the rate of evaporation. A droplet moving in an airstream must 

 have a certain minimum momentum in order to penetrate through the 

 layers of air flowing around it. Because of the greater influence 

 of drag force the smaller droplets traveling in relatively slow 

 airstreams tend to follow the random turbulent fluctuation of the 

 airstream more closely and therefore travel a more devious path 

 than the larger droplets. 



Considering these facts it is evident that impingement of 

 droplets produced by low volume sprayers would be lower during 

 periods of low R.H. or in slow moving airstreams. Workers in New 

 York have shown that under conditions of high evaporative potential 

 which commonly occur during the growing season, spray droplets may 

 lose more than 40-6 of their original volume during transport time 

 from sprayer outlet to the foliage. They found that when the R.H. 

 was 95% there was only about 5% water loss at 30 feet from the 

 sprayer outlet, while 20-251 was lost when the R.H. was M% . Spray 

 deposits in the top of trees was only 37% as much at 351 R.H. as 

 when the R.H. was 951. 



Summary of Conditions Affecting Airblast Sprayer Performance 



A number of experiments designed to evaluate the performance 

 of several conventional and low volume sprayers for apple pest 

 control have been conducted in recent years. During the past 2 

 years Dr. L.A. Hull, Entomologist at the Fruit Research Laboratory, 

 and I have evaluated several sprayers for control of green apple 

 aphid and spray distribution patterns. Control levels of aphids 

 have been correlated with chemical deposits on leaves as measured 

 chemically using dicofol and visually using a fluorescent tracer. 

 A number of conclusions can be drawn from these experiments and 

 a summary of several follows: 



1. Sprayer size and design directly affects spray coverage and 

 pesticide deposits and determines the size of tree that can 



be properly sprayed. Conventional airblast sprayers having an 

 airmass volume of 65,000 cu. ft. per min. or greater with velo- 

 cities of 120 mph or more and the larger low volume sprayers 

 may be used effectively on standard orchard trees up to 22 feet 

 in height. Low volume sprayers of the small to intermediate 

 size v\?hich are power take-off operated perform better in dwarf 

 or semi-dwarf trees with heights of 12-15 feet. 



2. The tree size in height and density directly affects the velo- 

 city of the airmass by blocking or slowing air movement and 

 subsequently affects the amount of chemical deposit. Sprayers 

 should have sufficient air volume and velocity to blow through 

 the top of the trees to be sprayed. 



