5.1.5
USE OF SOLARIZATION DURING AUTUMN FOR REDUCTION OF SOILBORNE PATHOGENS OF LANDSCAPE ORNAMENTALS IN A WET SUBTROPICAL CLIMATE

RJ McGOVERN1, R McSORLEY2 and ML BELL1

1University of Florida, Gulf Coast Research and Education Center, Bradenton, FL 34203, USA; 2University of Florida, Department of Entomology and Nematology, Gainesville, FL 32611, USA

Background and objectives
Solarization has been most successful in suppressing soilborne pests in hot, arid to semi-arid temperate or tropical regions with limited rainfall and cloud cover during summer [1]. The effects of solarization have been more variable in subtropical and tropical locations with frequent rainfall, including Florida [2]. The majority of experiments in Florida were conducted during the rainy summer months from June to August. Our objective was to evaluate soil solarization in autumn (September to November) during a drier, yet still relatively hot period. Our target pests included Phytophthora nicotianae on Madagascar periwinkle (Catharanthus roseus), Rhizoctonia solani and Pythium spp. on Impatiens wallerana, and various phytoparasitic nematodes in both crops.

Materials and methods
Field sites in Bradenton, Florida (27░ 27.12 N, 82░ 29.04 W) were used. Solarization versus P. nicotianae in periwinkle was tested in ten 3.6x3.6-m plots artificially infested with the fungus. On 29 September 1995, five plots were covered with 25-Ám, clear, low-density polyethylene (LDPE) mulch. On 9 November, the mulch was removed and periwinkle planted. Phytophthora blight incidence was monitored for 40 days. Solarization versus R. solani and Pythium spp. in Impatiens used ten 3.0x3.0-m naturally infested plots. On 26 August 1997, five plots were covered with a double layer of LDPE. The mulch was removed on 13 October, each plot was subdivided four times, and planted with Impatiens treated with Pseudomonas aureofasciens, Streptomyces lydicus, fludioxonil, or controls. Rhizoctonia crown rot incidence was monitored for 2 months, then plant biomass, root rot severity and infection by Pythium spp. were determined. Indigenous nematodes were enumerated and identified before and after solarization, and at the end of each experiment. Soil temperatures were monitored daily at 5, 15 and 23 cm during both experiments.

Results and conclusions
Solarization increased soil temperatures at all depths monitored. Phytophthora blight incidence in periwinkle reached 99% in non-solarized plots 40 days after planting. Solarization reduced (P<0.05) both the progress of Phytophthora blight and final blight incidence (9.0%). The only two plant-parasitic nematodes (Dolichodorus heterocephalus and Paratrichodorus minor) present in periwinkle in significant numbers were also controlled. Solarization and fludioxonil significantly decreased Rhizoctonia crown rot incidence in Impatiens. Root rot severity, Pythium infection, Meloidogyne incognita and other nematodes were suppressed in Impatiens by solarization, but not by P. aureofasciens, S. lydicus or fludioxonil. Solarization also increased (P<0.05) Impatiens biomass.

References
1. Katan J, 1980. Plant Disease 64, 450-454.
2. McGovern RJ, McSorley R, 1997. Chapter 12, in Rechcigl NA, Rechcigl JA, eds, Environmentally Safe Approaches to Crop Disease Control. CRC Press, Boca Raton, Florida.