Research shows that just one plant/sq m can result in a 1% yield loss in wheat and 1.24% yield loss in oilseed rape, which AICC agronomist Steve Cook calculates is worth about £150/ha at present crop prices.
“Cleavers are the most competitive broad-leaved weed and they can cause great yield loss, harvest difficulties and loss of quality because they tend to drag the crop down,” he says. “Uncontrolled, with current high crop prices, these are major losses to the grower.”
Mr Cook, an independent agronomist at Hampshire Arable Systems, says residual autumn herbicide programmes, including pendimethalin and diflufenican, have helped reduce the number and size of cleavers this season.
However, cleavers growing in untreated crops are much bigger and should be taken more seriously, he adds. “If there hasn’t been any control in the autumn, you need to be in earlier with your spring herbicide treatments.”
Three timing windows are available in the spring when different products can be used to control cleavers before they can compete with the crop and Mr Cook says growers should choose the one strategy that best suits their situation.
First, for early timings around the beginning of March (pre-T0) in brome or blackgrass situations, Mr Cook recommends adding Boxer or Eagle to one of three grassweed herbicides – either Atlantis, Pacifica or Othello.
“This combination will finish off any cleavers and any remaining broad-leaved weeds and it does a thorough job in one go,” he says.
However, for good blackgrass stewardship, Bayer CropScience says that spring is not the best time to apply Atlantis. Therefore, the company is not actively promoting the use of Atlantis + Eagle in a tank mix this spring, although it is still allowed.
For growers who do not have grassweeds to contend with, Mr Cook says Starane XL or Dow AgroScience’s new product, Spitfire, can be combined at T1 to ensure that cleavers are controlled before they compete with the crop at GS31-32 onwards.
Spitfire has the same active ingredients as Starane XL, but contains twice the rate of florasulam, which will increase its activity in cooler conditions, he explains.
AICC agronomist Hamish Coutts from Perthshire says Spitfire could be particularly useful in Scotland.
“Many Scottish growers who use Starane XL have to wait until it is warm and by then you have got some pretty hefty cleavers about. But growers may be able to get on a bit earlier thanks to the double rate of florasulam.”
But Mr Cook believes product choice will ultimately depend on which broadleaved weeds need to be targeted alongside cleavers.
“If there is charlock or mayweed, then Starane XL or Spitfire will be good. But if we’re looking at thistles or poppies, we might need some Ally with Starane to do the job,” he says.
However, growers using Starane XL or Spitfire should be careful over sulfonyurea sequencing to ensure that the sequence is approved and that total permitted doses of florasulam are not exceeded, he says. “Generally, these products tank mix well so they are ideal to go in with a T1 fungicide.”
Finally, cleavers can germinate up until May and Mr Cook says some growers may experience a late flush of small cleavers. These will need dealing with at T2 when Starane XL or a straight fluroxypyr-based product, such as Starane, can be added to the tank mix up to GS47, he says. “When it is warm, fluroxypyr will work very well.”
Whichever strategy is chosen, Mr Cook strongly recommends removing cleavers while they are still small, before they start competing with the crop. “Ideally, we want to knock cleavers out before GS32, but if they have come from an autumn treatment where they have been held back, then they will be small enough and not be competitive until the flag leaf stage – and that’s when we want to hit them hard.”
Product dose will depend on the size of the weeds and the temperature at time of application, he adds.