Recent cold weather might have brought black-grass growth to a halt, but warmer times mean that action is not far off when this pernicious weed needs to be hit hard.

Growers should consider applying a post-emergence herbicide in wheat crops as soon as conditions are warm enough to take advantage of small, susceptible weeds, according to industry expert, Bayer’s Darren Adkins.

While the recent cold spell arrived at just the right time – after a fairly mild Christmas – it allayed the danger that black-grass would grow vigorously. He said: “It was slightly worrying through December and we didn’t have any really cold weather until mid-January.

“At one stage, it was beginning to look similar to 2015-16 where everything looked great going into winter, but wet and mild conditions caused black-grass to tiller like crazy. That season it was too wet to apply any post-em and the subsequent headcounts very high even where plant counts were quite small.”

The danger of a situation as bad as 2015-16 seems to have passed, largely thanks to the cold weather but black-grass is still present in crops. Where populations are low enough, the priority is to apply a post-em such as Monolith (mesosulfuron + propoxycarbazone) as soon as possible.

“Like any post-emergence herbicide, the aim is to apply it when the weed is as small as possible,” said Mr Adkins. “At the moment, most black-grass is still at the 2-3 leaf stage, if conditions warm up and the plants wake up, we would expect decent results applying in February or early March.”

Plant size is one of the main enemies of post-em efficacy. Most black-grass has some degree of metabolic resistance where it can break down the herbicide before it takes effect, so hitting plants when they are small is much more effective.

Although small plants are the norm at the moment, there is already some black-grass tillering, according to AICC agronomist, Peter Brumpton, who is based in Nottinghamshire. “The situation is variable but, in general, later drilled crops are cleaner with smaller surviving black-grass plants.

“However, there are patches in some fields that have higher black-grass numbers that are beginning to tiller. In these areas, I think the best option is probably to spray off with glyphosate because the plant counts are too high to get any useful additional control.”

If post-ems are planned, finding a suitable application window is always a challenge in early spring. Unlike spring 2016, ground conditions are reasonable for this time of year, so heavy land farms may be dry enough for sprayers following a week of decent weather.

“Active growth is essential to get a good result,” added Mr Adkins. “Ideally, you want to apply about a week after the end of a cold spell – this means black-grass will be awake and taking in the herbicide, but it won’t have grown too much and still be susceptible.”

In addition, the weather needs to be settled with little wind and good drying conditions – which at this time of year probably means sunshine as overcast days tend to remain damp.