Effectiveness of cow's milk against zucchini squash powdery mildew (Sphaerotheca fuliginea) in greenhouse conditions

Abstract

Efficacy of fresh cow milk was tested in five greenhouse experiments against powdery mildew (Sphaerotheca fuliginea) on zucchini squash (Cucurbita pepo). Plants were sprayed with milk at 5, 10, 20, 30, 40, and 50%, either once or twice a week. Additional treatments were fungicides (fenarimol 0.1 ml/l or benomyl 0.1 g/l) applied once a week and water as a control treatment. Severity of the powdery mildew was visually evaluated on individual leaves at weekly intervals and scored as percentage of leaf area infected for infected leaves. A negative correlation was found between the infected leaf area per infected leaf and milk concentration sprayed on plants for the five experiments. High concentrations of milk were more effective than the conventional fungicides tested. This study demonstrated that milk is an effective alternative for the control of powdery mildew in organic agriculture.

Full text

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Crop Protection 18 (1999) 489}492
E!ectiveness of cow's milk against zucchini squash powdery mildew
(Sphaerotheca fuliginea) in greenhouse conditions
Wagner Bettiol*
Brenno Domingues Astiarraga and Alfredo Jose&Barreto Luiz Embrapa Environment, CP 69, 13.820-000 Jaguariu&na, SP, Brazil
Abstract
E$cacy of fresh cow milk was tested in "ve greenhouse experiments against powdery mildew (Sphaerotheca fuliginea) on zucchini
squash (Cucurbita pepo). Plants were sprayed with milk at 5, 10, 20, 30, 40, and 50%, either once or twice a week. Additional
treatments were fungicides (fenarimol 0.1 ml/l or benomyl 0.1 g/l) applied once a week and water as a control treatment. Severity of
the powdery mildew was visually evaluated on individual leaves at weekly intervals and scored as percentage of leaf area infected
for infected leaves. A negative correlation was found between the infected leaf area per infected leaf and milk concentration sprayed on
plants for the "ve experiments. High concentrations of milk were more e!ective than the conventional fungicides tested. This study
demonstrated that milk is an e!ective alternative for the control of powdery mildew in organic agriculture. !1999 Elsevier Science
Ltd. All rights reserved.
Keywords: Powdery mildew; Zucchini squash; Milk; Alternative control; Organic agriculture
1. Introduction
Cucurbit powdery mildew, caused by Sphaerotheca
fuliginea (Schlecht.) Pollacci, is a serious disease on cu-
curbits grown worldwide. Powdery mildew occurs on
leaves, stems and fruits. Control methods currently avail-
able under commercial conditions include the use of
repeated applications of elemental sulphur (Kimati et al.,
1980) and other fungicides (Kimati et al., 1997). The
constant use of fungicides, however, can result in the
environmental contamination and selection of resistant
populations of S. fuliginea (McGrath, 1996; McGrath
et al., 1996). For these reasons, alternative control
measures are warranted.
Several alternatives to conventional fungicides have
been evaluated for cucurbit powdery mildew. Reuveni
et al. (1995) and Garibaldi et al. (1994) veri"ed that
powdery mildew was controlled signi"cantly by a single
spray of aqueous solutions containing various phos-
phates and potassium salts. These authors concluded
that phosphates and potassium are appropriate foliar
fertilizers, with a potential bene"cial in#uence on disease
control. Pasini et al. (1997) veri"ed that JMS Stylet oil,
canola oil, Synertrol, and neem extract provided satisfac-
tory control of powdery mildew on rose. Marco et al.
(1994) described the suppression of powdery mildew on
squash by applications of whitewash, clay, and antitran-
spirant materials. Sodium and potassium bicarbonates
combined with Sunspray ultra-"ne spray oil, both at
0.5%, were e!ective in the control of powdery mildew
(Ziv and Zitter, 1992). Ampelomyces quisqualis has been
described as a biological control agent for cucurbit pow-
dery mildew (Falk et al., 1995; McGrath and Shisko!,
1996; Pasini et al., 1997).
The objective of this work was to "nd possible antifun-
gal compounds that would provide e!ective disease con-
trol under practical conditions, while also minimizing
environmental impacts. We have demonstrated that the
residue of glutamic fermentation of molasses and a prod-
uct of milk fermentation released by Lactobacillus were
e!ective for the control of powdery mildew on zucchini
squash (Bettiol, 1996; Astiarraga and Bettiol, 1997; Bet-
tiol and Astiarraga, 1998).
This paper reports on the control of powdery mildew
on zucchini squash with milk under greenhouse condi-
tions. This study was conducted to obtain an alternative
for controlling powdery mildew in organic agriculture.
Preliminary information has been reported recently
(Bettiol and Astiarraga, 1997).
0261-2194/99/$ - see front matter !1999 Elsevier Science Ltd. All rights reserved.
PII: S 0 2 6 1 - 2 1 9 4 ( 9 9 ) 0 0 0 4 6 - 0

Fig. 1. Relationship of powdery mildew (Sphaerotheca fuliginea) sever-
ity on leaves (%) of zucchini squash to concentration of milk sprayed
twice a week at 22 d after the "rst spray (R!"0.94; 0.96 and 0.94, for
the "rst, second and third experiment, respectively), and once a week at
24 d after the "rst spray (R!"0.89 and 0.96, for the fourth and "fth
experiment, respectively).
2. Materials and methods
Zucchini squash plants (Cucurbita pepo, cv. Caserta
}CAC) were grown in 2.0 l aluminium pots containing
oxisol and composted cattle manure (3 : 1) amended with
10 g of NPK fertilizer (4-14-8). Plants were kept in a
greenhouse without inoculum of Sphaerotheca fuliginea
until they reached the developmental stage of four ex-
panded leaves. At this stage, plants were transferred to
a greenhouse with high S. fuliginea inoculum potential.
They were sprayed to runo!with either fresh cow milk
[5, 10, 20, 30, 40, and 50% (per volume in water)] once
("rst, second, and third experiment) or twice (fourth and
"fth experiment) a week, or fungicide (fenarimol 0.1 ml/l
or benomyl 0.1 g/l) once a week. Check plants were
treated with water only. Applications were performed
with a compressed-air paint sprayer at 10 lb/pol!. The
"rst application was made immediately after the plants
were transferred to the greenhouse with high S. fuliginea
inoculum. Experiments were set up in a randomized
design with "ve replicates per treatment. Each replication
consisted of one pot containing one plant. In order to
insure randomization, the pots'positions were reran-
domized once a week. The temperatures in the green-
house during the experiments varied between 20 and
323C. Zucchini squash plants infested with powdery mil-
dew were placed under the ventilating fans of the green-
house to distribute spores.
The severity of powdery mildew infestation was vis-
ually evaluated on individual leaves, and scored as per-
centage of area infected at weekly intervals (Garibaldi
et al., 1994; McGrath and Shisko!, 1996).
Statistical analyses were done using GLM and NLIN
procedures of SAS (SAS, 1993). The analysis of variance
(ANOVA) for all trials and the contrasts of fungicide with
the control and each of the milk dosages was done using
the Ftest to evaluate signi"cance. A nonlinear regression
model was "t to the data with infected leaf area as a
function of milk dosages, using the control treatment
(water) as the zero milk dosage (0%). The regression
model was >"!"!"!#![1!exp (!!!!X)]#,
where >"infected leaf area; X"milk dosage;
!""mean infected leaf area in the absence of disease
control; !#"maximum reduction of the infected leaf
area obtained by milk treatment; and !!"parameter
associated with the speed in which the maximum is
reached (Souza, 1998). The parameter estimates were
used to calculate EC$" values (the milk concentration
that reduced infected leaf area by 90%).
3. Results and discussion
Powdery mildew severity was very high in all the
experiments on zucchini squash plants receiving the con-
trol treatment of water applied once or twice a week.
Infected leaf area per infected leaf exceeded 50% by 22 d
after the "rst spray. A negative correlation was found
between the infected leaf area per infected leaf and milk
concentration sprayed on plants for the "ve experiments
(Fig. 1).
Milk applied twice a week at concentrations of 10%
and higher controlled powdery mildew on zucchini
squash at least as e!ectively as conventional fungicides
(Table 1). Several concentrations of milk were more e!ec-
tive than the fungicides fenarimol and benomyl. When
the applications were done once a week, milk concentra-
tions of 20 and 50% were required to achieve the same
level of disease control as fungicides in the fourth and
"fth experiments, respectively (Table 2). Mold grew on
the adaxial side of the leaves treated with milk at concen-
trations of 30% and higher, but plants did not appear to
be injured.
The goodness of "t of the regression model was mea-
sured by the squared correlation coe$cient (R!) between
the observed and predicted values. Estimated parameters
and R!for each trial are in Table 3. EC$" values for
experiments 1}4 indicate that milk dosages ranging from
3.8 to 19.7% would reduce disease severity by 90%. EC%&
was calculated with data from the "fth experiment be-
cause 90% reduction was not reached with the tested
dosages.
Cow milk may have more than one mode of action in
controlling zucchini squash powdery mildew. Fresh milk
may have a direct e!ect against S. fuliginea due to its
germicidal properties (Salle, 1954). Milk contains several
salts and amino-acids (Martins Filho, 1987). These sub-
stances have been shown to be e!ective in controlling
powdery mildew and other diseases (Reuveni et al., 1993,
1995; Mucharromah and Kuc, 1991; Titone et al., 1997;
Pasini et al., 1997). Several authors have shown that
sodium bicarbonate, oxalate, dibasic or tribasic
potassium phosphate, and other salts and amino-acids
490 W. Bettiol /Crop Protection 18 (1999) 489 }492

Table 1
E$cacy of milk sprayed twice a week to control zucchini squash powdery mildew (Sphaerotheca fuliginea)
First experiment Second experiment Third experiment
% infected leaf area per infected leaf % infected leaf area per infected leaf % infected leaf area per infected leaf
Treatment Days after the "rst spray Days after the "rst spray Days after the "rst spray
22 d 29 d 15 d 22 d 15 d 22 d
Water ['] 50.72!['] 56.94 ['] 32.46 ['] 53.29 ['] 39.99 ['] 64.23
Milk 5% ['] 21.71 (57) ['] 17.47 (62) ['] 10.99 (66) ["] 10.51 (80) [(] 6.32 (84) [(] 7.06 (79)
Milk 10% ["] 11.52 (77) ["] 9.99 (82) ["] 7.97 (75) ["] 7.10 (87) [(] 2.98 (93) [(] 1.92 (97)
Milk 20% [(] 7.47 (85) ["] 5.45 (90) ["] 2.84 (91) [(] 2.75 (95) [(] 1.23 (97) [(] 1.30 (98)
Milk 30% [(] 6.63 (87) ["] 5.06 (91) ["] 1.24 (96) [(] 1.84 (97) [(] 1.28 (97) [(] 1.35 (98)
Milk 40% [(] 4.61 (91) ["] 3.53 (94) ["] 0.86 (97) [(] 0.82 (98) [(] 0.50 (99) [(] 0.75 (99)
Milk 50% [(] 4.23 (92) ["] 3.79 (93) ["] 0.50 (98) [(] 0.50 (99) [(] 0.65 (98) [(] 1.00 (98)
Fungicide 15.66 (69) 8.80 (85) 2.95 (91) 7.53 (86) 15.13 (62) 15.58 (75)
F(ANOVA) 65.92"89.18"30.37"133.25"23.9"61.29"
CV (%) 27.9 30.7 58.4 31.5 67.3 50.4
!Symbols in square brackets indicate if the infected leaf area is greater ['], equal ["], or smaller [(] in contrast with the fungicide by the Ftest
(P"0.05). The numbers in parenthesis are the percentage of disease control in relation to the control treatment. The "rst and the third experiments
received fenarimol (0.1 ml/l) and the second experiment benomyl (0.1 g/l). The fungicides were sprayed once a week.
"Indicates signi"cance at P"0.01.
Table 2
E$cacy of milk sprayed once a week to control zucchini squash powdery mildew (Sphaerotheca fuliginea)
Fourth experiment Fifth experiment
% infected leaf area per infected leaf % infected leaf area per infected leaf
Treatment Days after the "rst spray Days after the "rst spray
24 d 31 d 17 d 24 d
Water ['] 44.20!['] 56.28 ['] 53.65 ['] 68.55
Milk 5% ['] 24.77 (39) ['] 35.31 (37) ['] 33.41 (38) ['] 44.10 (36)
Milk 10% ['] 17.84 (60) ["] 14.31 (75) ['] 21.27 (60) ['] 29.86 (56)
Milk 20% ["] 10.56 (76) ["] 9.18 (84) ['] 14.70 (73) ['] 18.93 (72)
Milk 30% ["] 10.23 (77) ["] 8.31 (85) ['] 14.55 (73) ['] 13.07 (81)
Milk 40% ["] 7.24 (84) ["] 8.10 (85) ['] 10.01 (81) ['] 11.87 (83)
Milk 50% ["] 4.59 (90) ["] 4.82 (91) ["] 8.75 (84) ["] 9.58 (86)
Fenarimol 0.1 ml/l 5.74 (87) 7.88 (86) 3.72 (93) 5.09 (93)
F(ANOVA) 59.90"26.54"67.77"125.08"
CV (%) 27.0 48.1 22.2 17.2
!Symbols in square brackets indicate if the infected leaf area is greater ['], equal ["], or smaller [(] in contrast with the fungicide by the Ftest
(P"0.05). The numbers in parenthesis are the percentage of disease control in relation to control treatment.
"Indicates signi"cance at P"0.01.
have been e$cient in the induction of systemic resistance
(Reuveni et al., 1993, 1995; Mucharromah and Kuc, 1991;
Titone et al., 1998; Pasini et al., 1997; Van Andel, 1966).
Therefore milk may also indirectly a!ect S. fuliginea by
inducing systemic resistance.
Milk is not a potential environmental or food
contaminant, consequently it can be used in organic
agriculture. Several organic growers have been spraying
5% cow milk once a week to control powdery mildew on
zucchini squash and cucumber.
W. Bettiol /Crop Protection 18 (1999) 489 }492 491

Table 3
Estimated parameters, squared correlation coe$cients and EC$" values for nonlinear regression models "tted to data from each of the "ve experiments
Non linear regression parameters and coe$cients
Milk applications Trial Days after "rst spray !"
!!#!!R!EC$"
Twice a week First 22 50.63847 45.18634 0.20096 0.94 11.4
29 56.81017 52.19949 0.26584 0.95 8.5
Second 15 32.08936 30.71073 0.19662 0.85 6.5
22 53.16968 51.12401 0.33233 0.96 5.6
Third 15 39.97214 38.87656 0.38995 0.86 3.8
22 64.22808 63.08247 0.47188 0.94 4.2
Once a week Fourth 24 43.66734 36.55757 0.12877 0.89 19.7
31 57.22086 50.90511 0.14216 0.80 18.5
Fifth 17 53.55440 42.88504 0.12899 0.92 17.8"
24 68.24291 57.69084 0.10596 0.96 24.2"
!!""mean infected leaf area in the absence of disease control; !#"maximum reduction of infected leaf area obtained by milk treatment; and
!!"parameter associated with the speed with which the maximum is reached.
"Corresponds to EC%& values and not to EC$".
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