Vermont Apple IPM

Orchards in the highest elevation and coolest areas are at or just past petal fall, so all the advice I’ve had for other growers applies there as well now. All orchards should have started or completed chemical thinning by now. Fabulous thinning weather occurred last week and those who applied the usual materials should see the effects by now. If a little more ‘nudge’ is needed to break up clusters, carbaryl , 6-BA 9 (Maxcel, etc.), and NAA (Refine, etc.) will still work so long as the fruit you’re thinning are under 15 mm diameter.

Where petal fall insecticides were applied against plum curculio (PC) and European apple sawfly, you’re probably good until another is needed for PC due to rain washoff or codling moth rears its head. As for the former, PC is only ‘programmed’ to lay eggs and cause fruit damage for about 308 degree days (base 50) after McIntosh petal fall, and we’re only about 1/2 there at the UVM Hort Farm. It would be wise to check for PC damage to fruitlets and consider reapplication at the first sign of fresh damage.

Figure 1. Plum curculio damage on a developing fruitlet. This damage is about a week old, note the dried surface and lack of sap. Fresh stings after an insecticide has been applied indicate potential need to reapply.

Codling moth have now been trapped in many orchards in the state. To best manage the first generation of this pest, calculate degree days (base 50°F) from the date of first capture in pheromone traps. Most materials should be applied at 200 degree days after catch, which should be in the next week or so. Retired Cornell entomologist Dr. Art Agnello offers the following specific recommendations for CM management the June 10, 2019 Scaffolds newsletter: “The best products for controlling both CM and OFM in apples and stone fruits are those in IRAC Group 28 (containing a diamide; i.e., Altacor, Exirel, Minecto Pro, Voliam Flexi or Besiege) or IRAC Group 5 (mainly spinetoram, Delegate; spinosad, formulated as Entrust, is an organically approved option). Two applications from either of these groups on a 10–14-day interval would be recommended starting at 220 DD50 from biofix…Products with insect growth regulator activity, such as Rimon, Intrepid or Esteem, would also be suitable options in apple sites at the lower end of these values. Other products with activity against internal leps include the neonic Assail, the biological Grandevo (also organically approved) and, in orchards where resistance has not developed to the newer pyrethroids, also Baythroid, Danitol, Endigo, and Leverage (note: I like to avoid pyrethroid use in orchards if possible sonce they can substantially disrupt beneficial insect populations- TB). Most older broad-spectrum materials like Imidan, Lannate, and the older pyrethroids, which were formerly more effective, are generally not as good choices because of insecticide resistance issues…This would also be an appropriate time for an application of a granulosis virus product in pome and stone fruits such as Cyd-X, Madex, Virosoft CP4 or Carpovirusine (apples and pears only), in addition to the larvicides discussed above. These are biological insecticides, which must be ingested to initiate the infection, after which the virus replicates inside the larva until it is killed; this releases more virus particles into the orchard. This is a very useful approach for long-term population reduction, particularly when used in at least 2 applications per generation. Madex, and now Virosoft CP4 (see “Chem News” in this issue) contain an isolate that is also effective against OFM.”

As for diseases, all sites should be nearly done with primary apple scab season. That doesn’t mean that scab management is done, you should keep covered for at least one more good infection period. Inland/cooler sites likely have inoculum left through next week, so you’ll have at least two sweeks more of fungicide coverage before backing off. Scout your orchard regularly for scab, especially in the tops of the trees, ends of rows where nozzles may have turned off, or on susceptible varieties. f you have scab, plan on maintaining some level of preventative fungicide (Captan is about all you have, sulfur if organic) for the next month or so until fruit and foliage become resistant. Do not use single-site fungicides like DMIs, strobilurins, or SDHIs (FRAC codes 3,7, 9,11) on active lesions to reduce development of fungicide resistance.

Keep your eyes out, especially in blocks that have had a history of the disease or on susceptible cultivars like Gala and Paulared, and cut strikes out as you see them.

If using nitrogen fertilizers in your orchard, plan on wrapping up applications in the few weeks to give trees time to harden off for winter. Potassium fertilizers can go on any time now.