Damping-off Incidence Research Articles

水耕栽培におけるミツバ立枯病の発生と遊走子形成におよぼす水耕養液濃度の影響について

水耕栽培におけるミツバ立枯病の発生と遊走子形成におよぼす水耕養液濃度の影響について

Effect of Time of Application of Diphenamid on Pepper, Weeds, and Disease

The effect of timing of preemergence application ofN,N-dimethyl-2,2-diphenylacetamide (diphenamid) on phytotoxicity to pepper(Capsicum annuumL.), efficacy of weed control, and damping-off incidence was studied in greenhouse and field experiments. Delay of application from day of sowing to close to emergence reduced phytotoxicity to pepper while only partially reducing herbicidal action. Addition of a mixture of the contact nonresidual herbicides 6,7-dihydrodipyrido[1,2-a:2′,1′-c]pyrazinediium ion (diquat) and 1,1′-dimethyl-4-4′-bipyridinium ion (paraquat) to a late preemergence application of diphenamid resulted in control of weed seedlings which emerged after sowing of pepper and significantly increased the yield. The increase ofRhizoctoniadamping-off incidence due to diphenamid was also reduced by delayed application.

EFFECTIVE FUNGICIDE DOSAGE IN RELATION TO INOCULUM CONCENTRATION IN SOIL

A quantitative relationship was established between the fungicide dosage required to control a soil-borne disease and the concentration of mycelial inoculum in soil. The incidence of pre-emergence damping-off was observed in pea seedlings grown in non-sterile soil artifically infested with a series of concentrations of inoculum of Pythium irregulare or Rhizoctonia solani and treated with a dosage series of thiram or methylmercuric dicyandiamide. Parallel linear dosage–control curves were obtained which indicated that the logarithm of the fungicide dosage at the 50% control level increases proportionately with the logarithm of the inoculum density. This linear relationship provides a basis for evaluation of the activity of fungicides against various pathogenic fungi in soil.

A disease of lilies caused by Fusarium bulbigenum Cooke & Mass

A disease of seedling lilies was found to be due to Fusarium bulbigenum Gooke & Mass. Disease symptoms and the morphology of the pathogen are described in detail. A similar fungus was isolated from lesions on mature bulbs. Inoculation experiments showed that the fungus can enter unwounded roots of Lilium regale and of seedling lilies but cannot penetrate unwounded bulb scales. A strain of Fusarium bulbigenum from Narcissus caused rotting of wounded bulb scales but rotting was slower than with the lily strain. A high incidence of both pre-emergence and post-emergence damping-off of lily seedlings occurred in autoclaved soil contaminated by soil from the vicinity of diseased seedlings or by sand and cornmeal cultures of Fusarium bulbigenum . The strain from Narcissus caused less heavy losses. Old isolations of the lily strain were less virulent than fresh ones. Watering the seed boxes with a suspension of spores of Fusarium bulbigenum caused losses. The addition of a formalin dust to the seed boxes before sowing gave good control. Watering the soil in frames with liquid, formalin before planting, or watering the growing seedlings with a weak solution of Uspulun gave some control.