Blackgrass sufferers are urged to wait before cultivating fields as the grassweed’s seed is unlikely to germinate in such dry soils.

Soil cultivations risk burying any blackgrass seed under the surface where it will be protected until there is enough moisture for germination.

Dick Neale, technical manager at agronomy group Hutchinsons, advised growers to leave any weed seed on the soil’s surface where the sun’s radiation will help destroy it.

“The most beneficial thing you can do when conditions are hot and dry is to leave blackgrass seed on the surface after harvest to let it degrade naturally in sunlight,” he said.

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Mr Neale added a lot of blackgrass seed got buried in dry soils in 2011 and didn’t grow until the first rain in November, but as soon as the moisture came it emerged quickly.

Even where there is moisture, peak blackgrass emergence is between mid-September to end-October, so there is still plenty of time before the true extent of the threat to 2018-19 crops is known.

“Soils are very warm, so any significant rain in August or September is likely to spark a major flush of autumn-emerging blackgrass. But remember, you still need to allow around three weeks for seeds to emerge, so don’t rush in,” he said.

He added many soils will easily take 100mm of rain and still produce good seed-beds, so there’s no need to panic, while waiting for sufficient soil moisture is also vital for pre-emergence herbicides to work effectively.

Research shows that about 160mm of rain is needed during September and October for the optimum efficacy of residual herbicide chemistry.

“Soil has to be wetted to a significant depth for residual herbicides to work well,” he said.