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Primary Apple scab models
- background
Ascospore maturity is calculated as per David M. Gadoury and William
E. MacHardy, "A Model to Estimate the Maturity of Ascospores of Venturia
inaequalis", Phytopathology 72:901-904, 1982.
Target size and tissue susceptibility calculated as per criteria in
"Recent Developments in the Epidemiology of Apple Scab" by David M.
Gadoury, Robert C. Seem, Arne Stensvand, and Stuart P. Falk (unpublished article).
The same criteria are described in "A review of apple scab with particular
reference to the 1998 growing season in New York", by David M. Gadoury and Robert C.
Seem, in "Cornell Apple IPM In-depth School Proceedings", Geneva NY, March 9-10,
1999.
Temperature and rain amount effect on ascospore release calculated
as per "New Developments in Forecasting the Risk of Apple Scab" by David M.
Gadoury, Robert C. Seem and Arne Stensvand in New York Fruit Quarterly.
Infection period duration evaluated according to William E. MacHardy
and David M. Gadoury, "A Revision of Mills's Criteria for Predicting Apple Scab
Infection Periods", Phytopathology 79:304-310.
"Surface fungicides" are commonly called protectant or
contact fungicides.
Primary scab surface fungicide residue
depletion is based on a commonly stated Extension "7-day" guideline.
The 7-day guideline is supplemented by
degree day accumulation to identify periods of fast tissue growth
with reduction of the allotted number of days protection in the absence of rain
down to the equivalent of 8 days average degree accumulation (base 43F).
Similarly, the 7-day guideline is also supplemented by
degree day accumulation to identify cool periods of abnormally slow and increase
duration in absence of rain to the equivalent of 6 days average degree
accumulation (base 43F), with a maximum value of 9 calendar days.
An amended version of a "2-inch" rain depletion rule is
used, based work by Franzine D. Smith and William E. MacHardy, "The Retention and
Redistribution of Captan on Apple Foliage", Phytopathology 74:894-899.
The amended version adjusts the allowable amount of accumulated rain since the
application according to the the number of days since the application. For
example, more than 2 inches rain is required to deplete coverage on the first
day after application, but by day 6, less than 2 inches rain is enough to
deplete protection.
Protectant applications of full dose sulfur wettable
powder (5 lbs. active ingredient per 100 gallons dilute) are estimated to be
depleted after 0.5" rain. This is a 'best guess' based on anecdotal
reports. Micronized sulfur, or sulfur applied in combination with a
sticker adjuvant may provide longer residual protection.
Recommended deadlines for post-infection
use of sterol inhibitor and strobilurin fungicides are capped at 72 hours based
on concerns arising from research on scab resistance to these materials in New
York and Michigan. For a synopsis of a conservative approach to use of
these materials see
http://www.nysaes.cornell.edu/ent/scaffolds/2004/040322.html#disease
Post-infection activity for "Surface fungicides"
are commonly called protectant or contact
fungicides) based on temperatures since beginning of infections periods is based on:
J.M. Hamilton and M. Szkolnik, Proceedings of the New York State Horticultural Society,
1958, 75-77.
J.M. Hamilton and M. Szkolnik, Proceedings of the New York State Horticultural Society,
1962, 137-145.
J.M. Hamilton and M. Szkolnik, Proceedings of the New York State Horticultural Society,
1965, 214-217.
F.D. Smith and W.E. MacHardy, Phytopathology:74:894-899
M. Szkolnik and J.M. Hamilton, Proceedings of the New York State Horticultural Society,
1954, 107-110.
M. Szkolnik and J.M. Hamilton, Proceedings of the New York State Horticultural Society,
1956, 210.
M. Szkolnik and J.M. Hamilton, Proceedings of the New York State Horticultural Society,
1959, 164-168.
M. Szkolnik and J.M. Hamilton, Proceedings of the New York State Horticultural Society,
1960, 142-144.
M. Szkolnik and J.M. Hamilton, Proceedings of the New York State Horticultural Society,
1961, 242.
M. Szkolnik and J.M. Hamilton, Proceedings of the New York State Horticultural Society,
1966, 168-169.
W.F. Wilcox, W.W. Turechek, and D.A. Rosenberger, plant pathology section
editors, "Pest Management Guidelines for Commercial Tree Fruit
Production 2001", Cornell Univ. Cooperative Extension, Ithaca New York.
Fruit Production Recommendations 1998-1999, Ontario Ministry of Agric., Food and Rural
Affairs, Toronto, Canada.
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