Scaffolds Fruit Journal, Cornell University NYSAES

Diseases |Insects | Credits


Volume 6, No. 17							July 14, 1997


COMING EVENTS

						    43°F      50°F
Current DD accumulations (Geneva 1/1-7/14):         1550       985
                       (Highland 1/1-7/14):         1882      1220

Coming Events:                              Ranges:
American plum borer 2nd flight begins           906-1876  973-1337
Peachtree borer flight peaks                    864-2241  506-1494
Oriental fruit moth 2nd flight peaks           1000-2908  577-2066
Spotted tentiform leafminer 2nd flight peak    1295-2005  824-1355
Codling moth 2nd flight begins                 1355-2302  864-1549
Obliquebanded leafroller 1st flight subsides   1420-2452  899-1790
San Jose scale 2nd flight begins               1449-1975  893-1407
Redbanded leafroller 2nd flight peaks          1479-2443  952-1698
STLM 2nd gen tissue feeders present            1504-2086  952-1201
Comstock mealybug 1st flight peak              1528-1782  981-1185
Dogwood borer peak catch                       1551-1952  986-1306
Apple maggot 1st oviposition                   1566-2200 1001-1575

PEST FOCUS
   Highland: Spotted Tentiform Leafminer 2nd flight began 6/16; DD (43 
             F) = 819 (from 6/27).
             1st Apple Maggot trap catch 7/11.
             Degree Days (base 50 F) since first codling moth catch = 
             983.
     Geneva: Spotted Tentiform Leafminer 2nd flight began 6/23; DD (43 
             F) = 574.

TRAP CATCHES (Number/trap/day)
Geneva:   
                                  6/30    7/3    7/7   7/10   7/14
Redbanded Leafroller                 0    0.8    5.0    2.7    5.6
Spotted Tentiform Leafminer        406    570    463    618    470
Lesser Appleworm                     0    0.5    0.5    2.8    1.0
Oriental Fruit Moth (apple)        0.1    1.0    0.9    8.0    3.0
Oriental Fruit Moth (peach)          0      0    0.1    0.2      0
San Jose Scale                       0      0      0      0    0.1
Codling Moth                       0.8    1.3    1.3    2.5    0.3
American Plum Borer                0.6      0    0.5      0    0.1
Lesser Peachtree Borer             1.6    0.7    0.6    0.3    2.0
Peachtree Borer                    2.0    0.8    0.1    0.2    0.6
Pandemis Leafroller                0.5    2.0    0.5      0      0
Obliquebanded Leafroller           0.6    0.8    0.4    0.7      0
Apple maggot                         0      0**  0.06*  0.3   0.06

Highland (Dick Straub, Peter Jentsch):
                                  6/16   6/23   6/27    7/7   7/14
Redbanded Leafroller                 0      0    0.9    5.1    9.1
Spotted Tentiform Leafminer        7.4   74.0   39.4   85.3   59.7
Oriental Fruit Moth                1.4    0.3    0.9    1.3    1.3
Lesser Appleworm                   1.3    0.4    2.0    0.2    0.4
Codling Moth                       1.6    5.6    2.6    1.9    0.6
Fruittree Leafroller                 0      0      0      0      0
Tufted Apple Budmoth               2.0    1.3    2.9    1.3    0.4
Obliquebanded Leafroller           1.8    0.9    0.3    0.6    0.2
Sparganothis Fruitworm               0    1.3    1.4    3.9    0.7
Apple Maggot                         -      -      0      0    0.1*
                                       * = 1st catch
                                      ** = 1st catch in other area traps



Diseases

DISEASE UPDATE

by Dave Rosenberger
Plant Pathology, Highland

SOOTY BLOTCH AND FLYSPECK

In northeastern United States, fungicides are applied to apples from mid-June through August primarily to control sooty blotch and flyspeck. Four or five summer fungicide applications may be needed to control these diseases in wet years, whereas only two or three well-timed applications are needed in dry years. Omitting summer fungicide sprays is risky, however, because gaps in fungicide protection during critical periods in summer can result in the sudden appearance of numerous flyspeck infections just before harvest.

Field research conducted in the Hudson Valley over the past 10 years has been used to develop a model for timing apple fungicide sprays during the summer. The model targets flyspeck because fungicide programs that control flyspeck will nearly always control sooty blotch under N.Y. conditions. The N.Y. Flyspeck Model has worked well in small-plot tests where fungicides were applied with a high-pressure handgun. The model is currently being tested in commercial orchards with funding supplied by the New York State IPM program.

The concepts used to develop the N.Y. Flyspeck Model are outlined below. Because the model has not yet been validated with airblast sprayers in commercial orchards, we are not yet recommending this approach for timing summer fungicides. Omitting fungicides is always risky because potential losses from disease on fruit can quickly obliterate any savings that accrue from withholding sprays. Nevertheless, the information and concepts used to develop the N.Y. Flyspeck Model may be useful in deciding how to time summer fungicides even if the ultimate decisions on fungicide timing end up being considerably more conservative than those suggested by the model.

The first step in constructing the N.Y. Flyspeck Model was the development of a table of estimated residual activities for various summer fungicides (Table 1). This table was developed using data from small-plot field trials conducted in the Hudson Valley from 1987-1996. Residual activities shown in the table are shorter during summer than for the last spray before harvest because cooler conditions in the fall slow development of sooty blotch and flyspeck, and also because late infections will fail to develop symptoms before harvest and therefore are of no concern.

In addition to the residual activity of fungicides shown in Table 1, research has shown that Benlate and Topsin M provide limited eradicant activity against sooty blotch and flyspeck. Their eradicant activity decreases as the time between infection and fungicide application increases. Benlate has reasonable eradicant or suppressive activity against flyspeck infections that have accumulated fewer than 100 hours of wetting after infections occurred. (The eradicant activity for Topsin M has not yet been defined, but Topsin M probably has less eradicant activity than does Benlate.) Working in North Carolina, Brown and Sutton showed that sooty blotch and flyspeck appear on fruit only after fruit are exposed to 275-300 hours of accumulated wetting following infection. Thus, it appears that Benlate will provide eradication of flyspeck and sooty blotch provided the infections are less than one-third of the way through the incubation period, with "incubation period" defined as 275-300 hours of accumulated wetting after infection.

By taking advantage of both the residual activity of fungicides and the eradicant activity of Benlate, it may be possible to eliminate one or two summer fungicide sprays after the last scab spray is applied in early to mid-June. The logic is as follows:

  1. Assume that the last spray for apple scab (usually first or second cover spray) will provide the residual activity noted in Table 1. If mancozeb is used for the last scab spray, then fruit will be protected for the shorter of either 21 days or through 3.5 inches of accumulated rain following the mancozeb application.

  2. After the residual activity from the last scab fungicide spray is exhausted, a "protection gap" of up to 100 hours of leaf wetting (including dew periods) can be tolerated if Benlate is used as an eradicant later in the season. A leaf wetness recorder will be required to monitor hours of leaf wetting, but data from a regional recording station may suffice for orchards within 10-15 miles of the recording station. During the protection gap, fruit will not be protected by fungicides, so sooty blotch and flyspeck infections will occur on fruit if inoculum is present in the vicinity of the orchard.

  3. At the end of the protection gap, Benlate-captan or Benlate-ziram sprays must be applied to eradicate infections. To be conservative and allow for unexpected rains that might intervene before sprays are completed, the Benlate program should be initiated after the accumulated wetting during the protection gap reaches 80 hours. A minimum of two Benlate applications should be used following the protection gap and prior to harvest to ensure complete suppression of incubating flyspeck infections. The Benlate sprays should be 14-21 days apart and, in dry years, will most likely coincide with insecticide applications timed to control apple maggot. Including Benlate in August applications should also control black rot infections that may develop in fruit lenticels as the fruit begin to ripen.

CAUTION: Omitting fungicide sprays during July is not recommended if tree canopies are dense (as in trees left unpruned last winter) or if fruit are clustered. In orchards with dense canopies or clustered fruit, complete fungicide coverage will almost certainly be impossible during late summer when the canopy reaches maximum density and the clustered fruit prevent fungicide from reaching the center of clusters. In such orchards, Benlate should be applied during July when the likelihood of decent coverage is better than it would be in August. Even a very tight fungicide program may fail to control flyspeck during wet seasons in orchards with dense canopies.


Table 1. Estimated residual activities (under New York conditions)
of fungicides used for controlling sooty blotch and flyspeck.

                             June/July       From last spray til harvest
                      
Fungicides     Rate per  spray     maximum   total   max. inches of
grouped by     100 gal   interval  rainfall  # of    rain allowed before
effectiveness  dilute    (days)    (inches)  days    Aug. 30 without
                                     /1              re-spray

   Benlate+? /2   3 oz
OR Mancozeb       1 lb     21        3.5      50           4.0
OR Ziram/Sulfur   1+1 lb

   Topsin M+? /2  3 oz
OR Ziram 76W      1.5 lb   21        2.5      45           3.0
OR Captan 50W     2.0 lb

   Ziram 76W      1 lb     21        2.0      45           2.5

   Captan 50W     1 lb     14        2.0      30           2.5

/1 As soon as the rainfall amounts are exceeded, fungicide coverage should be renewed.
/2 Must be applied with a contact fungicide (captan or ziram).


Insects

AFRAID OF THE DOCK

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 some graders are inclined to attribute this damage to apple maggot or European corn borer, cutting open these apples reveals a bright green worm with a lightish 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..

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.

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.)

JAPANESE BEETLE

This perennial pest overwinters as a partially grown grub in the soil below the frost line. In the spring the grub resumes feeding, primarily on the roots of grasses, and then pupates near the soil surface. Adults begin to emerge during the first week of July in upstate N.Y., and judging from the reports and phone calls we've been receiving lately, they appear to be on schedule this year. The adults fly to any of 300 species of trees and shrubs to feed; upon emergence, they usually feed on the foliage and flowers of low-growing plants such as roses, grapes, and shrubs, and later on tree foliage. On tree leaves, beetles devour the tissue between the veins, leaving a lacelike skeleton. Severely injured leaves turn brown and often drop. Adults are most active during the warmest parts of the day and prefer to feed on plants that are fully exposed to the sun.

Although damage to peaches is most commonly noted in our area, the fruits of apple, cherry, peach and plum trees may also be attacked. Fruits that mature before the beetles are abundant, such as cherries, may escape injury. Ripening or diseased fruit is particularly attractive to the beetles. Pheromone traps are available and can be hung in the orchard in early July to detect the beetles' presence; these products are generally not effective at trapping out the beetles. Fruit and foliage may be protected from damage by spraying an insecticide such as Sevin or Penncap-M when the first beetles appear.

(Information adapted from: Johnson, W.T. & H.H. Lyon. 1988. Insects that feed on trees and shrubs. Cornell Univ. Press.; and Howitt, A.H. 1993. Common tree fruit pests. Mich. State. Univ. Ext. NCR 63.)

OBLR CLOCK

Leafroller larvae averaging about the 2nd instar in development are now starting to damage unsprayed fruit in western N.Y. orchards, although the fireblight and dearth of much terminal growth makes them somewhat more difficult to find than they often are. This should be a good week for those waiting for the 600 DD (base 43°F) mark to begin scouting for treatment decisions; our current (7/14) readings follow:

SITE              FIRST CATCH       DD TOTAL     
Highland            June  9         1008
Knowlesville        June 16          773 (Waterport)        
Geneva              June 17          704
Wolcott             June 19          617 (Sodus)

Check pp. 83, 91-92, 95 and 100 in the 1997 Recommends for guidelines on sampling procedures.


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Photographs courtesy of New York State Integrated Pest Management Program