Diseases | Credits

SCAFFOLDS Fruit Journal, Geneva, NY                              Volume 4 
Update on Pest Management and Crop Development                May 8, 1995 


                                                     43F       50F
Current DD accumulations (Geneva 1/1-5/8):          290       124
                       (Highland 1/1-5/7):          324       130

Coming Events:                              Ranges:
Tarnished plant bug adults active                 71-536     34-299
Obliquebanded leafroller larvae active           149-388     54-201
European red mite egg hatch                      157-358     74-208
Green fruitworm flight subsides                  170-448     75-251
Redbanded leafroller 1st peak                    180-455     65-221
Spotted tentiform leafminer 1st flight peak      180-420     65-217
White apple leafhopper nymphs present            236-708    123-404
San Jose scale 1st adult catch                   189-704     69-385
Peach at bloom                                   229-446     95-199
Pear at bloom                                    242-402    117-225
Sweet cherry at petal fall                       257-448    131-251
Tart cherry at bloom                             257-448    131-251
McIntosh at bloom                                310-425    152-225

Geneva, 5/8
   Apple (McIntosh): Early Pink
   Pear: Green Cluster
   Sweet Cherry (Windsor): Bloom
   Tart Cherry (Montmorency): White Bud
   Peach: Early Bloom
   Plum: Green Cluster
Hudson Valley Lab, Highland, 5/8
   Apple (McIntosh): 75% Bloom
      (Golden Del.): King Bloom
   Pear (Bartlett): Full Bloom

TRAP CATCHES (Number/trap/day)
                                  4/24    5/1   5/8
Green Fruitworm                    0.3    2.7   0.8
Redbanded Leafroller               1.0*   0.6   1.3
Spotted Tentiform Leafminer        157    371   349
Oriental Fruit Moth (apple)          0      0   8.9
Oriental Fruit Moth (peach)          0      0     -
Lesser Appleworm                     0   0.07*  7.5

Highland (Dick Straub, Peter Jentsch)
                                  4/17   4/24    5/1    5/8
Green Fruitworm                    0.3    0.7      0      0
Pear Psylla eggs (/terminal bud)   2.5   12.6      -      -
Redbanded Leafroller               2.6   10.4    8.7    0.8
Spotted Tentiform Leafminer       <0.1*  13.0   45.6    6.0
Oriental Fruit Moth               <0.1*     0    9.3    0.8
Fruittree Leafroller                 -      0      0    0.1*
Rose Leafhopper nymphs               -      -      -    1.2
White Apple Leafhopper nymphs        -      -      -    0.1*
European Red Mite motiles            -      -      -    0.1
                                                       * = 1st catch

Geneva: STLM eggs being laid.
Wayne Co: STLM eggs being laid.  
          ERM eggs hatching.
Highland: 1st White apple leafhopper nymphs observed.  
          ERM eggs hatching.
          1st STLM sap-feeding mines observed.


By: D. Rosenberger

Highland, NY:       Immature     Mature   Discharged   Tower shoot
Peru, NY, 5/1         68%          32%       0.5%      820 spores
Highland, NY, 5/2     51%          37%        12%    >2000 spores


Dave Rosenberger, Plant Pathology, Highland

Moderate daytime temperatures and cold nights have resulted in very slow bud development during the past week. By May 4, we had full king bloom on early-blooming cultivars such as McIntosh, good pollination weather, and good bee activity. Weather conditions from May 5-8 was too wet, cold, or windy to allow bees to work.


In the Champlain Valley (Peru), ascospore maturity jumped dramatically since April 25 and economically important spore discharges can be expected with the next infection periods. In the lower Hudson Valley, we are now well into our peak risk period for apple scab. In the lower Hudson Valley, we had another light Mills' infection period Friday, May 5, with 16 hours of wetting at a mean temperature of 53 degrees. This morning (May 8), Gil Lasher at our local Agchem outlet reported that he had found a few scab lesions in a local orchard. These lesions most likely developed from infections that occurred April 21-22.


Although we had a rain on Friday with Bartlett pears in full bloom, there was only a moderate risk of fire blight according to the MaryBlyte model. Temperatures during the rain were too cold to favor infection, and the degree-hour temperature accumulation prior to the rain was only 72% of what is needed to trigger a blossom blight infection period.


The two most common rust diseases on apples are cedar apple rust and quince rust. Cedar apple rust causes yellow or orange lesions on both leaves and fruit of susceptible apple cultivars. Quince rust infects apple fruit, but not leaves.

Apple fruit are most susceptible to rust infections during the period from tight cluster through bloom. The tissue that will develop into the apple fruit is exposed just below the blossom and can become infected with rust as soon as the cluster leaves fold back from the flower clusters. However, in most years rust spores are not abundant until apples reach pink or full bloom.

Wetting and temperature requirements for cedar apple rust infection are noted on page 42 of the 1995 Pest Management Recommendations for Commercial Tree-Fruit Production. When using the table, be sure to read the footnote. It indicates that the wetting durations listed in the table are the periods required for infection after (basidiospore) inoculum is available. However, in most cases, an initial 4 hrs of wetting is required for the galls on cedar trees to exude the gelatinous orange teliohorns and to produce basidiospores. After basidiospores are produced on the galls, the wetting period required for infection can range from 2 additional hours at 68-76F to 24 additional hours at 36F. Little cedar rust develops during wetting periods with mean temperatures below 46F.

Wetting requirements for quince rust infection have not been clearly defined. However, I have only seen severe quince rust infections when extended wetting periods (at least 30 hours, usually >48 hrs) with moderate temperatures (50-75F) have occurred between tight cluster and late bloom. Under these conditions, more than 50% of fruit on unprotected trees can develop quince rust. More commonly, 5-15% of fruit are affected. Delicious, Golden Delicious, Rome, and Cortland appear to be the most susceptible cultivars for quince rust in the Hudson Valley, but quince rust can occur on nearly all cultivars. Because of the limited period of susceptibility and the extended wetting period required for significant infection, conditions favoring severe quince rust infection occur only once every 5 to 7 years.

Unlike apple scab, none of the apple rust diseases have a secondary infection cycle. Primary lesions on apple fruit or leaves will never result in secondary spread to other apple leaves. All of the inoculum must come from cedar apple rust galls or quince rust cankers on cedar trees. After this primary inoculum is exhausted (usually about June 15 in the lower Hudson Valley), no further infections on apple can occur until the following season.

If ideal conditions develop for quince rust infections between the tight cluster and petal fall bud stages, growers using SI fungicides (Rubigan, Nova) need to be especially cautious about spray timing. SI fungicides are less active against infections on fruitlets and flower parts than they are for infections on leaves. Quince rust may be especially difficult to control with SI fungicides if the SI's are used in an eradicant mode. I suspect that SI fungicides may eradicate quince rust infections if the fungicides are applied within 48 hours or perhaps even 72 hours after the beginning of the infection period. However, if applications are delayed until 96 hours, the quince rust fungus may have too much of a head start and infections may no longer be controlled by eradicant sprays.


by: Craig Telgheder, Cornell Cooperative Extension, Hudson

The perennial question of the legal label uses of Terramycin (Mycoshield) in N.Y.S. has again come up. Here's a quick rundown of the legal uses of Terramycin in N.Y.S.

Pears - Fire blight. Data shows that Terramycin is not as effective as Streptomycin against fire blight on pears. It can, however, be useful as a resistance management strategy. During seasons that call for more than 3 strep sprays, it can be useful in rotation. That's if you can figure out you need more than three strep sprays by the time you need to make the fourth spray.

Peaches and Nectarines - The only antibiotic available for control of bacterial spot in N.Y.S. other than copper. Primarily a problem in Long Island and sporadically in the Lower Hudson Valley.


By: Roger Morse, Entomology, Ithaca

The increasing incidence of the "new diseases" of honeybees, chalkbrood, tracheal mites and Asian varroa mites, increases the importance of care and timing in placing and managing colonies for pollination in orchards. The following guidelines are especially critical. Honey bees will visit plants with the greatest quantities of pollen and the highest sugar concentrations in the nectar. The nectar of dandelions and yellow rocket is as rich as that of apple. Orchardists should mow flowering weeds in orchards or apply weed killer. Weeds in fields adjacent to orchards may also attract bees away from the trees to be pollinated.

Colonies of honey bees in orchards should be kept in full sunlight to warm the hives rapidly in the morning and entice the workers out of the hives. We suggest placing colonies in groups of 3-5 to take advantage of the best locations. Good locations should slope to the east or south with entrances facing in these directions and should be protected from the wind. Colonies should be placed on pallets, cinder blocks, old tires, or any objects that will keep the bottomboards 6-8 inches above the ground. Hives with wet bottomboards will be cooler, which slows bees' flight. A hivestand will also keep colonies above grass, which may shade or block the entrance.

Bees often collect large quantities of water to dilute the honey they feed their young. It is impractical to carry sufficient water into an orchard or to fill all wheel ruts and holes with dirt or sand and force the bees to forage outside of the orchard for water. But growers must understand that water contaminated with pesticides can kill bees that collect it. 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. Beekeepers expect some losses and figure them into their rental fee.

Pesticides are less of a problem to bees and beekeepers today than they were 10 and 20 years ago. Nevertheless, it is still important to read the label and to avoid using materials that are especially toxic to bees. Honey bees are most often killed by pesticides when they ingest contaminated pollen. Avoid spraying when flowers, including weeds, are open and attractive to bees.

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.

New York growers currently use about one colony of bees per three acres for apple pollination. This number may be adequate in small orchards, which may be visited by feral honey bees and solitary and subsocial bees such as bumble bees from adjacent hedgerows and woods. Growers with larger blocks may wish to increase the number of colonies to one per two acres, especially considering the new diseases.

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.

Bees will visit flowers and pollinate only if they can fly. Cool, rainy, and windy weather will delay, slow, or stop flight. In warm years bees may over-pollinate during bloom, and growers must thin the flowers. Unfortunately, we cannot predict the weather. For the above reasons, you should contract for bees for pollination well ahead of when the colonies will be needed.


By: Art Agnello & Dave Kain, Entomology, Geneva

There have been increasing incidences in recent years of severe damage to certain apples, especially Red Delicious, caused by phytophagous mirid bugs that are related to the tarnished plant bug. This is a complex primarily composed of mullein bug, Campylomma verbasci (Meyer) and apple brown bug, Atractotomus mali (Meyer). Until recently, most reports of fruit damage came from research orchards at the Geneva Station, but increasing numbers of commercial orchards are starting to be attacked; these species are already perennial pests in Canadian apple orchards, particularly in southern Ontario.

The two species exhibit some differences in life history and feeding habits. Mullein bugs (MB) are beneficial most of the year, when they act as predators of mites, aphids and leafhoppers. However, mullein bugs may feed on fruit for a breif period after petal fall. Damage is often localized, but it may be quite severe. MB overwinters as an egg laid in the bark of the last season's growth. Eggs hatch during bloom and the nymphs may (or may not) feed on young fruit; most fruit injury occurs starting at this time. Apple brown bug (ABB) overwinters as an egg on the apple twig; the nymphs hatch during the bloom period and all hatching is completed by the petal fall stage. Adults first appear about 4 weeks after bloom, with peak numbers occurring about 2 weeks later, when males and females are equal in numbers. Oviposition occurs at this time, and the numbers of adults decline rapidly thereafter.

It is believed that the nymphs normally feed on phytophagous mites and other prey, and when these are absent the insect attacks young fruit. Initially, injury appears as a tiny pin prick on the fruit, surrounded by a water-soaked area that is not easily noticed. As the fruit enlarges, mirid injury forms a raised pimple on the surface of the fruit. This damage is most serious in early cultivars and Red Delicious, Golden Delicious and Northern Spy, although injury to McIntosh is becoming more common. Much of the injured fruit will drop with the June drop, but fruit remaining on the tree can be badly deformed. In some Station plots evaluated during the 1993 season, as much as 60% of all fruit harvested exhibited mirid damage, even in plots receiving normal pesticide sprays. ABB has one generation per year and MB two generations. Second generation MB do not damage the apple.

Canadian management guidelines call for monitoring to begin for MB nymphs during bloom and continuing at least once a week until 2-3 weeks after petal fall. Mullein bug nymphs, which are very small (smaller than an adult aphid), can be detected by tapping limbs over a tray. There are no proven thresholds for MB control. However, a threshold of 3-5 nymphs per 25 tapped branches has been used in Ontario, although guidelines allow for the possibility of increasing this threshold if large numbers of alternative food sources (aphids or mites) are present. There is some debate over the choice of a pesticide for MB control. One opinion holds that mirids are tolerant to most conventional organophosphate materials and that a product such as Thiodan or Diazinon should be used; another school of thought maintains that OP's are perfectly effective, but timing of the spray with nymphal appearance is critical. Field trials we conducted last year using different materials at pink, petal fall, or both timings, gave inconclusive results because of unexpectedly low populations, so these trials will be repeated this year. However, as a best guess until further data is available, the most sensible approach in orchards with a history of this problem would be limb-tapping during bloom, and if warranted by a high nymphal count, a petal fall application that includes something besides the standard OP's, on the assumption that most local populations have already had considerable exposure to these materials.

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

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