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SCAFFOLDS Fruit Journal, Geneva, NY             Volume 5 
Update on Pest Management and Crop Development  August12,1996

Coming Events

                                                     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



DISEASES

NECROTIC LEAF BLOTCH OF GOLDEN DELICIOUS

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 86/79F 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 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!




INSECTS

PROGRESSION OF EVENTS

By: Dave Kain and Art Agnello, Entomology, Geneva

Things are a little slow this week so we thought we'd catch you up on our comparison of events so far this year with last season and the "normal":


		DD (base 43F)

DD43 to date (6/10)	882	949	742
PPS 1st oviposition	80	111	48
PPS 1st nymphs	242	236	-
GFW flight peak	134	230	206	
ERM egg hatch begins	284	290	-
RBLR 1st flight peak	298	406	379
STLM 1st flight peak	308	439	379
OFM 1st flight peak	428	439	379
CM 1st catch	484	439	505
LPTB 1st catch	589	563	602
APB 1st flight peak	741	692	625
SJS 1st flight peak	674	692	-
OBLR 1st catch	915	911	962	
PTB 1st catch	1084	692	851
STLM 2nd flight begins	1067	1055	1034
OBLR 1st flight peak	1151	1055	1034
AM 1st catch	1338	1276	1481
APB 2nd flight begins	1550	1546	1748	
AM 1st oviposition 	1670	2200	-
CM 2nd flight begins	1929	1872	1847
CMB 1st adult catch	1453	1276	1396
CMB 1st flight peak	1617	1580	1661
CMB 2nd gen. crawlers emerging	2379	-	-
LAW 2nd flight begins	1780	1276	1748
LPTB peak	1535	1095	962
OFM 2nd flight begins	1461	1276	1481
PTB flight peak	1706	1095	962
RBLR 2nd flight begins	1495	1546	1305
SJS 2nd flight begins	1721	1546	1748
STLM 2nd flight peak	1646	1729	1748
OBLR 2nd flight begins	2528	2292
AM flight peak	2370	2172
APB 2nd flight peak	2305	2292
CM 2nd flight peak	2472	2514
SJS 2nd flight peak	2326	2172
STLM 3rd flight begins	2501	2710

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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