Abstract
Four corn (Zea mays L.) hybrids, grown at Lethbridge, Alberta, in 1975, 1976, and 1977, were sprayed on three dates with paraquat in an attempt to produce symptoms similar to those of a first killing frost. Interactions among hybrids and treatments were rare for characteristics such as grain yield, test weight, and kernel moisture content. The most pronounced effect of paraquat was that yield was reduced by about 1000 kg/ha for each week the simulated frost occurred before maturity. Development was affected less than yield. Treatments that resulted in a yield reduction of 60% only caused a 15% reduction in test weight. Kernel development was closely related to the accumulation of growing degree days with a base of 12 °C. Kernel moisture content was higher immediately after paraquat treatment, but rate of moisture loss was also slightly higher so that the paraquat treatments caught up to the checks and finally had a slightly lower moisture content. The earlier the paraquat treatment was imposed, the greater was the reduction in growth rate of grain. In addition, a very early paraquat treatment resulted in a longer effective filling period duration (EFPD), and a later imposition of the paraquat treatment caused a reduction in the EFPD compared to the check treatments.
Published Version
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