder to target and more difficult to wet. Unlike larger and flatter broadleaf weeds, vertical grasses don’t intercept larger droplets as efficiently, so it stands to reason that vertical grasses retain smaller droplets better than larger droplets.
“The application somewhat depends on the type of herbicide application parameters you use,” says Johnson. “We know growers like to cut their water volumes, and in most cases you can go down to 5 gallons per acre (56 litres per hectare) with most grass herbicides. However, with contact herbicides such as most Group 1/ACCase herbicides, using really low water volumes plus very coarse spray qualities can compromise control.”
At low water volumes, medium or coarse sprays should be used; very coarse sprays should be avoided. In most studies, water volume appears to have more of an effect on herbicide efficacy than spray quality.
“The Group 2/ALS herbicides, especially those with soil and foliar activity, don’t seem to be as affected by these variables compared to Group 1 herbicides,” explains Johnson. “The Group 2 herbicides that have soil activity offer a bit more flexibility in application parameters. Selecting those products means you automatically have greater weather latitude and can optimize timing because you can spray with a coarser spray under slightly windier conditions.”
Referring to research that compares time of weed removal and spray quality, Johnson says, “We found that although we lost some grass weed control using very coarse droplets, as long as we sprayed at the optimum timing we were able to maintain crop yields. Using coarse to very coarse spray nozzles or low-drift nozzles provides a little more flexibility to apply those herbicides at an optimum timing.”
Research conducted by Dr. Tom Wolf, research scientist with AAFC in Saskatoon, Saskatchewan, showed that Everest®, a Group 2 herbicide with soil activity, demonstrated consistent and high wild oat control at all water volumes and spray qualities. There was no significant reduction in efficacy when spray quality was coarser or volumes were lower, even at the low herbicide rate. However, the consistency of control was not as great as it was at the higher rate.
Nozzles are probably the most important part of the sprayer and largely determine the efficacy of the herbicide, the amount of drift and expected outcomes. They are also relatively inexpensive compared to the cost of a sprayer unit, since they usually make up less than one percent of the investment cost. The key differences between most types of nozzles are the materials used (plastic, ceramic and steel), the pressure ranges and fan angles.
Wolf says that the way nozzles are used has the biggest impact on the outcome of the spray application. Identify the optimal overlap for the particular nozzle to make sure there aren’t any skips or uneven application. Canopy penetration is best when nozzles are pointed backwards. However, coverage of vertical targets like wheat heads or grassy weeds is best when nozzles are pointed forward.
Using a double nozzle provides the best of both worlds, but they work most efficiently with a coarse spray. A double nozzle with a fine spray will mostly increase drift potential with few other benefits.
“Controlling grassy weeds early and taking the right steps to optimize the herbicide application will help maximize crop yields,” says Johnson. “To add flexibility to the timing of application, using Group 2 herbicides with dual foliar and soil activity can be a good option. Making your herbicide application more effective and efficient takes a good applicator making the right product and equipment decisions at the right time.”
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How to get good coverage on vertical weeds.
Spraying grassy weeds is a little tricky in terms of optimizing herbicide performance. To get good coverage on a vertical spray target, you’ll need to get your water volume, nozzle selection, spray pressure and timing all working for you.
“In most cases, you want to control grassy weeds as early as possible,” says Eric Johnson, weed biologist at the Scott Research Station with Agriculture and Agri-Food Canada (AAFC) in Saskatchewan. “Although early is important, the weeds must be emerged to be controlled.”
If you’re working in a less competitive crop such as flax, a herbicide application applied too early may not result in enough spray retention to give you the control you want. “We found that in some situations where the grass weeds were just emerging or in the 1-leaf stage, we didn’t get adequate levels of control. It didn’t make much difference in a competitive crop such as barley, however, in a non-competitive crop like flax, there was a benefit to applying a bit later between the 2- and 4-leaf stage of the weed.”
Start good control by correctly identifying the weeds. For example, in Saskatchewan the dominant foxtail species is green foxtail. Manitoba has yellow foxtail as well as other foxtail types. “Weeds should be actively growing at the time of application,” Johnson says. “This enhances their ability to take up and translocate the herbicides.”
Grassy weeds have more vertical leaves, making them harder to target and more difficult to wet. Unlike larger and flatter broadleaf weeds, vertical grasses don’t intercept larger droplets as efficiently, so it stands to reason that vertical grasses retain smaller droplets better than larger droplets.
“The application somewhat depends on the type of herbicide application parameters you use,” says Johnson. “We know growers like to cut their water volumes, and in most cases you can go down to 5 gallons per acre (56 litres per hectare) with most grass herbicides. However, with contact herbicides such as most Group 1/ACCase herbicides, using really low water volumes plus very coarse spray qualities can compromise control.”
At low water volumes, medium or coarse sprays should be used; very coarse sprays should be avoided. In most studies, water volume appears to have more of an effect on herbicide efficacy than spray quality.
“The Group 2/ALS herbicides, especially those with soil and foliar activity, don’t seem to be as affected by these variables compared to Group 1 herbicides,” explains Johnson. “The Group 2 herbicides that have soil activity offer a bit more flexibility in application parameters. Selecting those products means you automatically have greater weather latitude and can optimize timing because you can spray with a coarser spray under slightly windier conditions.”
Referring to research that compares time of weed removal and spray quality, Johnson says, “We found that although we lost some grass weed control using very coarse droplets, as long as we sprayed at the optimum timing we were able to maintain crop yields. Using coarse to very coarse spray nozzles or low-drift nozzles provides a little more flexibility to apply those herbicides at an optimum timing.”
Research conducted by Dr. Tom Wolf, research scientist with AAFC in Saskatoon, Saskatchewan, showed that Everest®, a Group 2 herbicide with soil activity, demonstrated consistent and high wild oat control at all water volumes and spray qualities. There was no significant reduction in efficacy when spray quality was coarser or volumes were lower, even at the low herbicide rate. However, the consistency of control was not as great as it was at the higher rate.
Nozzles are probably the most important part of the sprayer and largely determine the efficacy of the herbicide, the amount of drift and expected outcomes. They are also relatively inexpensive compared to the cost of a sprayer unit, since they usually make up less than one percent of the investment cost. The key differences between most types of nozzles are the materials used (plastic, ceramic and steel), the pressure ranges and fan angles.
Wolf says that the way nozzles are used has the biggest impact on the outcome of the spray application. Identify the optimal overlap for the particular nozzle to make sure there aren’t any skips or uneven application. Canopy penetration is best when nozzles are pointed backwards. However, coverage of vertical targets like wheat heads or grassy weeds is best when nozzles are pointed forward.
Using a double nozzle provides the best of both worlds, but they work most efficiently with a coarse spray. A double nozzle with a fine spray will mostly increase drift potential with few other benefits.
“Controlling grassy weeds early and taking the right steps to optimize the herbicide application will help maximize crop yields,” says Johnson. “To add flexibility to the timing of application, using Group 2 herbicides with dual foliar and soil activity can be a good option. Making your herbicide application more effective and efficient takes a good applicator making the right product and equipment decisions at the right time.”
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- Required fields are marked with *.