Winter rates of copper
Growers should now be moving to winter rates of copper. Copper use reduces through summer and coverage needs to be rebuilt as the risk of frost and hail increases and wetter conditions prevail. Leaf spotting from spring infection still provides inoculum sources and heavy morning dews can provide sufficient moisture to re-activate Psa.
Growers beginning winter work on Gold3 are noting some dehydrated cane and cane die-back in their canopies; and some Hayward growers in the Katikati region have also commented they are seeing new spotting on Hayward leaves. This indicates recent Psa infection and reminds us that Psa has not disappeared.
Frost damage, leaf-fall, wounds created when dropping strung canes and pruning activities all create opportunity for Psa to enter. Therefore levels of inoculum in the canopy must be managed.
After harvest, a copper and Actigard™ mix is recommended if leaf condition remains strong (leaves must be actively photosynthesizing to maximise the value of Actigard™). Do not apply Actigard™ to stressed vines. Further applications of copper will be needed through the leaf-fall period and before and after winter pruning. Protection through dormancy presents much lower risk of phytotoxic effects.
Also, check the coverage of sprays applied. Slow down to maximise the value of the applied products and avoid product waste through run-off. Addition of spreaders will improve coverage and penetration into cracks and crevices. Time on target is important, and alternating the direction of travel for consecutive spray passes will help compensate for shadowing from pergola structures.
Linda Peacock, KVH Operations