The advantages of spray concentrations of greater than 3X may be outweighedby a decrease in effectiveness for some pests (mites, aphids, scale, sporulatingscab lesions). Dilute sprays are generally more effective for applying oil,growth regulators and foliar nutrients.
As the gallons of water are reduced, errors in calibration or spray patternbecome more critical. Concentrate spraying creates greater sensitivity towind speed (should be no more than 5 mph), drying conditions, sprayer speed(should be no more than 2.5 3 mph), and accurate sprayer calibration. Problemswith phytotoxicity and incompatibility between spray materials are increasedwith higher concentrate sprays. The amount of oil used should not be morethan 3 times the recommended rate per 100 gallons dilute even if the sprayconcentration is over 3X.
The increase in efficiency from using less water per acre reaches a pointof diminishing returns, and increasing problems, when spray concentrationis increased beyond 8X.
A 20% reduction from the recommended dilute rate pesticide dosage is typicallymade when the pesticide is applied in a 3X or higher concentrate spray.This is based on the idea that, compared to a dilute application, less pesticideis needed in a concentrate spray because less is lost to runoff. Concentratespray dosage reduction seems to work well for most pests and pesticides,but it is not appropriate for some growth regulators. Caution is advisedbefore taking the 20% reduction for situations where coverage or controlis difficult. Concentrate pesticide dosage reduction is definitely not recommendedfor sterol inhibitor fungicides.
EXAMPLE D: Suppose your sprayer is set up to deliver 1/3 of the TRVdilute gallons per acre, and that you are preparing to apply captan 50WP.The recommended dosage is 2 lbs./100 gals. dilute. Because this is a 3Xspray, the 2 lbs./100 gals. could be tripled to 6 lbs./100 gals. However,because spraying at 3X or higher is thought to result in less chemical beinglost to runoff, a 20% reduction in the chemical rate is usually made. Thus,the amount of captan used would be 6 x 0.8 = 4.8 lbs./100 gals. for a 3Xspray mix.
Even for the materials which have been used successfully with the concentratespray dosage reduction, the 20% reduction should not be taken as a fixedrule. Consider foliage density, pest biology, pest abundance, applicationconditions and other factors affecting spray effectiveness before reducingthe concentrate spray dosage.
Some (but not all) research indicates that more consistent pesticide dosagecan be had by adjusting the estimate of TRV dilute gallonage upward as canopydensity increases in the summer. Rather than having to recalculate TRV,an easier way to adjust pesticide dosage is to take less than a 20% reductionin pesticide dosage for concentrate sprays made after first cover. Yourown experience and orchard history are the best guide to fine tuning pesticidedosage.
A TRV dosage method used in Maryland calls for spraying at 1/7th to 1/8thof the dilute spray volume(i.e. 78X concentrate spray), but mixing pesticidesat no more than 35 times the label rate per 100 gallons dilute, with nofurther discount for concentrate spraying. The Maryland method calls forlower pesticide dosages than the TRV method described in this guide. Forexample, in the method described above for New England, dosage for a spraymade at 7X would be about 7 x 0.8 (i.e. taking 20% dosage discount) = 5.6times the label rate per 100 gallons dilute. The Maryland method has notbeen field tested in New England. There may be regional differences in thepest complex and spraying strategy that make the Maryland method unsuitablefor New England. Lower doses that work where regular applications are madeto maintain protective residue to manage continuous pressure from multiplepests may be inadequate for single targeted applications delayed until thresholdlevels or infection conditions have occurred.
A number of products are sold with the claim that they help with or improvethe efficacy of spray applications. These materials are known collectivelyas adjuvants. Two of the most common adjuvant types are spreader (wettingagent and surfactant are similar) and sticker. A spreader is formulatedto allow spray droplets to spread more evenly on the leaf or fruit surface.A sticker is formulated to increase adhesion of spray chemicals to a surfacein order to reduce loss from weathering. Other functions offered by typesof spray adjuvants are: acidify or buffer the pH of the spray solution,reduce tank foaming, improve compatibility of tankmixes, reduce spray drift,improve uniformity of deposit, modify spray evaporation, and enhance penetrationor translocation.
Selecting and using adjuvants requires the same attention to detail thatis given to selecting and using pesticides. Read the adjuvant and pesticidelabels to see if they are suitable for each other, and for the sprayingconditions and other particulars of your situation. Use a jar test to seeif the materials are physically compatible. Follow adjuvant label rates.As with pesticides, more is not better and can cause serious problems. Ifpossible, evaluate product performance. For example, if a spreader is used,check spray deposit on foliage. With too much spreading, the spray willjust run off the leaves in a straight line.
Adjuvants can be valuable tools. However, many pesticide formulations alreadyinclude necessary adjuvants, and adding additional materials may cause plantinjury (especially with EC formula tions), reduced pesticide effect, ormay provide insufficient benefit to justify the extra cost.
ALTERNATE ROW SPRAYING
By traveling down only every other row when spraying, the amount of timeand pesticide used per acre can be cut in half for a given application.Alternate row spraying requires a sprayer that has adequate air volume andvelocity to provide at least light spray coverage on at least 90% the treewith each oneside spray. The sprayer should push some mist 10 to 15 feetbeyond the tree. For the next spray, the sprayer is driven down the rowsthat were not traveled during the previous spray. If alternate row spraycoverage is adequate, applications do not have to be made exactly twiceas often as an everyrow spray. In other cases, applications are made twiceas often, but the amount of pesticide used each time is less than half ofwhat would be used for an everyrow spray, because of the short intervalbetween renewed pesticide cover age. As a result, pesticide usage over theseason can be significantly reduced.
Alternate row spraying may increase the sur vival of beneficial species,and may reduce the chances of pests developing pesticide resistance. Inemergency situations it allows for twice as many blocks to receive someprotection in a given time period, as opposed to getting half of the blockstreated with full block application while the other blocks receive no protectionat all.
Mention of alternate row spraying in this publication is not meant to bean endorsement. The first spray of the season should achieve full blockcoverage. Contact the Cooperative Extension for more information.
BORDER ROW SPRAYS
Border row sprays have been used effectively in situations where an insectpest is not arising from within the orchard, but only enters from beyondthe perimeter. If the pest's behavior is such that it will stop in borderrow trees before penetrating further into the orchard, then an insecticidein the border row trees may give sufficient control without having to treatthe whole block. With block history of low or moderate pest pressure, knowledgeof hot spots, and monitoring of pest activity and the weather, this tacticmay be useful for the beginning and end of the plum curculio and apple maggotegglaying periods. Until further research and grower experience demonstratesotherwise, it may be too risky to depend on border row sprays during theperiod of peak damage activity for these pests.
Do not spray the edge of woods adjoining the orchard. Problems with thisare legality and disruption of habitat for natural control species.
Border row treatments may not provide satis factory control if the populationof immigrating pests in the surrounding area is very large, if the bordertrees are small, or if they are lightly cropped. When a borderonly treatmentis used, monitor for pest activity inside the block to see if pests arepenetrating the border.
USING AERIAL APPLICATION SERVICE
Qualified aerial applicators have effectively controlled severe pest problemswith the possible exception of mites and powdery mildew. To reduce the potentialfor phytotoxicity and fruit russeting from aerial pesticide application,give special consideration to pesticide selection and combinations.
Availability of pesticides in forms adaptable to ultra high concentrateapplication is essential for aerial spraying. Location of sensitive andother nontarget areas must be identified and communicated to the pilot.
The following precautions are to be used as a guide in obtaining satisfactoryresults from aerial pesticide application, and in reducing the risk of injuryto foliage and fruit finish. Check pesticide label and Special LocalNeeds registrations before use. A copy of the Special Local Needs (24C)label must be in the possession of the applicator.
1. All blocks being treated aerially should be thor oughly oiled with groundequipment before overwin tering European red mite eggs hatch.
2. Chemicals should not be applied in volume of water less than the amountstated on the label.
3. Applications during hot or poor drying conditions should be carefullyavoided.
4. Blocks receiving aerial pesticide applications should be scouted forinsect and disease conditions each week. The grower should be prepared totreat with ground equipment if conditions warrant.
5. Due to the extremely low gallonage applied per acre, it is essentialthat growers have exact knowledge of block sizes for accurately determiningaerial application rates. Over or under application can easily result inphytotoxicity or unsatisfactory control. Knowing the acreage is also necessaryto accurately calculate the fee for aerial application.
6. Avoid combining more than two chemicals for any one application, unlessthe combination is known to be safe.
COMMON PROBLEMS IN SPRAY PROGRAMS
Problems with inadequate pesticide efficacy and phytotoxicity are oftendue to inaccurate sprayer calibration and pesticide dosage. Using the methoddescribed in the Sprayer Calibration section before the spray season beginsreduces the chance of errors made in haste.
COVERAGE / UNIFORMITY
Sprays applied in early morning, evening or at night are likely to resultin higher deposition of chemical on the trees, and with greater uniformitythrough the tree. This is because: 1) wind at these times is usually less;and 2) temperature is usually lower and humidity is usually higher, resultingin less evaporation of spray droplets in flight.
Best results are obtained when the sprayer has enough fan capacity to blowthe spray through the trees and at least 10 feet above the tree tops, evenwhen operating against a 5mph wind. The effective coverage is less thanthe extent of the visible mist. The mist that carries farthest from thesprayer contains very small droplets that reflect light but contain verylittle of the spray material.
Maximum spray deposit requires that the droplets be forced against the targetsurface. Spray that drifts at slow speeds past tree tops is not sufficient.
Excessive travel speed results in poor cover age of the more distant portionsof the tree. Adjust nozzles and air vanes to obtain the desired spray pattern.Deposit uniformity can be evaluated by use of watersensitive paper stripsplaced at tree top, interior and a couple of exposed locations. Water sensitivepaper is available from orchard suppliers.
Sprayers with small airblast capacity can provide satisfactory coverageif trees are small and open, and not far from the sprayer. If the sprayerproduces small droplet sizes (i.e. mist blowers and air shear sprayers withaverage droplet diameter of less than 100 microns), or has low air displacementcapacity, then travel speed should be no faster than 2 mph, and sprays shouldbe applied only when there is little or no wind.
Large trees require a sprayer with a large air displacement capacity. Matchthe sprayer capability to the tree size. Air displacement capacity and airspeed are different components of sprayer performance.
Adequate coverage for mite control and disease prevention with summer spraysmay require removal of water sprouts. This is best done before shoots hardenin June, while they can be pulled by hand.
Growers contemplating use of highly concen trated sprays (low volume) shouldbe aware of the increased difficulty in obtaining uniform coverage. Chemicaldeposit on foliage and fruits near the sprayer is often much higher thandesired when sprays are concentrated. This is particularly undesirable withgrowth regulator chemicals; and where deposit on fruit might exceed legalresidue tolerances at harvest; or where fruit finish might be damaged.
Relatively high water volume (not less than 1/4 Dilute Gallonage) for miticidesprays has provided better control than lower volume sprays, possibly becausemore mites were wetted with chemical. Relatively high volume spray shouldalso be used in situations where redistribution of chemical by subsequentrainfall may not improve protection, such as in postinfection or eradicationsprays for apple scab, streptomycin spray to prevent fire blight, or spraysfor powdery mildew control.
PESTICIDE SELECTION AND TIMING
In addition to its spectrum of activity, each pesticide has a uniqueset of characteristics that must be considered before using on the crop.Some of the most important of these are: applicator and environmental hazards,effects on beneficial insects and mites, restricted entry and preharvestintervals, tankmix compatibility and phytotoxicity risk, previous pesticideor likely subsequent applications, residual protection, sensitivity to weatherduring application or to temperature for optimum performance, and resistancemanagement.
The choice of pesticide can affect the timing of the application, or viceversa. Other factors that affect spray timing include: growth stage of treeor fruit; scouting observations; pest lifestage; activity pattern of pestor of honeybees and other beneficial species; weather conditions prior toapplication (e.g. scab infection period), weather during application (e.g.sterol inhibitors), or the weather forecast for afterwards (e.g. do notspray oil just before a frost).
PEST RESISTANCE TO THE PESTICIDE
Pesticide resistance, as manifested in the orchard, is when there is a measurablereduction in the efficacy of a pesticide due to heritable metabolic, physical,behavioral or other trait(s) within the pest population. Through a phenomenoncalled cross resistance, a population that develops resistance to one pesticidecan become resistant to other pesticides that are chemically similar eventhough the pests have never been exposed to the other materials. Also, apopulation may develop independent multiple resistance traits to differenttypes of chemicals.
Once acquired, the resistance may be stable, or it may decline if subsequentgenerations of the pest are not exposed to the pesticide. There are examplesof both cases among apple pests. Apple scab resistance to dodine (Syllit)is thought to be quite stable, but mite resistance to dicofol (Kelthane)can decline over several years if subsequent generations are not exposedto the chemical and the selection pressure for resistance.
In addition to fungicides and miticides, resistance is also a concern forother categories of pesticides used on apples: bactericides, herbicides,insecticide, and rodenticides. The loss of effective pesticide options fromregulatory decisions, and the fact that few new apple pesticides are beingregistered, increases the importance of practicing resistance managementto preserve the utility of the remaining materials.
Resistance management strategies: The potential for a pesticideresistantpest population developing depends on interaction between the biologicaland chemical factors of each situation. One consistent guideline is thatreducing the number of times a pesticide is used decreases the potentialfor resistance to that chemical. Making full use of biological, culturaland other nonpesticidal controls is a key factor in resistance managementbecause these methods suppress the pest population without exposing it tothe genetic selection pressure that leads to resistance. In addition, naturalenemies of pest mites and insects can actually reduce resistance becausethe enemies attack both resistant and susceptible individuals, thereby dilutingthe breeding advantage of the pesticideresistant individuals. Because ofthe differences among pests and pesticides, a resistance management strategymust be tailored for each situation. A resistance management strategy thatworks for one class of pesticides may increase the problem if used incorrectlyfor others. For example, combining two types of fungicide has worked tomanage resistance in apple scab fungus populations. This is because individualscab spores that are resistant to one fungicide are still killed by theother, and so the resistant spores cannot reproduce their resistant trait.But combining two or more insecticides or miticides has been found to failbecause the pest insect or mite population is likely to develop resistanceto all of the combined materials creating a much worse problem. Rotatingbetween products with different modes of action so that any one chemicalis used as infrequently as possible is a better approach for preventinginsecticide and miticide resistance.
BREAKDOWN OF PESTICIDES
In alkaline water mixture (pH above 7.0) many pesticide compounds breakdown to inactive forms. Carzol, Imidan, Lannate, and Vydate are known tobe susceptible to breakdown if kept in a solution with pH above 7.0. Informationon specific compounds is sketchy, but at pH well above 8.0, a pesticidemay lose of 50% or more of its effectiveness within one hour. To preventthis prob lem, it is important to:
€ Avoid tankmixing pesticides with materials that are strongly alkaline(observe label cautions);
€ Check the pH of the water source used to fill the sprayer tank; and
€ Check the pH of finished tankmix combinations. Test strips that indicatepH by color change are available from pharmacies and other sources.
Vinegar has been used to acidify alkaline spray mixtures. Caution shouldbe used in adding vinegar so that over acidification does not occur. Eightfluid ounces of 5% acid vinegar may be more than enough to acidify 300 gallonsof water. Buffering additives are available that can hold the spray solutionto about pH 6.0.
Pesticide can also loose efficacy because of breakdown in storage. Labelsgive storage requirements, some of which is presented in Table 11.
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