When you think of Kochia as a weed problem, one thinks of western Minnesota, the Dakotas and other states farther west. Kochia, a tumbleweed, has long established itself as a weed problem in these dryer western areas. In southern Minnesota, U.S. Highway 71 is generally considered a rough boundary for what might be considered western Minnesota. That said, I wouldn’t have expected to find this weed infesting a soybean field in south central Minnesota near I-35 (Fig 1). It will be prudent to keep tabs on this weed if it is expanding its range east.
Kochia characteristics
What do we know about kochia? It's an early emerging annual weed which is both drought and cold tolerant that produces seed with very little dormancy. The low level of dormancy can be a benefit to weed management because if you control kochia before it produces seed, it can be a shorter term weed problem.
For perspective, take a weed like waterhemp; it may take four years of weed management preventing seed production to minimize it as a weed problem. Kochia is an early emerging weed (Fig 2), and continues to emerge into early May. However, some recent conversations have led me to question whether this weed, while still emerging early, might be extending emergence later into the season. This certainly is a possibility because in recent years we have seen later emergence with our more common early emerging weeds giant ragweed and woolly cupgrass.
Kochia can move!
As a tumbleweed (Fig 3), Kochia is uniquely equipped for long distance dispersal both by wind and/or by hitching a ride on something (e.g. rail car).
Herbicide resistance concerns
Now for the bad news. There are kochia populations with known resistance to the Group 2 ALS inhibiting herbicides, Group 4 growth regulator herbicides, Group 5 photosystem II inhibitors, Group 9 EPSP synthase inhibitors, and Group 14 PPO inhibitors.
In addition, there are populations with resistance to multiple herbicide groups. For more information on herbicide resistant populations and their known locations please check the International Herbicide-Resistant Weed Database. The population found in south central MN was not adequately controlled with glyphosate, indicating it is likely resistant to the Group 9 herbicides and could be resistant to more groups.
Source : umn.edu