Submitted to: Crop Protection Journal
Publication Type: Peer reviewed journal
Publication Acceptance Date: 12/17/2002
Publication Date: 3/10/2003
Citation: HARRISON JR, H.F., KEINATH, A.P. PUMPKIN CULTIVARS VARY IN SENSITIVITY TO THE HERBICIDE CLOMAZONE. 2003. CROP PROTECTION JOURNAL 23:795-798. Interpretive Summary: Weed control is a serious problem for pumpkin growers, and weeds severely limit productivity in the southeastern region of the U.S. where the warm wet climate favors rapid weed growth. Losses due to weed interference are increased by the sparse plant spacing for pumpkins. Relatively few weed control options are available to pumpkin growers. Few herbicides are registered for pumpkin and cultivation for weed control is limited by its vining growth habit. Of the herbicides used in pumpkin, only clomazone controls several broadleaf weeds that are predominant in the southeast. However, some pumpkin varieties are sensitive to the herbicide. The yield and quality of sensitive varieties may be reduced by clomazone. The objective of this study was to evaluate commercial and experimental pumpkin varieties in order to identify those most sensitive to the herbicide. Pumpkin varieties in the species Cucurbita maxima were least sensitive, but varieties in the species C. pepo, the most important pumpkin species, varied in sensitivity and several highly sensitive varieties were identified. The identification of sensitive varieties will allow growers to avoid quality and yield losses associated with clomazone injury to sensitive varieties by not growing these varieties when they plan to use clomazone. Avoiding sensitive varieties will help ensure the availability of the herbicide for pumpkin production.
Technical Abstract: A greenhouse experiment was conducted to assess the differences in clomazone response between two Cucurbita maxima (Duch.) pumpkin cultivars and one C. pepo L. pumpkin cultivar that were first observed in a field variety trial where the herbicide was used for weed control. The two C. maxima cultivars, Big Max and Mammoth Gold were highly tolerant and did not exhibit shoot weight reduction at a potting medium clomazone concentration of 64 ppm (w/w), four times the clomazone concentration that severely injured and reduced the shoot weight of the less tolerant C. pepo variety, Magic Lantern. A subsequent experiment to assess the response of 66 pumpkin cultivars demonstrated that while most C. maxima cultivars tested were not sensitive, the response of C. pepo cultivars varied greatly.