M. Reuveni et al., SUPPRESSION OF CUCUMBER POWDERY MILDEW (SPHAEROTHECA-FULIGINEA) BY FOLIAR SPRAYS OF PHOSPHATE AND POTASSIUM-SALTS, Plant Pathology, 44(1), 1995, pp. 31-39
Powdery mildew, caused by Sphaerotheca fuliginea, was significantly co
ntrolled by a single spray of aqueous solutions (25 mM) containing var
ious phosphates and potassium salts. Phosphates were suppressive when
applied alone; however, treatments in combination with Tween-20 were m
ore effective in causing the disappearance of powdery mildew pustules
from diseased foliage. Efficiency of control, as expressed by the disa
ppearance of 99% of pustules, was recorded 1 or 2 days after applicati
on of single sprays of phosphate and potassium salt solutions. Treatme
nt was effective for up to 12 or 15 days, respectively, following appl
ication to small or large greenhouse-grown plants with established mil
dew infection. Treatments also markedly reduced (> 99%) the production
of conidia from colonies. A further application of these salts to the
same plants resulted in the elimination of about 50% of mildew coloni
es present prior to the application. Further spray application inhibit
ed disease development compared with water-sprayed plants, but did not
reduce the number of existing lesions. Phosphate was more effective t
han the systemic fungicide pyrifenox and reduced established powdery m
ildew infection up to 11 days after application, but the converse was
true when assessments were made after 15 days. These properties of pho
sphates and potassium salts make them appropriate for use as foliar fe
rtilizers with a potential beneficial influence on disease control.