Scaffolds Fruit Journal, Cornell University NYSAES

Diseases | Insects | Chemical News | Credits


Volume 6, No. 7							May 5, 1997


COMING EVENTS

                                                     43F       50F
Current DD accumulations (Geneva 1/1-5/5):          266       124
                       (Highland 1/1-5/5):          369       163

Coming Events:                              Ranges:
Green fruitworm peak flight                       64-255    19-108
Pear psylla eggs hatch                           111-402    55-208
Green apple aphid present                        127-297    54-156
Oriental fruit moth 1st catch                    129-587    44-338
Spotted tentiform leafminer 1st oviposition      141-319    48-154
Obliquebanded leafroller larvae active           149-388    54-201
European red mite egg hatch begins               157-358    74-208
Spotted tentiform leafminer 1st flight peak      180-544    65-275
McIntosh at pink                                 258-356    96-182

Phenologies (Geneva):  Apple (McIntosh) - Tight Cluster to Early Pink
                       Pear - Green Cluster
                       Sweet Cherry - Bloom
                       Tart Cherry - Late Bud Burst
                       Plum - Bud Burst
                       Peach - Early Bloom
          (Highland):  Apple (McIntosh) - Full Bloom
                              (Liberty) - 75% Bloom
                       Pear (Bartlett) - Full Bloom

PEST FOCUS
   Geneva: OBLR larvae active in apple terminals 4/30 (H. Reissig)
 Highland: Rose Leafhopper hatching on rose 5/1
           First European Red Mite motiles observed 5/2

TRAP CATCHES (Number/trap/day)
Geneva:   
                                  4/17   4/21   4/24   5/1   5/5
Green Fruitworm                      0      0    0.2   0.1     0
Redbanded Leafroller                 0    0.4*   1.0   6.5   1.8
Spotted Tentiform Leafminer          0    0.4*  43.7   301   278
Lesser Appleworm                     0      0      0     0   0.3*
Oriental Fruit Moth (apple)          0      0      0     0     0
Oriental Fruit Moth (peach)          0      0      0     0     0

Highland (Dick Straub, Peter Jentsch):
                                   4/7   4/14   4/21   4/28   5/5
Green Fruitworm                    0.1*   0.4      0    0.6   0.1
Redbanded Leafroller               0.4*   2.4    8.6   18.1  18.8
Pear Psylla (eggs/leaf)            1.4*   3.1    3.1    2.3   2.5
Pear Psylla (nymphs/leaf)            -      -      -      -   0.1
Spotted Tentiform Leafminer          0    0.8*  11.9   49.7  53.2
Oriental Fruit Moth                  -      0      0    0.6*  3.0

                                                       * = 1st catch

APPLE SCAB ASCOSPORE MATURITY (D. Rosenberger)
                                                       Tower   DD (32F)
Date     Location      Immature   Mature  Discharged   Shoot  Since GTip
4/29  Ulster (Highland)  61%       34%       5%        1195      408

Scab infection periods in Highland:
April 12-13	22 hrs wetting, 48F, 0.48 in. rain; trees Half-Inch Green
April 17-19	42 hrs wetting, 40F, 1.29 in. rain; trees HIG to Early TC
April 27-28 20 hrs wetting, 49F, 0.78 in. rain; trees TC
May 3-4  21 hrs wetting, 55F, 1.03 in. rain; trees King Bloom


Diseases

DISEASE UPDATE

by Dave Rosenberger
Plant Pathology, Highland

Pear Blossom Blast

Pear blossom blast was severe in some orchards in the northern part of the Hudson Valley last year. Pear blast is a bacterial disease caused by Pseudomonas syringae. Infection is favored by cool wet weather (as compared with fire blight bacteria, which are favored by warm wet weather). Pseudomonas syringae survives and grows on the surface of many different plant species and is distributed by splashing rain and by insects. Severe outbreaks of blossom blast on pears are usually associated with spring frosts because frost injury provides entry sites for infection.

Symptoms of pear blast include blackening of the calyx end of individual fruitlets, blackening of entire blossom clusters with cluster leaves remaining unaffected, or complete death of clusters including both the blossoms and the leaves. Young leaves near affected clusters may have small nondescript necrotic leaf spots. Unlike fire blight, blossom blast does not spread into larger limbs or cause extensive damage to pear trees. Infections can seriously reduce fruit set. Because the mildest symptoms (blackening of the calyx cup on small fruitlets) can easily be confused with other factors that cause poor fruit set, the economic importance of this disease is often underestimated.

Pear blast has been a significant problem in Oregon where the pear producing region commonly has cool, wet weather that persists during long, extended bloom periods. Researchers and pear growers in Oregon have noted that orchards severely affected by pear blast one year are more likely to be affected again in subsequent years. The recommended control for this disease in Oregon has been application of a dormant copper spray followed by two applications of streptomycin during the early part of the bloom period using the labelled timing and rates indicated for fire blight.

Pear blast has been only a sporadic problem in New York, with severe outbreaks usually occurring in years when light frosts occurred during bloom. There is no recent research on pear blast in eastern United States, so we can only base control recommendations on older data and on experiences in other regions. With pears in bloom in the Hudson Valley and cool wet conditions predicted for much of the next week, I suspect that pear blast may become a problem again in orchards that were severely affected last year.

Pear growers with orchards that suffered from pear blast last year may wish to apply streptomycin at 10% bloom as indicated for fire blight. If cool wet conditions persist, a second application may be needed 5-7 days after the first application. NOTE: Streptomycin as labeled for fire blight calls for applications beginning at 10% bloom. These early applications may help suppress pear blast, but they are NOT required for fire blight unless the MaryBlyte program indicates that sufficient degree hours have accumulated to trigger a blossom blight infection. Thus, timing for streptomycin sprays will be completely different for orchards concerned only about fire blight and for orchards where both pear blast and fire blight are a concern.


Insects

LEAFHOPPER LOGIC

by D. Straub and P. Jentsch
Entomology, Highland

Leafhoppers are pests of apple throughout the apple growing regions of New York State. While feeding, adults and nymphs produce excrement that appears as black spots, resulting in unsightly fruit - a particular problem for fruit not passed through a water bath before packing or sale.


Apple spotted by dried honeydew produced by white apple leafhopper feeding

Moreover, adults can be a considerable nuisance to commercial fruit pickers and pick-your-own customers during harvest; it is not unusual for growers to make a specific insecticide application close to harvest to alleviate the nuisance factor. Of primary concern, however, are the effects of leafhopper feeding. Both adults and nymphs pierce the underside of leaves and remove cellular contents from the palisade cells. This feeding has been shown to significantly decrease photosynthesis. Additional factors such as drought and pest stress (often caused by phytophagous mites or leafminers) combined with season- long leafhopper damage, contribute to overall reductions in fruit size, return bloom and tree growth (trunk cross-sectional area).


White mottling damage of apple leaves caused by white apple leafhopper feeding

The complex of leafhoppers in NY apple orchards is composed of three species. Potato leafhopper, Empoasca fabae (Harris), is an occasional pest that immigrates from southern regions. It is a secondary pest in mature orchards, but because it injects a salivary toxin while feeding, unchecked infestations can be detrimental to the establishment of young orchards. White apple leafhopper (WALH), Typhlocyba pomaria McAtee, an indigenous species, is the perennial favorite leafhopper attacking apple. Because it overwinters in the orchard and is present every year throughout the state, it is considered the primary leafhopper pest on apple. Finally, a third regional migrant species, the rose leafhopper (RLH), Edwardsiana rosae (Linnaeus), occurs annually in the Hudson Valley. This species, closely resembling the WALH, has been found infesting more than 70% of the Hudson Valley orchards surveyed and is often the predominant species present. The nymphs are almost identical in size and color to WALH, but can be distinguished in the later instars by prominent dark setae (spots) at the base of hairs on the thorax.


Rose leafhopper

Its damage potential is largely dependent on the density and proximity to orchards of the primary overwintering host, florabunda rose - a wild species that is rampant in the lower Hudson Valley. We suspect that the scarcity of RLH in the other major apple production areas in NY is due to the relative absence of this critical overwintering host.

First generation WALH nymphs hatch in early May from overwintering eggs laid in the young wood of apple (hint: a generation starts with the egg; ends with the adult).


Overwintering white apple leafhopper egg on bark surface


Newly hatched white appple leafhopper nymph

They move to cluster leaves to feed, passing through five stages or 'instars'. Adults appear in early June, mate and lay eggs in apple foliage, giving rise to second generation nymphs that persist from late July through harvest. Nymphs of the RLH, on the other hand, complete the first generation on florabunda rose and the ensuing adults move into apple orchards and lay second generation eggs. This immigration to apple begins early in June, just prior to the time second generation WALH adults first appear.


White apple leafhopper adult

Adults of the RLH begin emigration back to florabunda rose in late summer, continuing into late fall. The RLH may have a partial third generation on apple during August. Thus, in regions where both WALH and RLH occur, leafhopper infestations are present throughout most of the season. This interaction and overlapping of species has no doubt added to the confusing character and control of the leafhopper complex in the Hudson Valley of N.Y. and New England. Fortunately, RLH occurs in damaging numbers only in regions south of Albany.

The current approach to leafhopper management in N.Y. is to evaluate populations by monitoring cluster leaves of apple shortly after bloom. If the action threshold of one nymph/leaf is exceeded, insecticides are recommended against early instars while the insect is most vulnerable. Multiple applications, for two generations, may be needed during seasons of high populations and prolonged hatch periods.

Organo-phosphorous insecticides (e.g., azinphos-methyl; phosmet) have little effect on leafhoppers. Carbamates (e.g., methomyl; oxamyl) are effective but are detrimental to predators. Imidacloprid (Provado 1.6F) applied around petal fall or first cover, has a remarkably high degree of efficacy against both WALH nymphs and RLH migrating adults, and is relatively safe to predators - but as most of you know, it may be prohibitively expensive for leafhopper control. Research results over the last four years at the Hudson Valley Lab have shown that the use of carbaryl in a thinning program (14-21 days post bloom) has a significant impact on both WALH nymphs and immigrating RLH adults.

For thinning of most varieties, carbaryl is recommended at either 0.5 or 1.0 lb AI/acre; our results have consistently shown that the 1.0 lb rate is preferable for leafhopper control because, in many instances, it provides season-long suppression of both species. Carbaryl is relatively safe on the predacious mite complex in NY. The Sevin XLR is much safer on pollinators than are the other formulations.

GETTING THE MOST POLLINATION FOR YOUR DOLLAR

by Nick Calderone
Entomology, Ithaca

Pollination of tree fruits, small fruits, and many vegetable crops, especially the vine crops, requires a large population of pollinating insects in order to insure maximum yield and high quality. A number of insects pollinate crops, but the honey bee is the most versatile pollinator. Honey bees are generally available in large numbers throughout the growing season, they pollinate over 90 commercial crops, they are easily transported by truck, and they can be easily distributed throughout large plantings. Look for rental fees in the $35-$50 range. Colonies seem to be surviving well this winter, but overall numbers are down a bit and honey prices remain high, motivating beekeepers to choose honey production over pollination.

Select good locations for your bees. Good locations slope to the east or south, are protected from the wind, and have as much exposure to sunlight as possible. It is important that colonies of honey bees be kept in full sunlight in order to warm the hives rapidly in the morning and entice the workers out of the hives. Place colonies in groups of 4-6 to take advantage of good locations. Entrances should also face south to east. Keep colonies on pallets or cinder blocks to keep the bottom boards 3-6 inches above the ground. Hives with wet bottom boards will be cooler and have less foraging activity. A hive stand will also keep colonies above grass, which may shade or block the entrance. If you live in an area with known bear problems, use an electric fence to protect the bees. Keep nearby flowering plants mowed to reduce competition for the bees' attention. Never move bees while they are on location for pollination!

Growers are usually concerned about the number of colonies they need to rent. New York growers have traditionally used about one colony of bees per three acres for apple pollination. This number may have been adequate in small orchards visited by feral honey bees and by solitary bees and bumble bees from adjacent hedgerows and woods. However, feral honey bee populations have been greatly reduced in recent years, and modern agricultural practices have eliminated many natural nesting sites for solitary bees and bumble bees. In addition, the flight range of solitary bees is not generally sufficient to ensure coverage of the center portions of large plantings. Growers with large blocks of apples may wish to increase the number of colonies to one per two acres. If your fruit set is lower than expected or your fruits are lopsided or misshapen, you probably need to use more bees.

Most other crops are adequately served by a single strong colony per acre - that's a colony in two, 9-5/8" hive bodies filled with bees. However, some crops have special requirements. Red Delicious and a few other apple varieties have flower structures that are different from most other common varieties such as McIntosh. Their anthers are widespread, and bees learn to insert their mouthparts between the anthers to obtain nectar. In this way, the bees do not contact the flower's sexual parts and no pollination occurs. It takes time for bees to learn to obtain nectar in this way. To counteract this problem, the number of colonies in the orchard must be increased so there are more bees that have not learned this technique. One to two colonies per acre may be needed in large stands of Red Delicious apples.

Pollination of pears will probably always be a problem because pear nectar contains only about 15% sugar versus 40% for apples, dandelions, and yellow rocket. The answer is to move the bees into the center of the pear block when the pears are in full flower. It will take several hours for the bees to discover the better sources farther away, and in that time the pears may be adequately pollinated. An alternative is to use more colonies per acre, which will increase the number of naive bees.

Fortunately, pesticides are less of a problem to bees and beekeepers today than they were 10 and 20 years ago. Nevertheless, serious poisoning incidents still occur, so it is still important to read the pesticide label and to avoid using materials that are especially toxic to bees whenever there is a safer alternative available. Carbaryl (Sevin) and micro-encapsulated methyl parathion (Penncap-M) are especially toxic to bees. Honey bees are most often killed by pesticides when they ingest contaminated pollen. However, bees can also be poisoned by pesticides that have contaminated small pools from which foragers collect water to dilute the honey they feed their young. Bees will collect water from the closest available source, including standing water in wheel ruts in your fields. A problem exists if more than 10 dead bees are found in front of a hive in the morning. If too many bees die, it may be necessary to rent more bees. You can help the bees by providing them with clean water nearby. A small tub with a few wooden floats or a ridged screen placed diagonally in the tub will work well. If you don't provide floats or screens, the bees may drown. Avoid spraying when flowers, including weeds, are open and attractive to bees, and avoid spraying when there is any risk of drift to non-target crops or flowers. Keep flowering ground cover plants like clover mowed if you are going to spray in an orchard during the summer.

We recommend establishing good working relations with several beekeepers to ensure yourself a ready supply of bees for pollination. Any individual beekeeper's situation may change over time, but if you work with several beekeepers, you should always have ready access to a supply of colonies. Remember, bees are an essential part of your crop production system, but they are only one part. In many ways, they are like the fertilizers and chemicals that you buy. Each is essential, but none of them, by themselves, can guarantee a crop. Many things influence the quantity and quality of your crop. One is the weather. Bees will visit flowers and pollinate only if they can fly. Cool, rainy, and windy weather will delay, slow, or stop flight, and the beekeeper cannot do anything about the weather. Excessive heat during the summer can cause problems with fruit set in certain crops, like pumpkins. Again, this is beyond the beekeeper's control. Be clear up front about your expectation concerning the strength of the colonies you rent and satisfy yourself that you have received what you expected. This will eliminate most misunderstandings down the road.


Chemical News

ON SECOND THOUGHT

Last week's article on the approval of Agri-Mek for use in N.Y. turned out to be a little too timely for its own good. The day after distributing that issue, we were informed of a further (and one would hope, final) quirk in this matter that can only be ascribed to the innate complexity of the bureaucratic processes that govern pesticide regulatory affairs in our state. Agri-Mek is indeed registered for use in apples and pears according to the federal label, but unfortunately it's according to *last year's* federal label, as that is the version that the D.E.C. had in front of them during the review process. This means that the new wording regarding the adjuvants besides horticultural oil that are allowable for mixing with the product is unfortunately NOT in effect, and N.Y. growers wishing to use Agri-Mek must abide by the directions on last year's label: (Apples) "Use Agri-Mek 0.15 EC in combination with a paraffinic spray oil approved for use on apples." and (Pears) "Use Agri-Mek 0.15 EC with a minimum of 0.25% paraffinic spray oil in the dilute spray mixture and not less than 1.0 gallon of paraffinic spray oil per acre in the final finished spray."

This may put a crink in the plans of people who had been intending to use another adjuvant so as to circumvent potential compatibility problems with their fungicide programs, but there's not much that can be done about it at this point. Presumably, things will all be straightened out by next season, but for the time being we can only recommend the course of action prescribed by the label.


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


Photographs courtesy of New York State Integrated Pest Management Program


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