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Spray drift at all times is an important issue that has been discussed in depth. The difference now is that there is clear evidence that drift has caused some significant damage in the North West NSW. Reportedly thousands of hectares have been affected by off target spray drift in the area around Burren Junction. Affected cotton growers were also reported further east towards Moree.

Cotton Australia and the local Cotton growers in northern NSW have jointly expressed disappointment that some “local broadacre farmers have not followed proper advice or attention to detail when spraying out weeds”. It is a blow for the affected but hopefully here we are able to explain how this can be avoided.

Reasons for off target spray drift

In our 10 years of experience here at SprayerBarn we have found that there are a few reasons for off target spray drift:

  • Wind Speed: Ideal spraying conditions are approximately between 4km/h and 16km/h. Spraying outside these conditions only increases the risk for dangerous air movement and spray drift damage.
  • Low wind Speed: at wind speeds less than 4km/h there is an increasing risk of spraying in a temperature inversion layer. This is where the temperature of the air increases relative to the height off the ground. Droplets of (cool) spray from nozzles are therefore caught under a layer of warm air and hang in the air until such time as the air cools, when the spray droplets settle on the ground ...or on the coolest crop.
  • High wind speed: When the wind increases to a speed greater than approx.. 16 km/h the likelihood of spray drift increases. Spraying in these conditions should not be attempted.
  • Delta T: Delta T is the relationship between humidity and temperature and is displayed as a graph that is readily available. A Delta T of greater than 10 and less than 2 is referred to as not optimum for spraying. Why? … a delta T of greater than 10 refers to conditions of high temperature and low humidity where to the droplets from your sprayer have the potential to evaporate (albeit partially) before hitting the plant.

A delta T of less than 2 can result in high humidity and lower temperatures – ideal conditions for for an inversion layer to occur.

Some are facing complete crop loss due to off target spray drift and as a result of the the Christmas Day damage reported a group has been formed to discuss the issues and formulate a response. The group comprising of the Department of Primary Industries, Environmental Protection Authority, Cotton Australia, growers and SprayerBarn as sponsors met in Dubbo on 23 February to discuss the issues. With all the attendees voicing their opinion, the emergency meeting decided to produce flyers to be distributed to growers detailing some of the information discussed above and to recommend the use of TeeJett TTI nozzles.

Use of TeeJett TTI nozzles

The meeting concluded that the use of TTI nozzles would be the best way to combat the marginal conditions that we are often faced with (Deta T less than 2 or greater than 10, and wind conditions of greater than 16km/h and less than 4km/h) as the droplet size is large enough to deal with inversion layers and reduced efficacy due to high temperatures.

The nozzles can be purchased at SprayerBarn to assist growers during this difficult time.

Bonus: 24 hour risk profile for summer spraying infographic made by Nufarm