Controlling summer weeds is the largest single contributor to improving the water use efficiency of cropping systems across southern Australia. In a study completed by Grains Research and Development Corporation (GRDC) under the Water Use initiative which completed in 2013 found that for every dollar invested into summer weed control there was on average a $5 return on investment. This is not only in stored moisture but also in nutrition and other system benefits.

Given recent rainfall events that have occurred at the start of summer it is even more important to control summer weeds for a longer period to get moisture conserved through to winter crop planting. Fallow efficiency is driven by ground cover to prevent runoff and evaporation however also includes other factors that remove moisture including predominantly summer weeds.

The study found that the highest return was controlling summer weeds 10 days after rainfall but also found benefits to treatment up to three weeks after rainfall compared to doing nothing.

Grazing systems always find it difficult to balance the use of weeds for fodder or feed prior to spraying however the study found that the loss of grain production far outweighed the gain in meat or wool production provided under the circumstances.

With this in mind, growers and spray contractors need to take every step possible to avoid off target drift, especially onto sensitive crops such as grapes, cotton and horticulture crops.

Current application guidelines require that:

  • Applicators must keep accurate spray records for a minimum of 2 years – including nozzle brand, size, type, system pressure and boom height as well as current requirements such as location, weather conditions, product used, product rate etc.
  • Mandatory down-wind no spray zones
  • Use nozzles that produce Extremely Coarse (XC) to Ultra Coarse (UC) droplets, higher water rates, slower ground speeds and lower boom heights from 1st October to 15th April when using Phenoxy based herbicides
  • Apply during the day if possible – vertical mixing of the air makes surface inversions less likely to cause off target drift
  • Do not apply unless wind speeds are between 3 and 15km /hr
  • Do not apply if there are surface temperature inversion conditions present at the application site during the time of application. These conditions exist most evenings one to two hours before sunset and persist until one to two hours after sunrise.

A lack of suitable weather conditions for spraying over extended periods is not an excuse for spraying in unsuitable conditions.

With ever increasing pressure on herbicide use, especially 2,4-D and other Phenoxy based herbicides it is extremely important to make sure they are used correctly to enable them to be used into the future.

If you would like further assistance don’t hesitate to call your YPC agronomist for advice on application and nozzle selection.

Call the Yenda branch: 02 6961 3300
Call the Griffith branch: 02 6966 8900
Call the Leeton branch: 02 6953 9000