Premium
Greenhouse evaluation of chemicals for control of powdery mildews
Author(s) -
KIRBY A. H. M.,
FRICK E. L.
Publication year - 1963
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.1744-7348.1963.tb03675.x
Subject(s) - powdery mildew , rootstock , biology , inoculation , horticulture , spore , ammonium nitrate , greenhouse , ammonium , mildew , relative humidity , humidity , botany , agronomy , chemistry , physics , organic chemistry , thermodynamics
SUMMARY Apple rootstocks placed in the settling‐tower 24 hr. before introduction of spores of Podosphaera Zeucotricha developed more lesions than those placed in position immediately before inoculation; a period of 24 hr. in the tower after introduction of spores induced more infections than one of 48 hr. Rootstocks kept at high temperature for a few hours immediately on removal from the tower (24 hr. after inoculation) developed only half as many lesions as those maintained at normal temperatures. This effect declined steadily as the heating was applied on successively later days until the 8th day when such heating had no effect. Plants kept at about 20°C. and a relative humidity not exceeding 70% grew satisfactorily and developed very similar numbers of lesions to those inoculated in the same tower but subsequently incubated in a greenhouse where R.H. reached saturation every night. High humidity therefore is unnecessary for the inoculation and development of apple mildew. The leaves initially produced by rootstocks potted in John Innes No. I compost and watered daily with ammonium nitrate solution, were no more susceptible to powdery mildew than those on similar plants given water only. However, when such rootstocks were grown for several weeks, cut back to a few buds, and allowed to break again, the leaves were larger and more susceptible if ammonium nitrate was given as a 0·005 to 0·015 M solution. The susceptibility of leaves on M. III rootstocks decreased with age by about 50% per leaf‐position down to the fourth and even faster below that position, so that the youngest leaf that is just unrolling is by far the most susceptible.