Field production of decorative pumpkins (Cucurbita pepo L.) in New York occasionally results in markedly delayed fruit production in spite of normal vine growth. These episodes of fruitlessness appear to be associated with periods of high temperatures. To determine the link between temperature and pumpkin flowering and fruiting, a series of multilocational field trials and confirmatory greenhouse experiments were carried out. The field trials were conducted in the summer seasons of 1996 and 1997 in Ithaca and Albany, N.Y.; Queenstown, Md.; and Bradenton, Fla.; and in Ithaca and Bradenton in 1998. Mean growing season temperatures were 20, 21, 24 and 28 °C, respectively, at the four locations in 1996 and 1997. Delay in fruit formation was indicated by the main stem node number at which the first fruit developed. In Ithaca and Albany, the six cultivars formed their first fruit at node 17, but fruit production shifted to node 24 at Queenstown, and to node 26 or more at Bradenton. The prolonged delay in fruiting at the warmest site resulted in a 74% decrease in total yield of the C. pepo cultivars in 1996 and 1997, compared to Ithaca and Queenstown. In contrast, the yields and yield components of the C. maxima cultivar Prizewinner were similar at all four sites. Greenhouse trials in which `Howden' and `Baby Bear' were grown at 32/27, 25/20, and 20/15 °C confirmed that high temperatures delay formation and anthesis of female flowers. This and other published work indicates that there are genetic differences in susceptibility to high temperature flower delay that could be exploited to improve pumpkin performance.
H.C. Wien, S.C. Stapleton, D.N. Maynard, C. McClurg and D. Riggs
J.P. Mitchell, C. Summers, T.S. Prather, J. Stapleton and L.M. Roche
Observations that tomato transplants died or were severely stunted when set into unincorporated sorghum-sudan hybrid surface mulch led us to further investigate the potential allelopathic impacts of this warm-season cover crop in a series of field experiments. Survival and dry weights of tomato, lettuce, and broccoli transplants were determined in fallow, incorporated sorghum-sudan-, and unincorporated sorghum-sudan-mulched soils. All three species transplanted into plots in which the sorghum-sudan had been cut and left on the soil surface had a significantly lower dry weight than plants transplanted into fallow soil or into soil where the sorghum-sudan had been incorporated. Additionally, fewer transplants survived in the mulch treatment. The surface mulch plots also significantly reduced weed biomass nearly 10-fold. We believe that a water-soluble compound that is leached out of the sorghum-sudan hybrid is toxic to all three of the plants tested. Further laboratory and greenhouse tests are under way to determine the exact nature of the toxic substance.