In the Upper Namoi, which takes in the Gunnedah region, 3000 hectares has been affected in the past month alone, while the Lower Namoi has recorded damage of 20,000 hectares.

Incidents have been reported in all cotton-growing regions in NSW and Queensland, with at least 60,000 hectares of cotton damaged already this season. That represents more than 20 per cent of the entire crop with the financial impact expected to be more than $20 million.

In the vast majority of cases, Cotton Australia said the damage was caused by Phenoxy (2,4-D-type) spray that travelled during temperature inversions – in some instances moving tens of kilometres from the intended target fields.

“Unfortunately, environmental conditions over December-January have combined to produce a ‘perfect storm’ for off-target spray drift damage,” Cotton Australia CEO Adam Kay said.

“Heavier than usual seasonal rainfall has encouraged weed growth which, in turn, led to more spraying by farmers and applicators and this has combined with temperature inversions to produce substantial off-target spray drift.

“I’ve been in the cotton industry for 30 years and this is the worst year in memory for spray drift damage to cotton crops, so we are taking this issue extremely seriously.”

In some regions, the damage to individual crops has been severe.

The national chemical regulator, the Australian Pesticides and Veterinary Medicines Authority is aware of the severity of the issue and is currently reviewing the 2,4-D pesticide and assessing environmental risks.

State agencies, in NSW and Queensland, including the NSW Environmental Protection Agency are also putting offices in the field to investigate.

Cotton Australia is urging cotton growers to report any damage suspected to have been caused by off-target spray drift and is working with other industry groups, including grain and pulse growers, and state and federal regulators to warn all farmers of the risks.