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Volume 7, No. 6                                                 April 27, 1998


COMING EVENTS

COMING EVENTS
                                                     43F       50F
Current DD accumulations (Geneva 1/1-4/27):          318       163
                    (Geneva 1997 1/1-4/27):          180        73
                (Geneva "Normal" 1/1-4/27):          209        90
                       (Highland 1/1-4/27):          476       246

Coming Events:                              Ranges:
Tarnished plant bug adults active                 71-536    34-299
Pear psylla nymphs present                       111-402    55-208
Lesser appleworm 1st catch                       135-651    49-377
Spotted tentiform leafminer 1st oviposition      141-319    48-154
Obliquebanded leafroller larvae active           149-388    54-201
European red mite egg hatch                      157-358    74-208
Redbanded leafroller 1st flight peak             180-455    65-221
Spotted tentiform leafminer flight peak          180-544    65-275
Comstock mealybug 1st gen crawlers in pear buds  220-425    82-242
Mirid bugs 1st hatch                             328-432   156-231
McIntosh at bloom                                310-544   130-275

Phenologies (Geneva): Apple (McIntosh) - Pink
                       (Red Delicious) - Early Pink
                      Pear (Bartlett) - Bloom
                      Sweet Cherry (Darrow) - 50% Petal Fall 
                      Tart Cherry (Montmorency) - Bloom
                      Peach - 10% Petal Fall
                      Plum - Bloom
          (Highland): Apple (McIntosh) - Bloom
                      Pear (Bartlett) - 80% Petal Fall
                      Plum (Stanley) - Fruit Set
                      Peach - Fruit Set
                      Apricot - Shucks Off

TRAP CATCHES (Number/trap/day)
Geneva:   
                                  4/13   4/16   4/20   4/23   4/27
Green Fruitworm                      0      0      0    0.2    0.1
Spotted Tentiform Leafminer       10.5    414     96    511    375
Redbanded Leafroller               1.5    8.7    9.6   11.5    4.8
Oriental fruit moth (apple)        0.1*   0.3    0.9    7.5    6.0
Oriental fruit moth (peach)          0      0      0      0      0

Highland (Dick Straub, Peter Jentsch):
                                   4/6   4/13   4/20   4/24   4/27
Pear Psylla (eggs/leaf)            5.5    9.3    9.6      -   16.3
Pear Psylla (nymphs/leaf)            -    0.5*   0.7      -    2.3
Green Fruitworm                    0.1    1.0    0.4      0      0
Spotted Tentiform Leafminer        0.1    0.1    0.1    404   17.2
Redbanded Leafroller                 -      -      -     34*   8.3
Oriental Fruit Moth                  -      -      -    2.5*   2.3
Codling Moth                         -      -      -      0      0
Obliquebanded Leafroller             -      -      -      0      0
                                                            * 1st catch

PEST FOCUS
 Highland: 1st Redbanded Leafroller caught 4/23.
           Serpentine Leafminer mines, and Rosy Apple Aphid causing leaf 
              curl on apple 4/24.
           European Red Mite eggs hatching.
           Pear Psylla hardshells observed.


General Information





EARLY BLOOM IN THE HUDSON VALLEY

McIntosh reached full bloom in the lower Hudson Valley on April 22. This is the earliest full-bloom date since 1977 when McIntosh reached full bloom April 22. Other years when full bloom on McIntosh occurred in April were 1976 (April 20), 1985 (April 29), 1986 (April 30), 1990 (April 28), and 1991 (April 27). In all other years since 1960, full bloom on McIntosh occurred between May 2 and May 19.



Insects

PSORTING OUT PSYLLA

by Art Agnello & Dick Straub
Entomology

Pear psylla nymphs were noted on the foliage in western N.Y. as early as April 15, and a couple of days before that in the Hudson Valley, so if things continue at this pace, it looks like we'll easily have the potential for some high nymphal numbers in the clusters by petal fall. This is a good time to formulate a management approach in those blocks with a history of high psylla pressure.

First of all, it should be remembered that Mitac is still effective in many orchards. This contact material has been around for some time and most growers are aware of how to use it and the results to expect. Results from our research trials have shown that two applications (3 oz/acre), as needed, often maintain populations below damaging levels. It is a decent rescue material in situations where previous treatments of something else have failed. Mitac is restricted to two applications per season.

Agri-Mek has also been available for several years, and although its effectiveness has sometimes been regarded as uneven, this is usually in direct relationship to how strictly the use guidelines have been followed. First of all, it's important to get the material into the leaf tissue, and in our trials this has meant applying it *soon* after petal fall, within 1-2 weeks, before the leaves harden off. This might even be more critical during a fast spring such as we seem to be experiencing this year. Apply it too late and it will just sit on the surface and be subject to rapid breakdown, and it's not a good contact material. Secondly, use it in combination with an adjuvant to get it into the leaves, preferably highly refined petroleum oil such as SunSpray Ultra Fine or Stylet-Oil. Finally, this is a product with a clear dose-response effect; there's no use trying to cheap out by using the low (10 oz/A) rate on a high pressure block. Use the 20-oz rate, and you'll have a better chance of staving off a summer resurgence.


Pear psylla nymph enclosed by its honeydew droplet

Because Agri-Mek has been the standard, usage of Provado (imidacloprid) has not been extensive in N.Y. Provado is also absorbed into the leaf and therefore acts primarily as a stomach poison. The label allows for two applications at 20 oz/acre, to be applied postbloom as needed. Provado has been included in our evaluations during the past six years. A summarization of the data suggests that an application at petal fall, followed by a second application within 14 to 28 days, works well against low to moderate populations. However, during two years with extremely high populations (1994 & 95), this two-application scheme did not work - but then, neither did anything else! Provado appears to be suitable for rescue situations. In 1997, a high pressure year in the Hudson Valley, Provado applied May 29 (9d post-petal fall) and July 9 had relatively high nymph numbers on the leaves, but low damage; it is possible that these treatments produced some sub-lethal effects that allowed nymphs to survive, but with reduced feeding and honeydew secretions. Results from Michigan in 1997 were similar.


Pear psylla "hard shell" (fifth instar) stage nymph

Pyramite, a new entry into the pear psylla arena this year, is likewise limited to 2 applications per season (with a 30-day interval, 7-day PHI). In 1997, its effectiveness was comparable to that of Provado in both the Hudson Valley and in Michigan. The high rate (13.2 oz/A) is likewise recommended here.

With a number of different options available, it is obviously possible now to attempt some combinations and rotations to manage your psylla susceptibility and prolong product field life. Maybe try Agri-Mek at petal fall, and one of the other materials for a midsummer rescue, etc. Regardless, don't be caught unaware this year; things could happen fast, and the successful pest managers will be anticipating instead of reacting.


Diseases

CONTROLLING SECONDARY SPREAD OF APPLE SCAB

by Dave Rosenberger
Plant Pathology, Highland

The first apple scab lesions appeared in unsprayed trees at the Hudson Valley Lab on April 21. Unfortunately, scab lesions also appeared in many commercial orchards at about the same time. In fact, apple growers in the Hudson Valley are facing the most severe scab year they have seen in at least a decade.

Why is scab appearing in so many orchards? Several contributing factors can be cited:

  1. The season started early. Trees reached green tip on March 27 and the first scab infection period occurred on April 1-2. No one was quite ready to apply fungicides so early in the season, so many orchards were not protected for the first infection period.

  2. Apple scab ascospores matured early because of the mild and damp winter. Thus, many orchards developed primary infections as a result of the April 1-2 infection period even though trees had not yet reached the tight-cluster bud stage.

  3. For the preceding six years, apple bud development has been quite late compared with the historical average. When tree development is delayed, temperatures tend to warm up quickly and trees progress rapidly from green tip to petal fall. When trees develop rapidly, scab is relatively easy to control with just a few sprays. After six years of easy scab control, the seriousness of this disease tends to recede in one's memory. However, the fungus has not changed.

Why be concerned about a few scab lesions? This is a common sentiment when a little bit of leaf scab is found in orchards around Memorial Day. Unfortunately, we still have four weeks until Memorial Day. That means four extra weeks for scab to spread around before disease progression is slowed by June heat and by the increasing natural resistance in the growing fruit. Four weeks is enough time for at least two extra cycles of secondary scab. As a result, a near-perfect fungicide program will be needed to keep scab off of fruit in orchards where primary lesions are now evident.

What is the best fungicide program for controlling a running epidemic of apple scab? Captan used in combination with an SI fungicide is the safest bet. The rate for captan should be 4.5 to 6 lb/A for the 50W formulation or 2.8 to 3.75 lb/A for the 80W formulation. Dodine (Syllit), benomyl (Benlate), and thiophanate-methyl (Topsin M) should not be used for scab control because resistance to these fungicides is common throughout New York State.

Captan is more effective against scab than is mancozeb. In a 1997 field trial at the Hudson Valley Lab, we compared the activity of Dithane 75DF, Polyram 80DF, and Captan 50W in a block with severe disease pressure. Sprays were applied to small plots with a handgun, so spray coverage was excellent. As shown in the table below, captan provided the best control of both leaf scab and fruit scab. In fact, captan used alone was just as effective for controlling fruit scab as was the combination of Nova plus thiram.

  

Treatment and rate of            % apple scab on McIntosh
product per 100 gals   cluster lvs    terminal lvs   fruit (June 17) 
____________________________________________________________________
Control*                   70              47           91
Captan 50W 1 lb             1 a             4 b          0 a
Dithane 75DF 1 lb           4 b             8 c          9 b
Polyram 80DF 1 lb           5 b            17 c          6 b
Nova 40W 1.33 oz
  plus 
Thiram 75 WDGF 14 oz        0 a             1 a          0 a
____________________________________________________________________
 *The control was not included in statistical analyses.  Mean separations were determined using Fisher's Protected LSD, P = 0.05.

If captan alone was just as effective as a Nova plus contact fungicide combination, why bother with the SI fungicide? Adding the SI fungicide will improve control of secondary spread to new leaves. Note that the treatment involving Nova provided the best control of scab on terminal leaves. In the trial conducted last year, secondary spread of scab during summer was limited by dry weather. In a wet year, the extra control of foliar scab provided by SI fungicides could translate into less fruit scab at the end of the year.

The bottom line is that captan is our best protectant fungicide for apples. An SI fungicide applied with captan will provide additional protection against foliar scab and will reduce the numbers of spores and the viability of spores produced in the existing scab lesions. Captan alone works well against a running scab epidemic in years when rainfall stays at or below average. If the spring turns unusually wet, then the SI-plus-captan combination will probably prove superior.

Using captan at petal fall and first cover creates problems for those wishing to use Agrimek plus oil for mite control because captan and oil are not compatible. Where scab has not been well controlled, the best strategy may involve applying captan during bloom and at petal fall, then switching back to mancozeb for a single spray when oil is applied with Agrimek.


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:

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Photographs courtesy of New York State Integrated Pest Management Program