By Gared Shaffer
Warm temperatures across South Dakota this spring could allow Kochia to get a head start in many areas of South Dakota. The minimum soil temperature that research has shown for Kochia germination is 39 degrees Fahrenheit. The recent warm weather in South Dakota could trigger an onset of Kochia germination. When air temperatures have been up and down in early spring, a common question from producers is, “Can early-emerged kochia seedlings survive freezing temperatures?” The answer depends on how long the freeze event is and how intense it is. Kochia is well-known to be frost-tolerant, but research has shown that kochia seedlings are not more tolerant to freezing temperatures than winter annuals, such as shepherds-purse, field pennycress and downy brome. If a few kochia seedlings are found from scouting fields, then you should expect more seedlings of kochia to emerge later.
Chemical Application Timing
If field and weather conditions allow, the best time to control kochia is before it emerges through a fall residual application. Rarely in South Dakota is there proper air temperature for spraying a spring residual before kochia emergence. Therefore, if a fall application was not completed, or it wasn’t effective, an early spring burndown application should be performed as soon as possible. There are widespread occurrences of acetolactate synthase (ALS) and glyphosate resistance in kochia populations in South Dakota, so choosing the proper herbicide treatment is of utmost importance. When controlling kochia in any crop, always choose a tank mix or a single chemical that is not in the ALS inhibitor (Group 2) family of chemicals or glyphosate (Group 9). If an ALS Inhibitor or glyphosate is used for chemical control, it needs to be tank-mixed with a different group number due to the potential resistance.
For the most-effective burndown activity, herbicides should be sprayed when air temperatures will remain above 55 degrees Fahrenheit for a few days when the kochia plants are small. When residual herbicides are mixed with burndown herbicides to control kochia, there must be a rain event to incorporate and activate the herbicide in the soil to suppress or control later-emerging kochia plants.
Kochia is seen as a problem in cropping systems due to its possible high levels of resistance and competitive ability with cash crops grown in South Dakota. Weeds are a symptom of a larger issue in cropping systems today. Tank mixing and switching chemical programs annually will not completely solve the problem. Crop diversity and extensive crop rotations will help defeat certain weeds from obtaining a stronghold on your property. Kochia control, like all weed control, takes proactive farm management to prevent weed establishment from occurring, rather than reacting to the latest problem.
Source : sdstate.edu