Apple Tree Diseases: Apple Scab Mills Table for disease development

In the previous post we discussed about general weather condition that are to be considered before forecasting of disease. Here we are going to discuss about the Mills tables that are to be taken into consideration for the prediction of disease. 

Table : Mills chart for predicting the occurrence of apple scab

Average Temperature (oC)	Wetting time required for infection in spring (hours)	Time required for scab lesions to appear (days)
5.6	30	More than 17
7.2	20
8.3	17
9.4	14.5	17
10	14	16
12.2	11.5	14
13	11
13.9 – 15	10	12 -13
15.5	9.5	9
16 – 24	9	8 – 10
24.5	9.5	9
25	11
25.6	13	10

 Infection is rare above 26 ^oC

PS: When rain begins after sunset, leaf wetness should be assumed to begin at sunrise.  For all other events, times should be computed from the start of rain.  Note that night-released ascospores could cause significant disease in orchards with poor scab control the previous year (i.e., greater than 1% leaf infection at leaf fall).  However, in low-inoculum orchards (most commercial orchards) when rain begins at night, ascospore release, and infection periods, should be assumed to start at dawn.  When alternating wet and dry conditions exist, add the wet hours together, unless the dry intervals are 8 hours or longer.

In coming post we shall be discussing about the holistic management of the disease