Dormant Oil Sprays: In recent growing seasons, San Jose scale and white peach scale populations have been causing increasing amounts of damage. These pests create a superficial spotted injury caused by crawler stage feeding on the skin of apples and peaches, making the fruit unmarketable. In severe infestations, heavy crawler populations feeding on the sap of tree limbs can cause severe dieback. Scale overwinter on the limbs of trees asimmature crawlers under their protective waxy covering. In the spring when temperatures begin to rise, they respire through this covering. Dormant oil sprays are your first line of defense as they work to coat the protective covering of the scale and prevent respiration. Dr. Anne Nielsen’s lab found that another effective option at the delayed dormant timing is Centaur at 34.5 oz/A.
European red mite is another pest of concern that can be targeted at this stage. These mites feed on the foliage of tree fruit causing a bronzing symptom. Feeding from this pest can reduce fruit quality and tree vigor. European red mites overwinter in orchards as eggs. These eggs begin to hatch just prior to pink through bloom in apples. Dormant oil efficacy improves the closer you are to egg hatch for this pest so an application should be timed for green tip-half inch green in apple.
Pear psylla typically become active and begin laying eggs in NJ in mid-late March. Nymph stage pear psylla feed on the sap of pear trees and excrete honeydew which causes black sooty mold on fruit making it unmarketable. This pest also injects a toxin into the leaves as it feeds causing the leaves to blacken and eventually leads to defoliation. Dormant oil works to deter pear psylla from laying eggs and acts as a first line of defense against this pest.
Proper coverage with dormant oil is essential for it to work properly. Due to this, dormant oil should be applied as a full block spray instead of alternate row middle. It is important to ensure your sprayer is properly calibrated and that you are using a sufficient spray volume. Dr. Brett Blaauw from the University of Georgia found that 100 gal/A is a sufficient volume for coverage IF the trees are properly pruned prior to the dormant oil application (see University of Georgia factsheet). It is possible to achieve almost 100% coverage by making multiple dormant oil applications. This strategy is optimal because it also allows you to target both scale and mites at their optimal timings. One application can be made early on when temperatures first begin to rise above 51°F to target scale and a second application can be made between green tip and ½” green to target mites and continue controlling scale. An oil application at ½” green combined with Esteem at 4-5 oz/A will also provide control of aphids including wooly apple aphid. Wooly apple aphid populations have been becoming more prevalent in NJ apple orchards in recent years, likely due to dry end of summer conditions and pyrethroid use flaring populations. The first place this pest will begin to pop up will be pruning cuts so be sure to keep an eye out as the season progresses since early action is critical for effective control.
Dormant oil application rates depend on the phenological stage and the crop you are spraying. Typically, oil is recommended at a 2% rate or 2 gallons of dormant oil per 100 gallons of spray mix. You can perform concentrated sprays of 6 gallons of dormant oil per 100 gallons of spray mix in pome fruit based on the dilute volume of 300 gallons per acre (amount generally considered to cover a mature semi dwarf apple to the point of drip). In stone fruit, a concentrated spray would include 4 gallons of dormant oil per 100 gallons of spray mix based on the dilute volume of 200 gallons per acre (amount generally considered to cover a mature peach tree to the point of drip). Oil can safely be applied up to the pink stage of tree fruit, but the rate should be dropped the closer you get to this stage. For example, in pome fruit a full rate can be applied up to ½” green, this rate should be halved up to tight cluster and then halved again up to pink.
When applying dormant oil, it is important that you do not make an application within 2 days of the temperature dropping below 32°F. Another important consideration is that oil should not be applied within 2 weeks of Captan due to phytotoxicity concerns. There are other insecticides that can be mixed with dormant oils to target these pests; however, results are variable on whether the addition of these insecticides improves efficacy over oil alone.
Dormant Season Copper Sprays: Fire blight can be targeted at the dormant stage using copper as your first line of defense. The copper targets cankers caused by fire blight and reduces the amount of bacterial inoculum present in the field. Early season copper sprays can also be effective against apple scab if some green tissue is present in the bud. Copper should not be applied after ½” green due to concerns with phytotoxicity and fruit russeting. If tank mixing copper with dormant oil, extra precaution should be taken to ensure there is no risk of freezing temperatures since this can exacerbate issues with phytotoxicity and injure the tree.
The bacteria causing fire blight can only survive inside of living tree tissue. The winter is an optimal time to remove infected branches since the sap is not flowing, this reduces the risk of spreading the inoculum to your next cut. Removing the cankers caused by this disease where most of the bacteria are surviving will reduce your inoculum levels and make this disease easier to manage during the spring. It is a good practice to flag limbs that were infected with fire blight in the previous season to make the cankers easier to find when it comes time to prune. Pruning crews should be trained to look for sunken, dark, cracked areas on the tree bark that may be cankers. A knife can be used to peel away the tree bark to confirm the presence of the canker. If it is in fact a canker, the sapwood will be brown. You can continue peeling the bark away until you find the margin of the canker where the sapwood is still healthy and green. The pruning cut should be made at least 8 inches below the canker to ensure no inoculum is left behind in the tree. All canker prunings should be removed from the orchard since they can still act as a source of inoculum if left behind on the orchard floor.
If peach leaf curl was not targeted in the late fall at leaf drop, a fungicide application is also effective in the late winter prior to bud swell. Copper, Ziram, and Bravo (Chlorothalonil) are the most effective options at this timing.
Dormant Season Urea Sprays: Dormant season urea sprays are an extremely effective tool to reduce inoculum in orchards with high apple scab pressure. These sprays help to break down the leaf litter more quickly, which isessential for orchard sanitation and reduction of foliar disease inoculum. Urea applications are most effective if applied after leaf drop in the fall, but if you didn’t have a chance to make the application, it is not too late! Urea can be applied to leaf litter in the late winter or early spring using an airblast sprayer with nozzles pointed towards the ground or a boom sprayer at a rate of 40 lb/A in 100 gallons of water. A flail mower can also be used to chop leaf litter,which allows it to decompose more quickly. By using these methods, you can reduce your apple scab inoculum by 80% or more, which will make management easier and more effective during primary scab infection.
