Diseases | General Information | Credits
Volume 7, No. 24 August 31, 1998
43°F 50°F Current DD accumulations (Geneva 1/1-8/31): 3285 2277 (Geneva 1997 1/1-8/31): 2744 1843 (Geneva "Normal" 1/1-8/31): 2941 2129 Coming Events: Ranges: American plum borer 2nd flight subsides 2841-3698 1907-2640 Apple maggot flight subsides 2764-3656 1904-2573 Codling moth 2nd flight subsides 2782-3693 1796-2635 Lesser appleworm 2nd flight subsides 2775-3466 2002-2460 Lesser peachtree borer flight subsides 2782-3474 1796-2513 Obliquebanded leafroller 2nd flight subsides 2809-3656 1930-2573 Oriental fruit moth 3rd flight subsides 2987-3522 2018-2377 Redbanded leafroller 3rd flight subsides 3103-3433 2013-2359 San Jose scale 2nd flight subsides 2494-3257 1662-2302 Spotted tentiform leafminer 3rd flight subsides 3235-3471 2228-2472 TRAP CATCHES (Number/trap/day) Geneva: 8/17 8/20 8/24 8/31 Spotted Tentiform Leafminer 428 352 107 73.3 Redbanded Leafroller 0.3 0.5 0.1 0.3 Oriental Fruit Moth (apple) 2.3 5.5 2.8 4.3 Lesser Appleworm 1.7 3.0 1.5 0.7 Codling Moth 5.2 2.2 1.4 6.4 San Jose Scale 7.8 1.3 0.6 2.9 American Plum Borer 1.0 0.3 0.9 0.4 Lesser Peachtree Borer 0.8 0.3 0.4 0.9 Obliquebanded Leafroller 0.3 0.3 0 0 Apple Maggot 0 0.1 0 0 Highland (Dick Straub, Peter Jentsch): 7/20 7/27 8/3 8/10 Spotted Tentiform Leafminer 26.9 45.1 25.9 19.6 Redbanded Leafroller 1.7 0.4 0 0.4 Oriental Fruit Moth 0.1 0.6 0.4 0.4 Lesser Appleworm 0.4 0.6 0.4 0.5 Codling Moth 2.3 3.4 8.3 0.9 Obliquebanded Leafroller 0 0.1 0.1 0.1 Variegated Leafroller 0 0.6 0.7 1.1 Tufted apple budmoth 0.3 0 0.1 1.2 Fruittree Leafroller 0 0 0 0 Sparganothis Fruitworm 0 0.1 0.4 0.5 Apple Maggot 0.2 0 0.09 0.2
Plant Pathology, Highland
Recommendations for controlling postharvest decays on apples remain largely unchanged from previous years and are summarized at the end of this article. Thiabendazole (TBZ, sold as Mertect 340°F) and captan continue to be the only chemical fungicides with postharvest labels for apples. Several biocontrol fungicides are registered, but they are either unavailable in New York or ineffective under commercial conditions. Effectiveness of TBZ has been decreasing in recent years because of fungicide-resistance problems. Captan provides good control of postharvest decays when used at the full label rate of 2.5 lb per 100 gallons of drench solution, but use of captan is limited by zero-residue tolerances for captan in some export and US processing markets. In the absence of fully effective postharvest fungicides, sanitation measures become increasingly important for controlling losses to storage decays.
Fungicide resistance problems with apple postharvest pathogens have gradually increased in severity over the past 25 years. Many strains of Penicillium and Botrytis developed resistance to TBZ and related benzimidazole fungicides (Benlate, Topsin M) soon after these products were introduced in the 1970's. However, the benzimidazole fungicides continued to provide acceptable control of postharvest decays for at least 10 years after resistant strains of the pathogens were present in storages. Research in the mid-1980's showed that most of the benzimidazole-resistant strains of Penicillium expansum and Botrytis cinerea were unusually sensitive to diphenylamine (DPA), an anti-oxidant used to control storage scald on apples. In commercial practice, TBZ and DPA are usually applied together, and that combination provided adequate control of both benzimidazole-sensitive and benzimidazole-resistant pathogens. Effectiveness of the benzimidazole-DPA combination decreased, however, as strains of Penicillium expansum with resistance to both chemicals gradually emerged in the 1990's. These doubly resistant strains have caused up to 15% decay in some lots of Empire fruit held in controlled atmosphere (CA) storage for 9-10 months after harvest.
Several biocontrol fungicides have federal registrations for postharvest use on apples. Biocontrol fungicides are formulations of bacteria or yeasts - living organisms that actually grow on the fruit after they are applied. Biocontrols do not act by killing pathogen spores or by inhibiting spore germination. Instead, they arrest decays by colonizing the wounds on apple fruit where decays are usually initiated. The biocontrol organisms presumably utilize all of the available nutrients in the wounds, leaving nothing to support initial growth of the decay fungi. The decay fungi utilize the apple juice and damaged cells in wounds as a source of nutrients for initial growth of spores. When this "start-up fuel" is consumed by the biocontrol fungi, the pathogens are left without the nutrients needed to initiate growth.
A series of experiments was conducted with the biocontrol product, Decco I-182, during the 1997 harvest season to determine if it could be used alone or in combination with TBZ to control mixed populations of TBZ-sensitive and TBZ-resistant P. expansum. Decco I-182 is a formulation of the yeast Candida oleophila that was formerly marketed as 'Aspire'. Results from the 1997 trials showed that although Decco I-182 was sometimes as effective as the standard DPA/TBZ combination, it was never superior and its effectiveness seemed to fade as the duration of storage increased. Furthermore, there was no additive effect or benefit from combining Decco I-182 with the standard DPA/TBZ treatment. With continued research, more effective ways of applying and using Decco I-182 might be devised. In the meantime, however, there seems to be little reason for including this expensive product in postharvest treatments of apples.
Research we conducted over the past 10 years has repeatedly shown that the predominant postharvest pathogen in apples receiving postharvest treatments is Penicillium expansum. In apples that are moved to storage without treatment, decays caused by Botrytis cinerea often predominate. (Apples with Botrytis decay come out of CA storage as firm, tan, completely-decayed fruit that look very much like baked apples.) The biology and epidemiology of Botrytis decays in apples has not been adequately researched under east coast conditions. However, it seems likely that Botrytis decays are uncommon in fruit receiving postharvest treatments because relatively few strains of Botrytis have developed resistance to both DPA and TBZ, whereas such resistance is common in Penicillium.
Empire apples from western NY may require postharvest treatment to control the Botrytis decays that predominate when Empire fruit are stored without any postharvest treatment. We do not know why Botrytis decays are more common in Empire apples from western NY than in those from the Hudson Valley. However, the prevalence of Botrytis in western NY may relate to growing conditions in the field. In some other crops (grapes, kiwi), researchers have shown that Botrytis infections that occur early in the season remain dormant until fruit begin to ripen. It is quite possible that latent Botrytis infections on apples are favored by the cooler summers (and perhaps cooler and damper conditions during bloom and petal fall) that generally prevail in western NY as compared with the Hudson Valley. If early season conditions contribute to latent infections of Botrytis on apples, and if these latent infections are a primary cause of postharvest Botrytis decays under NY conditions, then 1998 could be a bad year for Botrytis decays in stored apples because the extended wet periods that prevailed during and immediately after bloom would have favored higher-than-usual levels of infection.
Following are suggestions for controlling postharvest decays of apples for the 1998 harvest season:
Labor Day's late occurrence this year gives us one final opportunity to publicize this annual event, sponsored by the Depts. of Plant Pathology and Entomology, which has been scheduled for September 9-10 this year. All interested persons are invited to attend this preliminary presentation of field efficacy trials on the control of diseases and insects attacking N.Y. fruit crops. Results will be discussed from experiments on tree fruits and grapes. Once again, note the switch in the order of venues. The tour of research plots will start first in Geneva this year, on Wednesday, September 9, from 8:30 AM until noon. On Thursday, September 10, the activities continue at the Hudson Valley Laboratory, with presentations on disease and arthropod control in tree fruits. Registration begins at 8:30 at Barton Laboratory, NYSAES, Geneva (Wednesday, September 9) and at the Hudson Valley Laboratory in Highland (Thursday, September 10).
Scaffolds is published weekly from March to September by Cornell University - NYS Agricultural Experiment Station (Geneva), and Ithaca - with the assistance of Cornell Cooperative Extension. New York field reports welcomed. Send submissions by 3 p.m. Monday to:
Scaffolds Fruit Journal
Editors: A. Agnello, D. Kain
Department of Entomology, NYSAES
Geneva, NY 14456-0462
NOTE: Every effort has been made to provide correct, complete and up-to-date pesticide recommendations. Nevertheless, changes in pesticide regulations occur constantly, and human errors are possible. These recommendations are not a substitute for pesticide labelling. Please read the label before applying any pesticide.
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Photographs courtesy of New York State Integrated Pest Management Program