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Field trials of copper fungicides for the control of potato blight I. Foliage protection and yield
Author(s) -
Large E. C.
Publication year - 1945
Publication title -
annals of applied biology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.677
H-Index - 80
eISSN - 1744-7348
pISSN - 0003-4746
DOI - 10.1111/j.1744-7348.1945.tb06263.x
Subject(s) - phytophthora infestans , fungicide , blight , copper , bordeaux mixture , yield (engineering) , biology , horticulture , agronomy , materials science , metallurgy
Results are given of eight replicated‐plot trials of a number of copper fungicides in comparison with standard Bordeaux mixture under relatively severe conditions of potato blight incidence, in Devon and Cornwall during the years 1941‐4. Recent methods of disease measurement on foliage were applied and developed; characteristic curves were obtained defining the conditions of trial and the relations between spray timing and progress of blight attack. The time interval between half‐decay dates for sprayed and unsprayed foliage was taken as a numerical criterion of the direct protective effect of spraying. A linear relationship was found to hold between probit foliage decay and time, and this was accounted for by the close correspondence of the probit curve to that derived from a growth law, da = Ca(A ‐ a)dt , where a denotes the percentage foliage area affected by blight at time t after the beginning of the attack. Methods were found for preparing dispersible mixtures of bentonite with active copper compounds for use in spraying. With such admixture, to improve adhesion, both cuprous oxide and copper oxychloride preparations nearly equalled Bordeaux mixture at the same copper dosage. Without sticker, and compounded with water‐soluble dispersing agents, these materials were equalled by Bordeaux mixture at half their copper dosage. Suspensions of metallic copper were found to have pronounced fungicidal effect against Phytophthora infestans. A bearing of this result on the fungicidal mechanism of cuprous oxide is discussed. Results from 103 pairs of twice‐sprayed and unsprayed plots of main‐crop potatoes in Devon and Cornwall in 1941‐4 showed a mean prolongation of growth due to spraying of 16 1/2 days, and a mean gain in total yield of 2 3/4 tons/acre; but the gain in yield resulting from a given prolongation of growth varied greatly, according to the stage of crop development at which the prolongation of growth began. Spray retention data, for correlation with foliage protection and yields, were obtained in all four years.