Surface temperature inversions and spray decisions
Recent cooler temperatures have led to surface temperature inversions (when air temperature increases with height from the ground surface, which is opposite of what normally happens (i.e temperature profile is ‘inverted’). This results in a layer of cool, still air being trapped below warmer air).
If pesticides are sprayed during an inversion, the direction and distance which the droplets move becomes unpredictable resulting in considerable spray drift. Inversions are most likely to occur at night and two hours after sunrise, so avoid spraying at these times. More about surface temperature inversions and pesticide application can be found from DPIRD article on avoiding spray drift, Agriculture Victoria and GRDC.
There are a number of tools which can help making spray decisions, this includes DPIRD weather station network (the old DAFWA weather station app is no longer supported, so best to bookmark the weather station website on your phone) which gives an indication of spraying condition based on wind speed, humidity, dew point and deltaT. Examples for Beacon and Meckering North are shown below.
Thermal time
Cumulative thermal time graphs provide a snapshot of the current season allowing growers to assess water requirements of their crops and to gauge potential water stress. Including historical data puts the season in context in terms of the likely growth rate of crops or pasture.
Both maximum and minimum temperatures in June was much cooler than average, meaning thermal time is below average compared to past seasons (since 1975).
For comparison, thermal time for this year is compared to 2020, which in some cases had the highest thermal time (was the warmest) than any in the past, while 2023 has the lowest thermal time (is the coldest).
