Apple Season is right around the corner

By Terence Bradshaw

I’ve been seeing reports from areas south of us- recommendations for first scab spray in Connecticut; green tip on McIntosh in Massachusetts. And yet I awoke to another morning of accumulating snow and temperatures in the 20s. I haven’t seen a colder / slower start to the apple season in my roughly twenty years in this business, but rest assured that the trees will soon awake. We’re looking at a warm and dry trend next week, with temperatures in the 60s by Monday. I’d expect green tissue to be showing in warmer sites by the middle to late next week. That means that the season and all of the management it entails is right around the corner.

While the general rule of thumb is that tree phenology advances with temperatures in the 40s, apple scab inoculum matures at cooler temperatures. That means that overwintering scab inoculum can be ready before the trees are, which makes sense- the fungus evolved to stay just ahead of its host in terms of development. I expect that many orchards had issues with scab last year, and if you saw any on a casual inspection of the orchard or in the packing house, expect for there to be a lot of inoculum ready to infect this spring. This is one of those years to stay ahead of scab.

You can help to clean up inoculum at this time by increasing decomposition of leaf litter. That can be done by either flail mowing leaf debris (and you need to go slow, low, and thorough) or spraying urea (40 lb / 100 gal water to soak leaf litter), or both. If using urea, you should adjust your fertilizer rates downward, but only expect about half of that applied nitrogen in the urea s[pray to be there when the tree needs it in a few weeks.

That said, you need both inoculum (assume it’s there unless you did a Potential Ascospore Dose assessment last fall) and environmental conditions to cause apple scab infection. Starting now, keep an eye on the weather forecast and use NEWA to help guide spray decisions. The best and most conservative strategy is to maintain protective coverage of fungicides on tissues prior to infection to prevent disease rather than fight established infections all season long. The first fungicide application typically made between the silver tip and green tip bud stages is a copper spray which will also help to reduce overwintering fire blight bacteria on the surface of woody tissues. Copper can be applied at the usual, full rates any time before quarter-inch green tip, but once you see the beginning of the ‘mouse ears’ from the first two leaves, know that copper application can lead to fruit russeting (not necessarily an issue with cider apples, but this will quickly downgrade fresh fruit). Dave Rosenberger pulled together an excellent summary of the use of early season copper for scab and fire blight management in the March 25, 2013 issue of Scaffolds. Copper may be applied when there is a threat of freezing weather before or after application.

Oil, however, is a different story when it comes to applications before or after freezing weather. Delayed dormant, silver tip, and green tip are common times to apply an oil spray to help manage mites, aphids, scales, and other overwintering arthropods pests. When oil penetrates cells, it causes phytotoxicity that can affect fruit development, especially when cluster leaves which supply most of the carbo0hydrates to developing fruit early in the season are damaged. Oil is often applied at dilute rates, and the goal for a grower should be to fully saturate the tree as best possible. Application of oil just after or before freezing events (24 hours either way definitely, possibly 48 hours) can cause damage, so if you have seen or are expecting freezing temperatures, put the oil away for a couple of days.

Fortunately, oil can be applied right up to tight cluster-early pink bud stages, and in fact may be more effective then. We should be out of frost risk by then (otherwise we have bigger problems than oil on fruit cluster leaves), so maybe delaying your oil application would be prudent, so long as you can fit it around Captan sprays later in the season. Oil should not be applied within 7-1- days of a Captan or Sulfur spray. For more details on spring oil applications to manage mites and other pests, including rates and spray incompatibility issues, please refer to your 2018 New England Tree Fruit Management Guide.

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