Postemergence broadleaf weed control in asparagus

Kill Canada thistle, clammy groundcherry, hairy nightshade, crownvetch and quackgrass before it spreads.

Perennial weeds and persistent annual weeds are growing well in Michigan asparagus fields this year. The early season and frequent rains have provided excellent growing conditions for most weeds. Perennial and other broadleaf weeds are controlled postemergence more effectively if treated with herbicides during active growth.

Several weeds in the Asteraceae, Fabaceae and Solanaceae families are common pests in asparagus. Canada thistle and other thistles, spotted knapweed, rush skeletonweed, crownvetch and hairy vetch, clammy groundcherry, hairy nightshade and others are present in many fields. Fortunately, there are several postemergence herbicides labeled for use in asparagus. Spur from Albaugh, Inc. contains the same active ingredient (clopyralid) as Stinger and Clopyr-Ag, and asparagus is included on the label. The Stinger label for asparagus was discontinued several years ago, and UPI discontinued sale of Clopyr-Ag. Spur gives good control of most weeds in the above families. Deeply rooted perennials, such as Canada thistle, may require two or more applications for complete control. Use 0.5 to 0.67 pints of product per acre. Do not exceed a total of 0.67 pints/acre/year. It can be applied during the harvest season, with a 48-hour preharvest interval. Spur should be available from local distributors.

Other postemergence herbicides that provide good perennial and persistent weed control are dicamba (Banvel or Clarity) and Formula 40 (2,4-D). Halosulfuron (Sandea) is very effective against many broadleaves and yellow nutsedge. It is weak against common lambsquarters and all of the nightshades.

If quackgrass or other perennial grasses are a problem, growers should consider using terbacil (Sinbar) preemergence, if growing asparagus on soil with more than 2 percent organic matter. Sinbar may stunt asparagus on lighter soils. Annual applications of a postemergence grass killer (e.g., Fusilade, Poast or Select Max) during the growing season will suppress perennial grasses and help keep them from expanding. The grass killers also will kill emerged annual grasses, such as large crabgrass and sandbur before they set seed.

Please review MSU Extension Bulletin E-433, Weed control guide for vegetable crops, for these and other weed control recommendations. E-433 may be accessed on line at the MSUE Vegetable Team website. The Spur label may be found at CDMS.net.

Dr. Zandstra’s work is funded in part by MSU’s AgBioResearch.

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