I go away for a week and nothing happens in the orchard. Not quite, but with the cool weather, trees have been advancing slowly. We reached green tip on McIntosh on Friday, April 24 at the UVM Hort Farm in South Burlington. This signals the real start of pest management season for us. Other, warmer sites likely had green tip earlier and I have heard a few reports of half-inch green showing.
Last week’s rains likely occurred before emergence of green tissue susceptible to apple scab, but rain today and tomorrow cause enough wetting for an infection period. Estimated ascospore maturity based on degree day modelling is relatively low right now at 2-3%, but actual maturity may be higher. If you sprayed copper in the last week, you should be okay, but if not, and significant wetting occurs, application of a fungicide with kick-back activity may be important, especially if you had high levels of scab last year which would provide ample inoculum for infection this spring. Strobilurin and DMI fungicides may be effective if resistance is not an issue in your orchard, but they would be better used later in the season when their activity against other diseases that aren’t yet a threat such as cedar apple rust and powdery mildew are active. The anilinopyrimidine (AP) fungicides Scala and Vangard would be better choices now because they are effective at cool temperatures (<50 F) and have little to no activity against fruit scab which limits their at later times. Kick-back fungicides should be combined with at least a half-rate of a protectant material (EBDCs or Captan, but no Captan within 10 days of an oil application) to reduce development of resistance in the local apple scab population.
White rectangle traps may be hung at three traps per ten acre block any time for monitoring tarnished plant bugs in the orchard. A cumulative capture of three bugs per trap for wholesale orchards or five per trap for retail orchards by tight cluster may indicate a need to treat before bloom.
Weather continues to look good for tree planting this week.