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Insects |Diseases| Credits


Volume 7, No. 17                                                 July 13, 1998


COMING EVENTS

                                                     43°F       50°F
Current DD accumulations (Geneva 1/1-7/13):         1931      1265
                    (Geneva 1997 1/1-7/13):         1518       960
                (Geneva "Normal" 1/1-7/13):         1655      1165
                       (Highland 1/1-7/13):         2189      1448

Coming Events:                              Ranges:
Lesser peachtree borer flight peak               733-2330  392-1526
Peachtree borer flight peak                      864-2241  506-1494
Oriental fruit moth 2nd flight peaks            1000-2908  577-2066
Codling moth 2nd flight begins                  1355-2302  864-1549
Apple maggot 1st oviposition punctures          1566-2200 1001-1575
American plum borer 2nd flight peaks            1648-2612 1037-1840
Spotted tentiform leafminer 2nd flight subsides 1773-2514 1148-1818
Redbanded leafroller 2nd flight subsides        1927-3045 1291-2160

PEST FOCUS
   Geneva: Timing of control spray for 2nd brood Codling Moth = 1260 DD 
              (base 50°F) after biofix date (5/7). DD since then = 1024.
  
 Highland: Apple Maggot flies caught on baited red spheres are over 
              threshold.
           Japanese Beetles are causing damage to apple foliage.


TRAP CATCHES (Number/trap/day)
Geneva:     
                                  6/29    7/2    7/6   7/10   7/13
Spotted Tentiform Leafminer        516    665    385    314     52
Redbanded Leafroller               0.8    0.5    2.0    1.7    0.8
Oriental Fruit Moth (apple)        2.4    2.2    1.5    0.8    1.8
Lesser Appleworm                   1.1    1.3    1.3    0.5    3.0
Codling Moth                       7.6    2.8    1.6    7.5    2.7
San Jose Scale                     3.5    0.5    1.0    1.3    0.3
American Plum Borer                0.3    1.2    2.6    1.0    1.8
Lesser Peachtree Borer             2.3    0.8    1.6    0.5    1.8
Peachtree Borer                    2.0    1.0    2.3    0.7    0.3
Pandemis Leafroller                  0    0.3      0      0      0
Obliquebanded Leafroller           1.0    0.7      0      0      0
Apple Maggot                       0.1      0    0.1      0      0

Highland (Dick Straub, Peter Jentsch):
                                  6/15   6/22   6/29    7/7   7/13
Spotted Tentiform Leafminer       22.9*  23.5   40.1   43.0   13.6
Redbanded Leafroller                 0    0.3    2.4    2.4    1.0
Oriental Fruit Moth                0.1    0.1    0.4      0    0.2
Lesser Appleworm                     0      0      0    0.3    0.1
Codling Moth                       1.6    1.4    1.6    0.4    0.5
Obliquebanded Leafroller           0.4      0      0    0.1    0.1
Variegated Leafroller              1.5    0.2    1.1    0.6    0.1
Tufted apple budmoth               5.4    0.9    1.8    3.6    1.9
Fruittree Leafroller               0.1*   0.1    0.1      0      0
Sparganothis Fruitworm               0    0.9*   0.7    0.8      0
Apple Maggot                         0    0.1*   0.1    0.1   0.14
                                                            * 1st catch


Insects

KEEPING THE DOCK AT BAY

by Art Agnello
Entomology, Geneva

Before and during apple harvest in recent years, a number of growers and fieldmen have been unpleasantly surprised by the appearance of neat little (2 mm) holes bored into the side of their fruit, similar in appearance to those caused by a stem puncture. Although graders sometimes attribute this damage to apple maggot or European corn borer, cutting open these apples reveals a bright green worm with a light brown head, not feeding but lying inactive, in the burrow extending in from each hole. These are larvae of the dock sawfly, Ametastegia glabrata, a highly sporadic but nonetheless well documented apple pest that has been known to show up in our area since 1908.

Dock sawfly probably confines its feeding almost entirely to plants belonging to the buckwheat family (Polygonaceae), including numerous docks and sorrels, the knotweeds and bindweeds, or else wild buckwheat or alfalfa. In feeding on any of these plants, the larvae devour the leaf tissue and the smaller veins, eating out irregular holes in the leaves. Ordinarily, the midribs and the larger veins are untouched. This insect should not be confused with the related European apple sawfly, Hoplocampa testudinea, which has a whitish larva that lives and feeds in young apples, particularly prevalent in the eastern apple regions of N.Y.


Dock sawfly larva

Injury to apples by the dock sawfly is known to occur only in the late summer and early fall, when the fruit is approaching maturity and the sawfly is searching for an overwintering site. The greater hardness of immature apples probably deters the larvae from burrowing into these, so although 4 generations per year have been identified, only the last is of concern to apple growers. The injury to apples consists externally of the small round holes bored by the larvae, which after a few days show a slightly sunken, brownish ring around them and occasionally may be surrounded by a larger discolored halo. These holes may occur anywhere on the surface, but are most numerous around the calyx and stem ends, or at a point where the apple touches a leaf or another apple, since it is easier for the larva to obtain a foothold here. Inside, the injury is usually more serious, since the larva often burrows to the core and usually hollows out a pupal cell somewhat larger than itself. Apples may have three or four, or sometimes even eight, holes in them of varying depths, but contain only one or two worms.


Damage of the dock sawfly

Since the dock sawfly does not feed upon any part of the apple tree, but must live on the above-mentioned succulent weeds, it becomes an apple pest only where these plants are growing in or around the orchard. There is little danger from this insect in orchards where the food plants don't exist. Likewise, the possibility of the larvae coming into the orchard from neighboring meadows, ditch banks, or roadsides is slight, for the larvae are incapable of finding their way over any extent of bare soil. The adults, though active, are not strong fliers, and it is not possible for the insect to travel far in this stage. Now would be a good time to assess the weed situation in your orchard and make plans for such selective herbicide applications as may be appropriate regarding this insect. Even though common wisdom says this sawfly is a pest only every 10-12 years, this is only an average estimation, and it's not a bad idea to anticipate the unexpected when hardly any season is considered to be "average".

(Information adapted from Newcomer, E. J. 1916. The dock false-worm: An apple pest. USDA Bull. 265, 40 pp.)

APPLE LEAFMINER

by Dick Straub
Entomology, Highland

As occurs most years about this time, I have recently received some inquiries from Hudson Valley growers regarding considerable foliar damage by a leafminer. The pest is neither the spotted tentiform leafminer nor the apple blotch leafminer -- gracillariid species that are commonly found in this region. The culprit, apple leafminer (Lyonetia speculella Clemens), has been occurring sporadically here in isolated orchards since 1987.


Lyonetia speculella

Female moths oviposit in tender new foliage by piercing the undersides of leaves and depositing single eggs inside the leaf tissue. The hatched larvae form serpentine mines, which are visible as wavy brown lines on the tops of leaves. As the larvae grow, they enlarge their mines into brown blotches, within which they consume all of the tissue between the upper and lower epidermis. Unlike other leafminers of apple, L. speculella is characterized by frass (small black pellets) that is constantly expelled on a silken thread from the mine by the feeding larvae. Just prior to pupation, larvae spin cocoons, which are suspended by threads and resemble a hammock. Apple leafminer probably has 4 to 6 generations per year in southeastern New York.


L. speculella mines

Moreover, unlike our other leafminers, larval damage is confined to the youngest foliage, particularly terminal leaves of vigorously growing shoots. Root initials or water sprouts that are partially shaded are the preferred sites for feeding and pupation. Severely mined leaves turn brown and die; most such leaves drop off prematurely, thereby decreasing the number of the most photosynthetically active leaves. The potential for damage is greater in young orchards than in mature ones, and vigorous trees usually sustain higher infestations than do less vigorous trees.

Populations normally do not achieve high abundance or cause critical damage until the beginning of the harvest period of our earliest cultivars. Insecticidal control of larvae or adults at this time may not be a reasonable tactic because of the pre-harvest interval of most materials and, just as importantly, because infestations do not damage fruit or cause premature drop of fruit. Broad-spectrum insecticides typically used in cover sprays (OP's) are unlikely to provide significant control of adults or larvae. The optimum control tactic would be 1 or 2 sprays of either methomyl, oxamyl, endosulfan or a pyrethroid at petal fall or 1st cover. Undoubtedly, imidacloprid at the same timing would also do some good. We consider that sprays are necessary only on non-bearing trees where vigor is essential, or on bearing trees that had high infestations the previous season.

CODLING MOTH MODEL

The model for 2nd generation codling moth larvae predicts that a control spray should be applied in problem orchards 1260 DD (base 50°F) after the start of the FIRST flight (5/7 in Geneva, 5/4 in the Hudson Valley). As of today, 7/13, 1024 DD have accumulated in Geneva and 1141 at Highland, which means that any needed sprays should be started soon in both western N.Y. and the Hudson Valley. Keep your eye on the thermometer so that you will be timely with any OP applications you should decide to make.


Diseases




DISEASE CONTROL AND SPRAY COVERAGE

by Dave Rosenberger
Plant Pathology, Highland

Good spray coverage will be especially important for controlling apple diseases throughout summer and fall of 1998. Apple scab is present in many orchards, and a wet June has favored early development of summer diseases (flyspeck and sooty blotch) in many regions of the state. In "normal" years, apple scab disappears as a concern after mid-June, and the threat from summer diseases does not peak until late July or early August. This year, apple scab has remained a constant threat in many orchards where primary scab was not completely controlled. Wet weather in early summer has allowed summer diseases to build more quickly than normal in border areas that supply most of the summer disease inoculum for commercial orchards. As a result, complete spray coverage in the tops and centers of trees will be essential for preventing summer diseases and late-season fruit scab in 1998.


Flyspeck

Sooty blotch

Several approaches can be used to improve spray coverage. Proper sprayer calibration and nozzle orientation are obvious first steps. It may also be necessary to slow down travel speed while applying sprays, especially where smaller PTO-powered sprayers are being used to spray large or minimally-pruned trees. Complete spray coverage is possible only when the sprayer fan moves enough air to displace the air within the tree canopy. The volume of air per linear foot of tree row can be increased by slowing the travel speed of the sprayer.

Where apple scab is still a problem, fungicide spray intervals may need to be shortened. Benlate and Topsin M both provide up to three weeks of protection against summer diseases, but these fungicides probably will not control apple scab because resistant isolates are present in most orchards. Residual activity of captan is not reliable for more than 14 days. In orchards where scab is prevalent, spray intervals should be kept to 14 days except when hot dry weather supplies a natural brake for scab development.

Summer pruning will help to improve disease control by opening the tree canopy and thereby allowing better spray penetration. The interior of the canopy on a summer-pruned tree will dry more quickly than that of an unpruned tree, thereby minimizing the duration of wetting periods that favor disease development. Where scab was active through June, water sprouts in the center of trees often harbor the most recent scab infections because these actively growing shoots provide a constant source of susceptible tissue. Eliminating water sprouts can therefore help to eliminate some of the scab inoculum.

The benefits of summer pruning will be especially important if rainfall is abundant during August and September. As apple limbs begin to bend down under the crop load, it will become increasingly difficult to maintain good fungicide coverage on fruit in dense tree canopies. Effective summer pruning could result in significantly better control of late-season scab infections that would otherwise cause pinpoint scab of fruit during storage.


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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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