For continuous spear growth from one year to the next, weed specialists advise growers to take proactive steps by managing weeds at the beginning of the growing season.
“Controlling weeds in asparagus is best started early in the season, before spear emergence,” said Johnny Coley, the current North Carolina State University (NCSU) horticultural Extension agent serving Granville and Person counties.
He said growers during the early part of the season can tank mix glyphosate and Lorox at postemergence and preemergence to control grass and broadleaf weeds.
“After the final harvest of spears, these herbicides can be applied again in order to extend the weed control into the season,” he said. “Once ferns emerge and after the last spears are harvested, Poast can be used to control grass weeds.”
Coley said growers can control broadleaf weeds by applying a basal spray of 2,4-D using a backpack sprayer. He warns that 2,4-D may injure asparagus if it comes in contact with any ferns.
He added that growers can apply Lorox if they control broadleaf weeds extremely early in the growth stage. One such broadleaf weed is morningglory.
“Once this weed starts to climb the asparagus stalks it cannot be sprayed,” Coley said. “Early eradication of broadleaf weeds, either by spray or mechanical measures, is recommended for best control.”
Besides shading out young asparagus, weeds can stress the plants out and prevent adequate fern growth, according to former NCSU Extension agent Carl Cantaluppi, an expert on asparagus.
Cantaluppi indicated in one of the Virginia Vegetable, Small Fruit and Specialty Crops guides that asparagus can withstand a lot of salt, so growers may use salt to control weeds. However, heavy rains can leach out salts and may injure or kill nearby vegetables that aren’t as salt tolerant.
He pointed out that growers probably shouldn’t till asparagus just to control weeds because the cultivation may cut and injure roots, causing Fusarium root rot fungus to take hold and kill asparagus plants. He preferred herbicide use instead.
Horticulturalists at Clemson University advised growers to weed asparagus beds in early spring before any shoots appear in an effort to prevent spears from breaking off. During the plant’s growth period, they indicate growers probably should pull weeds if possible to prevent any injury. In addition, they advise application and maintenance of a 2- to 3-inch layer of mulch throughout the growing stage.
Weed control program
Weed management usually requires a year-long approach for successful control. Bernard Zandstra, a weed specialist at Michigan State University, has indicated in the past that a season-long management plan will keep asparagus weed free and produce well-developed spears when no weeds are present.
The first step to a weed control program, according to Zandstra, involves killing any weeds that have emerged and keeping any future weeds from germinating. Any pesky weeds that are hard to control may require more than one herbicide application.
Weeds of concern before the growing season, he indicated, are quackgrass, annual bluegrass, yellow rocket, dandelion, horseweed, mouseear, cress, henbit, purple deadnettle, white campion and wild carrot. To control them, he suggested that growers apply foliar postemergence herbicides before planting or when they use preemeregence herbicides. Some of these include a glyphosate, paraquat, 2,4-D and a fluazifop.
Zandstra stressed that growers will find quackgrass challenging to control. This weed will reemerge even after applying a glyphosate. In the spring, growers can use a high rate of Fusilade DX (a fluazifop) at 1.5 pints per acre in addition to a crop-oil concentrate. Because a 28-percent liquid nitrogen amount may increase fluazifop activity, he advised to reapply Fusilade 14 days later.
To control annual broadleaves, winter annuals and seedling perennial broadleaf weeds, Zandstra instructed growers to apply a glyphosate in the spring. A paraquat will take care of smaller seedlings. Weeds such as horseweed, pigweed and lambsquarter may require 2,4-D to be added to glyphosate in case these weeds are glyphosate or PS-II (photosystem II) resistant, Zandstra pointed out. If only horseweed is present, growers can apply a clopyralid in the mixture. Clopyralid also works well on ragweed, dandelion, mayweed and skeletonweed.
Zandstra indicated that a diuron is a good photosynethesis inhibitor to use as a preemergence herbicide. If growers know Powell amaranth and other resistant pigweeds are present in fields, they should add another preemergence herbicide with the diuron. He mentioned options such as Solicam, Spartan, Dual Magnum, Prowl H20 or Callisto.
When harvesting and to control broadleaves, he indicated that growers can use a halosulfuron, a linuron, a 2,4-D, a dicamba or a clopyralid. To control grasses, they can select a fluazifop, a sethoxydim or a clethodim.
He pointed out that after-harvest applications should include two that involve a different mode of action from those used in the spring.
As with any herbicide use, read and follow the label carefully for weed control and contact your local Extension agent or specialist for more information.
Read more: Asparagus Weed Control