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Chart version of thinner sensitivity ratings
Weather data for Sanford ME.  Forecast values begin May 18, 2013
Estimated Apple Sensitivity to Chemical Thinners
Other factors may outweigh the weather effects use for these estimates.  Other influences include: fruit diameter, fruit exposure to temperatures >=75 F, pollination, this year's cropload, last year's cropload, warm February-early April temperatures, frost and prolonged cool and cloudy weather during bloom, previous fall weather, foliage condition last summer)      Ratings below are for the influence of weather on fruit sensitivity to chemical thinning agents.  Ratings assume fruit are less than 13mm diameter.  Dates in bottom rows are beyond 18mm diameter for most cultivars, and are intended only for late cultivars.  Look at your fruit!
Rough guess McIntosh King fruit diameter dates:  12mm - November 1, Friday         15mm - November 1, Friday          18mm - November 1, Friday
Date after which fruit have exposure to 2 days of daily high temperature of at least 75 F:  Sunday,  July 21
Very warm night temperatures (average > 69F = 19 heat units in table) can lead to "EXCESSIVE THINNING RISK", especially if combined with cloudy weather, or if combined with use of NAA. Warm nights + Cloudy days  ----->  Increased sensitivity, maximum thinning. Warm nights + Sunny days   ----->  Intermediate senstivity, moderate thinning. Cool nights + Cloudy days    ----->  Reduced sensitivity Cool nights + Sunny days     ----->  Reduced sensitivity, minimum thinning.
THINNER APPLICATION DATE Estimates assume morning application. For afternoon application use rating for next day.	Average % CLOUD SHADING on application day and the next two days. < 20% = "sunny blue sky"  > 40% = "cloudy" Cloudy weather on 3 days after application increases thinning.		Average NIGHT HEAT UNITS = degrees above 50 F for 7pm--7am for 3 nights after application.  Example:  If average night time temperature is 55F, then value = 5.      Values above 10 for three nights after application increases sensitivity to thinning.			SUMMARY Influence of weather on sensitivity of fruit to thinning agents for 3 days following a morning application Ratings assume that fruit are within diameter range of susceptibility for thinning.
McIntosh 95% Petal Fall Mon, May 20	75%		12			Increased sensitivity
100% Petal Fall Tue, May 21	38%		13			Increased sensitivity
Wed, May 22	29%		7			Intermediate
Thu, May 23	31%		10			Intermediate
Fri, May 24	30%		5			Reduced sensitivity
Fruit Set Sat, May 25	31%		4			Intermediate