Borers and moths, plus a little on orchard diseases

By Terence Bradshaw

June 26, 2017

There’s pretty much no question that apple scab ascospore release is done now, and only lesions from that primary scab season that became established in the trees can continue to spread the disease. There is a bit of scab out there; if you have any, then keep covered with Captan for about four weeks until those lesions are finished spreading secondary spores. Sooty blotch and flyspeck are going to be active this year, and if you’ve had more than 2” of rain since a fungicide, it would be prudent to apply one soon against those diseases.

Apple maggot traps should be up now in Vermont orchards. These red sticky spheres should be hung in a very clearly visible location at the corners of a block and baited to better attract flies to them- see last week’s message for more details. Codling moths may need management if you haven’t yet done so, but the window to manage the first generation is closing rapidly. Another set of insects to consider targeting soon are dogwood borer (DWB) and roundheaded apple borer(RAB). The former is a clearwing moth that looks like a wasp upon first sight, and its larvae tunnel in trunks, especially in burr knots on rootstocks, and cause a general decline in tree health. The latter is a beetle whose larvae tunnel into trunk tissue and hollow out trees, especially those between 3-8 years of age, and can eventually kill the tree. Infestations can be found by looking closely for a roughly 1/4” drill hole low on the trunk with frass coming out. If you see that, the larvae is either in there or has already done the damage and left. RAB tend to affect low-spray orchards most, especially those surrounded by woods and with brushy undergrowth. For both insects, a directed trunk spray right about now is the best option. Older (>7 year-old) trees may not be as susceptible to damage; young trees should be protected if you have ever had problems. Many growers aren’t familiar with either- in a typical orchard in which insecticides are applied, RAB is typically controlled, DWB is more subtle however, and we have caught the adult moths in every orchard we have monitored in the state this year. The Cadillac material for effectiveness is chlorpyrifos (Lorsban, also sold as a generic), but it is one of the old, highly toxic organophosphate materials that we would rather see left to history. That said, especially on young, high-density (and thus high-investment) orchards, it could greatly improve tree health moving forward. Chlorpyrifos can only be used once per year, and after bloom, only in a directed (i.e., handgun-applied) trunk spray with no contact to fruit or foliage. Cultural practices that can improve control include maintaining clean ground under the trees (you should be able to clearly see all trunks) to reduce refuge sites and increase biological control from birds, etc; removing solid trunk guard like the white spiral wraps during the growing season to expose the trunks; or (conversely) maintaining tight weave window screen trunk guards and closing the tops with elastic bands to prevent intrusion from above.

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