Damage evaluation of the apple scab, Venturia inaequalis (Cke.) Wint., in Santiago, Nuevo Leon Sate (Mexico)

Abstract

It nave been determined how pernitious is the apple scab Venturia
inaequalis. Samples of 160 trees were used, during May to August of
1979. Infection percentages were obtained both in leaves and fruits,
wich were correlationatsd against total yield, as well as wlth the parameter
of the sample dates. The maximun infection percentage on
leaves was 32.3%; reaching to 100% on fruits, into a little time after
it begin. The infectioD percentages both in leaves and in fruits against
total, yield, were little (r= 0.38). Used only the healthy fruits, against
the same indepeiidient variables, the coefficient r was 0.93 with the
following equation: Y= 28.54 - 0.82 X, - 0.23 X2 - 0.17 X3, where
Y= healthy apples in kg., Xf = leaves infection percentage,
X2= apple infection percsntage, and X3 = sample date. The total
average of fruit mfection was of 49.9% wich meang a severe damage,
with a yield loss of 37.5% of total. When 15% leaves infection comingon,
the fruit infecticn began and spreaded rapidly, so that we could
take this leaves infection as a critic point of control.