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The use o£ Promalin at full bloom (FB) to improve the "typi- 

 ness" of'Delicious ' (increase the length to diameter ratio o£ the 

 fruit) has been found by Dr. Duane Greene and others to be capable 

 of thinning this variety and its strains. The use of a chemical 

 thinner such as carbaryl (Sevin) following an application of Pro- 

 malin, might result in overthinning , excessive fruit size and a 

 severe yield reduction. 'Delicious' requires freedom from frost 

 damage and ideal crop pollination conditions for good commercial 

 yields. It is not desirable to apply a chemical thinner (carbaryl) 

 or Promalin (which has the potential to reduce fruit set) on young 

 'Delicious' which invariably set light crops. In blocks of older 

 'Delicious' trees having a history of oversetting the use of Pro- 

 malin at FB may be entirely satisfactory but the use of carbaryl 

 for thinning should be delayed for at least 14 days after PF so 

 that the need for additional chemical thinning can be reasonably 

 well determined. If a Promalin treatment at FB or adverse weather 

 conditions have already limited the initial fruit set there may 

 be no need to reduce the set further with a post petal-fall appli- 

 cation of carbaryl. 'Delicious' apples are too valuable for such 

 risks. 



NAA or NAAm thinning sprays applied when the temperature is 

 less than 650F, are usually less effective. Temperatures of 70-75OF 

 are necessary for optimum results. When temperatures rise above 

 850F, there is a rather sharp increase in NAA or NAAm penetration. 

 If the high temperatures are accompanied by humid conditions that 

 prevent spray droplets from drying rapidly, overthinning may result. 

 In this case, the concentration of the thinning spray should be 

 reduced. Once the foliage has dried after application of these 

 materials, do not respray if rain occurs shortly thereafter. 



NAA or NAAm are best used alone in dilute form. NAA will often 

 cause more foliage injury and thin more than NAAm or carbaryl. 

 Carbaryl is the least injurious to foliage. Mixing a wetting agent 

 with the thinning chemicals may sometimes increase thinning but 

 invariably increases foliage injury so the addition of a wetting 

 agent is not suggested. 



Since the best day to apply a treatment cannot be accurately 

 determined in advance, it may be wise to spray a different fraction 

 of the more valuable mid- and late-season varieties at 3 or 4 day 

 intervals during the suggested period. An occasional grower may 

 delay his decision to thin until 3 weeks or more after PF. Apply- 

 ing NAAm or NAA later than 3-4 weeks after PF may result in no 

 thinning and reduced fruit size since these compounds have some 

 temporary fruit size inhibiting action. Carbaryl is usually ineffect- 

 after about 21 days from PF. 



Most commercial formulations of NAA contain 1.0 gram of NAA 

 per oz. (a few may have 2 grams per oz.). A material containing 

 1.0 gram per oz. will yield a 10 ppm concentration when 4 oz. per 

 100 gallons are used. Four oz. of NAAm per 100 gallons will give 

 a concentration of 25 ppm. It is assumed that the carbaryl (Sevin) 

 used is a 50% wettable solution. 



