Group-2 herbicides were the products of choice for controlling kochia in peas. Now your options are limited. Two recent studies have confirmed that group-2 herbicide resistant kochia is now widespread across the Prairies.
“It’s a big problem, “ says Hugh Beckie, a weed specialist with Agriculture and Agri-Food Canada in Saskatchewan. “A survey we conducted in 2007 determined that about 90 per cent of randomly picked fields had group-2 resistant kochia.”
Kochia can germinate and emerge very quickly — within one to three days — so it can effectively overtake less competitive crops, like pulses, that allow lots of sunlight to penetrate and warm the soil.
Other classes of herbicide can successfully control kochia in cereal and oilseed crops, but pulse growers don’t have the same options. Pulse growers rely on group-2 herbicides, which are, in most cases, the only ones registered for use on peas, chickpeas, beans and lentils.
WHAT TO DO
Probably the best option for pea growers, in the absence of effective herbicide treatments, is to plan ahead.
“An option that producers do have is to set the pea crop up by aggressively controlling the kochia in the previous two to three years in cereal or oilseed crops,” says Clark Brenzil, provincial weed control specialist at the Saskatchewan Ministry of Agriculture.
This method is effective thanks to kochia’s short seed persistence in the soil. Although, being a tumbleweed, the mature plant has the ability to scatter seeds over a fairly wide area once dislodged, they are relatively short-lived in the soil. Roughly 80 per cent of kochia seeds germinate the first year after they are shed. The following year, less than five per cent germinate and in year three less than half a per cent emerge.
Kochia also does best in warmer, dry conditions, so seeding cereals or oilseeds as early as possible, in narrow row spacings will also help to slow down emergence of the weeds and reduce populations for future pulse crops.
Group-4 herbicides containing just 2,4-D are not highly effective against kochia, Brenzil says. These products have to be applied before the four-leaf stage to do a good job of controlling kochia. He suggests that producers growing a cereal crop can look for products with fluroxypyr (Attain or Trophy), dicamba (various), pyrasulfotole, (Infinity, Velocity M3) as the active ingredients to be effective against resistant kochia. Be sure to check for re-cropping limitations on these products as pulse crops can be sensitive to many of them.
Products with mixes of bromoxynil plus MCPA or 2,4-D can also be effective, but only when the kochia is very small and high water volumes are used.
As a preceding oilseed crop, Brenzil suggests using a glysophate tolerant canola, although he adds that kochia is more prevalent in brown and dark brown soil regions where canola is not generally grown.
Another option, although results are not always consistent, is using ethalfluralin (Edge) as a pre-emergence treatment to at least try and suppress kochia. “It wouldn’t get high levels of control but it’s an option,” says Eric Johnson, a weed biologist at AAFC’s Scott Research Farm in Saskatchewan. “It’s a soil applied herbicide that provides suppression, so it’s variable.”
Johnson has also been testing another herbicide, sulfentrazone (Authority), that has proven to be an effective kochia killer. You apply it either prior to seeding or emergence. Currently, however, it is only registered in Canada for chickpea production, but could provide another option for pea growers in the future. “There is some work underway right now to expand the label to field peas because they are tolerant,” says Johnson.
One of the new products to come on the market recently, that claims to be effective against resistant kochia, is Viper by BASF, which combines Group-2 Solo with Group-6 Basagran.
Johnson has conducted tests with Viper in dry beans. “It’s rated for suppression of kochia and I would agree that it does that,” says Johnson. “I anticipate that it will do a better job in peas than dry beans because peas tend to be a little more competitive.”
Early application of the product is also very important says Johnson. “It is critical that growers apply it quite early because it’s the Basagran part that is controlling the kochia, and it’s pretty much a contact herbicide, so you want to get good coverage of the weed and get it relatively small or you’ll just burn off part of it and it will re-grow.”
Other cultural control options may also help in reducing infestations of kochia, like the use of shelterbelts to catch tumbleweeds and limit their spread. Any plants that remain at the end of the season should be completely shredded if possible with a mower, as tilling them can dislodge the stems and encourage their spread.
Saskatchewan Agriculture has a fact sheet on control of tumbleweeds such as kochia and Russian thistle on its website at www.agriculture.gov.sk.ca.Search “tumbleweed” or go through the menu by selecting “Production” then “Crops — Weeds” and look for Control of Tumbleweeds in the list of publications.
Angela Lovell writes from Manitou, Man.