Vermont Apple IPM: Midsummer management

This has really been a bit of a goldilocks season, with relatively mild, or dare I say ‘normal’ temperatures, few significant weather calamities, and just enough rain to keep us from complaining too much. That generally means low tree stress, and with the reports I’m hearing from growers and the observations I’ve made around the state, it appears that we’re headed toward a decent apple crop for 2022. But there’s still work to be done.

While it has been dry, there have been enough showers that we do need to think about keeping some fungicide coverage on against the summer diseases. The first that comes to mind is the purely cosmetic sooty blotch / flyspeck complex. If you are growing apples for cider, this disease is of no concern to you, but if you are selling fresh fruit, it does need to be considered. That said, if you follow the standard recommendations for management of a fungicide applied every 10-14 days or after 1-2 inches of rain, you will likely have visible fungicide residue on the fruit at harvest, which in a PYO or direct sales situation is just as tough to explain as a few spots are. That doesn’t mean that I suggest ignoring the disease. There is a good NEWA model for planning your sprays to manage it. Dr. Dave Rosenberger gave a good synopsis of SBFS management in a 2014 issue of Scaffolds. In it, he mentions considering both this summer disease complex as well as black rot, which can be especially bad on Honeycrisp, Cortland, and Northern Spy. The take-home message is to consider keeping your fungicide coverage up at least every three weeks or after 180-200 hours of leaf wetting. Captan plus a phosphite is a good option, but for better black rot control, captan plus a DMI (e.g., Inspire Super), strobilurin (e.g., Flint), or the old standby Topsin would be a better choice.

For organic growers, sulfur remains the material of choice, although Lifegard may have some efficacy. Bitter rot is another disease of concern that is caused by a different fungus which thrives in hot conditions and is more common when fruit finish is compromised by sprays (e.g. summer oil, lime sulfur) or when trees are drought or heat stressed.

This brings up water. It is essential, especially on young or dwarf trees, to maintain adequate water to ensure good tree growth. NEWA has a good apple

irrigation tool, but a god rule of thumb is one inch of rain per week. If you receive less than that, it is good to make up the difference with irrigation. One inch of rain equals about 27,000 gallons of water. However, if using drip irrigation, you can assume that you only need to irrigate the dripline of the tree canopy, which I’ll say requires about 15,000 gallons of water per week. The actual amount needed is more complicated than that determined in my quick calculation there, and takes into account many factors- soil type; soil organic matter content; temperature, wind, and solar radiation; tree size; tree age; crop load; etc. The point is, if it’s still dry and you have the capability, consider watering your trees.

On the insect from, we’re still in a bit if a between period, where codling moth has finished its first generation activity and we’re waiting on apple maggot. Apple maggot flies have started to be trapped in some high pressure orchards, so keep on-guard and be ready to treat when an average of one fly per four unbaited traps or five flies per four baited traps per block is reached. In the meantime, if you have seen lepidopteran larvae (caterpillars) on growing terminals, you may have a population of obliquebanded leafroller which can be managed with a cheap, effective, and low-risk application of Bt insecticide. Sprays are typically timed for 360 degree days (base 43°F) from first trap capture of the ‘summer generation’. In my experience, we don’t get strong peaks in weekly monitoring for this pest, so I like to include some Bt in any sprays in June and July that don’t have another insecticide in the mix.

Every spray this time of year should contain a calcium product for optimum fruit quality, and varieties highly prone to bitter pit- Honeycrisp, Northern Spy, Cortland, William’s Pride- should get sprays of calcium even when you’re not spraying for diseases or insects. While we’re talking about nutrients, it’s time to start thinking about foliar tissue testing to assess orchard nutrition. Samples are usually collected between July 15 – Aug. 15. The UVM Agriculture and Environmental Testing Lab can provide analysis, but at this time their output does not generate fertility recommendations. The following are potential options of labs for analysis. It is recommended that you contact the lab for instructions and costs before samples are sent. Plus, it is important to confirm that they will send recommendations along with the analysis.

(1) University of Maine Analytical Lab:
(2) Agro One:

Samples should be collected separately per variety, per block. Each sample should contain 25-50 leaves collected from the middle section of current season’s terminal leaves- do not collect young pubescent leaves nor the oldest leaves on a shoot. Leaf samples should be washed quickly and gently in a basin of warm water with one crop of detergent, then double or triple rinsed. Wet leaves can ne loosely placed on a paper lunch bag left open in a breezy or sunny area to dry before shipping.

That should be enough for now. Please let me know if you’re seeing anything of interest in your orchards. I do have a little time left this and next month for field visits, so if you’re interested in one, let me know that, too.


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