Ecological control of grape powdery mildew ( Uncinula necator )

V.A. Bourbos ¹ , M.T. Skoudridakis ¹ , E. Barbopoulou ¹ and K. Venetis² 

NAGREF, Institute of Subtropical Plants and Olive Tree of Chania, Laboratory of Plant Pathology, Agrokipio, 73100, Chania, Crete, Greece.

INTRACHEM HELLAS, Kiffisias 31, 11523, Athens, Greece.

ABSTRACT

Grape powdery mildew caused by the fungus Uncinula necator (Schw.) Burr. is responsible for serious damages in the vineyards of Crete. At the ecological vine cultivation, the elemental sulfur has been used applied as a dust or as a wettable powder, following the approval of the organization for the control and certification of biological products. These methods of applying sulfur induce problems, such as the residues remaining in the wine and the irritation causing to the people who use it. The aim of this study is to control the pathogen by incorporating in the soil a soil-improving product, acceptable for the ecological farming, known with the commercial name Acidam AVC 50. This product contains, apart from the other ingredients, 50% fine-granuled sulfur and microorganisms of Thiobacillus genus. The experiments were performed on wine vineyard of "Romeiko" cultivar during two cultivation periods. The product Acidam was incorporated in the soil on February, at the dose of 0,1 kg/m 2 on the first year and at the dose of 0,05 kg/m 2 on the second year. The conventional fungicide pyrifenox was used as a reference product, applied with three sprayings (stages D-E, G, J) at the dose of 20 ml/hl of the commercial product Dorado 20 EC. The product Acidam restricted the infected berries and infected leaves by 82,3-84,1 and 82,4-83,8% respectively, while the reduction of the reference product was 93,4-93,9 and 92,4-98% respectively. The plants treated with Acidam presented earliness on grape maturity at about 12 days and increase of production by 27,6-27,9%, cane diameter by 0,13-0,14 and internode length by 0,3-0,33 mm during 20 days interval with respect to the control.

INTRODUCTION

Grape powdery mildew caused by the fungus Uncinula necator (Schw.) Burr. constitutes a serious problem at the dry and warm conditions of vine cultivation. The control of the pathogen, at the ecological vine cultivation, is based on the reception of several cultivation measures, the use of varieties with reduced sensitivity to the pathogen and the application of various biological and chemical methods, following the relevant approval by the responsible organization for the control and certification of biological products.

Among the biological methods, particular interest presents the growth of products based on competitor microorganisms, such as Ampelomyces quisqualis (1). Nowadays, the use of soft fungicides is of significant importance, as part of the new phytopathological direction of phytomineralotherapy (2). In this connection, there is a great interest in bicarbonates of sodium, potassium and ammonium (3,4,5,6) and phosphonic acids (7,8).

Elemental sulphur, the fifth in quantity element of our planet, is one of the older fungicides used for the control of grape powdery mildew (9). It is applied as a dust or as a wettable powder and it's efficiency depends on the prevailing temperature conditions. Applying sulphur on the leaves of the plant, might cause problems such as phyto-toxicity, irritation of the eyes, inhibition of the microbial activity during the fermentation of the grape must and residues remaining in the wine (10,11).

Recently, it has been found that the incorporation of elemental sulphur as nutrient in the soil of the Brassica napus cultivation, interferes not only on the growth of the crop, but also on the control of Cylindrosporium concentricum by the stimulation of the plant defensive system, the emission of H 2 S through the epidermic cells and the production of isothiocyanates fungi-toxic compounds (12).

The control of grape powdery mildew is attempted in this study, by the incorporation of elemental sulphur in the soil of the vineyard.

MATERIALS AND METHODS

The experiments were performed on a 15 years old vineyard during two cultivation periods. The wine cultivar "Romeiko" was used.

Sulphur was used in the form of the commercial product Acidam AVC 50. This product is approved for the ecological farming as soil-improving and as sulphur fertilizer. It contains 50% fine-granuled sulfur, 26% biological origin organic matter, 10 4 propagules microorganisms of Thiobacillus genus and 0,3% Fe. The incorporation of Acidam AVC 50 in the soil was performed on February with a digging and milling machine at the dose of 0,1 Kg/m 2 for the first and 0,05 Kg/m 2 for the second cultivation period.

The conventional fungicide pyrifenox was used as a reference product at the dose of 20 ml/hl of the commercial product Dorado 20 EC. It was applied using a portable hand operated sprayer. Three sprayings were performed at the stages D-E, G and J.

The experimental design was randomized plots and every experimental unit included 10 plants in 5 replications.

The evaluation of the efficiency was determined by counting the number of infection spots per leaf and the infected berries per plant. The effect of Acidam AVC 50 on the growth of the cane, the time of grape's ripening and the total production was also evaluated. The effect on the growth of the plants was based on the length and diameter measuring of the third from the base internode for each cane at 20 days intervals.

RESULTS

The infection of leaves expressed as spots per plant and the infected berries per plant, at the experimental units treated with Acidam AVC 50, were significantly reduced and ranged from 1,64 (1996) to 1,84 (1997) and 1,9 (1996) to 2,53 (1997) respectively. These values were also sufficiently reduced for the reference product (0,2-0,28 and 0,73-0,95). On the contrary, the infection of leaves and the infected berries per plant were sufficiently high for the control (10,12-10,46 and 11,94-14,31) (Table 1, 2).

Table 1. Efficiency of Acidam AVC 50 in controlling grape powdery mildew (criterion: infection of leaves)

  
Table 2. Effect of Acidam AVC 50 on the control of grape powdery mildew (criterion: infection of berries)

Table 3. Effect of Acidam AVC 50 on the growth of canes(criteria: cane diameter and internode length)

Table 4. Effect of Acidam AVC 50 on the earliness of ripening and the production

DISCUSSION

On the conditions of the experiment, where Acidam AVC 50 was applied in the soil, it was able not only to control the grape powdery mildew at practically tolerable percentage, but also to affect positively the growth of the canes, shorten the time of ripening and increase the provisional production.

These findings present particular interest, since the unpleasant effects from the foliar application of sulphur are avoided and in addition the growth and the production of the cultivation is supported.

It seems that sulphur, in the presence of organic matter, iron and Thiobacillus which are included in Aacidam AVC 50, is transformed very quickly to the assimilative, from the plants, sulphuric radical, increasing by this way it’s reserves into the soil (13). It should be biochemically researched the role of cysteine in the stimulation of the plant’s defensive system with the biosynthesis products from the primary (methionine or glutathione) and secondary metabolism (glucosinolates) (14). The participation of the glucosinolates in the defensive system of the plant Brassica napus has been clarified (15). It should be also studied the action of the emitted H 2 S through the epidermical cells during the biosynthesis of sulphur and the produced isothiocyanates compounds for the restriction of the pathogen (14).

REFERENCES

1. Falk S.P., D.M. Gadoury, R.C. Pearson, and R.C. Seem, 1995. Partial control of grape powdery mildew by the mycoparasite Ampelomyces quisqualis . Plant Dis. 79, 483-490.
2. Homma Y. And Y. Arimoto, 1993. Phytomineralotherapy, as a concept on plant protection. 6 th International congress of Plant Pathology, Montreal, 73.
3. Ziv O. and T.A. Zitter, 1992. Effects of bicarbonates and film forming polymers on cucurbit foliar diseases. Plant Dis., 76, 513-517.
4. Cooley D.R., V. Mohr and A. Tuttle, 1995. Fungicide and formulated bicarbonate effects on apple scab, flyspeck and mite incidense. Fungicide and nematicide test, 50, 4.
5. Fallik E.,O. Ziv, S. Grinberg, S. Alkalai and J.D. Klein, 1997. Bicarbonate solutions Control Powdery Mildew ( Leveillula taurica ) on Sweet Pepper and Reduce the Development of Postharvest Fruit Rotting. Phytoparasitica 25 (1), 41-43.
6. Bourbos V.A., M.T. Skoudridakis and E. Barbopoulou, 1998. Sodium bicarbonate for the control of Erysiphe polygoni on greenhouse tomato. 6th ISHS International symposium on the proceccing tomato, Pamplona, Navarra, Spain.
7. Reuveni M. and R. Reuveni, 1993. Efficacy of phosphates in controlling powdery mildew fungus on field-grown winegrapes. 6 th International Congress of Plant Pathology, Montreal, 214.
8. Darakis G.A., V.A.Bourbos and M.T.Skoudridakis, 1997. Phosphates compounds in controlling plant diseases. Geotechnical scientific issues, Vol. 8, no3,58-69.
9. Forsyth N.,1802. In «a treatice on the culture and management of fruit trees»: Nicols and son.London.
10. Bourbos V.A.,G.A. Darakis, E. Barbopoulou and S. Sgouros,1998.Ecological control of powdery mildew (Uncinula necator) by the use of soft fungicides. XII International Scientific Conference IFOAM 98,102.
11. Schutz M and R. Kunkee,1977. Formation of hydrogen sulfide from elemental sulfur during fermentation by wine yeast. Am.Journ.Enol.Vitic.28,3,133-144.
12. Coleno A.,1987. Role fongicide du soufre. Compte rendus du Symposium International du soufre elementaire en agriculture, Nice-France,vol.1,31-37.
13. Schnug E and S.Haneklaus, 1994. Sulphur deficienncy in Brassica napus. Biochemistry, Symp [tomatology, Morphogenesis. Ed.Sonder heft 144, 33 p.
14. Fenwick G.R. and A.B.Hanley,1989.Glucosinates, alliins and cyclic disulphides sulphur containing secondary metabolites. In Damani, L.A.Ed. Sulphur-containin drugs and related organic compounds,-Chemistry,Biochemistry and Toxicology Vol. Part B.E. Horwood series in Biochemical Pharmacology pp.273-315.
15. Schnung E. And J.Ceynowa,1991. Phytopathological aspects of glycosinates in oilssed rape.J.Agron.andCrop Science 165,12-124.