SCAFFOLDS Fruit Journal, Geneva, NY Volume 5 Update on Pest Management and Crop Development August12,1996
43F 50F
Current DD accumulations (Geneva 1/1-8/12): 2382 1619
(Highland 1/1-8/12): 2851 1964
Coming Events: Ranges:
Codling moth 2nd flight peaks 1587-3103 1067-2212
Apple maggot peak flight 2033-2688 1387-1778
San Jose scale 2nd flight peaks 2136-2591 1567-1874
Oriental fruit moth 3rd flight starts 2172-2956 1553-2013
Obliquebanded leafroller 2nd flight starts 2199-3040 1490-2076
STLM 3rd flight starts 2215-2783 1567-2123
Comstock mealybug 2nd gen. crawlers peak 2350-2649 1642-1736
TRAP CATCHES (Number/trap/day)
Geneva:
7/25 7/29 8/1 8/5 8/8 8/12
Redbanded Leafroller 0 0 0 0 0 0
Spotted Tentiform Leafminer 409 167 67 66 163 96
Oriental Fruit Moth 12.7 13.1 77.2 3.9 4.2 5.6
Lesser Appleworm 1.8 1.8 3.3 0.8 1.0 2.5
Codling Moth 6.3 1.8 6.2 13.9 17.7 8.5
San Jose Scale 3.0 0.9 0.2 6.3 7.0 1.4
American Plum Borer 2.3 3.9 6.0 3.9 3.7 1.6
Lesser Peachtree Borer (peach) 0.3 0.1 0.3 0.4 0.3 0.8
Peachtree Borer 3.7 1.1 1.3 4.8 2.7 3.0
Obliquebanded Leafroller 0 0.1 0 0 0 0
Apple Maggot 0 0.4 0.3 0.3 0.4 0.1
Highland (Dick Straub, Peter Jentsch)
7/8 7/15 7/22 7/29 8/5 8/12
Redbanded Leafroller 13.0 3.8 0.1 0.3 0.2 0.3
Spotted Tentiform Leafminer 33.9 38.3 27.9 19.1 109 152
Oriental Fruit Moth 0.9 0.5 0.9 0.2 0.1 0.5
Lesser Appleworm 0.2 0.1 0.4 1.9 2.5 3.5
Codling Moth 1.4 0.2 1.4 6.2 8.9 4.9
Fruittree Leafroller 0 0 0 0 0 0
Tufted Apple Budmoth 1.1 0.9 0.4 0 0.1 0.2
Obliquebanded Leafroller 2.6 0.4 0.2 0 0.3 0.7
Sparganothis Fruitworm 0.9 0.3 0 0 0 0.1
Variegated Leafroller 0 0.1* 0.1 0.2 0 0.6
Apple Maggot 0.3 0.3 0.8 0.9 3.4 2.1
* = 1st catch
By: Dave Rosenberger, Plant Pathology, Highland
Near the beginning of August, apple growers in the Hudson Valley noted yellow leaves accumulating on the ground beneath Golden Delicious trees, and more partially-yellow leaves were evident in the tree canopies. Affected leaves frequently had irregular, brown, necrotic areas between veins. Small areas of the leaves remained bright green against the predominant deep yellow color. Growers feared the worst and wondered what additional fungicide would be needed to combat this new threat.
The good news is that no treatment is required. This disorder is called necrotic leaf blotch. Affected trees do not drop all of their leaves, and fruit do not drop or become blemished. The bad news is that plant pathologists have been unable to determine the cause of necrotic leaf blotch, and therefore we have no idea how to prevent it. In some seasons, more than 50% of terminal leaves can become affected and drop from the tree by early September.
Necrotic leaf blotch was extensively studied in the early 1970's by Dr. Turner Sutton in North Carolina. He found that the disorder is not caused by a fungus, bacterium, or air pollution and that it is not related to foliar nutrient levels. Symptoms and subsequent leaf drop frequently occur in distinct "waves" in mid to late summer, but Sutton noted that there was considerable variability in severity between and within orchards. The rootstock on which Golden Delicious were propagated did not appear to influence susceptibility or severity. All strains of Golden Delicious were susceptible, but Sutton did not find the disorder on other apple cultivars unrelated to Golden Delicious.
In controlled environment tests, Sutton showed that the disorder failed to develop on leaves of trees held at 86/79¡F day/night temperatures, whereas 33% of leaves on trees held at 79/72 or 72/64 day/night temperatures developed leaf blotch. He also showed that potted trees watered every day had roughly three times more leaves affected than did similar trees watered only every second or third day. One might conclude that necrotic leaf blotch is favored by relatively cool, wet weather in late summer Ñ conditions that accurately describe our weather pattern this year. If the cool, wet weather continues, additional waves of leaf drop can be expected in Golden Delicious blocks.
Sutton evaluated various fungicides and found that mancozeb fungicides and Dikar applied during summer suppressed necrotic leaf blotch, whereas Captan, Benlate, and Topsin M were ineffective. Dikar is no longer available and mancozeb fungicides cannot be applied during summer. Thus, there is currently no fungicide program available for reducing the severity of this disorder.
Although necrotic leaf blotch does not cause fruit drop or fruit blemishes, it may have adverse effects on fruit size and perhaps on the strength of flower buds for the following year. No studies have reported on the effects of this disorder on fruit size because no one has figured out how to maintain affected and unaffected trees in the field for side-by-side comparisons.
In the absence of any more scientific approach, following are two suggestions for dealing with necrotic leaf blotch: (1) Enjoy the intrinsic beauty of the sudden bursts of yellow leaves, and (2) be thankful that there is no need for additional sprays in this wet season when fungicide bills are already approaching record levels!
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
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