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SCAFFOLDS Fruit Journal, Geneva, NY                             Volume 5 
Update on Pest Management and Crop Development            April 22, 1996

Coming Events

COMING EVENTS
                                                     43F       50F
Current DD accumulations (Geneva 1/1-4/22):          122        52
                       (Highland 1/1-4/22):          245        98

Coming Events:                             Ranges:
Pear psylla adults active                          2-121      0-49
Pear psylla 1st oviposition                       25-147      1-72
Green fruitworm peak flight                       64-255    19-108
Spotted tentiform leafminer 1st catch             73-433    17-251
Rosy apple aphid nymphs present                   91-291    45-148
Green apple aphids present                       127-297    54-156
Redbanded leafroller 1st flight peak             180-455    65-221
McIntosh at half-inch green                      112-221    54-101

Phenologies (Geneva): Apple (McIntosh) - green tip
                      Sweet Cherry (Windsor),
                      Tart Cherry (Montmorency) - swollen bud
                      Pear, Peach - swollen bud
          (Highland): Apple (McIntosh) - tight cluster
                      Pear (Bartlett) - bud burst

Pest Focus
   Geneva - Redbanded Leafroller 1st catch 4/22
            Tarnished Plant Bug adults active
 Highland - 1st Spotted Tentifrom Leafminer 4/19
            Oriental Fruit Moth first catch 4/22
            Pear Psylla eggs beginning to hatch
              

TRAP CATCHES (Number/trap/day)
Geneva:   
                                   4/1   4/8  4/11  4/15  4/18  4/22
Green Fruitworm                      -     -     0   0.1*    0   1.0
Redbanded Leafroller                 -     -     0     0     0   0.1*
Spotted Tentiform Leafminer          -     -     -     -     0     0

Highland (Dick Straub, Peter Jentsch)
                                  3/39   4/1   4/8  4/15  4/22
Green Fruitworm                    0.1*  2.2   0.4   0.2   0.2
Pear Psylla (eggs/bud)            0.01   0.2   0.5   1.0   2.5
Redbanded Leafroller                 -     -   0.2*  0.3   7.7
Spotted Tentiform Leafminer          -     -     0     0   4.3*
Oriental Fruit Moth                  -     -     -     -   0.1*
                                                       * = 1st catch

APPLE SCAB ASCOSPORE MATURITY (D. Rosenberger)

Date     Location        Immature    Mature     Discharged   Tower Shoot
4/15     Highland          85%         15%         0%           27
4/15     Columbia Co       84%         16%         0%            0
4/15     Saratoga Co       83%         17%         0%           18
4/18     Peru              75%         25%         0%           22
4/19     Highland          65%         34%         1%          208



APPLE SCAB UPDATE

By: Dave Rosenberger, Plant Pathology, Highland

Counts for the Champlain Valley (Peru, NY) from leaves collected April 18 were very similar to counts from the lower Hudson Valley on April 15. Thus, it appears that apple scab is on about the same schedule through the entire eastern part of New York State. Champlain Valley growers should be prepared to protect trees from scab as soon as they have green tissue unless they are very certain that their orchards were free of scab last year. With the early spore maturity that we are witnessing this year, it will not be a good year to gamble on delaying early scab sprays in orchards that had any carry-over inoculum from scab infections last year.

In the lower Hudson Valley (Highland, NY), a few spores discharged during the moderate Mills' scab infection period that occurred April 16-17 when early varieties were at green tip. Warm temperatures following the rains favored rapid spore development. With trees approaching tight cluster, we are now in the peak period for apple scab ascospore discharge.




A BASELESS ARGUMENT

By: Art Agnello, Entomology, Geneva

The long-awaited spring weather patterns finally seem to have arrived, and with continuous days of 50-degree highs, it won't take long for the buds to realize they've got some catching up to do, so I guess it's time to rerun our annual message about the effect of spray water pH on pesticide activity. To review, there may be times when you don't get the expected results from a pesticide application, even though you used the correct concentration of the recommended material and applied it in the same way that has given acceptable control at other times. Although you may suspect a bad batch of chemical or a buildup of pesticide resistance, the poor results may in fact be due to alkalinity - that is, a solution with a pH higher than 7.0. A close inspection of the pesticide label will often reveal a caution against mixing the chemical with alkaline materials such as lime or lime sulfur. The reason for this is that many pesticides, particularly insecticides, undergo a chemical reaction under alkaline conditions that destroys their effectiveness. This reaction is called alkaline hydrolysis, and can occur when the pesticide is mixed with alkaline water or other materials that cause a rise in the pH.

Hydrolysis is the splitting of a compound by water in the presence of ions. Water that is alkaline has a larger concentration of hydroxide (OH-) ions than water that is neutral; therefore, alkaline hydrolysis increases as the pH increases. Insecticides are generally more susceptible to alkaline hydrolysis than are fungicides and herbicides, and of these, organophosphates and carbamates are more susceptible than pyrethroids. A survey of fruit-growing areas in N.Y. showed that water from as many as half of the sites in western N.Y. had pH values above 8.0. Water at this pH could cause problems for compounds that will break down in only slightly alkaline water, such as ethephon (Ethrel). Compounds that break down at a moderate rate at this pH, such as Carzol and Imidan, should be applied soon after mixing to minimize this process in the spray tank. A smaller number of sites (less than a quarter of them) had pH levels greater than 8.5. Above this level, the rate of hydrolysis is rapid enough to cause breakdown of compounds such as Carzol and Imidan if there is any delay in spraying the tank once it is mixed. In a few sites having a pH above 9.0, compounds such as Guthion and malathion, which would not break down in most situations, may have problems. It is also important to note that in any one site, ground water pH can vary substantially (by nearly 2 pH units) during the season.

To prevent alkaline hydrolysis, you should:

1- Determine the pH of your spray solution; because of seasonal variability, this should be done more than once during the growing season. Measuring your spray water pH before mixing can be misleading, because the chemicals you use can raise or lower the pH of the overall spray solution. It makes more sense to take the time to run some bottle tests of your most-used spray materials after they have been mixed with your spray water. The most accurate method is by using an electronic pH meter; however, these are expensive and not very practical. Another, less accurate method uses dyes that change color in response to pH. These are available in the form of paper strips, or in solution for use in soil pH test kits. In general, the indicator is mixed with or dipped into the water, and the resulting color is compared against a standard color chart.

2 - To minimize loss of chemical effectiveness from hydrolytic breakdown in the tank, it is a good practice to apply right after it is mixed (as much as is allowed by the weather and other factors). If a delay occurs, a buffering agent may be added to the tank if the pH is high and the chemical you are using is susceptible to alkaline hydrolysis; these agents work by lowering the pH and resisting pH change outside of a certain range. A pH in the range of 4-6 is recommended for most pesticide sprays. Buffering agents are available from many distributors; some examples are: Buffer-X (Kalo, Inc.), Buffer P.S. (Helena), Spray-Aide (Miller), Sorba-Sprays (Uniroyal/Leffingwell), and LI 700 (Loveland/AgChem Service). Some sources for pH testing materials are (pH Indicator Paper): Ward's Natural Science Est., PO Box 1712, Rochester, NY 14603; VWR, PO Box 1050 Rochester, NY 14603; Fisher Scientific, PO Box 8740, Rochester, NY 14642; (Soil pH Test Kits): Agronomy Soil Test Lab, 804 Bradfield Hall, Cornell Univ., Ithaca, NY 14853.

Growers may add technical flake calcium chloride to the tank when spraying cultivars such as McIntosh, which is susceptible to storage disorders related to inadequate levels of fruit calcium. However, research done in Massachusetts indicates that, although calcium chloride does not itself affect pH, a contaminant present as a result of the manufacturing process does increase the pH of the solution; this could in turn encourage alkaline hydrolysis. There are a few pesticide materials that should not be acidified under any circumstances, owing to their phytotoxic nature at low pH. Sprays containing fixed copper fungicides (including Bordeaux mixture, copper oxide, basic copper sulfate, copper hydroxide, etc.) and lime or lime sulfur should not be acidified. But if the product label tells you to avoid alkaline materials, chances are that the spray mixture will benefit by adjusting the pH to 6.0 or lower.

For further information on water pH and pesticide effectiveness, refer to N.Y. Food & Life Sci. Bull. No. 118, "Preventing decomposition of agricultural chemicals by alkaline hydrolysis in the spray tank", by A. J. Seaman and H. Riedl, from which much of this information was adapted (available from Communications Services Bulletins, Jordan Hall, N.Y.S. Agric. Expt. Sta., Geneva, NY 14456; 315-787-2249, FAX: 315-787-2276. Cost is $0.50 per copy; make checks payable to "Communications, NYS Agricultural Experiment Station"; postage stamps acceptable for payment of sums less than $1.00).




A PINK MOMENT

By: Art Agnello, Entomology, Geneva

A few more thoughts about the pink bud period would be in order now, because depending on the weather pattern over the next week or two, this stage might not last too long. As discussed in last week's issue, the last of the prebloom sprays should be applied at pink for the most effective control of a variety of arthropod pests. In general, the three most important insects to be concerned with are tarnished plant bug, rosy apple aphid, and spotted tentiform leafminer. If all three are present in sufficient numbers to warrant a treatment at this time, the only materials with enough broad sprectrum activity and residual effectiveness to do a good job are the pyrethroids: Asana, Ambush or Pounce. However, if careful consideration is given to all the factors necessary to make this option advisable, probably only a minority of orchards qualify.

Tarnished Plant Bugs: As a rule, pyrethroids give the best control of plant bugs because they have sufficient residual activity to protect against the extended adult feeding and egg-laying period of this insect. Cygon and Thiodan are other possible alternatives; Thiodan is easiest on mite predators, but probably least effective against TPB. If your fruit has been showing no more than 2-3% plant bug damage at harvest, a spray is of questionable value, because low-level damage is difficult to eliminate completely, and packout studies have shown that any increases in packout gained by spraying for TPB are usually offset by the cost of the spray. If TPB is not a problem, but rosy aphids and leafminers are at threshold, a recommended option would be Vydate; for rosy apple aphid control alone, use Lorsban 50WP at 12 oz, or Thiodan at 1 lb of the 50WP (2/3 qt of the 3EC) per 100 gallons.

Leafminers: First generation STLM isn't necessarily a huge problem in any year; we have given recommendations for its control mainly so growers can hedge their bets on the likelihood of economic damage from the summer generations. However, in our experience, there's been a fairly low predictability between first brood numbers in an orchard and second brood in the same block that year. Moreover, this generation tends to be the least problematic overall and in many cases might even be ignored completely (even if eggs do reach the 23 per leaf level), considering the availability of Provado after petal fall, rather than having to use a more conventional material that generally does your predator populations no good. Nevertheless, for those who may opt for a traditional first brood management strategy, Vydate applied at pink will act as an ovicide against the eggs, 90% of which are generally present by bloom, and its long residual activity will also work against the larvae as they hatch.

Lannate is also effective at pink, but has a shorter residual life, which may be a concern if egg-laying gets slowed down by cool weather. Also, there is little or no ovicidal action with this material, so you are aiming at the young larvae. These materials can also be used at petal fall, but Vydate thins the fruit, so if you don't want this thinning action, Provado or Lannate at petal fall are preferred. The recommended threshold for this brood of STLM is 2 eggs per fruit cluster at pink. Examine leaves 2, 3, and 4 on three clusters from each tree sampled, and use the sequential sampling table (No. 16, p. 87 in the Recommends) or chart (Fig. 1, p. 9) to determine how many trees to sample. Remember that a decision can also be made by sampling with a threshold of 1 sap-feeding mine per leaf at petal fall (same table, or chart on p. 93, Fig. 3). For rosy apple aphid at pink, 1 infested cluster per 100 (check 10 on each of 10 trees) warrants treatment.

Leafrollers: Growers may feel it is necessary to control obliquebanded leafroller in their pink spray. A number of materials, most notably the pyrethroids, are suitable for this purpose; however, even if you do kill some larvae during the pink stage, it will still be necessary to come back again after bloom to finish the job, because not all of the population has emerged from their overwintering sites by this time. We consider petal fall to be a preferable time to control these caterpillars, if indeed you elect to do so. Considering the complete lack of any benefit in controlling the summer generations obtained by wiping out the overwintered brood, and the increased selection pressure for resistance being exerted on this species (and its apparent willingness to oblige), we are not convinced of the wisdom of doing anything about OBLR until bloom (when you can use a B.t. material) or petal fall, when you can include Lorsban or Lannate into your curculio spray. Also, we hopefully await a favorable decision on the Section 18 application for Confirm, which would be a good choice for the summer population.

Plum curculio: Some growers favor a pyrethroid at pink to help take care of the first curcs immigrating into the block during bloom, because they don't feel they will get in soon enough with a petal fall spray to control every single one. This is an especially popular practice in mixed plantings, where some varieties are still in bloom while others have already reached petal fall.

Although it may be possible to kill some curculios this way (and it may not be very many if the residue has to last through a very protracted pink and bloom stage), the majority of adults begin damaging the fruit clusters after the petals fall; in fact, it takes a couple of warm days after this point until any are actually working in the trees. Despite the philosophy that ANY curcs that can be killed justify a spray, it is our opinion that the long-term effects of excessive pyrethroid sprays constitute a strong argument against this practice. Multiple-year field trials conducted by Harvey Reissig have shown that the addition of a pink pyrethroid spray does not reduce fruit damage by curculio when compared with normal programs consisting of petal fall-plus-cover sprays. You would come out ahead by spot-treating the trees that reach petal fall earlier, or by making a quick border row spray to hold off the invasion for a few days while the straggling varieties catch up, after which a full cover petal fall spray could be applied.

Rosy Apple Aphid:In case you've forgotten, pink is the time to address RRA control also; don't wait until petal fall. Refer to last week's issue for details on the recommended approach.

ERRATA

In last week's article on "Mite Control Without Omite" by Regina Rieckenberg, one of the statements about Morestan in the second paragraph said the opposite of what was actually intended, and we failed to pick up on it. The sentence in question should have read: "Morestan has activity primarily on eggs, and has a very short residual, so back to back sprays are needed."

Remark [3] regarding pear psylla control in the Recommends (p. 118) has already had some attention in the April 1 issue because of outdated information, but I should have kept on reading to discover an old chestnut pertaining to Pydrin that's certainly outlived its usefulness. Instead, substitute the following: "Seasonal maximum for Asana is up to 0.2 lb a.i. during the dormant to white bud stage and up to 0.225 lb a.i. between bloom and harvest (but no more than 0.375 lb total a.i./Acre per season)."


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
Dep. of Entomology, NYSAES
Geneva, NY 14456-0462
Phone: 315-787-2341 FAX:315-787-2326
E-mail: art_agnello@cornell.edu


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