Common milkweed has become a severe weed in cultivated cropland due to an extensive, deep root system, insulating winter snow, moist to wet summer conditions, tolerance to many commonly used herbicides, reduced tillage, and lack of human persistence in chemical, mechanical, and cultural control measures. Common milkweed is tolerant to most labeled herbicides. Control requires multiple herbicide application. Preventing establishment and spread of common milkweed patches requires continuous scouting and persistent control efforts.
Prevent seed production. Milkweed seed is highly viable and will germinate readily. Pappus on seeds allows long-distance travel and is responsible for establishment in fields. Common milkweed becomes perennial (capable of reproducing from underground roots) approximately 3 weeks after emergence. New shoots developing from established roots begin emerging in late April and grow more rapidly than spring seeded crops.
Milkweed control is expensive. Individual plants and small patches are easier and less expensive to treat than entire fields. Patch spraying covers only a fraction of the area of a broadcast application. Patch spraying allows use of higher herbicide rates with less expense than broadcast spraying.
NDSU Research Data -- Applied June of 1988
Herbicide Rate
pt/A
Fall 88 Spring 89
% control
2,4-D 4 36 48
Banvel 2 71 61
Banvel + 2,4-D 0.5 + 2 26 15
Curtail 4 13 6
Tordon 2 86 83
Roundup 6 56 99
Apply herbicides when milkweed is in the late-bud to flowering stage and actively growing. Control patches when small. Patch-spray glyphosate at 6 to 8 pt/A (up to 10 pt/A is allowed). Apply at late bud to flowering. Add ammonium sulfate at 8.5 to 17 lb/100 gallons of water. Do not apply after small grain is headed and only a maximum of 10% of the field can be treated. After heading, the application is regarded as a pre-harvest application and maximum use rates are limited to 2 pt/A. Patch-spray Tordon at 4 to 8 pt/A. Tordon residue will help prevent other shoots from emerging. CAUTION: Tordon residue will be present for several years after application.
