RESUMO
In December 1999, typical signs of powdery mildew-dense white mycelium in irregular patterns often covering almost the entire upper surface of leaves-were observed in production greenhouses on tomato cv. Tradiro. Microscopic observations revealed mycelium with lobed appressoria and large, approximately cylindrical conidia that measured 38 to 45 × 16 to18 µm. Short germ tubes were at one end of the conidium and ended in a lobed appressorium. Conidiophores were straight with cylindrical foot-cells (≈40 to 42 µm), followed by two short cells (14 to18 µm). Based on these characteristics the fungus was identified as 0idium neolycopersici Kiss et al. (2) (formerly O. lycopersicum Braun [1]). Disease-free tomato cv. FL47 plants were inoculated at the fourth true-leaf stage with conidia by transferring fungal colonies collected from plants in production greenhouses with a single-edged razor blade to the adaxial surface of the test plants (six plants and three leaves per plant). Plants were grown in the greenhouse at 20 to 25°C. Powdery mildew, exhibiting the same morphological features, was observed 12 days later on inoculated tomato leaves. Powdery mildew on tomatoes in Suwannee Valley area greenhouses in Florida was quite common and severe in 1999 to 2000. Secondary cycles of the disease were observed, resulting in disease incidence up to 50 to 60% in some greenhouses, requiring repeated applications of sulfur for its management. This disease is expected to become a significant problem in greenhouse tomatoes, requiring regular disease control measures. This powdery mildew has not yet been observed in field-grown tomatoes in Florida. The pathogen has been reported in Connecticut on tomatoes grown under greenhouse and field conditions (3). To our knowledge, this is the first report of O. neolycopersici on greenhouse-grown tomatoes in Florida. References: (1) U. Braun. The Powdery Mildews (Erysiphales) of Europe. Gustav Fisher Verlag, New York, 1995. (2) L. Kiss et al. Mycol. Res. 105:684, 2001. (3) J. A. LaMondia et al. Plant Dis. 83:341, 1999.
RESUMO
The effects of eight summer rotation crops on nematode densities and yields of subsequent spring vegetable crops were determined in field studies conducted in north Florida from 1991 to 1993. The crop sequence was as follows: (i) rotation crops during summer 1991; (ii) cover crop of rye (Secale cereale) during winter 1991-92; (iii) 'Lemondrop L' squash (Cucurbita pepo) during spring 1992; (iv) rotation crops during summer 1992; (v) rye during winter 1992-93; (vi) 'Classic' eggplant (Solanum melongena) during spring 1993. The eight summer crop rotation treatments were as follows: 'Hale' castor (Ricinus communis), velvetbean (Mucuna deeringiana), sesame (Sesamum indicum), American jointvetch (Aeschynomene americana), weed fallow, 'SX- 17' sorghum-sudangrass (Sorghum bicolor x S. sudanense), 'Kirby' soybean (Glycine max), and 'Clemson Spineless' okra (Hibiscus esculentus) as a control. Rotations with castor, velvetbean, American jointvetch, and sorghum-sudangrass were most effective in maintaining the lowest population densities of Meloidogyne spp. (a mixture of M. incognita race 1 and M. arenaria race 1), but Paratrichodorus minor built up in the sorghum-sudangrass rotation. Yield of squash was lower (P
