Apple scab, codling moth, and general prebloom orchard management

By Terence Bradshaw

As I mentioned Monday, we are in the middle of an extended apple scab infection period this week and trees will require sustained protection to protect against the disease. Our situation is not as bad as in the Hudson Valley, which Dave Rosenberger detailed in a blog post last night, where two inches of rain have fallen since the weekend with another inch expected the remainder of this week. However, trees are expanding leaf tissue every day, and the rain that we have seen (around 3/4”) has removed some residue from previously applied sprays. It would be prudent to apply another fungicide any time this week, and consider applying a material with kick back properties in the tank mix. I agree with Dave’s caution about using captan in tank mixes which contain any materials with adjuvant to reduce potential for leaf burn because leaves which have opened in this cool, cloudy weather have thin cuticle tissue and may be susceptible to phytotoxicity.

At the Hort Farm in South Burlington we are at tight cluster on most cultivars. Any time now would be a good time to apply foliar zinc, boron, and nitrogen. Wes Autio from UMASS has published a good fact sheet on prebloom foliar nutrients here. Soil applied nitrogen and boron applications may also be applied at any time now.

Insect activity should be picking up in orchards soon. Many orchards choose to apply a pink insecticide prophylactically to manage tarnished plant bug and European apple sawfly, but those pests are best managed based on trap capture data. White sticky traps hung three per ten-acre block at knee height for TPB and head height for EAS may be monitored to assess whether populations are above economic action thresholds. Traps may be ordered from Great Lakes IPM or Gemplers and should be hung as soon as possible if they are not up yet. Thresholds for scouted insects may be found here. For TPB, five captured bugs per trap (eight for retail orchards with higher damage tolerance) is the economic threshold for an insecticide spray at pink. At the Hort Farm, only one bug was seen on Monday May 2 on four traps located in an unsprayed orchard, with none observed in managed blocks. Cool weather this week is expected to keep activity low for the time being. EAS are typically managed at petal fall, and threshold for management is nine per trap averaged over all traps in the block for blocks that received a prebloom insecticide or five per trap for those where no spray was applied at that time.

Codling moth is an increasing pest in Vermont orchards and are best managed using degree day models to time insecticide sprays. CM are monitored using wing traps available from the sources listed above. Traps should be hung at pink and monitored daily to record the first moth capture. This biofix date may then be entered into NEWA or used in your own degree day calculations to time management sprays later in the season against this pest. Debbie Breth from Cornell Lake Ontario Fruit Program has a good fact sheet on codling moth and other internal lepidopteran management here: http://www.fruit.cornell.edu/lof/ipm/pdfs/codling_moth.pdf.

Some growers may be interested in using mating disruption (MD) against codling moth this year. We have been deploying MD for several years on an experimental basis at UVM since we had significant damage a number of years ago in the organic orchards, and feel that it has been relatively successful. MD is expensive, however, works best in large contiguous blocks, and should be deployed orchard-wide to be most effective. There is some question about registration status of MD products in Vermont, Eric Boire at Crop Production Services ((802)759-2022) would be a good contact to explore this option further.

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