With the warm weather coming in, we expect most Vermont orchards to be at green tip in the next few days if they have not gotten there yet. This is an ideal time to think about beginning your pest management season by applying a whole orchard copper spray. Copper should be applied to apples before the quarter inch green tip bud stage to reduce the likelihood of fruit russeting. Copper is a relatively weak fungicide, but can provide enough protection for the first one or two apple scab infection periods when ascospore maturity may be relatively low. The primary purpose for copper at this time of the season is to reduce the load of bacteria which may spread fire blight. Copper needs to be on the surface of the plant when bacterial ooze starts to exude from the tree around bloom. The specific type of copper is of less importance than the total amount of elemental copper that is on the surface of the plant after application. We generally recommend any of the main forms of powdered coppers including copper sulfate, copper hydroxide, or copper octanoate applied at label rates.
If you choose to get a jump on insect and mite management, you could consider applying spray oil at this time also. However, spray oil may be more effective if applied a little later in the season—say, between half inch green and no later than tight cluster. If applied at this point a 2% by volume mixture of spray oil in water could be used. Oil sprays should go on either at full dilute or at most a 2X concentration, so I would recommend most orchards be treated with at least 100 gallons of water when making that application. This makes oil sprays slow going and so it may be best to wait until a long window of agreeable application weather is available.
Speaking of weather, it looks like the best window to apply copper or any other spray material in the next few days is Sunday morning 4/12, as we will be between wind events at that time.
Separate from spraying, good orchard IPM practices include cultural and biological controls as well. One important practice to consider at this point which can be done even while the wind is blowing is flail mowing brush and especially leaves to help aid with decomposition and to reorient leaves now that ascospores have developed. Over the winter, the apple fungus develops pseudothecia in which ascospores are formed which result in the primary inoculum for the disease season. Pseudothecia develop facing the sunlight, and so even if 1/2 of leaves are flipped over during a mowing operation, those ascospores within them will eject into the ground rather than into the canopy during wedding events. Therefore, a careful mowing of foliage can have a significant impact on the potential inoculum as we head into the primary disease management season.
As always, check the New England Tree Fruit Management Guide or the Cornell Tree Fruit Management Guide and always follow the label for your specific materials.
The UVM Tree Fruit and Viticulture Program is supported by the University of Vermont Agriculture Experiment Station, UVM Extension, USDA NIFA E-IPM Program, and USDA Risk Management Agency.
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