The relationship between Botrytis cinerea inoculum concentration and Botrytis blight on Rosa hybrida flowers from production greenhouses was monitored in the fall of 1985 and 1986 and winter of 1986 and 1987 under laboratory conditions. ‘Golden Wave’ rose flowers were inoculated with 0 to 104 conidia per milliliter and stored in incubation chambers at ≥95% RH and 21°C. Disease severity was quantified by the number of lesions per flower 48 hr after inoculation. The relationship between inoculum concentration and disease severity was linear; the coefficient of determination ranged from 0.87 to 0.99. The slope of the inoculum concentration–disease severity relationship was used to quantify susceptibility, which ranged from 0.006 to 0.035. Slopes were significantly greater with roses produced in December, January, and February (0.018 to 0.035) than those produced in October or November (0.006 to 0.013). Susceptibility of the flowers to B. cinerea was correlated linearly (r = 0.98) and inversely to the overall mean vapor pressure deficit from 0800 to 1900 hr for the 5-week growth period before harvest.
The cut flower and bulb industry in California is an important part of the state's agricultural economy and it has relied heavily upon the use of methyl bromide as a treatment to control soil-borne pests. With the phase out of methyl bromide, it is important to develop alternatives that will maintain crop productivity. This report describes research testing the efficacy of propargyl bromide against selected nematode, fungal, and weed species. Three sites were selected in California to represent different soil types and environments. Propargyl bromide was applied to soil in large, buried containers at rates ranging from 28 to 168 kg·ha−1 and compared with standard soil fumigants. The citrus nematode (Tylenchulus semipenetrans Cobb) and an isolate of Fusarium oxysporum Schlechtend:Fr were both controlled at the lowest rate of propargyl bromide tested: 28 kg·ha−1. Weed species varied greatly in their sensitivity to propargyl bromide. A 100% reduction in common purslane (Portulaca oleracea L.) and pigweed (Amaranthus retroflexus L.) germination occurred at 112 kg·ha−1 propargyl bromide, regardless of geographical location. Results for annual bluegrass (Poa annua L.) control were more variable across locations and years, but more than 90% control was consistently achieved with 168 kg·ha−1 propargyl bromide. Cheeseweed (Malva parviflora L.) and field bindweed (Convolvulus arvensis L.) were never consistently controlled by propargyl bromide. When compared with the soil fumigants methyl bromide, iodomethane, and metam sodium, propargyl bromide provided comparable control of all soil-borne pests, but at much lower rates. Although higher rates of propargyl bromide, more than 112 kg·ha−1, were needed to control weeds, these rates still were almost half that required of the other standard fumigants.