Orchard management at petal fall (and then some)

By Terence Bradshaw

This week I’ll just say, “more of the same…” Apple scab primary ascospore season is done or nearly done in Vermont orchards. Check carefully for apple scab in your orchards before stopping fungicide coverage. Lesions can take two weeks to appear, so you may not see the latest infections for a bit. By now, growers who have been using more than three pounds per acre of mancozeb should put that away for the season, captan will be the protectant fungicide of choice. Sulfur should be the standard in organic orchards, although lime sulfur may be appropriate, especially if there are active lesions that need to be burned out and you want some thinning activity. Remember, lime sulfur is extremely caustic and corrosive to metal, to take care of yourself and your equipment if you use it.

Keep an eye out for fire blight strikes as you walk your orchards. We were generally on the ‘no conditions for infection’ side of the line in most orchards, but there is a chance that some got through, especially in warmer sites with a history of the disease where streptomycin was not applied. Prune out strikes as you find them.

Insects: still quiet. Codling moth has shown up in some sites, which means a targeted application of an effective product 250 degree days (base 50 °F) after the biofix of the first date caught in a pheromone trap. In the meantime, where you have 100% petal fall and no bees in the orchard, an insecticide application targeted at plum curculio and (if present) European apple sawfly may be warranted. Dogwood borer are rearing their heads more and more. If you have them (check burr knots on trunks, especially young trees on M9 or M26 rootstock), consider a coarse, soaking trunk spray. Best bet now is probably Assail; the old standby Lorsban (chlorpyrifos) is no longer registered for use in Vermont, and for good reason. Organic growers may consider Pyganic, and probably several applications.

Thinning: weather isn’t looking very good for 6-BA thinners like Maxcel until later this week. If planning to use those materials on smaller-fruited cultivars like Empire and Fuji, wait a bit. NAA thinners should be effective, but plan on using higher rates given the cool weather. Keep an eye on developing fruit following thinner applications, fruit will be susceptible to hormone sprays up to 17 mm diameter, after which we need to take more drastic and unreliable measures.

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