When you are attempting to control disease or pests, knowing the right time to spray your apple trees is imperative. Spraying at the wrong time can not only be ineffective in controlling the problem but can damage the trees.
The dominant stage for apple trees is in early spring, before any buds appear on the tree. Temperatures should not drop below 4.44 degrees C (40 degrees F) for 24 hours after the application. The use of horticultural oil at this time prevents scale insects and mites from infesting the apple trees.
When the green buds are about half of an inch long, it is time to apply a fungicide such as lime sulphur, captan, ferbam, mancozeb or one of several others. This treatment prevents scab. This is also the last time the horticultural oil can be applied on apple trees for the season.
Reapply a fungicide when the flower buds first appear. Some may be just opening but most should still be tightly closed. The fungicide controls scab and powdery mildew.
When the flower buds open it is time for the next treatment phase. The same fungicides are applied to continue preventing the diseases mentioned at the scab and powdery mildew. Insecticides such as malathion, diazinon, Thiodan or rotenone are suggested if the rosy apple aphid is present. Severely distorted leaves are the telltale markers of this aphid.
To prevent the apple tree from getting rust, reapply the fungicides, but keep away from the insecticides. About 20 per cent to 60 per cent of the blooms should be open at this time. Insecticides will prevent the bees from polinating the blooms.
When the last petals are dropping from the apple tree the final application of fungicide and insecticide can be made. The same fungicide choices are available for the treatment of scab, powdery mildew, rust, blotches, black rot and calyx rots. Insecticides for treating pests including leafrollers and plum curculio are methoxychlor, permethrin, pyrethrins or rotenone. This is the most critical time as these insecticides cannot be applied once all the petals have fallen.