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April 8, 2002 Volume 11 No.4 Update on Pest Management and Crop Development

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Table of Contents:
Upcoming Pest Events

     Apple scab update
     Managing fungicide resistance in apple orchards

     Provado Sect. 18
     Azinphosmethyl update
     New Esteem formulation
     ReTain with reduced PHI


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

Dept. of Entomology, NYSAES

Geneva, NY 14456-0462

Phone: 315-787-2341 FAX: 315-787-2326


Scaffolds 02 index

Upcoming Pest Events

Upcoming Pest Events | Phenologies | Diseases | Chem News


 Current DD accumulations
(Geneva 1/1-4/8):
(Geneva 1/1-4/8/2001):



(Geneva "Normal"):



(Highland 1/1-4/8):



Coming Events: Ranges:  
Green fruitworm flight peak 64-255 19-108
Pear psylla adults active 2-121 0-49
Pear psylla 1st oviposition 25-147 1-72
Redbanded leafroller 1st catch 32-480 5-251
Rosy apple aphid nymphs present 91-291 45-148
Spotted tentiform leafminer 1st catch 73-433 17-251
McIntosh at green tip 64-163 19-74
Pear at bud burst 68-245 33-117
Peach at bud burst 92-139 38-101
Plum at green cluster 137-282 63-138
Sweet cherry at swollen bud 62-181 17-68
Tart cherry at swollen bud 62-221 17-101

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Upcoming Pest Events | Phenologies | Diseases | Chem News



Apple (McIntosh):

Silver Tip

(Red Delicious):

Silver Tip


Swollen Bud


Swollen Bud

Tart Cherry:

Swollen Bud

Sweet Cherry:

Swollen Bud


Bud Burst


Apple (McIntosh):

Quarter-Inch Green

Pear (Bartlett):

Early Bud Burst

Apricot: Pink-Early Bloom


Orleans Co. (Albion): Pear Psylla eggs noted on 4/1 (D. Breth).
Highland: st catch of Spotted Tentiform Leafminer and Oriental Fruit Moth

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Upcoming Pest Events | Phenologies | Diseases | Chem News



(Dave Rosenberger, Plant Pathology, Highland)

This work was supported by the New York State Integrated Pest Management Program.

Apple scab ascospore counts as determined from squash mounts:



% Spores that are
% Empty





(Orleans Co.)




7 spores


Highland Site #1
(Ulster Co.)




4 spores


Highland Site #2
(Ulster Co.)




0 spores

Trees in Ulster County were at Quarter-Inch Green on April 8, but spore maturity is still developing very slowly. Spore maturity in Orleans County is more advanced compared with tree phenology. Trees in Orleans County are not yet at Green Tip. The more advanced spore maturity in Orleans County compared with Ulster County is consistent with the hypothesis that dry weather during February and March has retarded spore development in Ulster County. During the past 6 weeks, several storm systems have delivered considerably more precipitation to upstate N.Y. than to the lower Hudson Valley.

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(Dave Rosenberger, Wolfram Koeller, and Bill Turechek, Plant Pathology, Highland and Geneva)


Over the past 30 years, the apple scab fungus has developed resistance to dodine (Syllit), the benzimidazoles (Benlate, Topsin M), and the SI fungicides (Nova, Rubigan, Procure). The first indications from orchard tests clearly indicate that the new strobilurin fungicides (Sovran and Flint) will not be exempt from resistance. This article outlines recommendations for minimizing further selection for resistance and suggests strategies for controlling scab in orchards where many of the fungicides mentioned above are no longer fully effective.

Apple scab has never developed resistance to any of the "contact" fungicides, a broad grouping that includes copper, the EBDC fungicides (mancozeb, Polyram), captan, the other carbamates (ferbam, thiram, ziram), or sulfur. The contact fungicides are multi-site inhibitors. That means that they disrupt several metabolic pathways in fungi, thereby making it difficult for the fungus to circumvent the action of the fungicide. Contact fungicides prevent spores from germinating on the surface of susceptible tissue, be it leaves or fruits. Once spores are allowed to germinate and to infect tissue beneath the surface, contact fungicides can no longer control the infections.

By comparison, dodine, the benzimidazoles, the SI's and the new strobilurins can stop the scab fungus after apple tissue has already been infected. Therefore, these fungicides are effective when applied on a post-infection schedule (in the absence of resistance, of course). These fungicides arrest fungal development by interfering with a single critical metabolic pathway in the fungus, but resistance develops when the target fungus develops mechanisms for bypassing the blocked pathway. The mechanisms used to bypass the fungicide activity are different for the different fungicide groups. Initially, the number of resistant strains will be very low and will not compromise good control of scab. Because they survive treatment, however, they will multiply more rapidly than sensitive strains and will increase in proportion over time. At some point, they will cause scab even though the fungicide has been applied at the same rates and timings that provided good control in previous years. The goals of anti-resistance measures are to slow the build-up of resistant strains and to control existing resistant strains by using other fungicides that are still effective.

For the SI fungicides, Wolfram Koeller and Wayne Wilcox have demonstrated methods for slowing the expansion of SI-resistant populations and for controlling resistant strains that escape. SI-resistant strains are not immune, and many of them can still be controlled by using a high rate of SI fungicides. However, the level of control will still be less than for the sensitive strains and a contact fungicide must therefore be included in tank mixes to control SI-resistant strains. This strategy has worked well for more than a decade in many orchards. We have tested orchards where SI+contact fungicide tank mixes have been used in a regular program for 12 years, and scab in several of these orchards remains fully SI-sensitive. However, we have also identified orchards in which scab is fully resistant to the SI's. In the latter group of orchards, the SI's were routinely used in post-infection applications and not always in mixtures with contact fungicides. The current situation in most New York orchards is somewhere in between these two extremes, with scab populations that are neither fully SI-sensitive nor fully SI-resistant.

The new group of strobilurin fungicides (Sovran, Flint) provides an alternative for reducing selection pressure for SI resistance. Of course, two questions are important: How fast will the strobilurins develop resistance by themselves, and do they control SI-resistant strains as effectively as SI-sensitive strains? Proactive research conducted in Wolfram Koeller's lab and in cooperation with Wayne Wilcox has shown that development of resistance to strobilurin fungicides is more complex than it has been with previous classes of fungicide chemistry. Following are their essential findings and predictions:

1. There is no doubt that scab will develop resistance to the strobilurin fungicides. Lab experiments, orchard trials, and experiences from Europe suggest that development of resistance will proceed in two phases. First, scab strains that are not entirely immune to the strobilurins will emerge. As with the SI's, these strains will still be controllable by using higher strobilurin rates. In the second phase of resistance development, strains that are totally immune to the strobilurins will slowly emerge. How long will the first phase last? The first phase lasted for five years in Europe, and it still persists in a large majority of European orchards. Preliminary laboratory tests suggest that dependence on post-infection applications (especially applications >48 hr post-infection) might speed the development of strains immune to strobilurins.

2. Do the strobilurins control SI-resistant strains as effectively as SI-sensitive strains? Not necessarily. Scab isolates that are resistant to SI fungicides are somewhat less sensitive to post-infection activity of strobilurin fungicides. Where minimum label rates of strobilurin fungicides were applied in fully SI-resistant orchards, SI-resistant strains were not controlled as well as the SI-sensitive strains. At maximum label rates, the strobilurins controlled both SI-resistant and SI-sensitive strains equally well. This means that using low rates of strobilurins at post-infection timings will maintain selection pressure for SI resistance and that post-infection sprays of strobilurins may not perform well in orchards with SI resistance.

3. The strobilurin fungicides remain fully effective against SI-resistant scab when the strobilurins are used as protectants. This means that the strobilurins are not cross-resistant to the SI's because only the post-infection activity of strobilurins is compromised when they are applied to SI-resistant populations of apple scab.

The discovery that there is some linkage between strobilurin activity and SI resistance impacts the usefulness of strobilurins as tools for managing SI resistance. To conserve their usefulness, strobilurins should be applied at rates in the upper half of the rate ranges indicated on the product labels whenever they are used in post-infection timings.

Increased emphasis on resistance management for apple scab is warranted because, in orchards where dodine, benzimidazoles, and SI's are no longer effective, the strobilurins represent the last currently known chemistry that can provide any post-infection control of scab. Strobilurin resistance that resulted in total loss of post-infection activity would leave some growers with nothing but contact fungicides to control scab. Contact fungicides used alone are very unforgiving precisely because they lack post-infection activity. Thus, growers have a great incentive for preserving strobilurins (and SI's where they are not already compromised). These chemistries represent the only remaining tools that have the post-infection activity necessary for emergencies and for suppressing "escapes" (i.e., those few infections that escape control by protectant fungicides or by strobilurins and SI's used in preventive programs).

Key strategies for avoiding problems with fungicide resistance include the following:

1. Emphasize preventive fungicide timing. Over the past decade, various "IPM strategies" have been developed to reduce fungicide use by omitting early sprays in low-inoculum orchards, by using a 4-spray SI program that often stretched the interval between pink and petal fall sprays, or by using electronic scab predictors to time post-infection SI sprays. In retrospect, we believe that these programs often contributed to rapid selection for SI resistance, especially when they were used in high-inoculum orchards. The party is over: We now need to revert to more conservative scab-management programs to preserve fungicide activity.

Spraying preventively means the first scab spray should be applied early enough to ensure that no infections become established on young foliage. Sprays should be applied ahead of predicted infection periods rather than regularly depending on post-infection activity of the fungicides. Spraying preventively utilizes the strength of the strobilurin fungicides as spore germination inhibitors and the strength of the contact fungicides in SI+contact tank mixes. It also ensures that pathogen populations will remain low and that resistant strains will be controlled rather than left to "run wild". When used in post-infection spray timing, however, contact fungicides in tank mixes will not reduce selection pressure for resistance, nor will they control resistant strains.

The most rigorous preventive timing would involve spraying on a regular 5-7-day interval to ensure that new leaves are always protected ahead of any infections. In orchards with SI resistance, this level of preventive spraying may be needed unless growers believe that higher label rates of the strobilurin fungicides are more cost-effective than reducing the spray intervals. In orchards where the SI fungicides are still working, we believe that a 10-day spray interval is still OK when using strobilurin and SI+contact fungicides in rotations or alternations. However, remember that protection from these fungicides only lasts about 6-7 days. (The last 3-4 days in a 10-day schedule are dependent on the post-infection activity of the strobilurin or SI.) Therefore, if scab is still active when switching from a 10-day program to a contact fungicide, the contact fungicide should be applied within 6-7 days of the last strobilurin or SI+contact application.

2. Plan to use strobilurin or SI+contact fungicides beginning at tight cluster or pink. This is another aspect of preventive spraying that will help to ensure complete control of primary scab and mildew. Beginning mildew control at petal fall worked well in the early years of SI use, but it is no longer recommended.

3. When post-infection activity is needed, use higher rates. This is true for both strobilurin and SI fungicides. Using the low label rates on a post-infection basis is a recipe for disaster. ("High rates" mean at least the middle of the rate range given on the SI and strobilurin product labels.)

4. High rates of strobilurins may reduce selection for resistance more effectively than low strobilurin rates mixed with contact fungicides. Koeller points out that the high rates of strobilurins provide the best post-infection and protection activity. Low rates plus a contact fungicide may provide equal or better protectant activity, but the contact fungicide cannot compensate for the selection pressure exerted by the low rate of the strobilurin. However, Rosenberger suspects that a contact fungicide such as mancozeb or captan may redistribute to new foliage more effectively than strobilurin fungicides. If that suspicion is correct, then the redistribution of the contact fungicide applied as part of a tank mix would prevent infections on newly-emerged (and therefore unsprayed) foliage that would otherwise be controlled only via post-infection activity of the next SI or strobilurin spray. The jury is still out on whether growers should spend the extra dollars to buy a higher rate of a strobilurin used alone or whether they should buy a contact fungicide to use with the strobilurin.

5. Alternating strobilurin and SI+contact sprays is better than using blocks of two or three sprays before switching to the alternative chemistry. We are not certain why that is true, but we seem to get more effective disease control. More effective disease control means less selection pressure because there is less chance of generating secondary inoculum in trees.

In orchards where SI's are no longer effective, the key to effective scab control will be preventive timing, a tighter spray interval, and higher rates of strobilurin fungicides any time that post-infection activity is needed. Using a delayed-start program followed by low rates of strobilurins on a 10-day schedule will likely result in control failures where SI-resistant scab strains are present at high numbers. It will also speed the development of resistance to the strobilurins.

Resistance management strategies for apple powdery mildew are based on the same principles as those used for apple scab. The only problem with mildew is that none of the contact fungicides have mildew activity. Therefore, there is even more reason to start early and use higher rates of SI and strobilurin fungicides where mildew is a problem. "Starting early" with mildew means including a mildewcide beginning at about tight cluster and certainly no later than at pink.

For apple growers, managing resistance and selecting appropriate fungicides is difficult because there is no way to predict existing levels of resistance to the various fungicides within individual orchards. The proportion of fungicide-resistant scab strains varies from region to region and from orchard to orchard within regions. Even where resistant strains are present, the fungicides may still appear effective if the size of the resistant population is still low. Diagnosis of resistance problems is largely based on field experience. However, fungicide resistance can be implicated in control failures only in those cases where growers can verify that sprays were well timed, that spray coverage was excellent, and that appropriate rates of the fungicide were used.

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Chem News

Upcoming Pest Events | Phenologies | Diseases | Chem News


The EPA has issued a FIFRA Section 18 specific exemption for the use of Provado 1.6F (imidacloprid) on stone fruit in New York to control aphids, including the green peach aphid (Myzus perstcae), a vector for Plum Pox Virus. A maximum of 4 applications at a rate of 5-6 fluid ounces of product/acre may be made by ground equipment. No more than 24 ounces of product may be applied per acre per year. Similarly to the past two years, Provado is registered on peaches, nectarines, plums and apricots. A copy of the label, which can be obtained from the distributor, must be in the possession of the user at time of application.

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The following are details of EPA's most recent (29 March 2002) working draft of changes proposed for azinphosmethyl crop/category placement and mitigation, based on the comments received during the 60-day post-IRED comment period:


• Proposed Mitigation - limit to 3.5 lbs ai/A per year east of the Mississippi, 4.0 lbs ai/A per year west of the Mississippi. [Change being deliberated - Bayer would like 4.0 lbs ai/A nationwide.]

• Proposed Mitigation - increase REI to 14 days for all activities. [Change being deliberated - allow early entry at 7 days for fireblight pruning (requested by growers).]

• Proposed Mitigation - set PHI at 30 days for PYO operations. [Change being deliberated - phase out PYO operations in four years.]


• Proposed Mitigation - limit to 2 applications totalling 2.5 lbs ai/A per year. [Change being deliberated - limit to 3 applications and 3.0 lbs ai/A per year.]

• Proposed Mitigation - increase REI to 14 days for all activities. [Change being deliberated - allow early entry at 7 days for fireblight pruning.]

• Proposed Mitigation - prohibit use in PYO operations or restrict to early season. [Change being deliberated - set PHI at 30 days for PYO operations; phase out PYO operations in four years.]

Cherries, Sweet and Tart

• Proposed Mitigation - 4-year phase-out on tart cherries. [Change being deliberated - 4-yr time-limited registration on tart cherries.]

• Proposed Mitigation - Increase REI to 19 days for all activities; increase PHI to 19 days to match REI. [Change being deliberated - increase REI to 15 days for all activities; maintain PHI of 15 days.]

• Proposed Mitigation - prohibit use in PYO operations or restrict to early season. [Change being deliberated - set PHI at 30 days for PYO operations; phase out PYO operations in four years.]

Peaches and Nectarines

• Proposed Mitigation - immediate cancellation on nectarines. [Change being deliberated - 4-year phase out on nectarines.]

• Proposed Mitigation - limit 2 applications of 1.125 lbs ai/A per year. [Change being deliberated - maximum of 0.875-1.125 lbs ai/A per application; maximum of 3.375 lbs ai/A per season; minimum of 14 days between applications.]

• Proposed Mitigation - prohibit use in PYO operations or restrict to early season. [Change being deliberated - set PHI at 30 days for PYO operations; phase out PYO operations in four years.]

Plums and Prunes

• Proposed Mitigation - immediate cancellation on plums/prunes. [Change being deliberated - grower requests to maintain registration for export to Pacific Rim.]

[Still to be proposed and deliberated: number of applications and lbs ai/A per season; REI; PHI.]

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Valent has announced a N.Y. registration of its 35WP formulation of Esteem (pyriproxyfen), which is in addition to the 0.86EC formulation previously available, and should be lower in price. This material is a juvenile hormone mimic that prevents major molts in the insect's life cycle, and has shown effectiveness in the control of San Jose scale, pear psylla, and tarnished plant bug when used during the delayed dormant pre-bloom period.

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ReTain plant growth regulator now has a 21-day PHI in N.Y., down from 28 days. The recommendation to apply it 28 days before anticipated start of harvest remains unchanged, but it is now legal to pick the crop before the 28-day period has elapsed.

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This material is based upon work supported by Smith Lever funds from the Cooperative State Research, Education, and Extension Service, U.S. Department of Agriculture. Any opinions, findings, conclusions, or recommendations expressed in this publication are those of the author(s) and do not necessarily reflect the view of the U.S. Department of Agriculture.

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
Dept. of Entomology, NYSAES
P.O. Box 462
Geneva, NY 14456-0462

Phone: 315-787-2341 FAX: 315-787-2326


Online at <>

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