Insects | Diseases | Credits
Volume 6, No. 25 September 8, 1997
43°F 50°F Current DD accumulations (Geneva 1/1-9/8): 2905 1950 Coming Events: Ranges: Oriental fruit moth 3rd flight peaks 2389-3267 1712-2326 Spotted tentiform leafminer 3rd flight peaks 2415-3142 1728-2231 San Jose scale 2nd flight subsides 2494-3257 1662-2302 Redbanded leafroller 3rd flight peaks 2514-3225 1818-2625 Obliquebanded leafroller 2nd flight peaks 2634-3267 1789-2231 Apple maggot flight subsides 2764-3656 1904-2573 Lesser peachtree borer flight subsides 2782-3474 1796-2513 Codling moth 2nd flight subsides 2782-3693 1796-2635 Lesser appleworm 2nd flight peaks 2961-3328 1927-2359 Oriental fruit moth 3rd flight subsides 2987-3522 2018-2377 American plum borer 2nd flight subsides 3005-3698 2154-2640 Redbanded leafroller 3rd flight subsides 3103-3433 2013-2359 STLM 3rd flight subsides 3235-3471Ê2228-2472 TRAP CATCHES (Number/trap/day) Geneva: 8/25 8/28 9/2 9/5 9/8 Redbanded Leafroller 0 0 0.5 0 0.7 Spotted Tentiform Leafminer 363 485 228 665 627 Lesser Appleworm 2.4 0.8 0.7 7.5 10.5 Oriental Fruit Moth (apple) 2.0 0.8 1.3 24.8 44.2 San Jose Scale 0.8 1.3 0.3 0.5 1.7 Codling Moth 1.6 0 9.0 2.2 3.0 American Plum Borer 2.0 1.3 1.0 0 0.2 Lesser Peachtree Borer 0.1 1.0 0.6 0 0 Obliquebanded Leafroller 0.8 0 0.1 1.0 0.2 Apple maggot 0.06 0.75 0.55 0.25 0.5
by Art Agnello, Harvey Reissig, Jan Nyrop & Dave Kain
The apples are not all in the bin yet, and the pear crop was almost a non-event this year; peaches (and apricots!) made a relatively strong showing for once, and cherries and plums are always so low-profile we never know what to say about them - in short, we've reached the point where it's safe to talk about the season's insect and mite problems in the past tense and try to sound like we've been on top of everything all along. As usual, some pests gave a few anxious moments while others apparently took the year off; there didn't seem to be many occasions of true crisis, but fruit growers are accustomed to living on the edge of incident, so one never admits to 'breathing easy' until sometime around Christmas.
In N.Y. these days, there is no campaign more closely watched, ardently fought, or resolutely scrutinized than the annual struggle against mites. We've often remarked how it should be such a straightforward issue to either properly deal with these miniscule monsters, or else fail to do so, but for some reason the circumstances of each year always combine undpredictably to produce a scenario that aspires to high drama. Our 1997 spring weather was quite cool, and rather dry, so mite egg hatch and subsequent establishment went very slowly, and growers generally had a few opportunities for prebloom miticide sprays. Furthermore, we were notified of the passage of a state label for Agri-Mek before most trees even reached tight cluster, so the early season program had until after petal fall to be completed. Not much oil was applied, but a lot of Savey and Apollo were used again this year, and both did a generally acceptable job. Potential late-season problems had everyone a little apprehensive, however, since N.Y.'s lengthy internal review process for Pyramite didn't start until the federal label was granted in early May, so we encouraged a Special Local Need application effort on the part of the manufacturer.
To our dismay, the DEC initially took the position that the story was finished once Agri-Mek got approved, and didn't bother telling anyone their view until drought-stressed trees in the Hudson Valley started getting bronzed in mid-July, when we pointedly asked what was going on. Fortunately, thanks to the efforts of some influential growers (via their legislators), the N.Y.S. Hort Society, and a few loudmouths in this department, a little basic mite biology and economics served to expedite a favorable decision in this matter, in time for most of the state's problem orchards to receive a rescue treatment before it could become just another darn shame to commiserate over at the coffee shop.
As an obligatory note in hindsite, we should mention the other 8-legged players in this scene. First of all, the hot and dry conditions resulted in some predictable reports of twospotted and apple rust mite damage around the state, although it's not certain whether they actually were more numerous than their normal marginal levels, or if they only seemed more apparent because of the increased attention being paid to ERM. Nevertheless, they certainly had a positive role in another aspect of the mite story, the remarkable success of T. pyri, which exhibited some record populations in western N.Y. this year. Despite a bit less rainfall than we would like to see, the weather was relatively favorable to the populations of this important predator, and food sources were evidently abundant - not only red mites (alas), but also two-spots and rust mites. Also, if we might speculate, a relative wealth of carried-over apple scab condidia in many commercial orchards under our observation may have provided just the dietary supplement needed to send phytoseiid numbers beyond 2 and 3 per leaf, levels nearly unheard of this far from the west coast. (Leave it to entomologists to find virtue in a high inoculum.)
Also in the moderate-to-high column again this year, the snouted scar-maker made hay while the sun didn't shine during the weeks after petal fall, and most growers were well advised to back up their OP sprays for the extended oviposition period. Some did, but quite a few others will be finding more damage than they should in the coming weeks because they just didn't get around to it.
We haven't had an easy leafroller year in a long time, but as this is being written, we have yet to evaluate our OBLR plots, and it must be said that so far, leafrollers seem to have been notably less numerous and problematic this year than they normally are. Our sense is that, on top of this (perhaps) cyclical dip in populations, many growers with perennial OBLR problems may have used Asana, Lorsban and Lannate, and gotten good control with them. We didn't hear too much about B.t., and even less about Confirm.
It must have been that kind of year, but except for one oddball exception (see below), none of the standard homopteran visitors seemed to make more than a token effort this season. Rosy apple aphids showed up here and there, same as always, but there were no disasters. Green aphids looked to be poised for a party early on, but the dry summer effectively capped their good intentions. White apple leafhoppers likewise showed up and ultimately faded out. And in pears, we did finally hear of some respectable psylla gatherings by August, but the freeze that took out so much of the Bartlett crop in mid-May relegated pear insects in general to a sideline concern.
NO-SHOWS AND WILD CARDS
Spotted tentiform leafminers had a chilly time trying to establish a 1st brood infestation in our region, and perhaps for that reason, the 2nd brood simply wasn't able to take off. Also, for about the third year in a row, apple maggot numbers were very low, owing to the dry ground; most of them in the news this year seemed to be pestering our colleagues in Pennsylvania. However, the South did rise again, in a sense, by providing us with a formidable potato leafhopper immigration that incurred extended attacks on younger apple plantings around the state. And, arising from our own suburban lawns, Japanese beetles were so numerous in August that their feeding was noted and decried on peaches, apple foliage, shade trees, roses, and the clothing of small children.
by Dave Rosenberger
Plant Pathology, Highland
Most of the postharvest decays of apples are caused by Penicillium expansum or Botrytis cinerea. These fungal pathogens usually invade fruit at wounds, but they can also invade through the stem or through bruises. Penicillium and Botrytis have traditionally been controlled by applying postharvest fungicide drenches to apples before they are moved into controlled atmosphere (CA) storage.
In recent years, the most serious postharvest decay problems in New York apple storages have involved Empire fruit held in CA storage for six months or longer. Significant postharvest losses are occasionally noted with other varieties as well, but decay problems with Empire have been more persistent and more baffling.
Varieties such as Delicious and Cortland are highly susceptible to the physiological disorder known as storage scald. These varieties must be treated with diphenylamine (DPA) to prevent scald during CA storage. A fungicide is always included with the DPA treatment to control infections that would otherwise develop as a result of inoculum that accumulates in the postharvest treatment solutions. Some varieties, including Empire, do not develop scald and therefore can be moved into storage without any postharvest treatment. Many storage operators stopped applying postharvest treatments to Empire fruit in the early 1990's, but some of them have resumed applying postharvest treatments because they found the incidence of decay was unacceptable in fruit that were moved directly into CA storage without treatment. Unfortunately, application of a postharvest fungicide has not resolved all of the problems with decay in Empire fruit.
Over the past several years, we collected decayed Empire fruit from apple storages throughout New York State to determine which pathogens are involved causing decays. We found that Penicillium predominated in fruit that had received a postharvest treatment, whereas Botrytis predominated in fruit that were moved to storage with no postharvest treatment. Thus, postharvest fungicide treatments have been reasonably effective for controlling Botrytis, but the fungicides have not been as effective against Penicillium.
There are two possible reasons that postharvest treatments are failing to control Penicillium in Empire fruit. The first possibility, and the one with the easiest solution, is that fungicide concentrations in the postharvest drench may be too low. This can occur if the fungicide is not replenished according to label instructions as apples are processed through the drencher. It also occurs when the fungicides settles to the bottom of drencher holding tanks due to the lack of adequate agitation systems. Mertect 340F (thiabendazole, or TBZ) is the most commonly used post harvest fungicide. This fungicide appears to settle out of suspensions much more quickly and completely than did Topsin M or Benlate, fungicides that were used in the 1970's and 1980's. As a result, Mertect 340F may settle to the bottom of the holding tank and remains there in the absence of good agitation. This problem can be rectified by installing a grid of PVC pipes with outlet jets in the bottom of the holding tank so that the postharvest solution can be pumped under pressure through the grid, thereby creating turbulence that will resuspend the fungicide that has settled to the bottom of the tank.
A second reason that postharvest fungicide treatments are failing involves resistance to the fungicides. Fungicide resistant strains of Penicillium and Botrytis are resistant to all the benzimidazole fungicides including TBZ. In the mid-1980's, we discovered that most of the fungicide-resistant strains of Penicillium and Botrytis were unusually sensitive to DPA. Thus, the combination of DPA plus a benzimidazole fungicide continued to provide good control of Penicillium and Botrytis through the late 1980's. Even in the mid-1980's, however, about 2% of the P. expansum strains recovered from apple storages were resistant to both DPA and TBZ. It appears that these strains have gradually increased in importance and are at least partially responsible for declining effectiveness of postharvest treatments.
There are no easy solutions for controlling resistant strains of Penicillium. Sanitation measures that reduce the amount of inoculum harbored on bins and storage walls may help to reduce the incidence of decay, but the benefits of sanitation have not been studied or documented in apple storages.
One approach for controlling TBZ-resistant strains of Penicillium would be to add captan to the postharvest treatment solution. Captan is registered for postharvest use on apples and can be combined with DPA and TBZ in postharvest treatments. Researchers in Israel have reported that captan is reasonably effective against Penicillium when used at the full label rate of 2.5 lb Captan 50W per 100 gallons. In the US, where captan has usually been tested at lower rates and in combinations with one of the benzimidazole fungicides, captan has provided no benefits compared with using the benzimidazole fungicide alone. As the 1996 Food Quality Protection Act is implemented, captan may once again come under close regulatory scrutiny. Thus, the label of captan will very likely be revised sometime in the next 3-5 years and some currently labeled uses might be eliminated.
Several new biocontrol fungicides have been registered for postharvest use on apples and may eventually prove useful for controlling strains of Penicillium that are resistant to TBZ. Biocontrol fungicides are formulations of bacteria or yeast - living organisms that actually grow on the fruit after they are applied. Biocontrols do not act by killing pathogen spores or inhibiting spore germination. Instead, they stop decays by colonizing the wounds on apple fruit where decays are usually initiated. The biocontrol organisms apparently 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. This mode of action for biocontrols dictates that biocontrol fungicides will have good protectant activity but virtually no eradicant activity. If Botrytis or Penicillium become established before the biocontrol is present, then the decay fungi will usually predominate and continue to invade and decay the fruit flesh.
One biocontrol product, Decco I-182, is now registered in N.Y. State and should be available for use this fall. Decco I-182 is a formulation of the yeast Candida oleophila that was formerly marketed as 'Aspire'. The limited test data available for apples suggests that this product will provide only modest improvements in decay control when applied in combinations with TBZ. Storage operators may wish to experiment with Decco I-182 this fall, but we do not yet have enough information to recommend this expensive product.
Decco I-182 can be ordered through agrichemical suppliers but will not be warehoused with other agrichemicals. Because Decco I-182 contains a living organism, it must be kept refrigerated until it is used. When this product is ordered, it will be shipped directly from the manufacturing plant to the purchasers in insulated containers. Drench solutions that include Decco I-182 will have a characteristic yeasty odor that some individuals may find offensive, but the odor apparently is not retained on treated fruit.
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Photographs courtesy of New York State Integrated Pest Management Program