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Insects |Diseases| Credits

Volume 7, No. 7                                                 May 4, 1998


                                                     43F       50F
Current DD accumulations (Geneva 1/1-5/4):           400       209
                    (Geneva 1997 1/1-5/4):           262       123
                (Geneva "Normal" 1/1-5/4):           273       125
                       (Highland 1/1-5/4):           576       307

Coming Events:                              Ranges:
Tarnished plant bug adults active                 71-536    34-299
Redbanded leafroller 1st flight peak             180-455    65-221
Spotted tentiform leafminer flight peak          180-544    65-275
San Jose scale 1st catch                         189-704    69-385
American plum borer 1st catch                    194-567    55-294
Comstock mealybug 1st gen crawlers in pear buds  220-425    82-242
Lesser peachtree borer 1st catch                 224-946   110-553
Oriental fruit moth 1st flight peak              259-606    96-298
Codling moth 1st catch                           273-805   141-491
Spotted tentiform leafminer sap-feeders present  295-628   130-325
European red mite egg hatch complete             361-484   183-298
Lesser appleworm 1st flight peak                 372-851   181-483
McIntosh at petal fall                           418-563   210-317

Phenologies (Geneva): Apple (McIntosh) - Full Bloom
                       (Red Delicious) - 75% Bloom
                      Pear (Bartlett) - 25% Petal Fall
                      Sweet Cherry (Darrow) -  Petal Fall
                      Tart Cherry (Montmorency) - 75% Petal Fall
                      Peach - Petal Fall
                      Plum - Petal Fall
          (Highland): Apple (McIntosh) - Petal Fall
                      Pear (Bartlett) - Fruit Set

TRAP CATCHES (Number/trap/day)
                                  4/20   4/23   4/27   4/30    5/4
Green Fruitworm                      0    0.2    0.1    0.2      0
Spotted Tentiform Leafminer         96    511    375    580    741
Redbanded Leafroller               9.6   11.5    4.8    8.5   12.6
Oriental fruit moth (apple)        0.9    7.5    6.0   11.2    8.0
Lesser appleworm                     -      -      -      -    1.9*

Highland (Dick Straub, Peter Jentsch):
                                  4/13   4/20   4/24   4/27    5/4
Pear Psylla (eggs/leaf)            9.3    9.6      -   16.3   12.8
Pear Psylla (nymphs/leaf)          0.5*   0.7      -    2.3    3.7
Pear Psylla (hardshells/leaf)        -      -      -      -    0.2
Green Fruitworm                    1.0    0.4      0      0      0
Spotted Tentiform Leafminer        0.1    0.1    404   17.2   18.3
Redbanded Leafroller                 -      -     34*   8.3    7.4
Oriental Fruit Moth                  -      -    2.5*   2.3    3.0
Lesser Appleworm                     -      -      0      0      0
Codling Moth                         -      -      0      0    0.1*
Obliquebanded Leafroller             -      -      0      0      0
                                                            * 1st catch

   Geneva: 1st Lesser Appleworm trap catch.
           Mirid Bugs beginning to hatch in apple.
 Highland: Rose Leafhopper nymphs observed on multiflora rose.



by Art Agnello, Dick Straub, and Dave Kain

We've had three calls in the last week asking about three different pest borers, which could be just a coincidence; however, if that's what people have been noticing in their trees right now, maybe a review of some of the major boring insects would be timely.

Roundheaded Appletree Borer

Last August, we pointed out some of the fall duties to help keep these beetle grubs from getting out of hand; the spring part of this multi-year program follows.

May: Ring the bottom 12-24" of trunks with oviposition barriers made of wire mosquito netting, hardware cloth, or several layers of newspapers. Barriers should be loose except at the bottom (cover them with earth) and top (tie with a cord). You can mound earth up to 12" around the base of the barriers, although in some cases this encourages greater vole damage. Remove the barriers at the end of the season (October).

Roundhead appletree borer larva (left) and adult (right)

Late May through July: Apply a deterrent wash above the barriers on uninfested trunks using a paintbrush, consisting of an alkaline mixture of soap (e.g., M-Pede insecticidal soap @ 2.5 oz/gallon water) plus caustic potash (lye) mixed to the consistency of thick paint. Apply every 2-4 weeks, depending on rainfall, to deter egg-laying on the trunk. Alternatively, a 60:40 mixture of white latex paint and water painted on the base of trees will help repel egg-laying, and also makes it easier to find oviposition wounds and larval castings.

June 15 and July 1 (1st & 2nd cover sprays, 800 and 1030 degree days [from March 1, base 50°F]): Foliar sprays of any material such as endosulfan (Thiodan), chlorpyrifos (Lorsban), or diazinon will reduce the adult population. A spray during the last 10 days of July (1500-1800 degree days) will kill newly hatched borers.

Dogwood Borer

Infestations of this clearwing moth in apples are almost always located in burrknots or graft unions that are planted too high above ground level. Burrknots are aggregations of root initials that can develop on the above-ground portion of the rootstock; all commercial dwarfing and semi-dwarfing rootstocks have a tendency to develop burrknots. Some chemicals with hormone effects, such as NAA, can increase the expression of burrknots, as will failure to keep the area around the trunk weed-free and open to sunlight.

Burrknot tissue on clonal rootstock of apple, dogwood borer feeding sites

The adult seeks out these spots to lay eggs, particularly if they are surrounded by vegetation or protected by something, such as mouse guards. Moreover, mouse guards may frequently house weeds, and shield the lower trunk from incidental exposure to insecticide cover sprays. Sustained feeding by dogwood borer at the graft union may severely weaken the tree at this juncture, or girdle the trunk and cause a slow decline in tree health. Orchards in which mouse guards are emplaced should be examined for signs of damage.

Collections of frass produced by feeding of dogwood borer on burrknot surface

White latex paint brushed on the exposed portion of the rootstock will prevent new infestations of the borers, and also protect against southwest injury to the bark. Dilute trunk applications of an insecticide with good residual activity can provide control of established infestations. Lorsban 50WP or Thiodan 50WP are the most effective materials if applied during the period between July 15 and August 15, bearing in mind the specific pre-harvest intervals.

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. 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.

Cocoon of American plum borer

Directed trunk sprays are recommended in cherries at petal fall, when first generation adults are emerging. Adults begin to emerge during bloom and the flight peaks around petal fall or shortly thereafter. Lorsban 4E used for lesser peachtree borers at petal fall will provide control against any APB that may be present. Field trials indicate that if APB number just a few per tree on average, this single application at petal fall will probably be adequate, given the economic constraints of tart cherry production. Under 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.

Lesser Peachtree Borer

You should be applying trunk and scaffold sprays on peaches and cherries during the first week of June if borers are a problem in your blocks. This pest increases the severity of Cytospora canker infections in peaches and is often found within the canker; by feeding in the callous tissues, it interferes with the tree's natural defenses against the disease. Infestations can be determined by the presence of the insect's frass, which resembles sawdust, in the gum exuded from the wound. In peaches, you can use Lorsban, Thiodan, Asana, Ambush, Pounce, or Penncap-M for this application. In cherries, use Lorsban 4E, Thiodan 50WP, Asana, or Ambush 25WP as a trunk spray ONLY; do not spray the fruit. Sprays should be repeated the first week of July and the first week of August.


This pest, a primitive bee and wasp relative, shows a preference for early or long-blooming varieties with a heavy set of fruit. This insect is generally a pest only in eastern N.Y. The adult sawfly emerges about the time apple trees come into bloom and lays eggs in the apple blossoms.

European apple sawfly adult

Young larvae begin feeding just below the skin of the fruits, creating a spiral path usually around the calyx end. This early larval feeding will persist as a scar that is very visible at harvest.

European apple sawfly spiral scar at harvest caused by early instar feeding

Following this feeding, the larva usually begins tunneling toward the seed cavity of the fruit or an adjacent fruit, which usually causes it to abort. As the larva feeds internally, it enlarges its exit hole, which is made highly conspicuous by a mass of wet, reddish-brown frass. The frass may drip onto adjacent fruits and leaves, giving them an unsightly appearance. The secondary feeding activity of a single sawfly larva can injure all the fruit in a cluster, causing stress on that fruit to abort during the traditional "June drop" period.

Exit hole and frass of later instar European apple sawfly larva

Monitoring for this pest is not recommended in N.Y. because it is normally controlled by the initial spray applied at petal fall to control the plum curculio. Insecticides that control it also adversely affect bees, which can pose a problem at petal fall because certain apple varieties lose their petals before others. In blocks of trees where petal fall has occurred on one variety but not the others, the variety that has lost its petals is likely to sustain some fruit injury from the European apple sawfly until the insecticide is applied. Growers can remedy this situation by choosing pollenizer varieties that do not overlap widely.



by Dave Rosenberger
Plant Pathology, Highland

Powdery mildew is prevalent in many apple orchards this spring. The powdery mildew fungus, Podosphaera leucotricha, overwinters in buds. The primary infections visible right now resulted from buds that became infected last summer. These primary infections, also known as "strikes", usually cause all of the terminal leaves on an infected shoot to appear white. The white powdery deposit on the surface of the affected shoots is caused by the growth and sporulation of the mildew fungus on the surface of the leaves. Infected leaves are often narrowed and have shortened internodes.

Powdery mildew-infected fruit bud

Primary infections on fruit buds are less obvious. Infected fruit buds produce deformed flowers with yellowed or greenish petals. Fruit buds with primary mildew infections begin producing conidia earlier than infected terminal buds because fruit buds begin growing earlier in the season.

Conidia from primary infections blow to newly forming leaves or to fruit where they initiate new infections. When apple fruit become infected during bloom, the fruit may become severely russetted. Fruit are susceptible to infection from about tight cluster through first cover, but most fruit infections probably occur near pink.

Unlike apple scab, powdery mildew is favored by dry weather with high humidity rather than by rainy weather. Rains wash mildew conidia off the plant, thereby decreasing available inoculum and slowing spread of the disease. Spores do not germinate on wet leaves, but can germinate and produce new infections when relative humidity in the orchard exceeds 70%.

Development of mildew in 1998 has been favored by a dry summer last year that allowed inoculum to develop, a mild winter that allowed successful overwintering of the inoculum in buds, and a long, protracted spring that has provided ample opportunity for secondary spread. When winter temperatures drop below 10°F, some of the mycelium in buds is killed, thereby reducing the amounts of primary inoculum. When winter temperatures drop below -10°F, many infected buds are killed and less than 5% of overwintering inoculum survives. The past winter provided New York growers with very little assistance in controlling mildew!

The best fungicides for controlling powdery mildew are the SI fungicides (Bayleton, Nova, Procure, and Rubigan). Bayleton is probably the least expensive of the four SI fungicides, but Bayleton does not provide any scab control, whereas the other three are also effective against apple scab. The Bayleton label covers a range of rates from 1/2-2 oz per 100 gallons of dilute spray. Although the lowest rate produced acceptable results when the product was introduced, observers have noted that at least 1 oz per 100 gallons or 3 oz per acre are now required to get reasonable control of powdery mildew with Bayleton. The other SI fungicides provide good mildew control when used at the rates recommended for apple scab.

Benlate and Topsin-M are also labeled for powdery mildew, but many orchards contain strains of mildew that are resistant to these fungicides. Therefore, performance of Benlate and Topsin-M is unpredictable. Sulfur is a good mildewcide when applied regularly, but it is less effective than the SI fungicides when inoculum levels are high.

To obtain acceptable mildew control under high-inoculum conditions, applications should be made at 10-14 day intervals beginning at tight cluster and continuing through at least second cover. Mildew will continue to spread until terminal shoots stop growing in late June or early July, but the rate of spread will be slower as growth slows in late June. With the SI fungicides, applications at bloom, petal fall, and first cover are especially critical for obtaining maximum effectiveness with a minimum number of sprays. If the first application is delayed beyond petal fall, results will be disappointing.

Even a seasonal program of SI sprays will not totally eliminate the mildew fungus from shoots with overwintering infections. The SI sprays may allow these shoots to produce a few normal leaves, but the infected leaves will re-appear at the shoot tips after SI sprays are discontinued unless the spray program is extended all the way through June. Trying to totally eliminate mildew by applying mildewcides through July is not cost effective except for young trees that are growing vigorously and need to fill their spaces. In bearing trees, a small amount of mildew in midsummer is unlikely to adversely affect fruit quality or total yield.

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

NOTE: Every effort has been made to provide correct, complete and up-to-date pesticide recommendations. Nevertheless, changes in pesticide regulations occur constantly, and human errors are possible. These recommendations are not a substitute for pesticide labelling. Please read the label before applying any pesticide.

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Photographs courtesy of New York State Integrated Pest Management Program