Orchard management, June 21

By Terence Bradshaw

As we settle into summer, it’s time to shift our focus from weekly scab management to insects, and one disease in particular. Codling moth (CM) trap captures around the state declined last week, which indicates that the first generation flight has subsided. But it’s not the adult moths that we worry about, it’s the hatching larvae that will feed on fruit and cause damage (not to mention pupate and emerge as second-generation adults). Egg hatch is predicted to begin at 175-200 degree days (base 50F) after first sustained catch, but can extend for several hundred degree days after that. Spray treatment is recommended at 250-360 degree days, which were reached last week in most orchards; in orchards with heavy pressure, a second application may be warranted. Reduced-risk, CM-specific materials such as granulosis virus (Madex, CYD-X), molting disruptors (Intrepid, Rimon), and somewhat more broad-spectrum materials particularly active against lepidoptera (Altacor, Delegate) are good options at this time. Those last two materials are also effective against apple maggot (AM), and thus growers may want to save them for later applications when both CM and AM are targeted. Bt materials have little effect against CM, in my experience. Oriental fruit moth (OFM) have not traditionally been considered a major pest in Vermont, but trapping conducted by Eric Boire at CPS has shown high numbers in some orchards beginning around May 21 which is timed very closely with CM. Timing of spray materials against hatching larvae is the same for OFM as CM. Most materials recommended above (with the exception of CYD-X, which is specific to CM) will also target OFM, so management of one will typically target the other.

Oblique banded leafroller (OBLR) have been caught in traps since around June 1, but the overwintering larvae of that pest is generally well-managed with petal fall insecticides. Summer brood adults and newly hatching larvae may be controlled now with an application of any of the materials listed above for CM (except the carpovirusine materials CYD-X and Madex); additionally, Bt products are effective against OBLR. This pest has an extended flight and hatch period, with the worst damage occurring on fruit later in the season just prior to harvest. It would be prudent to ensure that all insecticide sprays in midsummer for orchards that have had a history of damage include a material with efficacy against OBLR. If not spraying for CM or AM, monitoring shoots for developing larvae is advised in order to best time control measure. The following is taken from an Ontario fact sheet on OBLR management; I have converted degree days (base 43F) to Fahrenheit: “The degree day accumulations for the obliquebanded leafroller degree model starts when first sustained moth catch occurs…

DDs are summed each day. At [439 DDb43F (degree days base 43F from date of first sustained trap catch)], egg hatch of the summer generation begins and at [780 DDb43F], 95% egg hatch has occurred. Immature larvae are very small and difficult to see. Larvae initially feed on tender growing terminals, water sprouts and developing fruit. After they reach the third instar, larvae cause more damage to fruit. Monitor for emerging larvae by examining 10 shoots and 10 fruit on 10 trees in a 4 ha block for the presence of larvae or feeding damage. Often damage is more apparent in orchards than are larvae. Management for the summer generation is recommended if 1% to 2% of terminals or fruit are infested. Resample the orchard in three to five days to ensure the population was not underestimated. Once [432-504 DDb43F] is reached and 1% to 2% of terminals or fruit are infested, an insecticide is recommended. Follow up sprays may be required because of the extended larval emergence of the summer generation (four to five weeks).” Note: June 7 was the first sustained catch at the UVM Hort Farm; 6/5 in the Shoreham area. I would use a date of 6/5 in the NEWA model to be conservative.

Apple maggot (AM) will soon emerge in Vermont orchards- now is the time to get sticky and prepare and deploy monitoring traps. Red sticky ball traps coated with Tanglefoot adhesive should be hung at four per ten-acre block and baited with an attractant to increase captures. AM traps are first and foremost visual traps, so they must be hung so that they can be seen from 10-20 yards away, which may mean trimming shoots and foliage around them. The traps should be located at the edge of the orchard, especially near woodlots and abandoned / unmanaged apples. Treatment is recommended when five adult flies per trap are caught. This typically occurs around mid-July, but variation in AM emergence can be great. More information on AM management may be found at: http://www.omafra.gov.on.ca/IPM/english/apples/insects/apple-maggot.html#advanced

Diseases, at least those which you can spray for, are quiet now, but fire blight remains a concern and I have heard many reports from growers with strikes in the orchard (and please, keep me posted). Keep cutting out every infection as soon as you see it; cut in dry weather only; and remove prunings from within the tree. If you have a lot of prunings, leave them on the ground but do not move or mow them until five or more days of dry, sunny weather dries them out. If it’s a more manageable amount, removing is advised as long as it can be done without dragging them through the orchard in contact with non-infected shoots. If you have fire blight strikes in blocks that were treated this year with streptomycin, let me know ASAP. A colleague in Connecticut is screening New England populations of Erwinia amylovera for streptomycin resistance, but any sample sent must be appropriately collected and handled.

Final horticultural notes: water those trees, especially new plantings. Include a calcium material ion all sprays for the rest of the season to increase fruit firmness and storability. Keep up with in-row weed management, but put the glyphosate away after July 1 to reduce likelihood of tree damage and make sure not to contact trunks or foliage any time you use it.

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