Soil solarization in a plastic house

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G. Cartia *, N. Greco**, and G. Cirvilleri*
*Istituto di Patologia Vegetale, Università di Catania, Italy
**Istituto di Nematologia Agraria, CNR, Bari, Italy

Abstract

Soil solarization trials to control Verticillium dahliae, Pyrenochaeta Iycopersici and Meloidogyne spp. on eggplant, were undertaken in Sicily during summer 1987 in a plastic house treated before and after covering. The effects of 30 and 50 day solarization periods, fumigation with methyl bromide, alone at 80 g/sq.m combined with 30 day solarization, were compared with controls. Climatic, agronomic, and phytopathological parameters were recorded during the growing season of the eggplant. Soil temperatures recorded during solarization were higher in the plastic house covered before treating, where 46.9 and 42.3°C. were reached at 5 and 15 cm depth, respectively. Control of all pathogens and yield increases were greater in the former than in the latter plastichouse. Moreover, soil solarization in the plastic house covered before treating was as effective as fumigation with methyl bromide.

Introduction

The extent of land devoted to greenhouse crops in Italy is continuously increasing. In the last 15 years it has risen from 9 000 to about 20 000 hectares. Most of the greenhouses are in the south of the country and especially in Sicily where 8 000 hectares are presently cultivated. Here plastic houses prevail and 83 percent of the total area is dedicated to solanaceous crops, such as tomato (40 percent), pepper (29 percent) and eggplant (14 percent).

In 1986-87, a high eggplant death-rate was observed in some plastic houses of the Ragusa area due to Verticillium dahliae Kleb. infection, despite soil fumigation. Furthermore corky root symptoms caused by Pyrenochaeta Iycopersici Schneider et Gerlach and root-knot nematodes Meloidogyne javanica. (Treub) Chitwood and M. incognita (Kofoid and White) Chitwood, were observed. These plastic houses were newly made using soil from a field that had been cultivated to potato for a long time.

In the past, only chemicals were used to control these pathogens. Recently, soil solarization (6), a non-chemical method of control, has shown promise to control soilborne pathogens in greenhouses (1,2,3,4)

In Sicily, summer temperatures are rather high and therefore suitable for soil solarization. Therefore it appeared interesting to undertake trials to compare the effectiveness of different periods of soil solarization with that of methyl bromide alone at normal dose, or at reduced dose in combination with soil solarization, in plastic houses covered before or after solarization and methyl bromide treatments.

Materials and Methods

The experiment was arranged on a farm near the sea al Donnalucata (province of Ragusa), with a sandy soil. The plastic house (1200 sq.m) was divided in two equal parts, each having 20 plots of 30 sq.m according to a randomized block design.

The following five treatments replicated four times, were compared:

1. Untreated control;
2. Methyl bromide 80 g/sq.m (MB 80);
3. Soil solarization for 30 days + methyl bromide 30 g/sq.m (Sol 30 + MB 30);
4. Soil solarization for 30 days (SOL 30);
5. Soil solarization for 50 days (SOL 50).

Half of the plastic house was covered with EVA film 150 mm thick before treating and the remaining half was covered before transplanting eggplants on 10 September, 1987. Soil solarization was started on 7 July 1987 using polyethylene film 50 m m thick, while methyl bromide was applied on 1 September 1987.

Eggplant (cv. Mission Bell.) seedlings were transplanted on 10 September 1987. The following parameters were recorded during the crop season:

1. Percentages of plants affected or dead because of Verticillium wilt
2. Incidence of P. lycopersici causing corky-root, according to 0-5 symptom scale:
3. Soil population densities of root knot nematodes, according to Coolen's method (5):
4. Root galling index caused by root-knot nematodes, according to a 0-5 scale;
5. Eggplant yield per plant;
6. Soil temperature at 5 and 15 cm depth.

All data were statistically analysed according to Duncan's multiple range test.

Results

Soil temperatures recorded during solarization were higher in the plastic house covered before treating, where 46.9 and 42.3°C. were reached at 5 cm and 15 cm depth, respectively. In the plastic house covered after treating maximum soil temperatures were, only 42.0°C. at 5 cm and 38.1°C. at 15 cm depth.

The infection of eggplant by V. dahliae (Fig. 1) was higher in the untreated than in the treated plots. However, more severe infections were observed in the plastic house covered after (55 percent of the plant infected) than in that covered before (24 percent) treating. Soil solarization for 30 and 50 days reduced plant infection to 4 and 3 percent and to 23 and 31 percent in the plastic house covered before and after treating, respectively. Methyl bromide at the reduced rate (30 g/sq.m) reduced eggplant infection to similar levels: 18.5-19 percent in the plastic house covered after and 11-13 percent in that covered before treating.

The incidence of corky-root disease (Fig. 2) in the plastic house covered after treating was in the range 2.7-3.3 percent in untreated and solarized plots and 1.6-1.7 percent in those fumigated with methyl bromide alone or in combination with soil solarization. This disease was less severe in the plastic house covered before treating (0.8-1.7 percent) and no significant differences were observed among the treatments.

Root-knot nematode population densities were not large before treating. However, they were slightly larger in the part of the plastic house covered after treating than in that covered before treating. Before planting, no nematodes were detected in the top 30 cm of soil in the part of the plastic house covered before treating, while a few were found in the other. After transplanting eggplants, the nematode population desities increased in all plots (Table 1), but they were much smaller in the part of the plastic house covered before treating. In January the population densities of the nematodcs were larger, although not significantly different, in the control and solarized (SOL 50) plots than in those treated with 80 g methyl bromide/sq.m or with a 30 day solarization period.

Before planting in the plastic house covered before treating, nematodes were found only in the control plots. At the end of the season the nematode populations had further increased, but to a lesser extent in the plastic house covered before treating.

Root galling indices were low in all treated plots. In general, root infestation was less in plots covered before treating than in those covered after, except when fumigated with 80 g methyl bromide/sq.m, which was similar in both parts of the plastic house.

Total yields of eggplant (Table 2) from all treatments were higher in the plastic house covered before than in that covered after treating. In the former, yields from treated plots were significantly more than from untreated plots. Plots solarized for 50 days or fumigated with 80 g of methyl bromide/sq.m gave the greatest yield increase.

Discussion and Conclusion

These investigations showed that in the plastic house covered before treating, soil solarization alone or combined with a low dosage of methyl bromide gave the best control of V. dahliae, P. Iycopersici and Meloidogyne spp. Methyl bromide at 80 g/sq.m was equally effective in suppressing corky-root disease and root galling in both plastic houses. Moreover, the results confirmed that soil solarization is effective in suppressing nematode damage to roots for several months after transplanting. This resulted in yield increases similar to those obtained by fumigation with methyl bromide alone. It is also noteworthy that better pathogen control was achieved in the plastic house covered before treating. Most probably this was due to higher soil temperature increases that may have killed or weakened a larger proportion of the fungus propagules, nematode eggs and second stage juveniles to a greater soil depth.

When, for cropping reasons, the plastic house covering has to be set up at the end of the summer, solarization plus fumigation with reduced rates of methyl bromide appears useful. In this case the soil can be solarized in summer and fumigated before or after the covering.

References

1. Cartia, G. and N. Greco. 1989a. Feasibility of soil solarization for controlling soil-borne agents of solaceous plants in Sicily. The First Israeli-Italian Phytopathological Symposium. Bet-Dagan, Israel, Feb. 1315, 1989.

2. Cartia, G., N. Greco, and T. Cipriano. 1989b. Effect of solarization and fumigants on soilborne pathogens of pepper in greenhouses. Acta Horticulturae 255:111-116.

3. Cartia, G., N. Greco, and G. Cirvilleri. 1988. Solarizzazione e bromuro di mettle nella difesa dai parassiti del pomodoro in ambiente protetto. Atti Gionate Fitopatologiche 1988, 1, 437-448.

4. Cartia, G., G. Noto, A. Nucifora, A. Paratore. 1989c. Effetti agronomici e fitosanitari della solarizzazione del terreno su pomodoro coltivato in serra. Colture Protette 18 (4): 73-77.

5. Coolen, W. A. 1979. Methods for the extraction of Meloidogyne spp. and other nematodes form roots and soil In: Root-knot Nematodes (Meloidogyne species) systematics. biology and control. F. Lamberti and C. E. Taylor eds. Academic Press, London, pp. 317-329.

6. Katan, J.A., Greenberger, H. Alon, and A. Grinstein. 1976. Solar heating by polyethylene mulching for the control of disease caused by soil-borne pathogens. Phytopathology, 66, 683-688.

Table 1. Effect of soil solarization and/or methyl bromide on population densities of Meloidogyne javanica and M. incognita in soil and roots of eggplant in a plastic house covered before (Cov.B) and after treating (Coy. A)

(cont'd)

Table 1 (cont'd)

1 Figures in the same column flanked with the same letter are not statistically different according to Duncan's multiple range test. Small Ietters for P = 0.05 and capital letters for P = 0.01.
2 According to a 0-5 scale: 0 = no galling; 5 = severe galling.

Table 2. Cumulative yield of eggplant (Grams/Plant) at different dates of the growing cycle (Sept. 11, 1987- May 31, 1988) in plastic house covered before (Coy. B) and after (Coy. A) treating

1 Figures in the same column flanked with the same letter are not statistically different according LO Duncan's multiple range test. Small letters for P = 0.05 and capital letter for P = 0.01.

Figure 1. Percentage of eggplants infected by Verticillium dahlias when the soil was solarized and/or treated with methyl bromide before and after covering the plastic house.

Figure 2. Incidence of corky root disease of eggplants when the soil was solarized and/or treated with methyl bromide before and after covering the plastic house.

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