Weed of the Week: cleavers

Cleavers are something many producers would like to chop from their fields.

The twisting and ropy vine-like weeds tangle through the crop, using up nutrients, water and farmers’ patience at harvest time.

Galium aparine and Galium spurium, also known as false cleavers, are designated noxious under the Weed Control Act. False cleavers have a notch at the tip of the leaf.

Both species are equally troublesome and difficult to control.

The weed is also known as white hedge, cleaver-wort, cathweed, scarth-grass and grip-grass.

Cleavers grow as annuals or winter annuals and are a problem in annual crops, particularly canola. If left to maturity, they can produce more than 3,500 seeds.

They are difficult to separate from canola seed because of their similar shape and size.

It is designated as a Class 2, primary noxious weed under the Canada Seeds Act, and there is no tolerance limit for it in all grades of pedigreed seed, whether foundation, registered or certified for cereals, forage crops and oilseeds.

Seed can remain viable for up to three years in dry soil.

Cleavers have weak, four-sided stems covered with prickly hairs. Shoes and pant legs will be entwined with cleaver plants after walking through a field with the weed.

The plant can grow up to two metres in length.

They usually show up in moist areas of the field, but don’t like wet feet.

The tiny, greenish-white flowers are inconspicuous.

The weed can be difficult to control in a cool spring because it can be a spring-germinating annual or a winter annual and grows well in cool conditions.

As a result, the weather may be cool and even though little else is growing, the window for effective cleavers control could be closed by the time producers burn off ahead of seeding or carry out post emergent applications.

The most effective way to control the weed is to spray early when it still has two whorls.

Products are available to deal with the pest, depending on the crops. Products containing fluoxypyr provide the broadest range of control in cereals.

Growers and agronomists should be vigilant when observing product failure during cleaver control. There have been more reports of Group 2 resistant biotypes, particularly in northeastern Saskatchewan. In Alberta, Group 4 and combination 2 and 4 resistance has shown up.

Hugh Beckie of Agriculture Canada predicts that cleavers are near the top of the list for developing glyphosate resistance.

Its tricky leaf surface makes it tough to spray, so higher pressures and water rates are required to ensure proper coverage.

Producers can increase the rate of glyphosate to a half or even .67 litres per acre when controlling over-wintering cleavers.

All the herbicides listed for controlling cleavers are more effective when applied early.

Caution should be observed when using products containing 2,4-D, such as Frontline 2,4-D, Attain and Retain, because crop staging restrictions must be observed to avoid crop injury. They should never be used on oats.

Focus, a Group 15 herbicide, might in the near future have a role in controlling cleavers. Its active ingredient is pyroxasulfone, which is registered for corn and soybeans.

FMC Corp. has applied for registration on spring wheat, winter wheat and lentils and will potentially add field peas, chickpeas, potatoes, carrots, fababeans and sunflowers.

The label is aimed mainly at grassy weeds and is narrow for broadleafs. However, the company has applied for cleavers, stinkweed, lamb’s quarters, kochia and wild buckwheat.

Focus is surface applied before planting or just afterward. Rainfall incorporates and activates it. It is not recommended on soil with more than seven percent organic matter.

Thom Weir is an agronomist with Farmer’s Edge. He can be reached by emailing thom.weir@farmersedge.ca.

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