Effect of air temperature, relative humidity and growth stage on rimsulfuron tolerance in selected field maize hybrids

The effect of temperature (T), relative humidity (RH), and growth stage (GS) of six field maize hybrids on the level of tolerance to rimsulfuron [N-((4,6-dimethoxypyrimidin-2-yl) aminocarbonyl)-3-(ethylsulfonyl)-2-pyridincsulfonamide] applied at 20, 40 and 60 g a.i ha^-l were evaluated. The hybríds tested are adapted to three climatic zones of Québec, Canada (zone 1: >2 700 maize heat units (CHU); zone 2: 2500 to 2 700 CHU; zone 3: 2 300 to 2 500 CHU).Two hybrids of each zone were considered. Three experiments were carried out under growth chamber and glasshouse conditions. Corn response to rimsulfuron doses was linear. Hybrids of zone 1 were more tolerant to rimsulfuron than hybrids from zones 2 and zone 3.Dry weight reduction of hybrids (DWR as a percentage of the untreated control 14 days after treatment) varied according to the dose from 22% to 29%, 31 % to 35%, and 36% to 38% in zones 1, 2, and 3, respectively. The response of maize hybrids to increasing temperaturewas linear, and the DWR was 12%, 28%, and 51 % at 14°C, 21 °C, and 28°C, respective1y.  Injury to maize hybrids grown under 60% and 75% RH averaged 31 % and 37% DWR, respectively.

Corn plants treated at the 2- to 3-leaf growth stages showed, in general, more sensitivity to rimsulfuron than those treated at the 4- to 5- leaf stage. These results confirmthat both environmental conditions and maize genotypesplay an important role in the injury caused by rimsulfuron.

Key words: herbicides, sulfonylurea, rimsulfuron, field maize hybrids, tolerance, environmental conditions.

Abbreviations: CHU, maize heat units; T. temperature;RH, relative humidity; GS, growth stage; DWR, dry weightreduction.