International Congress BIOLOGICAL PRODUCTS - Gruppo di ...

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NATURAL COMPOUNDS IN THE CONTROL OF POWDERY MILDEW ON CUCURBITS IN ORGANIC
AGRICULTURE
Fedele Casulli (1) , Agostino Santomauro (1) , Giuseppe Tauro (2) , Maria Antonia Gatto (1) , Franco Faretra (1)
(1) Dipartimento Protezione delle Piante e Microbiologia Applicata, University of Bari, Italy
(2) Centro di Ricerca e Sperimentazione in Agricoltura "Basile Caramia", Locorotondo (Bari), Italy
In Italy, Cucurbitaceae are important vegetable crops grown especially in Central and Southern Italy (Sicily, Latium
and Apulia). Melon (Cucumis melo L.), watermelon [Citrullus lanatus (Thunb) Matsum et Nakai], courgette (Cucurbita
pepo L.) and cucumber (Cucumis sativus L.) are the prevalent species being cultivated on a surface of 21,400, 14,200,
12,200 and 1,500 hectares, respectively (Istat, 2001). Powdery mildew, caused by Sphaerotheca fusca (Fr.) S. Blumer
[syn. S. fuliginea (Schlecht. ex Fr). Poll.] is the most common and severe disease on the crops. Many fungicides are
available for an effective control of the pathogen, but in view of their negative side effects, people look to more
consumer- and environment-friendly alternatives, including natural compounds. The present paper reports the results of
trials carried out under glasshouse and field conditions in order to evaluate the effectiveness of natural compounds in
the control of powdery mildew in organic agriculture.
Zucchini squash (Cucurbita pepo L., cv. Striato pugliese) and cucumber plants (C. sativus, cv. Mezzo lungo di
Polignano) were grown individually in plastic pots (10 cm in diameter) in a glasshouse at 20-24°C and RH 70-80%,
under daylight. Four-replicated plants, maintained at the two-three leaf stage by pruning were used for each thesis. The
plants were artificially inoculated with S. fusca by spraying a suspension containing about 5⋅10 5 fresh conidia per ml.
The tested compounds, including several natural substances allowed in organic agriculture (Table 1), were applied
either 3 days before or 3 days after the artificial inoculation with the pathogen. Untreated check plants were sprayed
only with water. Numbers and sizes of fungal colonies were assessed 11 days after inoculation on 10-cm 2 of the surface
of each leaf.
Natural substances were tested in field trials on melon (C. melo, cv. Barattiere) carried out during the summer. The
statistical design was the complete randomised blocks with four replications and plots were made up of 8-10 plants in
all trials. Spray schedules always were started before the appearance of first disease symptoms; treatments were
repeated at one-week intervals. The severity of powdery mildew symptoms was periodically assessed evaluating the
percentage of infected leaf surface. All data were submitted to variance analysis and mean values were separated by
Duncan’s Multiple Range Test.
According to the reduction of symptoms severity on treated plants as compared to the untreated check, the tested
compounds were grouped in effective (higher than 70%), moderately effective (from 40 to 70%) or poorly effective
(less than 40%) (Table 1).
A good control of powdery mildew fungi was achieved in glasshouse as well as in field by fresh and dried milk (10%),
which reduced infections over 90%. Among the other tested compounds, calcium and magnesium chloride, potassium,
sodium or ammonium phosphate dibasic, pinolene, sodium bicarbonate and the mixtures of mineral oil with sodium
bicarbonate or sodium silicate, significantly reduced the severity of S. fusca on leaves. These compounds showed the
highest effectiveness when applied 3-4 days after the artificial inoculation of S. fusca. In the field, the same compounds
yielded a satisfactory control of powdery mildew on the upper leaf surface of cucurbits, but they showed poor
effectiveness against infections on stems and lower leaf surface, especially under high disease pressure. Mineral oil was
effective when applied 3-4 days before artificial inoculation of S. fusca; this corroborate the finding that the compound
acts also as inducer of defence mechanisms in plants. Ammonium phosphate monobasic, sodium silicate, sodium
hydroxide, trisodium and tripotassium phosphate proved poorly effective at non-phytotoxic concentration while calcium
carbonate, calcium sulphate, calcium silicate, sodium and potassium chloride, sodium and potassium phosphate
monobasic were poorly effective against S. fusca.
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