Scaffolds Fruit Journal, Cornell University NYSAES

Diseases | Insects | Credits

Volume 6, No. 9						May 19, 1997


                                                     43F       50F
Current DD accumulations (Geneva 1/1-5/19):         360       162
                       (Highland 1/1-5/19):         537       252

Coming Events:                              Ranges:
Pear psylla eggs hatch                           111-402    55-208
Apple grain aphid present                        137-496    67-251 
Obliquebanded leafroller larvae active           149-388    54-201
Green fruitworm flight subsides                  170-544    75-280
Redbanded leafroller 1st flight peak             180-455    65-221
Spotted tentiform leafminer 1st flight peak      180-544    65-275
San Jose scale 1st catch                         189-704    69-385
Comstock mealybug 1st gen crawlers in pear buds  220-425    82-242
White apple leafhopper nymphs on apple           236-708   123-404
Oriental fruit moth 1st flight peak              259-606    96-298
Codling moth 1st catch                           273-805   141-491
European red mite egg hatch complete             361-484   183-298
McIntosh at petal fall                           418-649   210-340

Phenologies (Geneva):  Apple (McIntosh) - Bloom
                       Pear (Bartlett) - Bloom
                       Sweet Cherry (Windsor) - Petal Fall
                       Tart Cherry (Montmorency) - Bloom
                       Plum - 25% Petal Fall
                       Peach - 90% Petal Fall
          (Highland):  Apple (McIntosh) - 5 days post-Petal Fall
                              (Liberty) - Petal Fall
                       Pear (Bartlett) - 7 days post-Petal Fall

   Geneva: 1st catch of Oriental Fruit Moth and American Plum Borer
 Highland: Codling Moth and Lesser Appleworm 1st catch 5/16
           Flea Beetles and Apple Blotch Leafminer observed on McIntosh.

TRAP CATCHES (Number/trap/day)
                                   5/5    5/8   5/12   5/15   5/19
Green Fruitworm                      0      0    0.1      0      0
Redbanded Leafroller               1.8    0.8    0.9    2.2    2.3
Spotted Tentiform Leafminer        278    122    456    618    499
Lesser Appleworm                   0.3*     0    0.6   10.3    7.6
Oriental Fruit Moth (apple)          0      0      0    0.8*   0.8
Oriental Fruit Moth (peach)          0      0      0      0    0.1*
San Jose Scale                       -      0      0      0      0
Codling Moth                         -      -      -      0      0
American Plum Borer                  -      -      0      0    0.4*

Highland (Dick Straub, Peter Jentsch):
                                  4/21   4/28    5/5   5/12   5/19
Green Fruitworm                      0    0.6    0.1      0      0
Redbanded Leafroller               8.6   18.1   18.8    5.9    3.2
Pear Psylla (eggs/leaf)            3.1    2.3    2.5    3.5    1.8
Pear Psylla (nymphs/leaf)            -      -    0.1    1.0    3.4
Spotted Tentiform Leafminer       11.9   49.7   53.2   41.8   28.6
Oriental Fruit Moth                  0    0.6*   3.0    3.2    4.2
Lesser Appleworm                     -      -      -      0    0.3*
Codling Moth                         -      -      -      0    0.3*

                                                       * = 1st catch



by Dave Rosenberger
Plant Pathology, Highland

Recent Apple Scab infection periods in Highland:
May 9-10  12 hrs wetting, 51°F, 0.11 inches rain
May 13-14 14 hrs wetting, 47°F, 0.10 inches rain
May 17-18 15 hrs wetting, 47°F, 0.06 inches rain

At the Hudson Valley Lab, our degree-day total (base 32°F) is now >860. According to the degree-day model for ascospore development and release, the supply of ascospores is now depleted and primary scab will no longer be a concern after the warm rain of May 18-19 (infection period still in progress as of this writing). However, fungicide protection should be maintained for several more weeks to prevent secondary infections on highly susceptible fruit and foliage.

Fire Blight

Temperatures have remained too cold to trigger fire blight infection periods according to the MaryBlyte model. Pears are at or past petal fall in the Hudson Valley, and the degree-hour accumulations used to estimate epiphytic infection potential never exceeded about 50% of the hours needed to trigger an infection. However, we had conditions that triggered "high risk" periods on May 14 and May 18. Pear growers that had blight last year should have applied at least one strep spray to protect trees during these high risk periods.

Black Rot on Pears

Black rot causes fruit rots on pears as well as on apples. Last year, black rot appeared in some blocks of Bosc pears. The control for black rot on pears is similar to that for apples, but the choice of fungicides is more limited. Captan and Topsin M are not registered on pears. Therefore, Benlate is the only really effective fungicide for controlling black rot on pears. The mancozeb fungicides will be adequate under light pressure, but not where inoculum levels or weather conditions favor development of black rot.

Black rot infections can occur throughout the season. Therefore, in blocks where black rot is a concern, Benlate should be added to mancozeb sprays beginning at petal fall and should be included with ziram sprays applied during summer.

Fabraea on Pears

Fabraea leaf spot is a sporadic but very serious problem on Bosc pears. This disease is caused by a fungus, Fabraea maculata, that overwinters either in small (

Fabraea is relatively easy to control if fungicides are applied before the disease reaches epidemic proportions in an orchard. Mancozeb is the most effective fungicide for controlling Fabraea. Mancozeb fungicides cannot be applied within 77 days of harvest, but they should be used until the 77-day preharvest interval is reached. Because captan is not labeled for pears, ziram is probably the best choice for controlling spread of Fabraea during summer. Ferbam would be more effective, but it leaves a black residue on fruit. Benlate has been effective in some trials and ineffective in others. Ziram applied on a 3-week interval will provide adequate protection, except where heavy rains remove fungicide residues or where the disease was well established before the first spray was applied. Where disease pressure is very high (i.e., early infections were not controlled), sprays may need to be applied on a 14-day interval.

Pear growers should be especially careful to maintain fungicide coverage in pear blocks throughout June and early July. During this early summer period, fungicide programs on apples are often relaxed because the major scab threat has passed. However, this is the critical time period for controlling Fabraea on pears. Fabraea epidemics are usually reported in early July when the disease suddenly "explodes" in certain blocks. Fungicide protection during late June is necessary to prevent the early infections that provide inoculum for the July epidemics.



by Art Agnello and Dave Kain
Entomology, Geneva

Stone Fruit Aphids

Although green peach aphids not always as serious a problem as they can be, these greenish, smooth-looking aphids can start showing up in peach blocks around this time of the year. They cause curled leaves that may turn yellow or red in severe cases. The young aphids begin to hatch about the time of peach bloom and remain on the trees for 2-3 generations, until early summer, when they seek other hosts (mainly vegetable truck crops). Green peach aphids suck the sap from the new fruits and twigs, and are also found on plum, apricot, cherry, and many ornamental shrubs. These insects are difficult to control; Lannate or Thiodan are recommended postbloom, before excessive leaf curling occurs, in order to maximize the spray's effectiveness. Also, keep an eye out for black cherry aphid in your cherry trees after shuck fall. If colonies are building up on the foliage, recommended materials include Sevin, malathion, Imidan (tart cherries only), and Penncap-M.

Pear Psylla

The pear psylla is a "flush feeder", meaning that the nymphs feed and develop primarily on the newer, more tender growth. By midway through the growing season, the majority of leaves are hardened off and psylla development then may be limited primarily to the water sprouts. Once the nymph begins to feed, a honeydew drop forms over the insect; the psylla develops within this drop for the first few instars. Honeydew injury occurs when excess honeydew drips onto and congregates on lower leaves and fruit. The honeydew is a good medium for sooty mold growth. When it occurs on the fruit, it russets the skin and makes the fruit unsaleable. Ladybird beetles, lacewings, syrphids, snakeflies (Raphidiidae), and predatory bugs have been recorded feeding on the psylla. There are also two chalcid parasites of pear psylla in the U.S. However, to obtain commercially acceptable fruit in New York, pear psylla must be controlled with insecticides.

Pear russetting caused by sooty mold growing on psylla honeydew

For psylla control, we have historically recommended an application of an effective insecticide when nymphs start to build to the level of 1-2 per leaf after petal fall. More than one application of some material is often necessary. In the most recent past, the pyrethroids and Mitac have been the most widely used psylla products in our area. During the past 5 years, we have additionally been able to use Agri-Mek under Section 18 exemptions and as a Special Local Need use; this year, it is at last available under a full federal and state label. This chemical is absorbed into the leaf tissue and kills the psylla when it feeds; its mode of action is also different from the other contact toxicants. In field trials, it has provided 4-6 weeks or more of protection under normal growing conditions. Current guidelines call for it to be applied within the first 1-2 weeks after petal fall, which means that the effectiveness of a single application may not carry through the entire season, depending on how late the spray is made and how absorptive the tissue is at the time of application. Our dearth of warm temperatures so far this season has allowed the pear foliage to remain relatively succulent for the time being, but these things can change quickly. The Agri-Mek label allows for the option of a second spray, but considering the cost, late summer leaf condition, and resistance factors, a better approach would be to keep a watchful eye on the trees in mid- to late July, and switch to something different if needed, such as Provado or Mitac.

Codling Moth

Most New York apple growers have traditionally ignored the potential threat to their crop posed by this widely endemic orchard resident, as the regular OP sprays for plum curculio and apple maggot between petal fall and mid-August make fruit infestations by codling moth relatively rare. During the past few years, however, with the advent of trapping-based spray decisions for apple maggot, and a resulting decrease in cover sprays in some cases, we have begun to hear more about an unwelcome return of the worm in the apple, which is all the more unacceptable because it is a fairly easy problem to prevent. To that end, we will again publicize suggested codling moth treatment windows this season, for those growers who don't necessarily spray certain blocks for maggot each year, and who have evidence (or suspicion) that codling moth is starting to pose a significant threat.

Codling moth adult

Internal apple injury caused by codling moth larva

The Michigan model for predicting this insect's development gives fairly accurate predictions of codling moth activity in N.Y. As many as two insecticide applications may be made for each of the two generations per year, depending on the severity of pressure. Degree days are accumulated from the date of first sustained moth catch, and the first spray is applied at 250 DD (base 50°F), which corresponds with predicted 3% egg hatch. A second spray may be applied 10-14 days later. If pressure is not too severe, one spray will suffice, applied instead at 360 DD after the biofix date (which hasn't arrived just yet). To control the second generation, the timing is 1260 DD after this same biofix date. We will be providing regular updates to identify imminent spray dates.

American Plum Borer

Eggs of this moth are deposited on cherry and peach trees in cracks under loose bark and hatch in a few days. Larval tunnels are shallow with frequent openings to the outer bark, where red frass accumulates. The larvae can't bore into the cambium unless a wound of some sort is present. Because most of the tart cherries in New York are mechanically harvested, APB has become the major borer pest in some orchards in the Lake Ontario fruit growing region.

Fresh damage to a tart cherry tree caused by mechanical harvester

These susceptible trees are not only damaged by APB, but likely serve as reservoirs from which other susceptible crops (such as peaches infected with canker diseases) may be infested.

Split in peach trunk caused by disease canker

In Michigan, directed trunk sprays are recommended in cherries at petal fall, when first generation adults are emerging. Flight phenology in New York is similar. Adults begin to emerge during bloom and the flight peaks around petal fall or shortly thereafter.

Amercian plum borer adult

Lorsban 4E used for lesser peachtree borers at petal fall will provide control against any APB that may be present. Results of New York field trials indicate that if APB number just a few per tree on average, this single application at petal fall would probably be adequate, given the economic constraints of tart cherry production. Under conditions of more severe pressure, a second application around the beginning of August would be warranted against the second generation larvae. This would also correspond with the timing for the last of the season's peachtree borer sprays.

American plum borer larva

A new fact sheet on American Plum Borer, published by the New York State IPM Program, is now available. The fact sheet gives physical descriptions (with photographs) and describes the biology and life history, damage caused, and sampling and management considerations. It is available from Cornell Media Services in Ithaca (Resource Center-GP, 7 Business and Technololgy Park, Cornell University, Ithaca, NY 14850. Fax: 607-255-9946) for $1.50 per copy. Quantity discounts are available. Request Insect Identification Sheet No. I-24.

San Jose Scale

The San Jose scale (SJS) is a pest of tree fruit that attacks not only apple, but also pear, peach, plum, and sweet cherry. The minute SJS adult males emerge in the spring from beneath scale covers on the trees, usually during bloom, and mate. The first of this year's adults should be showing up any day now in our traps at Geneva.

San Jose scale adult male

The females produce live crawlers within 4-6 weeks of mating; these are bright yellow, very tiny insects resembling larval spider mites. About 24 hours after birth, the crawlers have walked or drifted to new sites and settled in by inserting their mouthparts into the tree and secreting a white waxy covering that eventually darkens to black.

San Jose scale crawler

SJS infestations on the bark contribute to an overall decline in tree vigor, growth, and productivity. Fruit feeding causes distinct red-purple spots that decrease the cosmetic appeal of the fruit. Control measures for SJS are recommended when the scale or their feeding blemishes have been found on fruit at harvest during the previous season. Insecticidal sprays are most effective when directed against the first generation crawlers, specifically timed for the first and peak crawler activity, which are usually 7-10 days apart.

Red and purple discolorations marking San Jose scale feeding sites on fruit

The most reliable method of determining first appearance of the crawlers in your specific area is by putting sticky-tape traps on the tree limb near encrusted areas and checking them at least twice a week, starting about the second week of June. Alternatively, a degree-day accumulation of 310 (50°F base) from the date of first adult catch has also been shown to be reliable if the degree-days are known with some accuracy.

Effective materials for SJS control include Lorsban 50WP, Guthion, Imidan and Penncap-M. These sprays may also help in the control of OBLR, apple maggot, and codling moth. Coverage and control are generally better if the pesticide is applied dilute and in every row. SJS is frequently more of a problem in larger, poorly pruned standard size trees that do not receive adequate spray coverage. Dormant or delayed-dormant sprays of oil, or 1/2-inch green applications of Lorsban 4EC or Supracide will have helped prevent populations from getting established. Early season pruning is important for removing infested branches and suckers, as well as for opening up the canopy to allow better coverage in the tree tops where SJS are often concentrated.


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

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Photographs courtesy of New York State Integrated Pest Management Program