Know your en­emy Kochia

The Southwest Booster - - FRONT PAGE - SHAN­NON CHANT, PAG. CROPS EX­TEN­SION SPE­CIAL­IST, SWIFT CUR­RENT

Driv­ing around Saskatchewan for dif­fer­ent events and sur­veys this sum­mer and fall, it was easy to find kochia in many parts of the prov­ince. Un­for­tu­nately, a com­bi­na­tion of kochia’s bi­ol­ogy and her­bi­cide re­sis­tant pop­u­la­tions makes it a dif­fi­cult weed to con­trol.

The best start to a weed con­trol plan is to know the en­emy! Let’s get started.

Kochia is an an­nual weed that has a type of pho­to­syn­the­sis known as C4. C4 plants, such as corn and kochia, pro­duce en­ergy more ef­fi­ciently than C3 plants, like wheat and soy­bean. C4 plants are tol­er­ant to hot, dry con­di­tions like we had this sum­mer.

Ger­mi­na­tion of kochia can oc­cur un­der a range of con­di­tions:

- Tem­per­a­ture: Seeds can ger­mi­nate in soil tem­per­a­tures as low as two to four de­grees Cel­cius and as high as 40 de­grees Cel­cius.

- Tim­ing: In Western Canada, rapid ger­mi­na­tion oc­curs from mid-april to early-may, but can ex­tend into June.

- Salin­ity: Seeds can ger­mi­nate in saline soils, but ger­mi­na­tion may be slower.

- Seed depth: The op­ti­mal depth for emer­gence is from the soil sur­face to two cen­time­tres deep.

ph: Seeds are tol­er­ant of ex­tremes in ph.

Longevity: Seeds are vi­able in the soil seed­bank for one to two years.

Con­sid­er­a­tions for con­trol with her­bi­cides:

- Tim­ing: Her­bi­cides in the 2018 Guide to Crop Pro­tec­tion reg­is­tered to con­trol or sup­press kochia have a range of ap­pli­ca­tion tim­ings, from be­fore kochia emer­gence to plants that are six inches high. Post-emer­gent her­bi­cide ap­pli­ca­tion tim­ing may miss the seeds that ger­mi­nate well into the grow­ing sea­son.

- Her­bi­cide re­sis­tance: Pop­u­la­tions in Saskatchewan are typ­i­cally re­sis­tant to Group 2 her­bi­cides. Sev­eral fields with sus­pi­cious lines of kochia have been sur­veyed for glyphosate tol­er­ance (Group 9) and re­sis­tant weeds were found. There has also been one field found that has a kochia pop­u­la­tion that is re­sis­tant to dicamba and flurox­ypyr (Group 4 prod­ucts). Two ex­am­ples of her­bi­cides with dicamba as the ac­tive in­gre­di­ent are Ban­vel II and Or­a­cle. Prod­ucts that have flurox­ypyr and 2,4-D as the ac­tive in­gre­di­ents in­clude At­tain XC, Oct­tain XL, Flurox-24 and Rush 24. Prod­ucts that have flurox­ypyr and MCPA as the ac­tive in­gre­di­ents are Rush M and Tro­phy. 2,4-D and MCPA are also Group 4 her­bi­cides.

- Plant char­ac­ter­is­tics: Her­bi­cides can have trou­ble get­ting into the kochia plant be­cause the leaves are cov­ered in a soft, downy hair and have crys­talline wax on the sur­face of the leaf. If a her­bi­cide droplet gets stuck above the sur­face of the leaf, it won’t be ab­sorbed into the plant. Sur­fac­tants can help over­come this for some prod­ucts and should al­ways be in­cluded if rec­om­mended. High tem­per­a­tures can re­duce the ab­sorp­tion or translo­ca­tion of cer­tain prod­ucts. Some her­bi­cides have a rec­om­mended min­i­mum or max­i­mum tem­per­a­ture for ap­pli­ca­tion. Spray­ing us­ing these guidelines will help get the best results from the ap­pli­ca­tion.

Me­chan­i­cal op­tions can be used to help con­trol kochia pop­u­la­tions:

- Kochia is associated with no-till pro­duc­tion sys­tems; seedlings ger­mi­nat­ing from the seed bank can be four times higher in a no-till sys­tem than a sys­tem with tillage. This does not mean that farm­ers should change to a pro­duc­tion sys­tem with more tillage over the long term, but, in patches or over the short term, tillage may help con­trol pop­u­la­tions. Tillage to bury kochia seeds be­low four cen­time­tres after a year with a very high kochia pop­u­la­tion may re­duce seedling emer­gence in the next year. In a green­house study, there was no emer­gence from seeds that were buried deeper than four cen­time­tres.

- Mow­ing in ditches and other ar­eas that do not have crops to con­trol plants.

- Cut­ting a crop for green feed be­fore kochia sets seed can be ef­fec­tive.

Kochia plants can pro­duce 10,000 to 25,000 seeds per plant that are spread by tum­ble weeds rolling across fields and these seeds can eas­ily es­tab­lish in the spring. Any prac­tice that can re­move plants be­fore seed set is an im­por­tant part of con­trol.

For more info: search Glyphosate Re­sis­tance Kochia at Saskatchewan.ca; see the 2018 Guide to Crop Pro­tec­tion; con­tact the Crop Pro­tec­tion Lab­o­ra­tory about Her­bi­cide Re­sis­tance Test­ing; or con­tact your lo­cal Crops Ex­ten­sion Spe­cial­ist.

AGRI­CUL­TURE

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