May 7, 2015
by Terence Bradshaw
This is an important week for orchard activities, as you likely know. I’ll try to be brief but thorough:
Apple scab: Depending on whether or not you had green tissue showing on April 23 or (more likely) April 27-28, you may not have even seen an apple scab infection period in your orchard yet. We have had some false alarms as far as predicted wetting events, but things have overall been pretty dry. The chance of rain showers is there on Saturday May 9 and increasing daily through Tuesday, but no widespread soaker is expected, although localized showers may trigger an infection period in your orchard. Ascospore maturity is healthy, although in some orchards which have received no rain for seven or more days, development in the NEWA model has stalled, so the next wetting event will potentially trigger a significant infection period.
Spray conditions are good today Thursday May 6 and tomorrow May 7, with increased winds expected later Saturday and especially Sunday (check the conditions in your orchard prior to spraying, of course). Take home message- make sure you’re covered with a protective fungicide going into this rain event.
Pink-stage insecticides: Many orchards are at pink or approaching it now, and I expect first bloom in the Champlain Valley by Monday or Tuesday. If you have not already brought bees in, and tarnished plant bug or European apple sawfly are a problem in your orchard, an insecticide in the next spray may be prudent.
Fire blight: risk is still looking to be high for fire blight infection when blooms open in most orchards, and any wetting could trigger infection (including heavy dew or a spray application). Be ready to apply streptomycin within 24 hours of a wetting event, and reapplication will be necessary after a couple of days as new blossoms open and the material effectiveness wanes. Remember the conditions required for blossom blight infection: open bloom, wetting, sufficient bacterial population to infect (driven by weather in the past week or so, which has been warm), and warm weather during infection. Cooler weather in the middle of next week will likely reduce fire blight threat, but bloom and wet will likely occur before then.
General orchard activities: water if you can, especially newly planted trees. The potential showers in the next few days don;t look to be enough to give new trees what they need. Now is the time to apply nitrogen fertilizers, including prebloom foliar fertilizers (another thing to put in that pink spray).