Weather influence on postbloom apple thinning

Background Information for this page
Return to radar list for Monmouth ME
Chart version of thinner sensitivity ratings
Weather data for Monmouth ME.  Forecast values begin August 3, 2010
     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 - May 26, Wednesday         15mm - May 29, Saturday          18mm - June 2, Wednesday
Date after which fruit have exposure to 2 days of daily high temperature of at least 75 F:  Monday,  May 24
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
Fri, May 14
cloudy  43% 1
Stronger influence for reduced sensitivity

100% Petal Fall
Sat, May 15
cloudy  50% 1
Stronger influence for reduced sensitivity

 
Sun, May 16
sunny  4% 1
Stronger influence for reduced sensitivity

 
Mon, May 17
sunny  1% 1
Stronger influence for reduced sensitivity

 
Tue, May 18
sunny  5% 0
Stronger influence for reduced sensitivity

 
Wed, May 19
cloudy  70% 1
Reduced sensitivity

Fruit Set
Thu, May 20
sunny  9% 8
Stronger influence for reduced sensitivity

 
Fri, May 21
sunny  1% 1
Stronger influence for reduced sensitivity

 
Sat, May 22
sunny  7% 3
Reduced sensitivity

 
Sun, May 23
sunny  14% 6
Intermediate

 
Mon, May 24
sunny  7% 12
Intermediate

 
Tue, May 25
sunny  3% 20
Reduced sensitivity
-- but true sensitivity may be less because of fruit exposure to 2 or more days with high temperatures >= 75F
 
Wed, May 26
sunny  12% 4
Stronger influence for reduced sensitivity
-- fruit >12mm probably have less sensitivity due to size and exposure to 2 or more days with high temperatures >= 75F
 
Thu, May 27
sunny  8% 2
Stronger influence for reduced sensitivity
-- fruit >12mm probably have less sensitivity due to size and exposure to 2 or more days with high temperatures >= 75F
 
Fri, May 28
sunny  5% 2
Reduced sensitivity
-- fruit >12mm probably have less sensitivity due to size and exposure to 2 or more days with high temperatures >= 75F
 
Sat, May 29
sunny  13% 9
Reduced sensitivity
-- fruit >15mm may have minimal sensitivity due to size and exposure to 2 or more days with high temperatures >= 75F
 
Sun, May 30
sunny  16% 6
Intermediate
-- fruit >15mm may have minimal sensitivity due to size and exposure to 2 or more days with high temperatures >= 75F
 
Mon, May 31
sunny  5% 5
Intermediate
-- fruit >15mm may have minimal sensitivity due to size and exposure to 2 or more days with high temperatures >= 75F
 
Tue, June 1
cloudy  48% 7
Intermediate
-- fruit >15mm may have minimal sensitivity due to size and exposure to 2 or more days with high temperatures >= 75F
 
Wed, June 2
35% 6
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 3
cloudy  64% 6
Increased sensitivity
-- fruit > 18mm are probably beyond predictable chemical thinning due to size and exposure to 2 or more days with high temperatures >= 75F
 
Fri, June 4
28% 10
Increased sensitivity
-- fruit > 18mm are probably beyond predictable chemical thinning due to size and exposure to 2 or more days with high temperatures >= 75F
 
Sat, June 5
cloudy  55% 11
Intermediate
-- fruit > 18mm are probably beyond predictable chemical thinning due to size and exposure to 2 or more days with high temperatures >= 75F
 
Sun, June 6
cloudy  64% 4
Reduced sensitivity
-- fruit > 18mm are probably beyond predictable chemical thinning due to size and exposure to 2 or more days with high temperatures >= 75F
 
Mon, June 7
sunny  15% 3
Reduced 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 8
34% 1
Reduced sensitivity
-- fruit > 18mm are probably beyond predictable chemical thinning due to size and exposure to 2 or more days with high temperatures >= 75F
  sunny  19% 5  
  cloudy  70% 1