Weather data for Sanford ME. Forecast values begin September 20, 2011

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 - June 3, Friday 15mm - June 7, Tuesday 18mm - June 9, Thursday

Date after which fruit have exposure to 2 days of daily high temperature of at least 75 F: Monday, May 30

     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
Fri, May 27

sunny 12%

Stronger influence for Increased sensitivity

100% Petal Fall Sat, May 28

57%

Stronger influence for Increased sensitivity

Sun, May 29

35%

Increased sensitivity

Fruit Set Mon, May 30

sunny 13%

Increased sensitivity

Tue, May 31

sunny 8%

Intermediate-- sensitivity may be less because of fruit exposure to 2+ days with high temps. > 75F

Wed, June 1

sunny 14%

Intermediate-- sensitivity may be less because of fruit exposure to 2+ days with high temps. > 75F

Thu, June 2

40%

Stronger influence for reduced sensitivity-- sensitivity may be less because of fruit exposure to 2+ days with high temps. > 75F

Fri, June 3

30%

Stronger influence for reduced sensitivity -- fruit >12mm probably less sensitive to thinning due to size and exposure to 2+ days with high temps. > 75F

Sat, June 4

sunny 4%

Stronger influence for reduced sensitivity -- fruit >12mm probably less sensitive to thinning due to size and exposure to 2+ days with high temps. > 75F

Sun, June 5

sunny 10%

Reduced sensitivity -- fruit >12mm probably less sensitive to thinning due to size and exposure to 2+ days with high temps. > 75F

Mon, June 6

sunny 9%

Intermediate -- fruit >12mm probably less sensitive to thinning due to size and exposure to 2+ days with high temps. > 75F

Tue, June 7

sunny 5%

Increased sensitivity -- fruit >15mm may have minimal sensitivity due to size and exposure to 2+ days with high temps. > 75F

Wed, June 8

sunny 5%

Increased sensitivity -- fruit >15mm may have minimal sensitivity due to size and exposure to 2+ days with high temps. > 75F

Thu, June 9

sunny 12%