Stylet-Oil performance is directly related to the quality of spray coverage ― the higher the quality of spray cov- erage, the higher the performance of the oil. This is true regardless of which pest or host plant is targeted. It follows then, that when spray coverage is compromised, so too is product performance.

Growers can do a lot to enhance the quality of their spray coverage. Regardless of the type of spray equipment utilized, sprayer efficiency will be only as good as the most recent calibra- tion. For this reason, spray equip- ment should be calibrated at the beginning of each season, then weekly thereafter.

Calibration is the most important step in producing and maintaining quality spray coverage because a miscali- brated sprayer is either applying too much material or not enough. Both conditions have a direct effect on 1) pest control programs and, 2) direct costs to run a spray program.

Of the many factors which affect quality spray coverage, worn spray nozzles may contribute more to poor coverage than any other factor. When a nozzle orifice wears, the spray pattern distorts resulting in larger spray droplets and uneven application. Larger droplets don’t coat the leaf with spray material but wet the leaf before rolling to the ground ― exactly where the material should not be!

Worn spray nozzles also affect the cost of chemical applications. If your spray tip orifices are showing 10% wear and your spray costs are $50 per acre, then you are spraying $5 per acre more in excess gallonage. Multiplying $5 per acre times, say, 300 acres and suddenly ‘once around the family farm’ takes on new meaning by increasing your spray material costs $1,500 more than is necessary. Generally, nozzle manufacturers recommend replacing worn nozzles when they eject 10% more gallonage than new nozzles.

Monitoring nozzle wear can pay huge dividends to a grower ― both in the efficiency of pesticide application as well as in pesticide cost savings. With chemical costs reaching hundreds of dollars per gallon today, growers can save considerable sums of money just by monitoring and adjusting  their spray equipment on a regular basis.

Maintenance costs may also be reduced by upgrading to a harder, more durable nozzle tip material. Brass orifice nozzles are the softest material followed by Stainless Steel, Hardened Stainless Steel, tungsten steel and ceramic. The harder the material, the more wear-resistant the orifice, especially at high spray pressures or when physically corrosive materials (such as copper) are being sprayed.

Monitoring nozzle wear is well within the capabilities (and responsibilities) of every grower spraying chemicals for pest control. If, as they say, "The devil is in the details." then nozzle wear is a detail worth tracking. Additional considerations regarding sprayer / application efficiency include ―

• Periodic cleaning of nozzle strainers or screens will prevent clogged nozzles. The holes in the screen should be slightly smaller than the smallest nozzle in your system. If your mesh size is too tight, replace it with a smaller mesh number ― the lower the number the larger the holes.

• Check and replace pressure regulators before the season begins.

• For an accurate measure of spray pressure at the nozzle, temporarily install a pressure gauge at the spray boom behind a nozzle. Now adjust the pressure regulator at the pump (to compensate for the pressure drop between the pump and the nozzle) to accurately set the spray pressure at the nozzle.

• Maintain a constant tractor speed for the size / density of the crop. Doubling the tractor speed reduces the amount of material sprayed on the target by 50% ― more than enough to alter the performance of most spray chemicals.

• Spray every row, never alternate rows.

• When replacing worn nozzles, replace all the nozzles at the same time, not just the ones you think are worn. NOTE: Reducing the size of the spray droplet by one-half results in 8 times more droplets to impinge on the target (see graphic).

• Air blast or air assist sprayers provide an opportunity to propel spray droplets long distances for use on large orchard trees. However, when spraying protectant chemicals, small droplets provide superior coverage (i.e., protection) than large droplets. The problem with injecting small spray droplets into an air stream is the potential to evaporate droplets before they impinge the target. For this reason, growers using air sprayers need to "tweak" their sprayers to produce spray droplets small enough to travel the required distance but large enough not to evaporate before hitting the target.

• Moving large spray droplets using large volumes of air at high velocity can propel spray droplets long distances but has potential to injure or damage foliage / fruit. This can put plants into stress conditions which set the stage for attack by pests. Try adjusting / retrofitting your air delivery system to move a large volume of air under low velocity to minimize plant injury.
   

• Measure nozzle flow rate immediately after installing new nozzles. Write down the flow rate and use it as a baseline to compare the nozzle flow rate of worn nozzles later in the season. Replace worn nozzles when they eject 10% more gallonage than new nozzles.

• Weather conditions can raise havoc with spray timing intervals. When given the choice between spraying less material more often vs. more material less often, it is almost always preferential to spray less material on a more frequent basis. (Foliage missed by the first spray application will almost certainly be contacted by the second spray application.)

• Don’t seem to be getting residual activity from your pesticides? Maybe the material is active ONLY when it is wet at the time of application. M-Pede, Kaligreen and MKP (a foliar nutrient) are examples ― they have no residual activity after they dry (even if they are re-wet at a later date). The best time to apply these types of materials is on a cloudy, foggy day when spray droplets don’t evaporate rapidly.

• Don’t apply pesticides to wet foliage (including wet leaves from morning dew) as the spray material will roll off the target leaving little residue on the plant.
   

• Windy conditions can compromise spray coverage. When the wind speed exceeds 10 mph ― park the tractor! Otherwise, you are wasting time, money, chemicals and doing a lousy spray job.....the proverbial worst case scenario.

• Do not apply chemicals at temperatures in excess of the manufacturer’s label recommendation. Plant physiology changes as temperatures rise which can sometimes cause spray liquids to be absorbed into leaf tissue. When spraying mineral oil, the oil needs to be on the outside of the plant ― not on the inside.

• Do not spray heat or moisture stressed plants. Just applying water alone to a sensitive, heat stressed crop can cause phytotoxicity.

• When spraying row crops with ground equipment, take whatever measures necessary to insure the tractor runs over smooth ground. Holes, ruts and soft spots contacted by the tractor wheels will cause the spray boom to sway from side to side resulting in nozzles being too close or too far from the intended spray target. Spray coverage (i.e., protection) will be seriously compromised.

• There is a practical limit to the length of a spray boom. Reducing the length of the boom from, say, 60 feet to 30 feet, will often yield superior spray coverage. It may take longer to spray an acre, but the tradeoff in chemical performance may be worth it.

• Is pest control marginal with your new, low volume electrostatic sprayer? We have found that the type of spray coverage plus the type of material plus the amount of pest pressure can have a profound effect on product performance when applied by this type of equipment. Application with toxic insecticides seem to work well but application with protectant fungicides (including Stylet-Oil) often fail when using this type of equipment. This is because protectant materials perform better when applied as "wetting" sprays and 5 to 10 gal per acre applications common with electrostatic sprayers will not produce wetting sprays.

• Dust accumulations on plant surfaces can absorb spray materials (including Stylet-Oil) and compromise product performance. (How many growers have had trouble controlling mite populations adjacent to dusty perimeter roads?) To compensate for dusty conditions, 1) minimize vehicular traffic and drive slowly on perimeter roads; 2) overhead irrigation can be useful so long as it is done in moderation; and, 3) application of dust retardant chemicals (such as lignum sulfonate) can be helpful.