May 20, 2021
It’s looking pretty hot out there in more ways than one. Many orchards are at or near petal fall, but those with bloom should be keeping the streptomycin sprays on, with all this heat we’re having. Fire blight remains a concern statewide, and I would expect some infection in any orchard that has sufficient inoculum. That last part is important, and yet hard to quantify. Certainly if you’ve has the disease in the past, especially in the last two years, it’s likely that it will show up. The next disease concern is apple scab. Any promised rains keep getting pushed back in the forecast, now Saturday-Sunday looks like the most likely chance for any substantial rainfall. Whenever it comes, we should be prepared with a good coating of protective fungicide. Most growers are switching over to captan now which is fine, but be careful not to mix with Regulaid if you’re using that wetting agent to improve strep penetration into blossoms, as the combination of that, captan, and heat will likely cause leaf burn. If you’re looking at a second application of strep after one that already had a wetting agent included, you can leave it out this time. It’s also nota bad idea to put something in that would provide broader disease control, like an SDHI, SI, or DMI fungicide (take your pick from materials with FRAC codes 3, 7, 11 here, and always rotate FRAC codes after two successive applications of the same one).
Growers at 100% petal fall may want to consider adding in an insecticide against European apple sawfly, plum curculio, and early codling moth. However, if you have any blooms remaining, including in the groundcover vegetation, I recommend holding off on applying any materials harmful to bees and other pollinators. I typically include some Dipel or other Bt product in this ‘almost petal fall’ spray to help keep lepidopteran pests like green fruit worm and obliquebanded leafroller at bay while I wait until the following week to apply something more broad spectrum like Avaunt, Actara, or even Imidan if you’re still using organophosphates. Sevin applied in a thinning spray will have some efficacy as an insecticide, but not a lot.
As for thinning, it’s time to get on it. Blooms are heavy this year, and the sooner you remove resource competition and gibberellin formation from excess developing seeds, the more likely you will get reasonable return bloom next year. If you still have any bloom, or just want to stay away from it, please leave the Sevin / carbaryl on the shelf. With the hot weather, trees are going to respond well to thinner applications anyway, so an NAA or 6 BA spray should suffice. Pick one- the former is typically good on McIntosh and most large-fruited cultivars, the latter on varieties that tend to produce smaller fruit (Empire, Gala, Fuji, Macoun). See specific recommendations here.
For cider apple growers, I don’t have a great recommendation for managing biennialism on European cultivars. The need to thin for fruit size is less of a concern than for dessert cultivars, but you don’t want to overstress the tree and have no crop this year. I would plan on multiple applications of NAA, say bloom, petal fall, and at 8-10 mm fruit size, to encourage return bloom.
For what it’s worth, here’s the tank mix I plan to apply tonight or tomorrow morning: Captan (5 lbs/ac), Merivon (5oz), Dipel DF (1 lb), Refine (8 oz), Harbour (24 oz). This is to a very mixed orchard of ~50 varieties in all stages of bloom to petal fall.