R. Reuveni et al., EFFECTS OF FOLIAR SPRAYS OF PHOSPHATES ON POWDERY MILDEW (SPHAEROTHECA-PANNOSA) OF ROSES, Journal of phytopathology, 142(3-4), 1994, pp. 331-337
Powdery mildew on plants of a local clone of Rosa indica Major was sig
nificantly controlled by a single spray of 25 mM aqueous solutions of
K2HPO4, KH2PO4 plus KOH, or NaHCO3, all plus Tween 20 (0.5 ml/l) or bu
pirimate (Nimrod) at 0.5 ml/l, which was applied 4 days before inocula
tion with conidial suspension of Sphaerotheca pannosa var. rosae. Dise
ase incidence was reduced by 79, 71, 54 and 50 %, as compared to contr
ols on plants sprayed with KH2PO4 plus KOH, K2HPO4, NaHCO3 or bupirima
te, respectively. Phosphates were suppressive and expressed by disappe
arance of 99 % of the pustules and conidia, as early as 2 days after a
single spray on mildewed foliage. This treatment was efficient for at
least 9 days after the first application when large infected greenhou
se-grown plants were used. Re-application of these salts on the same p
lants reduced the lesion area by about 90 % from that recorded before
the application. Phosphate and bicarbonate were more suppressive than
the systemic fungicide bupirimate in the early period (up to 2 days).
The suppresion effects of bicarbonate and bupirimate, however, were sh
ort-term and not persistent, while the phosphate treatments remained s
ignificantly suppressive for up to 23 days, when the experiment was te
rminated. The inhibitory and suppressive effectiveness of phosphate sa
lts is discussed in the light of their possible acceptance as ideal fo
liar fertilizers which should be considered for use in the field for d
isease control.