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SCAFFOLDS Fruit Journal, Geneva, NY                            Volume 5 
Update on Pest Management and Crop Development            April 1, 1996

Coming Events

                                                     43F       50F
Current DD accumulations (Geneva 1/1-4/1):            42        14
                       (Highland 1/1-4/1):           115        35

Coming Events:                              Ranges:
Green fruitworm 1st catch                         41-143      9-69
Pear psylla adults active                          2-121      0-49
Pear psylla 1st oviposition                       25-147      1-72
McIntosh at silver tip                            56-137     17-58

Phenologies (Geneva and Highland):  All dormant

Pest Focus
   Highland - Pear Psylla adults active, laying eggs
              Green Fruitworm 1st catch 3/29

TRAP CATCHES (Number/trap/day)
Geneva:   
                                  3/29    4/1
Green Fruitworm                      -      -
Pear Psylla                          -      -

Highland (Dick Straub, Peter Jentsch)
                                  3/39    4/1
Green Fruitworm                    0.1*   2.2
Pear Psylla                       0.01    0.2
                                                        * = 1st catch



CONTROLLING PEACH LEAF CURL

By: Dave Rosenberger, Plant Pathology, Highland

Peach leaf curl surprised some New York peach and nectarine growers last year. Peach leaf curl can be controlled with fungicide sprays applied either at leaf fall in autumn or prior to bud-break in the spring. The disease occurs only sporadically in upstate New York, however, and leaf curl sprays can sometimes be omitted without any serious consequences. This year, however, the dormant spray for peach leaf curl is especially important for orchards that had leaf curl last year because inoculum levels may be higher than normal.

Peach leaf curl is caused by the fungus Taphrina deformans. The fungus overwinters on twigs and bud-scales. Spores are washed into buds soon after the buds begin to swell in spring. The spores infect the developing leaf and bud tissue, and the fungus then grows with the expanding leaves and buds. The first symptoms are usually noticed when trees reach the Petal Fall stage. Affected leaves appear thickened and twisted and often have red raised patches within the leaves. Affected blossoms are also misshapen and frequently fail to set fruit. Occasionally, affected blossoms will be pollinated and remain on the tree, but the fruit that develops from these blossoms have a "lumpy" irregular surface and are of no commercial value. Most affected leaves drop from the tree after petal fall. Severely affected orchards may lose more than 50% of their leaves. The new growth that develops after petal fall is not affected and quickly hides the defoliation caused by leaf curl. However, severe infections that cause more than 10% defoliation can result in reduced fruit size. A few scattered infections cause no significant damage to the trees, but they can provide overwintering inoculum for the following year.

Three factors probably contributed to development of peach leaf curl during the past several years. First, most peach trees in NY had no crop in 1994 because of cold winter temperatures. The trees were either left unsprayed or received only minimal fungicide sprays during 1994. This allowed the population of the leaf curl fungus to develop unimpeded during the summer. Then, the winter of 1994-95 was unusually mild in some parts of the state. I am not aware of research showing that survival of the leaf curl fungus is affected by winter temperatures, but leaf curl is generally more severe in areas with moderate winter temperatures. Thus, I suspect that we had better-than-average survival of the fungus through the mild 1994-95 winter. Finally, the slow, cool spring of 1995 was also conducive to development of Taphrina. (Another Taphrina species, probably T. farlowii, was unusually common on wild black cherry, Prunus serotina, in 1995.)

To control peach leaf curl, an appropriate fungicide should be applied at bud swell before green tissue appears. Fungicides applied after bud break will still reduce the severity of peach leaf curl, but control is often less effective than when sprays are applied at bud swell. Copper sprays, Bravo, ziram and ferbam are all highly effective.

Fungicides used to control brown rot later in the season can affect the amount of leaf curl that develops the following spring. Dr. John Northover reported that at the Vineland Station in Ontario, three preharvest brown rot sprays with captan in 1971 reduced leaf curl in 1972 by 90% compared with the untreated control. Leaf curl was more severe in 1973, but four preharvest captan sprays applied in 1972 still reduced the incidence of leaf curl in 1973 by 49%. The preharvest captan sprays presumably reduced the survival of the leaf curl fungus on the twigs and leaves.

Most of our current brown rot fungicides are not effective against leaf curl. As a result, our current spray programs for brown rot may be allowing more summer build-up of the leaf curl fungus than occurred in the past when captan was commonly used in summer spray programs. The SI fungicides (Funginex, Nova, Orbit, Indar, Elite), the dicarboximide fungicides (Rovral, Ronilan), and the benzimidazole fungicides (Benlate, Topsin-M) are all ineffective against leaf curl. In orchards where leaf curl is controlled with a dormant fungicide application, no further control measures are needed during the season. However, in orchards where leaf curl escapes early control, using captan during summer may help to reduce inoculum for the following season.




OMITE STATUS

By: Art Agnello, Entomology, Geneva

After talking with Jim Cranney at the International Apple Institute and reviewing a memorandum sent by the IAI to their Executive Committee last week, I'd like to pass along the following information, much of which is excerpted from that memo, reflecting my perception of the current situation with propargite and other apple acaricides:

"The U.S. EPA has been reviewing re-registration studies relating to dietary risk from the use of propargite on a broad range of agricultural commodities including fresh apples and those processed into applesauce baby food. According to their assessment, the dietary risk for apples is several times greater than what is acceptable to EPA. (This issue is unrelated to the recent proposed revocation of the apple tolerance for propargite due to the court settlement involving the Delaney Clause)... Within the past few days, EPA has received letters from environmental groups calling for the immediate or emergency suspension of propargite and the halting of its sale, among other things. They indicated that if EPA did not act within a very short time, this would be made a media issue. There are various options available to address such a situation generically. These include:

"EPA has already reviewed a risk mitigation proposal from Uniroyal for propargite, and has found it not to be sufficient to address the risk. If the registrant did not voluntarily withdraw apples and other items from the label, EPA could place the material under special review, under which the risks and benefits of the material's use are assessed. This process typically takes several years, and... although the apple industry would have the material available for use, it would be vulnerable during the entire process to public questioning about the past or current use of propargite and debate about the safety of consuming apples treated with it or products made from such apples. This would obviously jeopardize the image and subsequent marketability of apples and apple products.

"EPA can only immediately withdraw the product from the market if it is declared to be an imminent hazard to human health. EPA has indicated propargite would not meet the criteria for this action."

According to the most recent information available, Uniroyal has been meeting with the EPA's Assistant Administrator to formulate a plan of action, and the following outcomes now appear to be imminent:

EPA is looking to work with the registrants of some other products to examine the possibility of expediting registrations for alternative acaricides that might be used in the commodities for which propargite is cancelled. At this time, we are not sure of the applicability of this approach to the New York apple industry, but it will be investigated (that is, phone calls are only starting to be made). Note that this decision does not affect the availability of Kelthane to apple growers this season, so the use potential for this product in mite management programs remains unchanged from its previous status. Obviously, growers should use the information available at this point to formulate as comprehensive a mite control plan as possible, taking into account the lack of Omite as a spray option. Needless to say, any further news on this issue will be forthcoming as it is made available to those of us in the trenches.




WORKING IN PEARS

By: Art Agnello, Entomology, Geneva

Although it's a bit premature to go on record about an issue that's still being settled, the following information is offered in the interests of rumor control and to avoid unnecessary panic. As many of you know, Agri-Mek received its federal label for pears shortly before Christmas, and we have been anxiously anticipating a state label in New York since then. However, the process for accomplishing this step was evidently underestimated by some of the parties involved, and the state did not actually receive all of the necessary pieces of the registration package until a couple of weeks ago. Since there is a 210-day period of review by various state agencies required after this point, the net result is that Agri-Mek will not have a full state label in pears for this growing season.

However, the DEC is very aware of the pear psylla problem in New York and is actively cooperating in efforts to make this product available this year under the auspices of a Special Local Needs label. Specifically, the New York Pear Growers Association has agreed to be a third-party registrant for a 24(c) Agri-Mek label in pears, and they are working with Merck, the DEC and Cornell's Pesticide Management and Education Program to finalize all of the details of this arrangement. It's not completed yet, but it looks like the label will allow use of this product in a manner similar to the previous Section 18 exemptions we have had; that is, use against pear psylla only, one application per season, with a buffer zone from bodies of water to be specified, etc. There may be a processing fee per user, but this is yet to be worked out. It looks like this should all be accomplished in plenty of time for the proposed application period 1-2 weeks after petal fall.

In the meantime, do the best job you can with your early season program, so that whatever you use in the summer won't have to fight an uphill battle. After the traditional oil applications, as discussed last week, Mitac and the pyrethroids are about the only options available for a white bud spray against adults. [ERRATUM: Ignore the comment on p.118 of the Recommends about not using Mitac on Canada-bound fruit; a food use tolerance was granted there over a year ago, and we missed this out-of-date statement during the editing process.] A final option that growers ask about is M-Pede insecticidal soap, which can provide some suppression when used in a seasonal spray program, starting at swollen bud. Keep in mind that uniform drying conditions are required to prevent droplet residue on fruit, and that it is solely a contact material with virtually no residual activity.

PEAR MIDGE

The pear midge is an old pest not commonly seen in blocks under a "standard" spray schedule. This insect is usually controlled by chemical applications for other pests, and in most cases of fruit infestation (whether commercial or homeowner), the problem comes down to the proper timing of an insecticide spray. The pear midge overwinters as a pupa in the soil, and the adults emerge in the lake plains area of NY in early May. The first flies will generally appear when Bartlett and Clapps are in the tight cluster bud stage, but no successful egg-laying occurs until the flower buds are a little more developed. The critical period for chemical control begins when the sepals have spread apart enough to show the first appearance of pink (the folded petals underneath), and continues until just before most of the blossoms are open. The flies disappear by the time of Bartlett full bloom. Larvae may be present inside the fruitlets on the tree, and do not affect fruitlet color. Full-grown larvae may leave the fruit or remain inside until it drops to the ground. In June and July, the maggots exit from the fruit (on the tree or the ground) and burrow into the soil as much as 3 inches to pupate later.

We know of no practice, either chemical or cultural (such as roto-tilling), that is effective enough to recommend for controlling the insects in the ground. These insects emerge in very large numbers, especially in a block continuously infested from year to year, and it is much easier to protect the fruit than to eliminate the pests at their source. If your pear block has a history of midge infestation and you wish to limit the area requiring chemical sprays, concentrate on those portions of the orchard most protected from the wind by trees, high ground, or buildings, as the midges tend to be most numerous in these spots. The most effective materials to use for midge sprays are organophosphates like azinphos-methyl; at least 2 sprays are recommended, one at first separation of the sepals, and one 7 days later (or at white bud, whichever comes first).

EUROPEAN RED MITE

The balmy temperatures of the last two days may have been only temporary, but they served as an incentive to remind us how rapidly things can proceed during an extended stretch of warmer weather. Red mite control should be an early priority in apples as soon as the orchard floors are dry enough to tolerate tractor traffic. Our preferred approach to early season mite (and to a lesser degree, San Jose scale) control in apples is still a delayed-dormant spray of petroleum oil from green tip through tight cluster, to conserve the efficacy of the contact miticides we still have (and the EPA is currently debating on the merits of maintaining registrations for both Omite and Kelthane, so there may be some changes in store for us along these lines this season). Technically, we have been advising that it is possible to get good control of overwintered eggs using 2 gal/100 at the green tip through half-inch green stage, or 1 gal/100 at tight cluster; this advice assumes ideal weather and excellent coverage. As we all know, oil applications don't always live up to our expectations, not only because of weather and coverage problems, but also because proper timing is difficult to manage in every block. Since we have seen mites start to hatch when the trees are at solid tight cluster, the oil naturally loses its ability to smother anything that can outrun a spray droplet. To be practical, you'll have the best success if you do the following:

  1. To assure that mites are in the egg stage, start on your blocks as early as the weather and ground conditions permit, even if it means using a higher rate.
  2. Tend toward the high end of the dosage range, especially if there's been no frost during the 48-hour period before your intended spray, and no danger of one for 48 hours afterwards. A compromise that might be worth making is to use 1.5 gal/100 if the buds linger somewhere between 1/2-inch green and full tight cluster during your chosen spray period.
  3. As an alternative, we obviously have a number of options now that Apollo, Savey, and Morestan are all available as pre-bloom treatments. It makes sense to take advantage of these materials' limited application windows in blocks where you can't oil. Naturally, inquiring minds will be asking about the advisability of mixing or following oil with Apollo or Savey, and we plan to conduct some field trials on these strategies this season. It's probably safe to say that either approach will likely buy you some extra period of mite control in the summer, but how much (and how good an investment it is) will obviously be the variables that we can only guess at for the time being.

Good coverage of the trees in the spring is essential to take advantage of oil's potential efficiency; this in turn requires adequate spray volume delivered at an appropriate speed. Experience and research show that a 1X concentration (300 gal/A) is clearly preferable; however, if all other conditions are perfect (weather, speed, calibration), then 3X, or 100 gal/A, is the highest concentration that might be expected to give acceptable control at any given time. Some growers have concentrated more than this to save time and the hauling of extra water, with no problems; you might get away with it, but it doesn't really pay to take the risk.

SAN JOSE SCALE

This may be one of those rare pests that is on the decline in N.Y., but for those blocks that are still affected, a 2% oil treatment at half-inch green will control the nymphs, and is the preferred treatment if no other problem insects need to be controlled. Combining the oil with an insecticide is usually not more effective in this case than using the oil OR insecticide alone.

If you choose not to use oil against the scale nymphs, or have rosy apple aphid or other early season insects to be controlled, an insecticide would be more appropriate. For both of these pests, Lorsban 4EC or Supracide 2EC have proven very effective during the green tip to tight cluster stage. Check the opening buds for infestations of rosy apple aphid; treatment would be advisable upon finding one colony per 100 clusters.


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
Phone: 315-787-2341 FAX:315-787-2326
E-mail: ama4@cornell.edu


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