Cotton Australia released some staggering figures last week on how much cotton had been damaged from spray drift this season.
From late last year to recently, a massive 20 per cent of Australia’s cotton crop had been damaged from spray drift, with about 60,000 hectares reported damaged.
Cotton Australia regional manager for Darling Downs, Mary O’Brien, Toowoomba, said there was a large number of farmers who were aware of what an inversion was, but were unable to tell when one was occurring.
Ms O’Brien supports cotton growers with issues regarding Phenoxy herbicides for Cotton Australia and with recent rain, they have become far too prevalent this season.
Inversion conditions are most likely to occur during the night, usually around sunset, persisting until after sunrise.
During daytime hours, air in contact with the ground is warm which creates turbulence, allowing it to mix.
This assists with diluting airborne chemical droplets and forces them to the ground.
During a surface temperature inversion, air near the ground is cooler and lacks “turbulence”, which prevents small spray droplets from settling.
Ms O’Brien said wind flow could then move the chemical tens of kilometres in an unpredictable direction, causing spray drift to occur and damage to sensitive crops such as grapes and cotton.
“Wind movement under inversion conditions can flow down slope, and cotton is grown on the lowest points of the catchment,” she said.
There are plenty of ways farmers and spray contractors can prevent spray drift, starting with not spraying Phenoxy chemicals at night.
Inversion conditions are hard to recognise as Ms O’Brien said weather conditions change constantly.
Applicators should constantly check wind speed and direction, which should be within 3 to 15km/hr during the day.
During the night, wind speeds less than 11km/hr may indicate the presence of an inversion.
Visual hints such as the presence of mist, fog, dew or a frost could also mean you’re spraying in inversion conditions.
Another indicator is when dust is caught above the surface and is moving sideways.
Ms O’Brien said in the last ten years, science and information regarding inversion and spray drift has been developed and there’s now plenty of accessible information.
In a lot of cases, Ms O’Brien said districts tend to blame individuals for spray drift damage however, she would encourage farmers to start looking at their own practices and ensuring they’re being done correctly.
“Farmers genuinely believe they’re doing the right thing, but in many cases they’re not,” she said.
