SILOAM ORCHARDS FRUIT TREE FOCUS
DORMANT OIL SPRAY
DO NOT: Spray dormant oil within 48 hours of freezing temperatures, apply on young trees, make more than one application per year. Dormant oil may injure some apple cultivars including Red Delicious.
If you have identified scale insects as a problem in your apple trees you may wish to apply dormant oil while the trees are fully dormant as a control measure. Scale insects are most common in older unpruned trees with rough bark and dense growth, and are usually kept in check in the home planting to a satisfactory degree by birds and beneficial insects.
You may wish to save your one annual oil application to use as a control against Red Spider Mite if this pest was a problem in the past year. Detection of spider mites requires a hand lens with the most obvious visual sign being the bronzing of the foliage particularly in hot dry weather in August. At the half inch green stage apply a dilute oil spray according to directions or as outlined in OMAFRA publication 360. Pear psylla on pear trees may also be controlled with oil applied at the half inch green stage.
Be aware that these are the only insect pests of apple that dormant oil is effective against. Claims are made every spring regarding this product acting as an effective control against all that ails your apple trees. This is not the case. The major insect pests of apple are not controlled by dormant oil or are overwintering elsewhere.
See also Ohio State factsheet on Oil Spray