Crops are at increased risk of damage from herbicide applications this autumn, a leading agronomist has warned, following evidence that crops have taken advantage of higher than normal soil nitrogen levels.

A dry spring and lower than average rainfall in many parts of the country has left "a significant proportion‟ of last year's applied nitrogen unused in the soil, says Chris Rigley, of Yorkshire Arable Marketing. While many crops, cereals and oilseed rape alike, are healthy and vigorous as a result, there could be knock-on consequences for post-emergence herbicide applications, Mr Rigley cautions.

“The lush, relatively rapid 'soft' growth is a dead giveaway that the crop may suffer after herbicide application.

“That extra growth will dilute levels of minor nutrients, such as manganese, zinc, copper and magnesium. The plant needs these to maintain its optimum health, physiological and biochemical status. Quite simply, any crops displaying deficiency symptoms or – more worryingly, those with "hidden" subclinical deficiencies are more likely to be damaged by herbicide applications if the underlying deficiency is not rectified.

“Remember, while we expect herbicides to kill weeds, they're also capable of crop damage were it not for the wheat plant‟s ability to metabolise the chemical and turn it into something harmless to itself. So put simply, if a plant doesn‟t have enough of these essential nutrients, it won‟t be able to defend itself against the rigours of powerful grass-weed herbicides such as Atlantis WG (iodosulfuron + mesosulfuron).”

The danger isn‟t limited to Atlantis, points out Mr Rigley, although he concedes that it‟s going to be the most common product in use this autumn, as part of growers‟ black-grass control strategies. “All herbicides have the potential to damage the crop if the plant is not robust enough to withstand it. We see the effects as crop scorch, symptoms that already exist on some crops following a pre or very early post- emergence herbicide.”

His advice to growers is to consider an immediate foliar application of key nutrients, in line with local soil conditions, before embarking on post-emergence herbicide applications in early to mid-November - the optimum timing for Atlantis.

“A cereal-specific blend containing all the above nutrients would be a good option for many parts of the country,” he says, “but soils known to have severe manganese deficiencies - light land, soils with a high pH and other calcareous soils - will probably benefit most from a single, concentrated nutrient product.”

“Whatever you do, don‟t be tempted to cut out a pass and tank-mix your nutrient with Atlantis. The crop needs about 7-10 days to take advantage of the nutrient application so applying them simultaneously won't have the desired effect.

“Not only that, but I would not, even if it were a possibility, consider tank mixing Atlantis with anything other than the prescribed adjuvant, biopower. Autumn is your one chance to hit black-grass where it hurts and it‟s not worth compromising the effectiveness of Atlantis in any way,” he warns.

Safagrow’s Andrew Low says that these autumn applications should always be considered, even if just from a crop establishment perspective. “Autumn-sown crops have a limited window of opportunity to establish themselves with sufficient root and leaf growth to survive over winter.

“Applying key minor nutrients at this stage ensures the crop has optimum nutrition to boost its early development. Many parts of the country are seeing more vigorous early growth than normal due to the left-over nitrogen, which means these minor nutrient inputs are vital.

“Later-drilled crops such as second wheats will have even less time for that early development, making the value of the autumn minor nutrient sprays even greater.”