A Generic Clopyralid (STINGER) Product Called SPUR is Labeled for Asparagus

Clopyralid, marketed under the trade name STINGER, was labeled for use in asparagus for years.  About eight years ago Dow removed asparagus from the Stinger label due to liability concerns.  A generic version of clopyralid called SPUR, produced by Albaugh Inc., is now available and includes asparagus on the label with a 48 hour PHI.

 Both clopyralid products are formulated with 3.0 lb a.e. per gallon.  Apply 5.3 fluid ounces (0.125 lb a.e./A) of SPUR to asparagus before or during the cutting season when the target weed is observed emerging.  Some crooking of spears emerged at the time of application may be observed.  Repeat at the end of the asparagus cutting season to extend control.

The SPUR label includes all the other vegetable crops listed on the STINGER label, including sweet corn, spearmint and peppermint, spinach, beets, turnips (roots and tops), strawberries, and Brassica (cole) leafy vegetables.  The Brassica (cole) leafy vegetables crop group includes broccoli, broccoli rabb, Brussels sprouts, cabbage, cauliflower, cavalo broccoli, Chinese (bok choy) cabbage, Chinese broccoli, Chinese mustard cabbage, Chinese (Napa) cabbage, collards, kale, kohlrabi mizuna, mustard greens, mustard spinach, and rape greens.

The weeds controlled by clopyralid fall into two botanical plant families, composites and legumes.  Common composite weeds found in our fields include Canada thistle and other thistles, mugwort (wild chrysanthemum), horseweed (marestail or stickweed), galinsoga and ragweed species.  Legume weeds include vetch species and clover species.  Apply clopyralid postemergence when the crop has 4 to 6 true leaves and the weeds are less than 2 inches in height (see table below).  No additives are needed or recommended.

SPUR Use Recommendations for Labeled Vegetable Crops.

The maximum labeled rate of clopyralid is one-third to two-thirds of a pint per acre (O.125 to 0.25 lb ai/A) per year, depending on the crop, but the rate needed varies, depending on the targeted weed species.  One and a half to two fluid ounces per acre (0.032 to 0.047 lb ai/A) will control seedling annual weeds such as common ragweed, annual vetch, and galinsoga.  Three to four fluid ounces per acre (0.070 to 0.094 lb ai/A) are needed to control perennial clover species and suppress or temporarily control Canada thistle.  Most other susceptible perennial weeds require the maximum labeled rate to eliminate the weed.

Optimum results controlling deep rooted and hard to control perennial weeds, including Canada thistle, perennial asters, goldenrod species, and mugwort (wild chrysanthemum) will be obtained if the clopyralid application is split.  Coordinate your crop rotation and planting date so half the maximum labeled rate of clopyralid can be applied in late April or early May when the perennial weed emerges in the spring.  Some weeds, especially mugwort, can “survive” for months on established existing foliage even though clopyralid suppresses all new growth.  Eliminate all existing foliage of mugwort with another postemergence herbicide, tillage, cultivation, hoeing, or hand weeding.  Flag or otherwise mark the parts of a field where the susceptible perennial weed was treated.

The application of clopyralid timed to match the emergence of the perennial weed in the spring coincides with the time of year when the carbohydrate food reserves in the plant are at the lowest point.  Treatment at this time reduces the weed’s chance of recovery and survival.

Apply the second half of the clopyralid to the marked areas of the field about sixty to ninety days after the first application.  Expect no growth of the target weed to be observed at the time of the second application.  Spray the second application even though no growth of the target weed is evident.  The second application is essential to the elimination of the hard to kill established perennial weeds.  If the second application is skipped, expect to see the weed re-emerge in late August or September.  Time both applications to maintain the PHI (PreHarvest Interval) listed for the crop, or treat after harvest.  Clopyralid is a residual herbicide with carryover potential.  Adhere to crop rotation restrictions, or follow with labeled crops.

Clopyralid is both a postemergence foliar absorbed herbicide and a residual herbicide.  The initial twisting and curling observed after application to susceptible weed species is due to the foliar absorbtion.  Control of established perennials is due to residual clopyralid in the soil which prevents regrowth from the roots.  In certain species such as mugwort, clopyralid prevents regrowth but does not kill the mature leaves.  The plant will survive unless existing foliage is killed.

Do NOT apply clopyralid in a hand held sprayer used to “spray until wet”.  clopyralid is a residual herbicide that must be applied on a rate per acre basis.  When treating “patches” of perennial weeds, apply the recommended rate per acre with a calibrated sprayer.  Treat ten to fifteen feet beyond the weed “patch” on all sides.