The fungi causin damping-off of carrot seedlings

When 136 samples of dying carrot seedlings from several fields were analyzed <em>Alternaria rudicina</em> proved to be the most common seedling pathogen (41%), followed by some <em>Fusarium</em> species (27%, mostly <em>F. avenaceum</em>).The less common seedling pathogens were <em>Pythium</em> spp. (13%), <em>Phoma</em> spp.(2,5%) and <em>Botrytis cinerea</em> (1,4%). Some other fungi (<em>Bipolaris sorokiniana, Sclerotinia sclerotiorum, Stemphylium botryosym</em> and <em>Ulocladium consortiale</em>) were found in less than 1% of seedlings examined.

Importance of Fungicide Seed Treatment and Environment on Seedling Diseases of Cotton

The importance of fungicide seed treatments on cotton was examined using a series of standardized fungicide trials from 1993 to 2004. Fungicide seed treatments increased stands over those from seed not treated with fungicides in 119 of 211 trials. Metalaxyl increased stands compared to nontreated seed in 40 of 119 trials having significant fungicide responses, demonstrating the importance of Pythium spp. on stand establishment. Similarly, PCNB seed treatment increased stands compared to nontreated seed for 44 of 119 trials with a significant response, indicating the importance of Rhizoctonia solani in stand losses. Benefits from the use of newer seed treatment chemistries, azoxystrobin and triazoles, were demonstrated by comparison with a historic standard seed treatment, carboxin + PCNB + metalaxyl. Little to no stand improvement was found when minimal soil temperatures averaged 25°C the first 3 days after planting. Stand losses due to seedling pathogens increased dramatically as minimal soil temperatures decreased to 12°C and rainfall increased. The importance of Pythium increased dramatically as minimal soil temperature decreased and rainfall increased, while the importance of R. solani was not affected greatly by planting environment. These multi-year data support the widespread use of seed treatment fungicides for the control of the seedling disease complex on cotton.

Seedling Establishment of Direct-seeded Guayule

The establishment of stands from directly sown seed may be a way to reduce the current high costs associated with guayule (Parthenium argentatum Gray) cultivation. These field studies were conducted to examine the combined effects of shade and fungicides on the survival of guayule seedlings established from directly sown seed. Soil in the experimental plot was a loam of pH 7.25. The following fungicides: a) Terraclor Super X, b) Ridomil 5G, c) Ridomil PC llG, d) Tilt 3.6E, e) Terracoat, and f) Vitavax + PCNB were tested alone and in combination with the nonwoven polyester shadecloth, Reemay, to identify treatments enhancing seed germination and seedling establishment. In all cases, seedling emergence in microplots covered with Reemay was significantly higher than in noncovered microplots. Terraclor Super X, Ridomil 5G, and Ridomil PC 1 lG were effective only when used in combination with the shadecloth. The long-term survival of guayule seedlings was strongly affected by severe climatic events. Since Reemay-protected seedlings were larger and more robust, they were more likely to survive the climatic extremes than unprotected seedlings. Two new guayule seedling pathogens were recorded -pythium dissotocum Drechsler and P. paroecandrum Drechsler. Chemical names used: 5-ethoxy-3-(trichloromethyl)-1,2,4-thiadiazole (Terrazole) + pen. tachloronitrobenzene (PCNB); N-(2,6-dimethylphenyl)-N-(methoxyacetyl)-alamine methyl ester Ridomil + PCNB; 7. bromo-5-chloro-quinolin-8-yl-acrylate; Terrazole 5,6-dihydro-2-methyl-l,4 -oxathiin-3-carboxanilide + PCNB.