Apple update

By Terence Bradshaw

As the calendar shifts into summer, things quiet down a bit in the orchard, and this year is no different. Especially with this dry weather we have been seeing, disease concerns are at a minimum. There have been few chances for sooty blotch and flyspeck to become established on fruit, but the upcoming rain expected this weekend could change that. Orchards without fungicide coverage in the past two to three weeks should receive an effective summer fungicide either before or soon after the rains. Fire blight continues to crop up, but these are symptoms of infections that occurred last month. If trauma (i.e. hail) occurs in your orchard and you have active fire blight (even if you’ve been cutting it out), be prepared to apply streptomycin within 24 hours to prevent spread of the disease to new sites. Some question the need for this now after terminal growth has subsided, but I feel it is cheap insurance in a heavy fire blight year like this one. Pay attention to harvest date, however, since strep products have a 50-day preharvest interval; an application today would mean no harvest until August 28.

Insects are of greater concern in midsummer. We are between generations of codling moth, with second generation flight expected to begin soon. Next sprays targeting this pest must target hatching larvae, which should occur in about three weeks. Obliquebanded leafroller (OBLR) is more active now, but likely only in orchards where this pest has historically been a problem. We caught our first OBLR in traps at the Hort Farm on June 7, and Eric Boire caught a few in Champlain Valley orchards in late May (which may have been the cousin redbanded leafroller) but the first sustained captures were caught the week of June 5 and all sites are showing increased flight activity beginning June 21. That said, trap captures at most orchards have been quite low, so a specific spray to manage this pest may not be necessary. That said, if applying a fungicide for summer diseases, consider applying an effective OBLR material at that time, even if it is just a Bt application. Apple maggot flies (AMF) have emerged and traps should be monitored to time sprays against this insect. At the UVM Hort Farm, we have an unrealistically high AMF population remaining from Dr. George MacCollom’s work with that insect in the 1980s in a now unsprayed orchard, and we reached management threshold this week. I expect most commercial orchards will have lower populations that may require management in the next couple of weeks. If you are not trapping for this insect, it may be prudent to apply a material effective against both AMF and OBLR (e.g. Altacor, Asana, Delegate, Imidan) next week.

Trees have been needing water, hopefully this expected rain July 9-10 will alleviate shortages of soil moisture. Dry soil conditions don’t just starve the tree from thirst, they also can lead to poor uptake of minerals such as boron, calcium, magnesium, and potassium. It is important to water trees if possible, and critical to water young and high density trees. All trees can use extra calcium during the rapid fruit expansion in summer, and all sprays moving forward this season should include a calcium material. If using calcium chloride (CaCl), that material will raise spray water pH to levels (i.e. pH 9-10) that can cause alkaline hydrolysis of materials like captan and Imidan, so 2/3 oz of plain white vinegar per pound of CaCl or a commercial formulated pH buffer like LI-700 should be added to the spray tank. Dr. Wes Autio has a good factsheet on Foliar Calcium Sprays for Apples available at: https://ag.umass.edu/sites/ag.umass.edu/files/fact-sheets/pdf/folcalcium.pdf.

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