Tree Fruit Disease - Predicting Infection Periods to Apply Protection

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.

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 49.9°F or below, look in Column A. If low temp is 50°F 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.

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.

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.

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.