Scaffolds Fruit Journal, Cornell University NYSAES

Diseases | Insects | Credits


Volume 6 Number 6						April 28, 1997


COMING EVENTS

                                                     43F       50F
Current DD accumulations (Geneva 1/1-4/28):         189        78
                       (Highland 1/1-4/28):         290       120

Coming Events:                              Ranges:
Green fruitworm peak flight                       64-255    19-108
Rosy apple aphid nymphs present                   91-291    45-148
Green apple aphid present                        127-297    54-156
Oriental fruit moth 1st catch                    129-587    44-338
Pear thrips in pear buds                         137-221    54-101
Spotted tentiform leafminer 1st oviposition      141-319    48-154
Obliquebanded leafroller larvae active           149-388    54-201
European red mite egg hatch begins               157-358    74-208
Redbanded leafroller 1st flight peak             180-455    65-221
Rose leafhopper 1st nymph on multiflora rose     188-402    68-208
McIntosh at pink                                 258-356    96-182

Phenologies (Geneva):  Apple (McIntosh) - Early Tight Cluster
                       Pear - Early Green Cluster,  
                       Sweet Cherry - Early White Bud
                       Tart Cherry, Plum - Bud Burst
                       Peach - Half-Inch Green
          (Highland):  Apple (McIntosh) - Early Pink
                       Pear (Bartlett) - Late Green Cluster

PEST FOCUS
   Geneva: 1st Rosy Apple Aphid nymphs 4/23 (H. Reissig)
 Highland: 1st Oriental Fruit Moth catch 4/28
           1st Pear Psylla nymphs observed

TRAP CATCHES (Number/trap/day)
Geneva:   
                                  4/17   4/21   4/24 
Green Fruitworm                      0      0    0.2
Redbanded Leafroller                 0    0.4*   1.0
Spotted Tentiform Leafminer          0    0.4*  43.7
Lesser Appleworm                     0      0      0
Oriental Fruit Moth (apple)          0      0      0
Oriental Fruit Moth (peach)          0      0      0

Highland (Dick Straub, Peter Jentsch):
                                   4/7   4/14   4/21   4/28
Green Fruitworm                    0.1*   0.4      0    0.6
Redbanded Leafroller               0.4*   2.4    8.6   18.1
Pear Psylla (eggs/bud)             1.4*   3.1    3.1    2.3
Spotted Tentiform Leafminer          0    0.8*  11.9   49.7
Oriental Fruit Moth                  -      0      0    0.6*
                                                       * = 1st catch


APPLE SCAB ASCOSPORE MATURITY (D. Rosenberger)
                                                       Tower   DD (32F)
Date     Location      Immature   Mature  Discharged   Shoot  Since GTip
4/15  Ulster (Highland)  71%       28%       1%         392      176
4/21  Ulster (Highland)  71%       27%       2%         918      252
4/22  Clinton Co. (Peru) 91%        9%       0%           1       --

Scab infection periods in Highland:
April 12-13	22 hrs wetting, 48F, 0.48 inches rain
April 17-19	42 hrs wetting, 40F, 1.29 inches rain
April 27-28 Potential infection period in progress with wetting initiated 
11:30 p.m. 27 April


Diseases

APPLE DISEASE UPDATE

by Dave Rosenberger
Plant Pathology, Highland

APPLE SCAB
The degree-day accumulations reported along with ascospore maturity counts in last week's Scaffolds were inadvertently expressed in Celsius. Fahrenheit degree days are shown above along with the ascospore counts previously reported for Highland. Ascospore maturation and discharge increase very rapidly after 175-225 degree days have accumulated. As of April 28, we have accumulated 391 degree days (Base 32°F.) since green tip in Highland. McIntosh buds are at the open cluster stage of development.

BROWN ROT BLOSSOM BLIGHT

by W. Wilcox
Plant Pathology, Geneva

Even without spray protection, brown rot blossom blight occurs sporadically in New York, depending on weather, inoculum abundance, and stone fruit species, in approximately that order. A quick review of these factors and fungicide considerations, including what's new.

WEATHER.
Brown rot likes it warm and wet. Ideal temperature is about 70 to 75°F. If inoculum is plentiful, significant infection can occur after only a few hours of wetness at these temps, but as temperatures get lower and/or inoculum gets scarcer, progressively longer periods of wetness are required. The current "best guess" (based on controlled-environment experiments) is that about 12-24 hr of wetness are required to produce infections of sour cherry blossom at 60°F under typical field conditions. Warm, muggy conditions following a rainy period are much more likely to result in blossom blight development than if weather is dry and/or cool afterwards.

INOCULUM.
In relative order of importance, the main sources of blossom blight inoculum are mummies retained in the tree, mummies on the orchard floor, and nearby wild or abandoned stone fruit trees. On peaches, twig cankers that developed from infected fruits last summer also can be very important. If you had more brown rot than usual last summer, expect to have more inoculum than usual this spring. Wet prebloom conditions will encourage the production of spores from these overwintering inoculum sources and provide more disease pressure, whereas dry prebloom weather has the opposite effect.

FRUIT SPECIES SUSCEPTIBILITY.
Apricots and sweet cherries seem to be the most susceptible to blossom blight, sour cherries the least. Peaches and plums are somewhere in the middle.

Remember also that the very young fruit (before pit hardening) of all species except sour cherries are fairly susceptible to infection during wet weather conditions, and the usual influences of temperature and inoculum pressure should be considered. Sometimes these early infections show up immediately, but often they remain latent until the preharvest period when they suddenly seem to appear from nowhere.

Thus, the first few weeks after petal fall can be an important time for protecting young fruitlets. Unfortunately, the people who write fungicide labels can't seem to get this concept through their heads. Labels generally allow two or three blossom sprays where one often is enough, since SI's, Rovral, and Ronilan have 2 to 3 days kickback activity on open blossoms and provide forward protection of unopened blossoms due to their systemic absorption. However, most labels make no provision for brown rot control between petal fall and preharvest, although some do allow sprays for control of other diseases (peach scab, cherry leaf spot) during this time. Read the labels carefully and treat as needed.

NEW FUNGICIDES.
Elite 45DF is an SI fungicide that received New York registration last fall (rate = 2 oz/100 gal), too late to make it into the Recommends. It is in the same chemical family as Orbit and Indar, which should be considered if you are trying to rotate fungicides for resistance management purposes. It is very active against the brown rot fungus in lab assays, but has not provided the residual control of fruit rot infections that Indar has. It has provided excellent control of blossom blight in our trials.

Orbit is a very active SI fungicide that has been labeled on peaches, apricots, and plums (but not "prunes") for several years. It now is ALSO LABELED ON CHERRIES, although this change became effective too late to be included in the Recommends. Field experience has been excellent.

FUNGICIDE CONSIDERATIONS.
To discourage resistance development, it's a good idea to use different fungicide classes during the bloom/early postbloom period and the immediate preharvest period. As a general rule of thumb, it is best to save your best materials until the preharvest period, since this is when the disease is most costly and hardest to control. Our trial results for several years and last year's field experience indicate that Indar (and possibly Orbit) now fit this ranking. Thus, if you're planning on using these materials (or Elite) preharvest, try to use a non-SI during bloom. Using SI's during bloom plus preharvest won't burn them out over a season or two, but it all adds up after awhile.

Other options include captan (cheap and reasonably effective), Bravo (not cheap, but gives good residual protection of young fruitlets), and Rovral or Ronilan (good protective and kickback activities; also excellent at inhibiting spore production from blighted blossoms, which can be important for preventing spread to developing fruit). As always, weather conditions, inoculum availability, and crop susceptibility should determine whether to spray, when, and with what.


Insects

ONE SHOE DROPS

by Art Agnello
Entomology, Geneva

We received notice that last Tuesday, the DEC made the decision to give Agri-Mek approval for a full state label in apples and pears, with no additional restrictions beyond those stated on the federal label. This means that, technically, a maximum of 2 applications per year are allowed, with a total of 40 fl. oz. per acre. In practice, however, we maintain our recommendations to apply no more than a single application per year (both in apples and pears), using 10 oz/acre in apples and 20 oz/acre in pears for best results. As for timing of the sprays, despite what the label says, we recommend that Agri-Mek NOT be applied any later than 2 weeks past petal fall to ensure maximum absorption and residual efficacy; for apples especially, the closer to petal fall the better.

You will recall that last year's apple label contained the following wording: "Always apply in combination with a paraffinic spray oil as directed." However, because of imcompatibilities of the oil with some fungicide programs, Merck made a slight change in the label for this year; i.e., "For best results, use Agri-Mek in combination with a horticultural spray oil (not a dormant oil)...Applications without horticultural spray oil may result in reduced efficacy and/or residual control." What this means, if you read through the obtuse verbiage, is that it is now not illegal to substitute some other adjuvant (such as LI-700, or Sil-Wet, or Regulaid, etc.) for the Ultra Fine or Stylet-Oil in the spray, but Merck isn't taking anybody's word that you won't get reduced efficacy of the product. So, it's your choice (the rate of the adjuvant is still 0.25% or 1 gal/acre).

This decision is obviously welcome news to growers who have been unsure of how to proceed for mite and pear psylla management this season, and it gives us all the opportunity to exercise some responsible product stewardship in (all of) our efforts to promote effective management of both pest problems and pesticide resistance. Probably the single most useful piece of advice we can offer to apple growers looking for ways to preserve the effectiveness of the acaricides we now have available is this: Don't Do It Again! That is, whatever mite control program was used last year, and even regardless of how well or how poorly it worked, wise resistance management practice would dictate a change to a different one in 1997.


European red mite adult female

The rationale behind this advice is that the time to manage pesticide resistance is before it starts to show up, and the options that now exist for mite control make this a practical, if somewhat controversial strategy for ERM. As we have said before, Apollo and Savey should be regarded as essentially the same material for purposes of resistance development, considering the well-known incidences of cross-resistance between these two products. By the same token, there is not yet any evidence of mite resistance to Agri-Mek, but there is also no reason to expect it not to occur at some time in the future. Nevertheless, with a number of early-season products to choose from, it's not difficult to formulate a few different rotation programs to begin using, the benefit being that many growers already have used one of these rotations during the past season.

One such program, which we were compelled to follow last year, would be a prebloom spray of Savey or Apollo, and then a summer rescue application of Carzol or Kelthane, if needed. Admittedly, these summer materials have certain limitations, but 1996 was fortunately a light mite year, and most growers didn't have a very serious problem with late season outbreaks. A possible 2nd-year rotation would be to use Agri-Mek at (or immediately after) petal fall; an oil spray before bloom could be elected, but this has actually proven not to be necessary in several field trials we have conducted with Agri-Mek, which has provided season-long control with a single well-timed application. In the 3rd year, another rotation might be to use oil prebloom, and then a summer application of Pyramite, which should have a federal label by then. By the following year, a return to Apollo or Savey would be recommended. Ideally, these rotation programs should be used on a farmwide basis, or on as large a scale as is practical. Although we have no evidence to indicate that mites from one block will "contaminate" (for resistance purposes) an adjacent block that has received a different miticide program, the chances of such an event occurring are obviously less if contiguous blocks are treated with the same program during the season.

Obviously, people may balk at the fact that Agri-Mek is likely going to be a bit more expensive to use than Apollo or Savey. The attractiveness of going with the cheapest effective product cannot be denied, but we would just urge you to keep in mind the overall cost of prematurely burning out a material (or two at the same time, in this case) by using it continuously for a brief period (maybe only 3 years, according to some field use patterns in other parts of the world). A final question arises about the potential availability of Pyramite this year. Obviously, it would be nice to have this product standing by for growers to use this season, either in a seasonal program or as a rescue treatment. However, we don't yet know the federal or state disposition of this label just yet, so for the time being, it's still a matter of exercising the best judgement we can while waiting for the other shoe to drop.


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


Photographs courtesy of New York State Integrated Pest Management Program


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