Vermont Apple IPM: Mid-late summer apple insects and diseases

Apple maggot fly captures are increasing in some orchards. At this point, unless you know you have really low or no AMF in your orchard, I would consider applying an effective material when you next apply a fungicide or foliar nutrient. This will allow for activity and eventual wash off prior to harvest. Check the options in the New England Tree Fruit Management Guide.

Second generation codling moth are due for management in many orchards. At UVM HREC, we caught our first codling moth on May 26. Using NEWA’s codling moth model, I know that I have accumulated 1215 degree days (base 50°F) since then. Sprays against a second generation should be applied around 1260 DD after first capture. I sprayed this morning. If you’re a little further behind, you can use NEWA’s degree day tool to calculate present and estimate near-future degree days, just enter your start date (first moth capture, or use the one generated in the CM model), end date (usually today), and base (50°F). This will allow you to use the six-day forecast to plan your best-timed spray. Precision tools like this allow for better use of fewer or more selective sprays. Using NEWA, monitoring, and knowledge of my market (retail with fairly high tolerance for cosmetic blemishes but not for wormy fruit) should allow me to get away with three insecticide applications this year. That’s half as many as we used to put on when I started 25 years ago.

Today I applied the Exirel I purchased earlier in the season. I only mention this product as a cautionary note to read your labels, every time you use a product and preferable a few days before. I bought this material for use against first generation CM, but it comes in an oil-based emulsion which will cause phytotoxicity when used with captan, which was my early summer fungicide of choice. I held off applying until this spray, but of course failed to order the more compatible fungicide I plan to use for my final fruit rot and sooty blotch / flyspeck spray. So, I was all set up, material already in the tank, so I sprayed anyway but now will need to put my fungicide on separately next week. Plan ahead.

On that note, I would consider one last fungicide against sooty blotch and flyspeck, but moreso against the summer fruit rots. The latter can be worse in doughty conditions with high heat and humidity- remember last week? Captan, especially combined with Topsin or a phosohorous acid product, are good summer fungicides, but leave visible residue on fruit surfaces at harvest if not washed off. Strobilurins (FRAC group 11) are also very effective, including some of the premix materials like Merivon and Luna Sensaton. The biological resistance promoter Lifegard is reported to have some efficacy as well. I had that left over in the shed from our fire blight management this spring so applied it this morning to improve natural resistance in the plant to disease. I don’t know how well that works, but there is some evidence of efficacy. I’ll be following up with a strobilurin next week.

For organic growers, the options get slim. I have seen where sulfur and high heat can damage fruit and actually allow fruit to rot more easily. A rotation of Lifegard with biologicals like Regalia or Serenade may help reduce disease.

Fruit need calcium now, especially Honeycrisp and other large-fruited varieties, so I’m okay making another trip out there to apply that again as well.