Pink bud in Vermont apple orchards, some thoughts on bloom and pest management

By Terence Bradshaw

May 5, 2017

Ugh. Vermont orchards are largely at tight cluster (inland, cooler sites and cider cultivars) to pink (most of the Champlain Valley, Honeycrisp of course is lagging) to early king bloom in a few spots and even a little full bloom in the warmest spots. Yesterday was a decent but not great ‘bee day’

for those with open flowers, but an extra 3-5 degrees would have moved their activity up a bit. My greatest concern going into the 2017 crop is this weather we’re facing as we go into bloom- gray, wet, and cool. Hopefully bud development will slow sufficiently so that by the time we get king or at least full bloom, we’ve got good bee weather. Pollen viability extends quite a bit in this weather, up to five days or more after a flower opens, so that’s a good sign as well. If you have the ability to get any extra bees in the orchard, consider doing so. And of course if you have any bees flying in the orchard, treat them right- no insecticides, especially neonics and any materials rated highly toxic to bees; lay off sterol inhibitor/DMI fungicides, at least until we learn more about their effects on pollinators; and mow competitive flowering weeds, if necessary, to funnel them to your apple blossoms. I wish I had a magic bullet that would improve pollination/fertilization/fruit set in a tough bee year, but there just isn’t any proven snake oil you can throw at the trees to compensate for this weather, so the best you can do is to promote and protect the pollinators (managed and wild) that we do have.

That said, this may be a year to consider supplemental pollen application. We have blown pollen at the UVM orchard as long as I have been around (over twenty years), and while it’s not a commonplace practice, it’s something I’ve done partly out of tradition (it was one of the first jobs I did when I started at the UVM orchard as an undergrad in May 1995) and partly to improve our overall pollination since we don’t bring in migratory bees (but we do have seven hives on the property). I was going to skip manual pollination this year, but this bad weather had me calling Firman Pollen to order some up to apply next week. I cannot point to a good peer-reviewed study that says it works in all conditions, but supplemental pollination has, anecdotally anyway, been successful for us. Application method is a little tricky and I don’t know if Firman has the leaf blower guns anymore, but it’s worth checking with them. They also have hive inserts that you add to bee hives to increase the amount of pollen that bees are carrying as they travel through the orchard.

Thursday’s weather provided an ideal spray day between rain events, and I assume everyone took the chance to get covered up. We maintained our spray coverage at the UVM orchards- scab sprays (mancozeb + Vangard) on the IPM and cider blocks, and insecticide (Aza-Direct and Dipel) in the Vf-gene scab resistant organic block where scab isn’t a problem but European apple sawfly and green fruit worn perennially are. Those two sentences covered most of what you need to be thinking about as far as pest management in the next week. Apple scab is the primary threat now, and I expect that when it’s all over, the models will call the period from April 30 through May 10 or so one long infection period. We are entering peak ascospore maturity right now, which means the guns are loaded and each wetting event will release more spores and infection will occur unless you’re protected. Keep covered with a protectant fungicide- mancozeb, captan if you haven’t applied oil recently, or sulfur if you’re organic (and same warning with oil). Five to seven days, max, between applications, and remember that an inch or two of rain removes the coverage you just put on. If you have another perfect, dry day like we has yesterday, add in a more broad-spectrum material with kickback activity (i.e. activity after an infection has occurred but before spores penetrate the leaf cuticle) that can broaden activity against rusts or powdery mildew. Remember the tables in the new spray guide to help guide your decisions. This is a good time to use your strobilurin or SDHI materials.

Notice that I just mentioned a disease concern, but didn’t bring up fire blight. Despite my warning last week to have some streptomycin on-hand for bloom this year, the onset of cool weather has almost completely shut down concern of blossom blight infection, for now anyway. Remember that in order to have a fire blight blossom infection, you need four conditions to occur: 1) open blooms through which bacteria can enter the plant; 2) wetting events during bloom to move bacteria into susceptible tissues; 3) sufficient heat (daily average over 60°F) during an infection event to permit bacterial reproduction in susceptible tissues; and 4) sufficient levels of bacteria present going into bloom. The cold weather has shut down bacterial population growth so the last condition isn’t a concern, and I don’t see any window in the next week anyway where mean temperatures will be over 60°F in any stretch of more than a few hours. Until I say otherwise, put fire blight out of mind, but remember that a warm/hot spell during bloom could turn the situation around quickly. In the meantime, this past week’s Scaffolds newsletter from the fruit team at Cornell has a great synopsis of the fire blight situation in the region.

Insect trap captures are very low across all monitored sites, nothing that I would treat anyway. That said, we are looking like we’re entering an extended bloom period, and that means that those pests waiting in the wings can start doing damage on early-blooming cultivars while you’re waiting for petals to drop on the later ones. Growers with low tolerance for cosmetic injury or history of European apple sawfly may consider a prophylactic pink spray, but I only say that because of the drawn-out bloom. Ideally, sprays will be based on quantifiable trap data, and in no orchard have we caught even remotely enough of either to warrant a pink spray.

In between sprays, this is still a great window to get your trees in the ground, apply herbicide, and fertilize orchards. We did all three this week at the UVM Hort Farm, or at least my technician Jess and chief engineer Andy did. I had one of those days yesterday when it took me as long to spray seven gallons of material (herbicide in the vineyard() with an electric backpack sprayer as it did Jess to spray 600 gallons of materials from three sprayers in multiple orchards. The lesson here is to make sure your equipment is ready to go the day before you need it. And maybe to not let the Professor play Farmer, but I’d say I still do all right at it when I prepare properly.

-TB

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