Scaffolds 01 index

(Andrew Landers ajl31@cornell.edu, Agricultural & Biological Engineering, Ithaca)

Maximum economic return will be obtained with a finely tuned sprayer as it provides better disease control and is more cost-effective.

There are three factors that affect application rate:

Forward speed affects both dose rate and volume rate – double the speed and you halve both. Remember to drive at a speed that provides a stable boom. Too fast will result in boom bounce, leading to incorrect nozzle height above the target. Too slow will result in not applying pesticides in a timely manner, failing to cover the ground and keeping on top of disease outbreaks.

Nozzle selection is so important. Droplets are measured in microns; 100 microns is about the thickness of a human hair. Remember that large drops bounce; such droplets are over 300 microns and are created by using low pressures, too large a nozzle orifice and/or worn nozzles. Too fine a droplet (less than 150 microns) will drift, resulting in damage to neighboring properties, nuisance complaints and equally important, reduced application to the target.

Select the correct nozzle for the target. Use a nozzle that creates a fine spray for fungicides and insecticides. A medium quality spray is ideal for herbicides. Coarse spray is ideal for applying liquid fertilizers and pre-emergent herbicides to bare soil.

The rate of nozzle wear will depend upon the pressure used, type of pesticide being used and nozzle material. Note that ceramic nozzle tips, while expensive, do last much, much longer than cheap plastic nozzles. Nozzles made from modern polymers are also superior to cheap plastics. Brass is the worst nozzle tip to use, as it wears out so rapidly.

Nozzle abuse is a problem caused by operators using a piece of wire to clean out a blocked tip. Rodding out a ceramic tip with a piece of wire is the kiss of death, it will damage it, thus affecting flow rate and spray pattern. Remember, good filtration and agitation will prevent nozzle blockage. If a nozzle does block, replace it with a spare and blow out the blockage with an airline or use a bristle brush; NEVER kiss nozzles!

System pressure affects flow rate, nozzle life, droplet size, fan shape and penetration into the target. Too low a pressure will result in large droplets dripping off the target. Too high a pressure results in off-target drift and poor application. Beware that some automatic electronic controllers will alter flow rate by using a butterfly valve to change system pressure. Always work within the boundaries recommended in the sprayer manual.

Table 1 The inter-relationship between the factors affecting application rate

Good pre-season maintenance and calibration is so important. Articles have been published by the author on this subject. They are also obtainable at: http://aben.cals.cornell.edu/extension/pestapp/boom.html

Remember, good pesticide application is a wonderful blend of technology and common sense.

So you think you are a good sprayer operator?

(Answers may be found at end of newsletter)

1. A radar type speed indicator obtains signals from

a) a wheel mounted induction coil.

b) the tractor transmission.

c) the field surface.

d) the sprayer pump drive.

2. Increasing the operating pressure of a sprayer results in

a) narrowing the nozzle jet angle.

b) decreasing droplet size.

c) increasing droplet size.

d) increasing output and droplet size.

3. Drift from a sprayer is most likely to be increased by

a) high operating pressures.

b) boom too near ground.

c) high application rates.

d) high forward speed.

4. With an automatic rate control system in operation on a sprayer, increasing forward speed causes increased output by

a) producing larger droplets.

b) increasing system pressure.

c) increasing droplet size and pressure.

d) reducing system pressure.

5. The use of 110° nozzles on a sprayer enables

a) the boom to be raised higher above the target.

b) nozzles to be placed closed together.

c) boom to be set closer to the target.

d) smaller nozzle orifices to be used.

6. The correct procedure when turning on headlands during spraying is

a) turn off power take-off.

b) continue to spray.

c) turn sprayer main control valve to off.

d) turn sprayer boom valves to off.

7. When calibrating a sprayer to apply 20gallons/acre results show 18 gallons/acre is being applied. To rectify this error, changes should be made to

a) pressure.

b) nozzles.

c) speed.

d) speed and pressure.

8. Sprayer calibration should be carried out

a) by the dealer before delivering the sprayer.

b) when poor spraying results can be seen.

c) at the beginning of each spraying period.

d) after at least 500 acres of spraying.

Chem News 5.14