Frost-hardened cleavers pose spray challenges

The coldest winter for many years, followed by cold late spring weather means that care is needed to achieve reliable cleavers control in winter cereals.

The four main factors are: size of cleavers; degree of frost hardening on these weeds; amount of new spring growth as soils warm; and air temperature at and shortly after spraying.

Many cereal crops have large cleavers populations that will soon require treatment. Yield potential will soon be lost as they start to grow away rapidly. However, they are all considerably more hardened than usual. A period of growth is needed for them to be effectively controlled by cleavers herbicides at standard rates.

Certainly hormone herbicides such as mecoprop will not control cleavers reliably at the moment. A hasty decision to spray any cleavers herbicide now may lead to poor results.

Dow AgroSciences are the recognised experts in cereal cleavers control, with a large database of technical information on herbicides, having trialled and marketed the leading cereal herbicides for over 20 years in a wide range of conditions.

“Boxer (florasulam) will work well on cleavers if applied at a full rate of 150 ml/ha when temperatures are as cold as 2-3 ºC, provided there has been some recent new growth,” says David Roberts, technical specialist for Dow AgroSciences. “If growers are still to apply Atlantis use Boxer at 100 ml/ha in the tank-mix.”

Once daytime air temperatures are around 5 ºC or above, and soil temperatures reach 6 ºC Mr Roberts advises that there will be sufficient weed growth for Starane XL (fluroxypyr + florasulam) at 1.8 l/ha, or 1.5 l/ha if tank-mixed with Atlantis, to provide better control of ‘blue’ winter hardened cleavers.

“At higher temperatures later in the season lower rates of Starane XL, from 1-1.25 l/ha, can be used reliably, but Starane 2 (fluroxypyr) should not be used until air temperature reaches 10 ºC consistently,” says Mr Roberts.