A study of 15 spray operators showed a 300% to 400% difference in volumes applied to treat the same bush. In this controlled study, all the applicators followed the same label directions and operated the same equipment. The large discrepancies in spray volumes were responsible for poor control due to under-spraying or increased costs from over-spraying.
How much coverage are you getting in your application?
The differences in the way herbicides are applied results in a wide variation in the control achieved. The most common error when spraying blackberry is to under-spray large bushes. Such bushes have an extensive surface area comprising the canopy, as well as leaves and canes at the centre of the plant. Spray operators may see that the outer foliage (canopy) appears wet and decide the plant is sufficiently sprayed. However, the inner parts of the bush may have received virtually no treatment. Experienced operators ensure that these larger plants get sufficient wetting of the inner leaves and canes.
When are you spraying your blackberries?
The optimum time to spray blackberry is when it is actively growing from flowering through to fruiting–usually during December, January, February and March. However, this may vary between regions and species. Blackberry can be sprayed before and after these months if conditions are suitable. Spraying summer active perennials like blackberry in autumn can increase the amount of herbicide
translocated into the root system, because translocation of starches and photosynthates to the root system is more pronounced when the season cools off.
Plants do this to store increased energy reserves into survival tissues when the season starts to limit growth. Although autumn may result in better kill, it is essential to ensure plants are actively growing at the time of herbicide application.
Once plants lose their leaves from frost, cold conditions, insect or disease attack, spraying with foliar absorbed herbicides should be stopped. Do not spray blackberry in spring unless there is enough top growth to absorb the herbicide and translocate it to the root system.
What is you water quality like?
Use the best quality water available. Water suitable for human consumption is generally also suitable for mixing with herbicides.
The acidity or alkalinity (pH) of water in field situations rarely affects the performance of herbicides registered for blackberry control. However, high-pH (alkaline) water is often associated with high levels of calcium in the water, which may affect the efficacy of some herbicides.
Water hardness and salt concentrations may reduce the efficacy of the herbicide by limiting the uptake by the plant. Dirty water that contains suspended clay particles can reduce the effectiveness of glyphosate. Other blackberry herbicides will tolerate muddy water.