Weed management in crop production used to be all about removing the problem weed from the competition for water and nutrients. While that is still the primary goal of weed control, producers must be diligent in their efforts to keep herbicides from moving off-target and to protect these herbicides to prolong their use.
Extension experts across the Cotton Belt say herbicides need to be used as part of a planned system of weed management and not relied upon alone to control target weeds.
Careful Use Of Current Tools
Eric Prostko, University of Georgia Extension weed specialist, says producers must be cautious from now on.
“We’ve got to protect these herbicides at all costs because that will be beneficial to you,” he says. “Producers are much more aware of how resistance occurs. We’ve been dealing with glyphosate resistance and ALS resistance, and we’ve had to change a lot of what we do because of this.
“We now have about 50 percent of the crop treated with glufosinate (Liberty), and we’ve got to watch how we manage that herbicide.”
Liberty (glufosinate-ammonium) has become a popular postemergence herbicide in Georgia due to its ability to control herbicide-resistant Palmer amaranth when applied in a timely manner, according to Prostko.
“If we don’t manage it well, it can develop resistance,” he says.
Prostko says cotton and soybean producers are anticipating 2,4-D and dicamba-related technology to become available in the future.
“Those herbicides by themselves are not enough,” he says. “We need glufosinate in those crops to help us with pigweed control. We’ve got to protect the products we have now.”
Part of that protection is in reducing off-target movement of herbicides.
More Potential For Drift
The proliferation of herbicide-resistant cultivars and the resultant prominent use of the herbicides have led to an increase in potential of off-target movement.
“Off-target movement is a big concern with the increase in vegetable production in Georgia in the last decade,” Prostko says. “It is not unusual to see cotton next to watermelons, tomatoes and onions.”
Vegetable production has increased in many Southern states, and Georgia has become a major producer, now ranking third in vegetable production with more than 200,000 acres. However, even peanuts are very sensitive to glufosinate herbicide.
Employ Drift-Reducing Techniques
University of Georgia Extension agronomist Stanley Culpepper says that there are two types of off-target movement, one of which is due to the volatility of the product even when the producer has done everything correctly. The other type, physical drift, can be improved upon.
“Physical drift is most often related to not following label recommendations,” he says.
Producers must use drift-reduction strategies and be conscious of wind speed and direction when applying a herbicide product. Also limit drift potential with the proper equipment setup and operator education and awareness. It is best to assume that a vulnerable crop is nearby and to do everything possible to keep the chemical on its target.
Prostko says one other concern is spray-tank contamination.
“That two gallons of liquid left in the sprayer that looks like water may not be just water,” he says. “It may be water mixed with something, and you’ve got to be careful. I strongly encourage you when moving from one crop to another that you make sure that spray tank is clean.
To keep problems with neighbors to a minimum and prolong the viability of herbicide products, producers need to use herbicides as one part of an overall weed management plan and keep herbicides from moving off-target as much as possible with drift-reducing strategies.
As part of planning a comprehensive weed management program, Guy Collins, University of Georgia Extension cotton specialist, offers some strategies, one of which is to have clearly drawn “weed maps” or written descriptions to help determine pre-emergence herbicide treatments and locate trouble spots within a field.
“Many farmers rely on memory or mental notes; however, the larger the area farmed, the less reliable this technique becomes,” he says.
Collins says effective banding of herbicides is a means of application used in conjunction with conventional tillage and cultivation as weed management strategies.
“Banding herbicide applications and tailoring herbicide treatments within a crop and/or field for areas of patchy weed problems not only reduces the threat of resistance, it also cuts down on herbicide usage,” he says.
In conservation tillage systems, Collins says, broadcast spraying pre-emergent herbicides is recommended.
Don’t overlook basic sanitation and cultivation that helps to reduce viable weed seeds, rhizomes and tubers present in a field.
“Cleaning equipment between fields, cleaning turnrows prior to harvest and harvesting weedier fields after fields with fewer weeds are simple and inexpensive ways to reduce the spread of undesirable vegetation,” Collins says.
“Row-middle weed control is best achieved by either banded spraying or cultivation, depending on your soil type and conservation practices.”
Finally, he says, hand weeding has become an effective line of defense in preventing those weeds from maturing to seed production and contributing to the seed bank.
Contact Amanda Huber at ((352) 486-7006 or firstname.lastname@example.org.
Future Sustainability of Liberty:
• Do not make more than two applications of Liberty per year.
• Spray Liberty when pigweed in the field is three inches or smaller.
• Never ever use a reduced rate.
• Wait one and a half hours after sunrise to begin spraying; stop one hour before sunset.
• Apply at a minimum of 15 gallons per acre using a speed, spray tip and pressure that delivers a medium spray droplet.
• Integrate with hand weeding, tillage and/or heavy rye cover crop residue.