Weather influence on postbloom apple thinning

Background Information for this page
Return to radar list for Sanford ME
Chart version of thinner sensitivity ratings
Weather data for Sanford ME.  Forecast values begin October 17, 2008
     Other factors may outweigh the summary statements made below! 
    
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 4, Wednesday         15mm - June 8, Sunday          18mm - June 9, Monday
Date after which fruit have exposure to 2 days of daily high temperature of at least 75 F:  Thursday,  May 29
Very warm night temperatures (> 69F) can lead to "EXCESSIVE THINNING RISK",
especially if combined with cloudy weather or if NAA is used as thinning agent.

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. 
Postbloom thinner
Application date
Calculations assume morning application.
If thinner applied after noon, use rating for next day.
% CLOUD SHADING
  Arbitrary categories:
40% or more = "cloudy"
20% or less = "sunny" 

High shading on 3 days after application increases thinning response.
AVERAGE NIGHT TEMPERATURE
relative to 50 F threshold
for following 7pm--7am.
Example: Avg. 52F night temp = 2.
Values rounded for display,
and range from 0 to 20+.

High temperature
for 3 nights after application increases thinning response.
SUMMARY
of weather influence
on sensitivity of fruit
to thinning agents
applied on morning
of listed date


Ratings assume fruit
are within susceptible diameter range for thinning.
McIntosh
95% Petal Fall
Mon, May 26
sunny  9% 15
Reduced sensitivity

100% Petal Fall
Tue, May 27
21% 3
Stronger influence for reduced sensitivity

 
Wed, May 28
sunny  1% 1
Reduced sensitivity

 
Thu, May 29
sunny  1% 7
Intermediate

 
Fri, May 30
sunny  4% 7
Intermediate
-- but true sensitivity may be less because of fruit exposure to 2 or more days with high temperatures >= 75F
Fruit Set
Sat, May 31
cloudy  51% 10
Increased sensitivity
-- but true sensitivity may be less because of fruit exposure to 2 or more days with high temperatures >= 75F
 
Sun, June 1
29% 9
Intermediate
-- but true sensitivity may be less because of fruit exposure to 2 or more days with high temperatures >= 75F
 
Mon, June 2
32% 7
Intermediate
-- but true sensitivity may be less because of fruit exposure to 2 or more days with high temperatures >= 75F
 
Tue, June 3
27% 12
Increased sensitivity
-- but true sensitivity may be less because of fruit exposure to 2 or more days with high temperatures >= 75F
 
Wed, June 4
cloudy  65% 5
Intermediate
-- fruit >12mm probably have less sensitivity due to size and exposure to 2 or more days with high temperatures >= 75F
 
Thu, June 5
cloudy  67% 6
Increased sensitivity
-- fruit >12mm probably have less sensitivity due to size and exposure to 2 or more days with high temperatures >= 75F
 
Fri, June 6
cloudy  69% 6
Stronger influence for Increased sensitivity
-- fruit >12mm probably have less sensitivity due to size and exposure to 2 or more days with high temperatures >= 75F
 
Sat, June 7
25% 20
Stronger influence for Increased sensitivity
-- fruit >12mm probably have less sensitivity due to size and exposure to 2 or more days with high temperatures >= 75F
 
Sun, June 8
sunny  6% 24
Stronger influence for Increased sensitivity
-- fruit >15mm may have minimal sensitivity due to size and exposure to 2 or more days with high temperatures >= 75F
 
Mon, June 9
sunny  18% 18
Increased sensitivity
-- fruit > 18mm are probably beyond predictable chemical thinning due to size and exposure to 2 or more days with high temperatures >= 75F
 
Tue, June 10
sunny  8% 19
Intermediate
-- fruit > 18mm are probably beyond predictable chemical thinning due to size and exposure to 2 or more days with high temperatures >= 75F
 
Wed, June 11
sunny  11% 15
Intermediate
-- fruit > 18mm are probably beyond predictable chemical thinning due to size and exposure to 2 or more days with high temperatures >= 75F
 
Thu, June 12
sunny  1% 6
Intermediate
-- fruit > 18mm are probably beyond predictable chemical thinning due to size and exposure to 2 or more days with high temperatures >= 75F
 
Fri, June 13
sunny  1% 12
Intermediate
-- fruit > 18mm are probably beyond predictable chemical thinning due to size and exposure to 2 or more days with high temperatures >= 75F
  sunny  8% 11  
  cloudy  68% 7