348 CONTROLLING INSECTS AND DISEASES 



triangular outline requires less material than one with dense 

 foliage and a full head circular in outline. The amount of 

 wind present during the spraying operation causes more varia- 

 tion in quantity of spray used than any other factor. The 

 nature of the organism to be fought is also a factor. Aphis 

 control, for example, requires a thorough drenching of the 

 affected parts and the consequent use of relatively large quan- 

 tities of material. For the dormant sprays 6 to 9 gallons, and 

 for the summer sprays 8 to 14 gallons, constitute standard 

 applications on mature apple trees in most regions. Since 

 every part of the trunk and branches must be covered in some 

 dormant sprays, the amount of material used may be as great 

 as for a foliage spray. 



(c) Applying Dust Materials, The proper time for dusting 

 is when the air is still. There is little waste of materials under 

 such conditions, and the dust hangs in a cloud or dry fog about 

 the trees for a considerable period. The proper atmospheric 

 conditions are found as a rule in early morning or late evening. 

 Most orchard dusting, with the exception of nicotine applica- 

 tions, is done at these times. The presence of more moisture 

 on the leaf surfaces at these periods than at midday causes the 

 dust to stick better. Sulfur dusts adhere well even when the 

 foliage is dry. Many dusts now in use contain adhesive ma- 

 terials. Some growers attach lights to the machines and op- 

 erate them through the night; air conditions are good then, 

 and the job is hastened by almost continuous operation of the 

 machines. 



Nicotine dusts, in order to be effective, should be applied 

 when the temperature is high. Fumes are generated more 

 readily then than at lower temperatures, and control is more 

 effective. For this reason they are best applied at mid-day 

 when the air is quiet. Breezes dissipate the fumes before they 

 can be wholly effective. In sections where the air is seldom 

 quiet at mid-day, early evening is often the best time to make 

 the applications. It is a waste of time and money to attempt 

 to control aphis with nicotine dust when the wind is blowing 



