Connecticut Fruit Growers Newsletter
March 26, 1997
IN THIS ISSUE:
* How important are beneficial mites in apple orchards?
* A pesticide program for preserving beneficial mites.
* How much pesticide per acre?
* Subscription reminder.
HOW IMPORTANT ARE BENEFICIAL MITES IN APPLE ORCHARDS?
In Connecticut there are 2 or 3 species of mites that can, under the right conditions, keep European red mites below damaging levels. The Aright conditions@ include an orchard environment with little or no exposure of the beneficials to certain harmful pesticides. As complex as pest management already is in commercial orchards, any additional limitation on which pesticides are appropriate, and which are not, must hold the promise of being worth the effort. If safe, effective pesticides are available at reasonable cost, there is little incentive to risk disappointment with an alternative program that attempts biological mite control.
Two new classes of chemical miticides, Agri-mek on the one hand, and Apollo and Savey on the other, seem to be safe and effective. While not cheap, they can be cost-effective, and if used wisely, should continue to be effective for many years into the future. But these new materials can be used only in the early part of the growing season. If early season treatment is missed, or not highly effective, there is no reliable Arescue@ miticide available for summer use. The BASF Corporation has a new miticide, Pyramite, that has been very effective in trials, and may be given a federal label for orchard use in 1997. If Pyramite becomes available, and proves to be cost-effective, we will again have to weigh the merits of trying to establish biological mite control. But only if one knows exactly what is required to make biological mite control work on ones own farm will one be able to judge the relative merits of new miticides.
I would therefore encourage growers to commit one block to a 2 year program aimed toward biological mite control. I have outlined a guide for such a program below. The guide is based on the observations and work of researchers in the Northeast and North Central states, and eastern Canada. It has resulted in successful biological control of ERM in my Tolland orchard, through strong full-season activity of Z. mali, augmented by variable populations of A. fallacis. These two beneficial mite species are present throughout Connecticut, but typically their populations are too low to provide ERM control, presumably because typical pesticide programs keep them suppressed.
A PESTICIDE PROGRAM FOR PRESERVING BENEFICIAL MITE POPULATIONS IN APPLE ORCHARDS
* Substitute captan for mancozeb and other contact fungicides;
* Use Benlate or Topsin M only in the final summer spray;
* Avoid use of synthetic pyrethroids before and after bloom;
* Avoid use of Vydate, Lannate, dimethoate, and Carzol;
* Minimize use of Lorsban, Sevin, Kelthane, and oil.
Notes About the Spray Program Below
(1) This program will be most appropriate in blocks that have not had a recent history of serious damage from Rosy Apple Aphid (RAA), Tarnished Plant Bug (TPB), or San Jose Scale (SJS). Where RAA treatment is necessary, a Half Inch Green application of Lorsban or Supracide is suggested, but you should expect there will be some damage to beneficial mites from either of these sprays. The only effective pesticides for TPB are the synthetic pyrethroids, Asana, Ambush and Pounce. Use of any synthetic pyrethroid can be expected to prevent development of effective populations of beneficial mites during the year applied. A discussion of SJS control options will be found in a separate article in this newsletter.
(2) Substitute dodine or thiram for captan in sprays that must be applied within 10 days before or after an oil application, in order to avoid oil-induced captan injury to foliage.
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Before Half Inch Green [Scab, San Jose Scale]
Captan alone, as needed before rains to protect against scab. (Dodine is an alternative if you are confident you do not have dodine-resistant scab.)
Delay SJS control to post-bloom.
Half Inch Green [Scab, ERM, SJS, RAA]
Captan alone as protective program. No treatment for ERM, SJS, or RAA at this time.
Tight Cluster to Pink [Scab, Mildew, Rusts, Black Rot, ERM, TPB]
Captan plus Rubigan, Nova, or Procure on 10-day intervals. If Apollo or Savey miticide was used last year, wait until the Petal Fall stage to treat ERM using Agri-Mek if needed. If neither Apollo nor Savey was used last year, use one of them now. A tank-mix addition of spray oil at the rate of 1% of final volume substantially improved ERM control in 1996 Cornell trials in Western New York. Substitute thiram or dodine for captan if you include oil.
Pink through Petal Fall [Scab, Mildew, Rusts, Black Rot, ERM, Leafminers]
Captan plus Rubigan, Nova, or Procure on 10-day intervals. Monitor for eggs of tentiform leafminers, but make no treatment for leafminers before Petal Fall.
Petal Fall through early June [PC, EAS, GFW, Leafminers, ERM, Scab, Mildew, Rusts, Black Rot]
Imidan or azinphos methyl as soon as conditions are favorable. Repeat once or twice as needed after 7-10 days. Monitor PC with inverted umbrella and Abumper@ at orchard border-rows.
If needed for ERM, apply Agri-Mek (plus 1 gallon summer oil per acre) within 2 weeks after Petal Fall. To minimize contact-kill of beneficial mites, apply in only one-third the full-wetting gallonage. If Agri-Mek is not needed for ERM, do not use it for leafminers. Instead, wait until second generation leafminer egg laying begins in late June, when Provado can be used for both leafminers and leafhoppers.
Also: Captan plus Rubigan, Nova or Procure.
Mid-June to Harvest [Sooty Blotch, Flyspeck, Bitter Rot, Black Rot, AM, Coddling Moth, Lesser Appleworm, Leafhoppers, Leafminers]
Captan 80 at 1 1/4 lbs per 100 gallons, 2 week intervals. In last spray only: add Benlate or Topsin M for extended protection beyond 30 days. (Note 14 day preharvest interval for Benlate).
Begin Imidan or azinphos methyl when AM captures on sticky lures exceed threshold, or by July 15, whichever comes first. Repeat at 2 week intervals through last week in August. (Note 7 day preharvest interval).
Also: Monitor weekly for leafminers, and leafhoppers. If leafminer threshold is exceeded (New York stop-sample method) apply Provado. For very high populations, apply a second Provado spray 10-14 days after the first.
If White Apple Leafhopper or Rose Leafhopper exceeds one per leaf, average, apply Provado according to label.
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IS OIL NEEDED FOR SAN JOSE SCALE CONTROL?
For many years, prebloom full-wetting 2% oil sprays have been recommended as important for control of European red mite eggs (ERM) and San Jose scale (SJS). The killing of overwintered scales by oil is most effective between Green Tip and Half Inch Green. If ERM can be controlled by rotating 2 or 3 effective non-oil miticides, or by beneficial mite populations, must oil still be applied for SJS?
There are no reports of SJS having been kept below economic levels by beneficial species, as far as I am aware. At Tolland, when I have omitted prebloom oil, and minimized summer use of insecticides, SJS has, within 2-3 years, built to an economic problem.
There are currently only two potentially effective options to an early oil spray: either an organo-phosphate directed at winged SJS males, at about bloom time; or a series of organo-phosphate sprays directed at the young crawler stage of the pest in the summer. The first option is not practical in bearing-age orchards, because the flight often occurs during bloom, when insecticide sprays would kill pollinator insects.
To understand the timing requirement for sprays directed at crawlers, we need to review some facts about SJS. Young SJS are born live under the protective coating of overwintered females. They then emerge and crawl about for only about one day, attach their mouthparts to bark, leaf, or apple tissues and remain in that spot for the few remaining weeks or months of their lives. Emergence of new crawlers continues over a period of 7-8 weeks, beginning during the second half of June in this area. A second generation begins in August, if the first generation is not killed.
Young SJS quickly become resistant to contact insecticides, as a consequence of the wax coating that soon covers them. Assuming residual pesticide activity of 2 weeks duration, effective contact pesticides must be applied at intervals of not more than 2 weeks during the period of crawler emergence. Excellent control of the first crawler generation would preclude appearance of significant numbers of a second generation, as the pest does not move far from its origin. Winds can move SJS only within a tree, or to an adjacent trees. (Eventually, new populations appear at greater distance from their origins, presumably having been carried there on the feet of birds.)
Imidan and azinphos methyl are still considered effective against SJS crawlers if applied at the correct time. I plan to monitor SJS emergence, and will announce in this newsletter the expected time of appearance, based on degree days, as well as first actual sighting at Tolland.
In addition to Imidan and azinphos methyl, good control of SJS crawlers is possible with biweekly sprays of Penncap M, Lorsban 50W, or Diazinon. Each has limitations. Diazinon is reported to sometimes produce fruit russeting on russet-sensitive varieties when used in June. Lorsban is harmful to A. fallacis and T. pyri beneficial mites. Penncap M is limited to those orchards where flowerings weeds do not attract honey bees into the orchard.. Provado is labeled for SJS, but there is not yet much evidence to indicate how effective it is.
Regardless of the pesticide used, unless you can obtain good coverage on all parts of the tree, summer sprays will not provide 100% control. Foliage may interfere with complete coverage if trees are not well pruned. But then, in the dormant season SJS control by oil is likely to be less than perfect, due to winds, frost, wet orchard floor, or proximity to captan application.
My suggestion: Choose one block where good spray coverage is not difficult to achieve. In all other blocks try to get a 1X, or 2X concentrate oil spray on before Tight Cluster, but in this block, plan to use the full-season captan program described above, omitting oil.
If SJS is already established in the block, you will probably need one or two more summer insecticide applications than you need where prebloom oil is effectively used for SJS control.
HOW MUCH PESTICIDE DOES ONE ACRE OF ORCHARD NEED?
Suppose the label on a package of Fry-It tells you to use one pound of the product per 100 gallons, dilute, in up to 400 gallons of water per acre. Let=s say you want to apply your spray in just 50 gallons of water per ace. How many pounds of Fry-It should you use for each acre you will spray?
Of course, the answer will be different for different orchards, depending upon the gallonage required to completely wet an acre. If the full-wetting gallonage is 100, that block should get one pound of Fry-It per acre. If full-wetting gallonage is 300 gallons, it should get 3 pounds of the hypothetical pesticide.
Because today=s orchardists use low-volume sprays, rather than full-wetting sprays, they typically don=t know the full-wetting (dilute) gallonage requirements of their orchard blocks. How, then, will they know how much pesticide to apply to an acre? Some say tree row volume (TRV) is the answer. I don=t agree, though I used to promote that method, and I still consider it better than the Aone size fits all@ approach. (Here I am referring to pesticide labels that indicate only per-acre amount, but not the amount per 100 gallons dilute.)
My complaint with the TRV method for estimating dilute gallonage per acre is just that it can be very inaccurate. Is there a better way? Yes, there is. The better way is not new - I first described the technique in the April 5, 1990 issue of this newsletter - but I think it is worth revisiting.
The TRV method is an indirect way to estimate full-wetting gallonage. But you will not know whether this estimated gallonage is within 10%, or even 50% of the true full-wetting gallonage. Full-wetting gallonage is a function not only of the tree surface area in an acre of orchard (which the TRV method attempts to approximate by row volume) but it is also very much influenced by spray deposit efficiency. A 100% deposit efficiency would indicate that all the spray departing the nozzles deposits on tree surfaces; no waste! One hundred percent spray deposit efficiency is unattainable. Some spray always goes over the top, or through the tree, or falls to the ground, or is otherwise prevented from impinging on target surfaces.
A Adilute@ spray is one that achieves full wetting of all tree surfaces with one pass on each side of the tree, using an airblast sprayer. A Alow-volume spray@ is one that requires 2 or more passes on each side of the tree to achieve full wetting of all tree surfaces.
Deposit efficiency of dilute sprays can be much different than that of low-volume sprays, because dilute spray droplets are larger and heavier. Thus, using a dilute spray to determine full-wetting gallonage is not useful where you will use low volume for pesticide sprays. In the technique described below, full-wetting gallonage is directly determined with your sprayer at the concentrate (low volume) settings that you currently use, or any other settings that you may prefer.
The relationship between full-wetting gallonage and low-volume gallonage is easily shown. You need only find out how many passes it takes to fully wet the tree with your equipment, as calibrated for low-volume spraying. If it takes 3 passes, you would be correct in concluding that each pass applied 1/3 the dilute gallonage, and that you should use 3X the Aper 100 gallon@ amount of pesticide recommended for dilute spraying.
To get the most from your spray calibration efforts, consider the following details:
1. Water-sensitive paper (WSP) makes it easy to see when the point of full-wetting has been reached. WSP is available from dealers of spray equipment and IPM supplies. It is commonly sold in packets of cards with one yellow side. Wherever a water droplet impinges on the yellow, a blue spot appears. When fully wetted by one or more passes of the sprayer, the card will be 100% blue. Anything less than 100% blue indicates it has not been fully wetted. I cut the cards to 1" x 2", fold them to one-inch squares, yellow side out, and mount them horizontally (one yellow surface facing the sky; the other facing the ground) on a pole at 2 foot intervals. For stability, the pole (hollow tubing) is placed on a steel pin, such as a horseshoe stake or 3 foot length of re-bar that has been driven into the ground at the center of a tree row.
2. You will endure less frustration if you try this technique first at a relatively windless site, when no fog is present. Fog will turn the cards blue.
3. With the first pass of the sprayer you can determine whether nozzling changes are needed to provide uniform coverage from the lowest to the highest paper card. Turn off any un-needed nozzles. Also, if the first pass turns all yellow surfaces blue, you will need to reduce the spray output. Aim for an output rate that will require at least 2 passes on each side of the sprayed row to fully blue the cards. Drive at the exact engine RPM and gear settings that you will use for pesticide spraying.
4. If some cards show blue mostly on the lower surface, it may be because the airblast is very strong, sending droplets into the next row. If so, make a pass from one row away from the cards to see whether the blow-through droplets are settling on the adjacent row. If blow-through droplets are too small, they may not settle. If considerable blow-through occurs from the adjacent row, you should include that spray when determining the full-wetting gallonage. Therefore, in running the test (in item #6, below) you may need to drive not only in the alley at each side of the pole, but also in the next-closest alley on each side of the pole.
5. If some cards show blue mostly on the upper (sky-facing) surface, it may be due to weak airblast, or inadequate liquid output from nozzles located below those card positions. Foliage that is very low is unlikely to get good deposit on its lower surface, and you should consider removing such low limbs.
6. When your trial passes show the spray pattern is uniform, install fresh WSP cards and drive by each side of the tree once. Inspect the cards and estimate percent blue. They should be not more than about 45-50% blue. Go again on both sides and check cards again. Repeat as many cycles as needed to produce a little less than 100% blue.
If the cards are, say, about 80% blue after 4 cycles, you are applying about 20% of a full wetting spray with each two-sided cycle (80 divided by 4 equals 20).
Because each pass of the sprayer applies 20% of a full-wetting dose in this example, you would need 5 passes to achieve 100% blue (100 divided by 20 equals 5). Therefore, you should use 5 times the recommended dilute amount of pesticide per 100 gallons when spraying this block of orchard with this sprayer, at the nozzle and speed settings used in this trial. Any different conditions, such as different speed or different make of sprayer, may result in a different deposit efficiency, which might result in a different full-wetting gallonage in this block.
7. The above technique provides an accurate determination of pounds of pesticide to be included in each 100 gallons of spray mixture, even if you have not determined how many gallons of mixture you apply per acre.
You should also know the Aper acre@ gallons you apply in each block, however, because that knowledge allows you to figure out how many pounds of pesticide you are applying per acre.
Gallons per acre can be determined by spraying as little as about one acre of the block. Begin with a full tank, spray a marked-out area, and go back to measure how many gallons it takes to bring the tank back up to the previous full level. One acre is 43,560 square feet. If you spray both sides for 1000 linear feet, in rows 20 feet apart, you will have spayed an areas of: 1000 x 20 = 20,000 square feet. Suppose you used 20 gallons. That would be a rate of 43.56 gallons per acre (20 x 43,560 ) 20,000 = 43.56).
Using the previous example, in which 5 passes with the sprayer would produce full-wetting, we now see that full-wetting gallonage for this example block is 5 x 43.56 = 217.8 gallons per acre.
8. Contact me if you would like information on making a pole, and attaching the cards properly.
REMINDER: Subscription renewal invoices were sent out this week to those who have not already renewed. To assure that you get the next 20 issues of this newsletter, return the invoice with a check for $11.00, payable to University of Connecticut, CES.
__________________________
David A. Kollas
Extension Pomologist
860-486-1944
dkollas@canr1.cag.uconn.edu
Editorial note: Well, no; this issue was not the continued discussion of points I heard at recent meetings, as promised in the February 14 issue. Later, maybe.
DAK
(WIN*3-17NEWS)