Tree Fruit Diseases - Predicting Infection Periods to Apply Protection

This article will help you manually determine infection periods for certain diseases. Also included is a table listing coppers available to manage bacterial spot during cover sprays.
Tree Fruit Diseases - Predicting Infection Periods to Apply Protection - Articles
Tree Fruit Diseases - Predicting Infection Periods to Apply Protection

A thermometer that records the maximum and minimum temperature is extremely useful for determining degree hours.

Predicting infection periods allows you to apply protection before an infection event. You will need a thermometer to record daily high temperatures and nightly low temperatures.

Predicting Apple Scab using the Revised Mills Table

  • Keep track of the average temperature (°F) - maximum and minimum temperature during wetting event.
  • When there is a wetting event, manually keep track of when rain starts and when leaves dry to calculate leaf wetness hours.
Revised Mills Table
Temperature (°F)Wetness hours
3441
3635
3730
3928
4121
4318
4515
4613
4812
5011
529
54-568
57-597
61-756
778
7911

Using Cougarblight to determine Fire blight infection

Cougarblight is a risk assessment model developed at Washington State University for determining the risk of fire blight infection on flower blossoms. Similar to MaryBlyt, this model should be used from first bloom until only a few blossoms remain. Cougarblight can be used with a paper, pencil, and a few reference tables to estimate the level of risk for fire blight infection based on degree days and history of fire blight in or around your orchard the previous growing season.

Cougarblight requirements:

  • Flowers are open
  • Heat accumulation (4 day accumulation of degree hours)
  • Wetting event (dew, rain, or spray treatment)

How to use the tables

  1. Keep daily record of daytime high temperature and nighttime low temperature during pink through bloom.
  2. Go to Table 1: Degree Hours
  3. To record the degree hours, look for the Daytime High Temperature, then the corresponding low number. If the low temp was 49.9oF or below, look in Column A. If low temp is 50oF or higher look in Column B.
  4. Determine where you are on a particular day: Add the degree hours: the current day + yesterday + 2 days ago + 3 days ago
  5. Based on the total numbers, look at Table 2: Blight History and first determine what your blight history is, then move along the row to your total for the 4 day accumulation of degree hours to determine your fire blight risk.
Table 1: Degree Hours
Daytime High Temperature (°F)Column A Degree Hours per Night if Low is 49.9°F or BelowColumn B Degree Hours per Night if Low is 50°F or Higher
6000
6225
63512
641022
651429
662035
672642
683350
694260
705270
716280
724792
7387105
74100120
75115134
76130151
77146169
78162189
79178209
80195230
81212250
82228265
83243280
84257292
85266302
86274310
87280315
88285320
89288325
90290330
92287335
93284333
94280330
95274325
96267317
97260309
98254302
99246293
100238285
101230275
102222268
103216259
104208250
105200240
Table 2: Blight History. Values for "Risk" are a 4-Day Degree Hour Sum
Blight HistoryLow RiskMarginal RiskHigh RiskExtreme Risk
None in your area during the past 2 seasons0-400400-500500-800800+
Blight in the region but not near your orchard in the last year0-350350-400400-650650+
Blight in or neighboring your orchard last year0-150150-300300-500500+
Active blight strikes or cankers in your orchard or a neighboring orchard0-100100-200200-350350+

Cherry leaf spot: Determining infection periods

Using Cherry leaf spot table

  1. Keep track of average temperature--maximum and minimum temperature during wetting event.
  2. When there is a wetting event, manually keep track of when rain starts and when leaves dry to calculate leaf wetness hours.

Cherry Leaf Spot Table: Approximate minimum number of hours of leaf wetness required to produce leaf spot infections caused by conidia on sour cherries. Requirements for primary (ascospore) infections are presumed to be similar.

Average Temperature (°F)Hours of wetness from the beginning of the rain
4628
4725
4823
4920
5019
5117
5215
5314
5412
5511
5610
579
588
59-607
61-626
63-685
69-706
71-727
738
749
7511
7612
7714
7816
7918
8021
8128

Data of S. Eisensmith and A. Jones, Michigan State University.
We wish to thank the New York State Agricultural Experiment Station for the use of this table. Taken from Tree Fruit Crops IPM Disease Identification Sheet No. 8.

Bacterial spot: Using copper for cover sprays

This is a table from Dr. Norm Lalancette from Rutgers University showing coppers labeled for peaches / nectarines and these can be used for cover sprays. He determined the 0.5 oz./A metallic copper was a rate that minimized phytotoxicity while still controlling the disease. You can increase the rate to 1 oz./A metallic copper - a little more phytotoxicity will occur, but the fruit will be less diseased.

Copper Treatments for Bacterial Spot
Product NameActive Ingredient% Active Ingredient% Metallic CopperREIPHIPost-bloom Label RatePost-bloom @ 0.5oz/A metallic copperPost-bloom @ 1oz/A metallic copper
CuevaCopper Octanoate101.84 hrs0 days0.5-2.0 gal.25 oz.50 oz.
NordoxCuprous oxide83.97512 hrs0 days10.7 oz.0.7 oz.1.4 oz.
Kocide 3000Copper hydroxide30DF3048 hrs0 days4.0-8.0 oz.1.7 oz.3.4 oz.
Mastercop (soluble)Copper sulfate pentahydrate21.465.448 hrs21 days4.0-8.0 fl.oz.7.4 fl.oz.14.8 oz.
Champ Formula 2 FlowableCopper hydroxide37.5F24.448 hrs21 daysnot listed0.9 oz.1.8 oz.
Copper-Count-N (soluble)Copper diammonia diacetate complex27.15848 hrs21 days1 qt.5.2 fl.oz.10.4 fl.oz.
Badge X2Copper oxychloride + Copper hydroxide23.82 + 21.4928.248 hrs21 days8.0-32.0 oz.1.8 oz.3.6 oz.
Nu-CopCopper hydroxide76.775048 hrs21 days1.0-3.0 lbs.1.0 oz.2.0 oz.
COCDFCopper oxychloride84.045048 hrs21 days1.0-3.0 lbs.1.0 oz.2.0 oz.

Use of trade or brand names in this publication is for clarity and information; it does not imply approval of the product to the exclusion of others that may be of similar, suitable composition, nor does it guarantee or warrant the standard of the product. When controlling for disease, weather and tree growth conditions need to be monitored at a local level within one's own orchard. Before chemical products are applied, be sure to be in compliance by obtaining the current usage regulations and examining the product label.

Authors

Apple and pear diseases Peach, cherry, other stone fruit diseases Tree fruit disease management

More by Kari A. Peter, Ph.D.