Pest management in orchards this week, May 5

By Terence Bradshaw

First note, please remember that we will be hosting an Orchard Scouting Field Workshop at the UVM HREC on May 16, 1-4 PM to help growers with implementing scouting programs and to discuss upcoming management strategies. I’ll have a registration link ready later this week. The event will be free, but I’m looking for a head count. Also. Don’t forget that we have hard copy New England Tree Fruit Management Guides available at: http://go.uvm.edu/netfmghc.

Bud stages in Vermont orchards run the gamut, from pink and maybe even the very beginning of bloom in the south to green tip at my house at 1500 feet elevation in Washington county. At the UVM Horticulture Research Center, trees are at a solid tight cluster and will move more tomorrow. We’re in a window of relative calm, so unprotected orchards may deserve some fungicide coverage before Tuesday when enough rain is expected to cause a scab infection period. It will be cooler and drier on Wednesday, so another option would be to apply on Wednesday after the rain, assuming that you already have some coverage remaining from last spray and you’re ready to apply a site-specific fungicide (like an SDHI, QoI, or DMI material) that will have some kick-back activity and cover for the prior day’s infection. Reliance on kick-back materials speeds development of resistance in the scab pathogen, so I only recommend that strategy if you already have some coverage like from a spray last Wednesday, and I always recommend tank mixing with a multi-site protectant like mancozeb, captan, or sulfur if organic. (For growers following an organic schedule, I don’t have a good answer for a recommended kickback material. Liquid lime sulfur is a very heavy bomb that will negatively affect trees and is better saved for rescue situations; Oxidate or one of the bicarbonate materials like Kaligreen can have some post-infection activity if applied very soon after initiation of an infection period, but I wouldn’t count on getting good control if you wait any real amount of time after to apply or if there is a heavy infection period.)

Cedar apple rust galls (sixth picture) are active on red cedar and other junipers in the Champlain valley, and I recommend treating for this disease in any orchard that has had an issue with it in the past as the cool, wet conditions of last week and this week are conducive to disease development. The good news is that mancozebs (a multi-site protectant fungicide class) are effective against CAR; DMI (Indar, Rally, Rubigan, etc.) and strobilurin (Flint) fungicides are highly effective, and SDHIs (Aprovia, Fontelis)have moderate efficacy. A tank mix of those materials (one protectant and one of the other single-site classes should provide good protection. Remember, do not apply single-site fungicides with the same FRAC code more than twice in succession before rotating to another chemistry (FRAC code).

As bloom approaches, plan on completing a few activities to improve tree’s response to pollenization and fertilization. A prebloom foliar nutrient mix of nitrogen, zinc, and boron should be applied. Rates are dependent on the products used, and are intended to boost blossom vigor as the trees enter the stressful bloom period Dr. Wes Autio’s (UMASS) recommendations for Prebloom Nutrient Applications for Apple Trees: 3 lbs/100 gallons (dilute equivalent) urea; 1 lb/100 gallon Solubor (or equivalent); and label rates of zinc chelate. Ground-applied or fertigated fertilizers can also start to go on any time now.

Now is probably past time to make bee plans, but growers should certainly plan on coordinating with their beekeeper on hive delivery and placement. We are focusing on pollinator health more than ever these days, so be smart about protecting both kept and wild bees on your farm. Avoid applying insecticides right before bees are brought in, only apply after mowing or when flowering weeds are absent from the orchard, and avoid DMI fungicides during bloom as they are now recognized as harmful to bees.

On the insect front, things are quiet but the first few tarnished plant bug and European apple sawfly are flying in certain orchards. If possible, we can avoid spraying for the former (TPB); the latter is best managed at petal fall except on problematic sites or when bloom is extended. If you have been trapping for EAS, keep an eye out for the threshold of five adults caught per trap to treat; that threshold should increase to about nine per trap after bloom if no prebloom treatment was applied.

Codling moth traps should be hung at pink and checked daily until first catch is seen. That capture date will be the biofix you use when calculating degree days for subsequent management actions.

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