Orchard IPM, June 24

By Terence Bradshaw

Things are a bit quiet in the orchards right now. Primary scab season is done, and there is little of it in commercial orchards where dry conditions and easy spray windows have allowed for decent disease management conditions. Fire blight- a minor annoyance in some orchards and absent in most, but keep an eye out for an errant strike here and there. Sooty blotch and flyspeck- these diseases require an accumulated 270 hours of leaf wetness to incubate between infection (e.g., a wetting event post-bloom in which you had no fungicide protection going in) and disease symptoms. We’re only halfway there, even if you had no fungicide coverage after bloom. That does mean, however, that summer fungicide protection may be needed in the next couple of weeks to manage these cosmetic diseases as well as the worse fruit rots (black, white, and bitter). See the New England Tree Fruit Management Guide for recommended materials, but generally, strobilurins, SDHIs, captan, and topsin are among those recommended. For organic growers, an application of a low-dose copper like Cueva or Badge may reduce fruit rots based on some preliminary work I did a few years ago, but watch your rates and don’t spray under slow drying conditions as fruit finish (russeting and lenticel blackening) may suffer. Maintaining trees via pruning, training, and appropriate rootstock/scion combinations to begin with can help to keep the canopy open to facilitate drying and reduce disease substantially.

Insects are relatively quiet. Mites (not an insect, but close enough for this sake) are nearly non-existent, even in a few of the hot spots I’ve seen over the years. Codling moth (CM) flight and egg hatch is still happening, and the timing for managing hatching larvae is now, either for your first or second spray for this generation. We’ve been trapping CM in every orchard we’re in this year, and while there’s no set threshold for when to spray, the general rule of thumb is that 5 or so moths per week in a pheromone trap is a light population, and more than ten indicates a larger problem. Where orchards are on the latter end of that spectrum, I recommend a second application during the first generation. Dr. Art Agnello at Cornell is recommending IRAC Group 28 (containing a diamide; i.e., Altacor, Exirel, Minecto Pro, Voliam Flexi or Voliam Xpress/Besiege) or Group 5 (spinetoram or spinosad) insecticides as the best options. For resistance management, it is best to use one IRAC class for the first generation, even if in two successive sprays, then switch to another class for the second generation.

Obliquebanded leaf roller still need some time to develop; I would plan to manage them along with apple maggot fly (AMF) or second-generation CM. Speaking of AMF, now is the time to hang red sticky traps in the orchard to monitor their populations. Baited traps placed four per block at the outside rows (to catch in-migrating flies) and checked regularly would indicate a population that needs management when a cumulative total of five flies is caught; unbaited traps are less effective at catching flies so an average of one fly caught per trap would indicate a need for treatment. We typically hit threshold at the UVM orchard in mid-July, but flies will start emerging from their pupae in the soil any day now. That also highlights an important management practice for this pest- removal or chopping (via flail mower) of dropped fruit to prevent pupation. Traps can be found at Gemplers and Great Lakes IPM.

On another note, for anyone looking for stimulating discussion this week, I’ll be part of a public panel with a number of my colleagues discussing Farming Practices and Ideologies this Tuesday at the UVM Davis Center. Information can be found at: https://www.facebook.com/events/187470125292645/. There is no fee for admission and we expect a lively discussion amongst the panel and the audience, so I encourage the Vermont orchard community to participate and weigh in. I’ll include specific information on the panel in another posting.

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