-11- 



A 0.21 dust o£ NAA is available for chemical thinning. The 

 dusts should be applied dry on dry foliage under good drying con- 

 ditions to reduce the possibility of foliage injury and overthin- 

 ning. When applied under such conditions, NAA dusts are often less 

 injurious to foliage and may reduce fruit set less than comparable 

 NAA sprays. 



Young trees generally require less thinning than older trees. 

 If treatment seems necessary, it may be desirable to use the lowest 

 suggested concentration of the chemical thinner, or even reduce this 

 amount by 1/2 to 1/4. 



Early fruiting on the leader of young trees can seriously affect 

 the shape of the tree. To reduce fruit load until the tree has 

 reached sufficient size to hold a crop of apples, chemically thin 

 at PF with carbaryl, 1 lb. plus 15 ppm NAA. 



Our suggestions for use of chemical thinners on several apple 

 varieties are included in the chart on the following p age! 



GROWTH REGULATOR SPRAY FOR GROWTH 

 SUPPRESSION ON APPLE TREES 

 Duane Greene and William J. Lord 

 Department of Plant and Soil Sciences 



Frequently there are blocks of young, non-bearing trees parti- 

 cularly Delicious that are growing too vigorously because of lack 



_ J- C ■^J1..^ J ^ -: 11,, T „„^^^ +„^„^ ,.,-; 1 1 ^ r^ c- r^ ^-\^a^^ r-^, 



Young, non-spur trees . Apply 500 ppm ethephon (1-2/3 pints) plus 

 1500 ppm Alar-85* (1-1/2 lbs.) in 100 gallons of water 10 to 14 days 

 after full bloom or when shoots are 4 to 6 inches long. 



Young spur trees or older trees with no crop . These trees are 

 more sensitive to a growth regulator spray than young non-spur trees. 

 Therefore, apply 300 ppm ethephon (1 pint) plus 1500 ppm Alar-85* 

 (1-1/2 lbs.) in 100 gallons of water 10 to 14 days after full bloom 

 or when shoots are 4 to 6 inches long. 



In addition to growth restriction, these growth regulators gen- 

 erally increase bloom the year following their use. Increased bloom 

 probably will of of no value on bearing trees that lost their crop 

 due to frost because bloom should be adequate the following year with- 

 out the use of these growth regulators. However, it may be more dif- 

 ficult to obtain adequate thinning the year following their use because 

 of excessive bloom. Additional bloom because of growth regulators use 

 could be of value on the young, vigorous trees but unfortunately fruit 

 set may not be increased on Delicious. 



We suggest that the ethephon plus Alar-85* spray not be applied 

 on young trees until they are large enough to bear a crop. 



*Trade Name 



