Q: What is the base temperature for kochia germination?

A: The base temperature or minimum soil temperature for the onset of kochia germination is 39°F. Warm weather in February has triggered the onset of kochia germination in parts of western Nebraska, where soil temperature has been above 39°F (Figures 1 and 2).

Q: Can early-emerged kochia seedlings survive freezing temperatures?

A: It depends on the intensity and duration of the freezing event(s). Kochia seedlings are considered frost-tolerant; however, research conducted in Canada showed that kochia seedlings are not as tolerant to freezing temperatures as winter annual weeds such as shepherd’s-purse, downy brome, henbit, common chickweed, and field pennycress.

Q: Where emerged kochia has been detected already, will additional seedlings emerge?

A: Yes. Expect additional cohorts of kochia seedlings during early season.

Q: When is the best time to spray for kochia control?

A: Before or shortly after they emerge. By the time corn and soybeans are planted, most kochia seedlings are emerged and actively growing. With the widespread occurrence of glyphosate-resistant kochia in Nebraska, trying to control this weed at or after crop planting will not result in satisfactory results. Growers in Nebraska are encouraged to take advantage of the atypical warm weather conditions to spray fields infested with kochia.

Q: What are the herbicide options for kochia control?

A: Active ingredient instead of commercial products are provided here. When selecting herbicides for kochia control, keep in mind that kochia populations resistant to Group 2 (ALS-herbicides), Group 4 (2,4-D and dicamba), Group 5 (atrazine), and Group 9 (glyphosate) have been reported in Nebraska.

• If planting corn, use an early season herbicide program containing burndown products such as glyphosate, dicamba, 2,4-D, paraquat and/or glufosinate along with soil residual product(s) such as atrazine, isoxaflutole, mesotrione, saflufenacil, flumiozaxin, and/or pyroxasulfone.
• If planting soybeans, use an early season herbicide program containing burndown products such as glyphosate, 2,4-D, paraquat and/or glufosinate along with soil residual product(s) such as metribuzin, sulfentrazone, flumiozaxin, saflufenacil, and/or pyroxasulfone.
• Under fallow, use an early season herbicide program containing burndown products such as glyphosate, dicamba, 2,4-D, paraquat and/or glufosinate along with soil residual product(s) such as atrazine, metribuzin, isoxaflutole, and/or sulfentrazone.
• In winter wheat, use post-emergence products such as 2,4-D, dicamba, fluroxypyr, pyrasulfotole + bromoxynil, carfentrazone-ethyl, prosulfuron, metsulfuron, and/or triasulfuron.

The burndown products listed for kochia control also can help manage established winter annual weeds such as henbit (Figure 3) and marestail (Figure 4).

For effective burndown activity, herbicides should be sprayed when air temperatures will remain above 55°F for a few days and kochia plants are small. When soil residual products are included in the tank-mix, precipitation is needed to incorporate and activate the herbicides in the soil.

Use of a herbicide program containing burndown plus soil residual activity is recommended because burndown products will control emerged seedlings and residual products will control cohorts that are yet to emerge. Keep in mind that using herbicides with multiple effective sites of action will help you in the battle against herbicide-resistant weeds. Practice rotation, rotation, and rotation!

Q: Will using an early season herbicide program for the control of kochia also effectively control common waterhemp and Palmer amaranth?

A: No. Early season herbicide applications will help manage winter annual weeds such as marestail and henbit, and early season summer annual weeds such as kochia and giant ragweed. Additional applications at planting and post-emergence will be necessary in fields where common waterhemp or Palmer amaranth are present. (Keep in mind that common waterhemp and Palmer amaranth typically emerge from May through August.)

For additional herbicide options, please check the Guide for Weed, Disease and Insect Management in Nebraska. Always check herbicide labels before application.