Diseases | Credits

SCAFFOLDS Fruit Journal, Geneva, NY                 Volume 5 
Update on Pest Management and Crop Development       September 16,1996

Coming Events

                                                     43F       50F
Current DD accumulations (Geneva 1/1-9/16):         3257      2250
                       (Highland 1/1-9/16):         3656      2573

Coming Events:                             Ranges:
Codling moth 2nd flight subsides                2782-3693  1796-2635
Lesser appleworm 2nd flight subsides            2775-3466  2002-2460
Oriental fruit moth 3rd flight subsides         2987-3522  2018-2377
Spotted tentiform leafminer 3rd flight subsides 3235-3471  2228-2472

TRAP CATCHES (Number/trap/day)
                                  8/29   9/3   9/5   9/9  9/12  9/16
Redbanded Leafroller               0.2     0     0     0     0     0
Spotted Tentiform Leafminer        420   208   269   556    38    32
Oriental Fruit Moth                6.0  29.3  29.3  50.0    36    34
Lesser Appleworm                   2.2   4.0   8.0  14.6   5.5   9.0
Codling Moth                       4.3   6.0   7.3   3.9   0.8   0.1
San Jose Scale                     1.5   1.3   1.3   1.3   2.7     0
Obliquebanded Leafroller           0.2   0.7     0   0.3   0.5     0
Apple Maggot                       0.2     0     0  0.03     0     0

Highland (Dick Straub, Peter Jentsch)
                                   8/5  8/12  8/19  8/26   9/9  9/16
Redbanded Leafroller               0.2   0.3   1.0   0.9   0.3     0
Spotted Tentiform Leafminer        109   152   153   102     -  18.4
Oriental Fruit Moth                0.1   0.5   0.2   0.1   0.5   0.4
Lesser Appleworm                   2.5   3.5   5.4   5.4   1.7   1.7
Codling Moth                       8.9   4.9   3.9   0.9   0.1     0
Fruittree Leafroller                 0     0     0     0     0     0
Tufted Apple Budmoth               0.1   0.2   0.4   0.6   0.5  <0.1
Obliquebanded Leafroller           0.3   0.7   0.4  <0.1   0.1     0
Sparganothis Fruitworm               0   0.1   0.2   0.7   1.4   0.8
Variegated Leafroller                0   0.6   0.5   0.4   0.1   0.2
Apple Maggot                       3.4   2.1   1.0   0.6   0.1     0



By: Dave Rosenberger, Plant Pathology, Highland

Foliar apple scab was unusually severe this summer in some orchards in the Champlain Valley and in Western NY. In these orchards, terminal leaves with multiple lesions were easy to spot in early September, more than five percent of terminal leaves were affected on some limbs, and average terminal leaf infection exceeded one percent. Scab problems developed for a variety of reasons. In some orchards, early scab was not controlled because dodine was used in orchards with high levels of dodine resistance. Extended wetting periods interfered with applications of pre-bloom fungicides in some areas. Ascospores matured unusually early throughout the northeast this year. Large ascospore discharges initiated scab infections at green tip before the first fungicides were applied in some of the problem orchards. Protectant fungicide programs never eradicated these early infections, and the cool, wet summer allowed secondary scab to "blossom" in July when spray intervals were stretched out. (In the Champlain Valley, orchards that received several sprays of SI fungicides during May appeared to fare better than those that received only protectant sprays.)

Orchards with severe foliar scab this fall will have very high inoculum levels again next year unless growers take action to reduce inoculum production in overwintering leaves. Researchers have investigated ways to reduce overwintering scab inoculum for more than 70 years, and some methods have reduced the production of ascospores by 90-99%. However, none of these inoculum-reduction methods have been widely recommended. Inoculum reduction is never 100% effective, and spring fungicides are still needed to protect young leaves and fruit as they develop

I usually do not recommend fall treatments aimed at reducing scab inoculum because I doubt the benefits of fall treatments in orchards that will be protected with a good fungicide program in the spring. However, there are several reasons to believe that fall treatments might pay for themselves this year. First, inoculum levels in some blocks are among the highest I have ever seen in commercial orchards, and there is likely to be continued build-up of underleaf scab through September and October. Second, if weather conditions next spring are a repeat of this year, with early spore maturity and difficult spraying conditions, then scab control will be exceedingly difficult. High inoculum levels will increase the risks of severe losses whenever there is the slightest gap in the spring fungicide program.

Postharvest scab treatments may be more important now than in the past because many growers have reduced their standard scab fungicide program to the point where it will no longer control scab under high-inoculum conditions. Mancozeb is our primary pre-bloom contact fungicide, but it cannot be used at more than 3 lb/A unless applications are terminated at petal fall. As a result, most growers have chosen to use the 3 lb/A rate of mancozeb even if they are depending on mancozeb alone for scab control. The 3-lb/A rate of mancozeb fungicides has worked well in low-inoculum orchards, but it will not provide adequate scab control in high-inoculum orchards that require more than 150 gallons of dilute spray when calculated on a tree-row volume basis. (On small trees, the 3-lb/A rate is equivalent to the old standard 6-lb/A rate recommended for larger trees.) Similarly, many growers have cut their use of captan to rates that are adequate for low-inoculum situations but that will fail when inoculum levels are high.

In orchards where inoculum levels remain high through winter, options for next spring will be limited to one of the following two strategies:

(1) Use mancozeb or captan on a weekly schedule at maximum labeled rates from bud-break through petal fall (and pray for good spraying weather); or

(2) Use 3-6 applications of SI fungicides in combination with lower rates of mancozeb or captan. Growers who dislike both options should take action this fall to reduce overwintering of apple scab and thereby preserve more options for adjusting their spring fungicide programs.

All of the following practices are known to reduce survival of apple scab through winter and/or production of apple scab ascospores in spring. Which practices are most feasible or cost-effective will depend on the farm and the kinds of equipment and materials that are available. Combining several of the following practices will be more effective than using a single practice alone.

Fall treatments for reducing apple scab inoculum for 1997:

1. Chopping leaves with a flail mower in late fall or early spring results in more rapid leaf degradation and reductions in ascospore production. Sutton and MacHardy evaluated this strategy in New Hampshire and reported that ascospore production was reduced by about 60% even though the off-set flail mower failed to reach all of the leaves along the tree line. Rotary mowers are likely to be less effective because they will pick up less of the leaves that are flattened on the ground by fall rains.

2. Urea sprays applied either to leaves on the trees just prior to leaf fall or to leaves on the ground speed degradation of leaves because the nitrogen stimulates growth of the saprophytic yeasts and bacteria that break down leaves. Coverage is generally better if the urea is applied to the trees prior to leaf drop rather than to leaves on the ground, but this advantage may be negated if leaves remain attached to the tree for more than several days after the urea is applied. In one test, urea completely suppressed spore development in leaves detached from trees 48 hrs after treatment, but it had little effect on leaves remaining on the tree 7 days after treatment. In tests conducted in 1992, Ed Stover found that foliar applications of urea in October had no adverse effect on winter hardiness as determined by subsequent laboratory evaluations of wood samples from sprayed trees, but he recommends against using urea on young trees that have not settled into full bearing and that might still have actively growing terminals in late fall. Five percent urea (5 lb urea/100 gallons of dilute spray) is the commonly suggested rate. Uptake may be improved by applying the urea at 4-6X.

3. Spreading lime after leaf fall increases the pH of the leaf litter and significantly reduces ascospore production. If lime applications are needed anyway to adjust soil pH, then this may be an added reason to have applications made after harvest this year.

4. In laboratory tests, 2,4-D applied to leaf discs reduced ascospore production by >50%. Applying 2,4-D in late October or early November can have the dual benefits reducing ascospore production and eliminating dandelions, which distract bees during apple pollination season.

Some fungicides (especially Benlate and Topsin M) have been reported to reduce ascospore production when applied after harvest and before leaf fall. However, we do not recommend postharvest fungicide applications because such applications are not included on the label, eradicant applications increase selection pressure for fungicide-resistant strains, and the effectiveness of postharvest applications is now questionable because most orchards already contain some fungicide-resistant strains of apple scab.

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

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