Weed of the Week: cleavers

Last week I addressed a weed that I called the scourge of the south. For more northern grain belt farmers, this week I will discuss the scourge of the north, more commonly known as cleavers.

Just as we saw a significant increase in the acres infested with kochia, we have seen cleavers spread across agricultural soils in the black and neighbouring soil zones.

Cleavers actually refers to two closely related species: galium aparine and galium spurium, also known as false cleavers. It is a very competitive weed.

There have been a number of theories about the spread of this disease.

Fine spines on the weed’s stems cause it to stick to anything it touches. Deer and geese have been blamed for cleavers dispersal.

The fact that the seed is almost identical in size to canola might also have led to farmers inadvertently planting cleavers when seed was open pollinated or when brown bagged canola was seeded.

Whatever the reason, cleavers is widespread across the dark brown, black and grey wooded soil zones.

Cleavers grows both as a winter annual and a spring annual weed. A higher number of weeds have been surviving our winters, whether because of a selection of hardier biotypes, warmer winters or other cultural shifts.

This version of cleavers is quite easily controlled with a shot of glyphosate in the fall, but like many winter annuals, it seems to be harder to control in the spring.

Because many populations of cleavers are Group 2 resistant, the use of a non-Group 2 add-in product with glyphosate is warranted when over-wintering populations are observed. These may include, but are not restricted to, products such as Heat, Conquer and CleanStart.

In fact, it has now got to the stage where if you have cleavers, you should consider them to be resistant to Group 2 products. This means managing cleavers just became a whole lot harder.

Fluroxypyr-containing products have been the chemical tool of choice in cereals, but there are populations of cleavers that are resistant to both Group 2 and Group 4 herbicides. Seeds can be sent to provincial crop protection labs for resistance testing if dual resistance is suspected.

Growing crops such as peas has become very troublesome with the increase in Group 2 resistant cleaver biotypes. IMI chemistry alone is no longer effective, and products containing bentazon (Viper) claim only suppression.

Products containing sulfentrazone (Authority or Authority Charge) control cleavers if applied as a pre-emergent product before the peas come out of the ground. Ethalflurin (Edge) will also provide suppression or marginal control of cleavers.

With canola, glyphosate provides the most consistent control of cleavers. However, the high rate or a second application should be made under heavy pressures or when winter annual populations have been poorly controlled.

Glufosinate (Liberty) is marginal at controlling cleavers with a single pass. When using this product, use two applications and use the maximum rate on the label.

Both of these products work best on small cleavers so plan to scout and spray your canola early. Clearfield canola is not advised if you have a cleavers problem because there are no alternatives to Group 2 products in this system.

Quinclorac (Clever) is a Group 4 product that provides excellent cleavers control in canola, especially when tank mixed with glufosinate or glyphosate. While registered on canola, maximum residue limits (MRLs) have not been established for quinclorac in China, so the use of this product is not recommended.

Clomazone (Command) is a Group 13 soil-applied herbicide, which will provide early residual control of cleavers. It can be applied pre-seed with a glyphosate burn-off application and works with all herbicide tolerant canola.

Clomazone reduces the initial flush of cleavers, reducing the pressure on in-crop herbicides that are also intended for the pest. Clomazone is registered for pre-plant application in canola and leaves no detectable residue on seed, oil or meal.

There are also products registered with multiple modes of action for cereals. Where possible, use one of the products containing fluroxypyr when targeting cleavers and use the maximum labelled rate for the chosen product. A product such as Infinity FX, which contains three modes of action, none of which is Group 2, is an excellent choice.

Strategies to follow in the battle against cleavers

  • Use a varied approach, including fall and pre-seeding burn-off products.
  • Use the maximum labelled rates for in-season products.
  • Tank mix or use pre-mixed products that contain multiple control products for cleavers.
  • Use multiple application of products, where allowed for on the label.
  • Avoid using Group 2 products if you suspect you may have a resistance issue.
  • Spray early because products are most effective on young cleaver plants.

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