Apple scab management

April 30, 2015

by Terence Bradshaw

Cool weather has kept bud development in orchards behind ‘normal’, and I’m hearing reports ranging from late dormant in high elevation inland orchards through early half-inch green in the warmer valleys. Bud development will be moving fast with expected warm temperatures through Tuesday, when rain showers are expected to arrive. Ascospore maturation is increasing fast as well, and a significant infection period can be expected if wetting hours are sufficient. Because buds are developing so quickly, protective fungicide coverage should be applied as close to Tuesday as possible the ensure that material is on emerged tissue going into the infection period. Most orchards have applied little if any fungicide this season, so coverage will good spray coverage is critical since any ‘base coat’ of material is limited. Saturday through Monday look to have good weather (i.e. low wind speeds) for spray application. The point is, if you are among the majority of orchardists with green tissue showing, you should be applying a fungicide this weekend. With the dry weather and adequate warning going into this event, protective fungicides (EBDCs, Captan or sulfur (for organic growers)) should be adequate. Remember, do not use Captan or sulfur if oil was applied within the past 7 days.

Green tip through tight cluster is a good time to apply nitrogen fertilizers in the orchard. Applications are best informed by foliar nutrient analyses which should have been conducted last summer. Many orchards on heavy soils with high organic matter content may not need any nitrogen applications in most years. Another concern is that overapplication of nitrogen may increase susceptibility of trees to fire blight infection. A conservative rate of nitrogen to apply in most orchards is 30 of actual nitrogen per acre. Recommended fertilizer materials can be found in the 2015 New England Tree Fruit Management Guide.