Asparagus season is approaching rapidly, and you should be making critical decisions about your weed control program for the year. Pigweed resistance to photosynthesis-inhibiting herbicides and ALS-inhibiting herbicides have been documented in several west Michigan asparagus fields, and you can be proactive in your weed control practices to suppress these resistant weeds and avoid development of more resistance. Fortunately, there are a number of pre-emergence and post-emergence herbicides labeled for asparagus, and most weed problems are manageable.
The photosystem II inhibitor herbicides (Karmex, Lorox, Sinbar, Tricor) have been used widely in asparagus production for over 50 years. This has led to resistance to this mode of action in several pigweed species. These herbicides are effective against many other broadleaf and grass weeds, and should be part of an asparagus weed control management plan. However, they should always be used with another residual herbicide with another mode of action. Depending on the weeds present in a field, tank-mix partners might include Prowl H2O, Dual Magnum, Callisto, Spartan or Command.
An early-season residual herbicide application also should include a weed surface-active herbicide, such as glyphosate (Roundup), paraquat (Gramoxone) or carfentrazone (Aim). This combination will kill emerged weeds and suppress new germination of most annual weeds. Unfortunately, several perennial weeds will not be controlled well with these combinations, and will need to be managed with post-emergence herbicides, either in the crop during harvest or after harvest is complete for the year.
A new herbicide label for 2018 allows using Quinstar 4L (quinclorac) after asparagus harvest is finished for the season for controlling several persistent weeds in asparagus fields. Quinstar controls field and hedge bindweed, and suppresses Canada thistle, perennial sowthistle, morningglory, common lambsquarters and Russian thistle. It also is active against large crabgrass, barnyardgrass and foxtail.
Quinstar may be applied at 12 fluid ounces per acre (0.375 pounds active ingredient per acre) in one application per year. Crop oil concentrate (COC) or methylated seed oil (MSO) plus a nitrogen source should be added to the spray mix to improve herbicide activity. This is a Supplemental label for Michigan. Copies of the label should be available from Michigan State University Extension educators and pesticide dealers.
Command 3 ME was labeled for asparagus in 2017. It provides good control of annual grasses, common lambsquarters, common groundsel, common ragweed and velvetleaf. Command has a mode of action different from all other asparagus herbicides, and its use will help avoid resistance to other residual herbicides used on asparagus. Command is a good tank-mix partner with the PS II inhibitors, but does not control pigweeds.
The following herbicides have demonstrated effectiveness on the listed weeds. The level of control may be variable, but using the herbicides will generally improve controlling the weeds. Please note that some are pre-emergence herbicides and some are post-emergence herbicides. Also, remember that herbicides have an active life in the soil of about four to eight weeks, after which they dissipate.
- Field pansy: Callisto, Chateau, Sandea, Sinbar.
- Russian thistle: Sinbar, Karmex, Tricor, Command, Chateau
- Puncturevine: Chateau, Prowl H2O, 2,4D, Clarity
- Smallflower geranium: Sinbar, Karmex, Tricor, Command
- PS II-resistant pigweeds: Dual Magnum, Prowl H2O, Chateau, Callisto, Spartan, Sandea
- Horseweed, Canada thistle, sowthistle, common ragweed, rush skeletonweed: Spur
Note and record the presence of weed species in each field, and mark perennial weed areas for treatment at the appropriate time. Weed-free fields result in better harvest conditions, cleaner product and higher yields.
Please see MSU Extension bulletin E0433, “Weed Control Guide for Vegetable Crops,” for current recommendations and a list of other weeds controlled by the herbicides.
credit:msue.anr.msu.edu