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Healthy Fruit 2008 Vol. 16:12

Jun 17, 2008

Current degree day accumulations

  • Belchertown, UMass CSO observed (01/01/08 – 06/16/08): Base 43, 880; Base 50, 514
  • Belchertown, UMass CSO SkyBit (01/01/08 – 06/16/08): Base 43, 1041; Base 50, NA

Observations from Belchertown

The storms that moved through western Massachusetts last night only dropped about half an inch of rain here in Belchertown, but the stormy pattern is apparently not over. Could be a long summer. Otherwise, it's pretty quiet. Although I got obliquebanded leafroller traps up late, we had a big catch of these pests over the weekend, indicating a need to treat. This trap catch 'biofix' indicates the trigger date for accumulating 360 degree days (base 50) when the larvae start hatching and are susceptible to treatment.  J. Clements

Borer woes

We continue to find instances where borers are causing problems. The latest in a 9-year-old peach orchard where peachtree borer activity was evident at the base of the trees with clearly observed 'gumming.' I did not realize that previously infested trees are more attractive to egg-laying adults, as pointed out in an excellent article by Nikki Rothwell on borers in a recent MSU Fruit Crop Advisory Team Newsletter. Mid-June into July is an excellent time to treat the trunks of apples and stone fruit with a directed spray of Lorsban. Both Lorsban 4E (Dow AgroSciences) and 75 WG (Gowan) allow for a post-bloom trunk spray targeting borers. (You must have the supplemental label for apples for 4E.) Another option for treating peachtree borers is mating disruption, althought it is probably too late for that. Unfortunately treating for borers takes two people and is somewhat time consuming, but in all young orchards is a worthwhile investment of time and energy. J. Clements

Azoxystrobin warning

This, I found interesting, from a recent apple-crop post. We have already seen this in Massachusetts — be careful. J. Clements

"A case of azoxystrobin fungicide toxicity was noticed in a central Kentucky apple orchard last week. The phytotoxicity developed as a result of a sprayer being used first on grapes and then on apples, even after emptying and rinsing between uses. Azoxystrobin is the active ingredient in the fungicide Abound, a fungicide used widely on grapes for management of black rot, powdery mildew and downy mildew. This fungicide is also sold as Quadris, which is used on vegetables, tobacco, and soybeans, and Heritage, which is used on landscape ornamentals.

"Phytotoxicity symptoms observed on apple trees included leaf distortion and chlorotic (yellow) blotches as well as fruit russeting. In more severe cases, leaf and twig necrosis (dead tissue), leaf drop and fruit drop can also occur. Chlorotic spots can occur when tiny spray droplets applied nearby drift into the orchard. Not all apple varieties were affected; indeed some trees in the orchard, located adjacent to affected trees showed no effect. In the case recently observed, the episode occurred a few weeks ago and now new shoot growth with normal leaves is appearing. Nevertheless, for the sensitive varieties, the injury will adversely affect fruit production.

"As it happens, only apple varieties genetically related to the variety McIntosh are affected. Thus, apple varieties known to be adversely affected are Akane, Asahi, Bramley, Cortland, Cox's Orange Pippin, Cox, Delbarestival, Discovery, Gala, Galaxy, Grimes, Imperial Gala, Kent, Kizashi, Lurared, Macoun, McIntosh, Molly Delicious, Mondial Gala, Ontario, Queen Cox, Royal Gala, Spartan, Stark Gala, Starkspur Mac, Summared, Warabi, Worcester, and Pearmain (information from Ohio State

University sources). We also noticed phytotoxicity on the variety Honeycrisp.

"Conditions favorable for drift have caused problems to apples elsewhere, e.g., azoxystrobin used in grape vineyards adjacent to apple orchards. The current label warns about spray drift and prohibits sprayers used with azoxystrobin for subsequent spraying of apple trees. Use of Quadris for soybean rust management or for foliar diseases of corn could cause problems for apple orchards or backyard trees adjacent to soybean fields, especially under unanticipated conditions favorable for drift.

"Apple growers who are also growing vegetables or grapes need to be aware of azoxystrobin phytotoxicity that can occur from use of a contaminated sprayer or from spray drift. In such cases, a separate sprayer for apples or the other crop might be a good solution along with spraying only on very still days. Apple growers will also want to communicate with nearby farmers who might be using azoxystrobin fungicide in their vineyards, on vegetable plantings or on fields of soybean or corn."

--

Megan Kennelly

Assistant Professor

Extension and Research: horticultural crops

4603 Throckmorton PSC

Dept of Plant Pathology

Kansas State University

Manhattan, KS 66506

A plant bug by any other name

A recent visit to a peach orchard turned up a lot of this injury. Most likely plant bug, but -- what kind? Possibly tarnished plant bug, but more likely the oak-hickory plant bug complex. Could be stink bug too, but maybe a little too early for that. I observe many growers using Imidan (Gowan) post-bloom to prevent this kind of injury (as well as curculio), but Imidan has only fair activity against plant bug. Much better choices include the pyrethroids (name your favorite) or Actara 25 WG (Syngenta Crop Protection). This kind of injury can persist until harvest, so a couple more sprays are in order — just don't use Imidan. J. Clements

Horticultural exercises

Hand thinning of apples (if necessary) should be started as soon as possible. The earlier the hand thinning accomplished, the greater impact on fruit size (larger) and return bloom (more next year). Waiting too long to do hand thinning does not pay as many dividends.

As apple fruit exceeds 1.25 inches, you can start using ethephon (Ethrel, Bayer CropScience) to enhance return bloom next year. It really works, and is particularly recommended for biennial varieties such as Gala, Golden Delicious, Fuji, and Honeycrisp. According to Dr. Autio:

  • start treatment when the fruit are about 1.2 inches in diameter
  • use a rate of 150 ppm (0.5 pints Ethrel/100 gallons dilute)
  • apply 3 to 4 treatments at weekly intervals (only 1 to 2 for early varieties such as Paulared)
  • avoid application when it is hot (>85 F.)
  • application may advance ripening somewhat, so watch that closely

For more information, see F-131 'Enhancing Return Bloom on Apple with Plant Growth Regulators'

J. Clements