Author : Chatchavijk Thanomthin

Summary : Five experiments (three laboratory, one greenhouse and one field) were conducted at the University of the Philippines Los Baños and Maejo University, Chiang Mai, Thailand from May 2003 to June 2004 to : (a) determine the effect of crop variety, concentration, formulation, duration of soaking and volume of metalaxyl solution on the root system of corn (Zea mays L.); (b) compare the effect of NAA with that of metalaxyl on the root system of corn grown in Hoagland's culture medium; and (c) evaluate the effect of metalaxyl on growth, yield and yield components, and competitive ability of corn under different degrees of weed control. Metalaxyl improved the root system of corn depending on variety, concentration, formulation, duration of soaking and volume of soaking solution. IES glutinous var. 1 corn seeds soaked in 30 ml of 50 ppm metalaxyl (Ridomil 25 WP) solution for 24 hours produced seedlings with longer primary roots and greater number of seminal roots than the untreated in petri dish experiments. Under greenhouse conditions, corn plants grown in Hoagland's solution and treated with metalaxyl or NAA produced broader and denser root systems than the control plants. The positive effect of metalaxyl on the root system of corn was short lived. A second application of the chemical after four weeks did not further improve the root system of the crop. Under field conditions, corn plants (IES glutinous var. 1) whose seeds were saoked in metalaxyl solution for 24 hours before sowing exhibited faster growth, greater yield and yield components than those not treated with the chemical. Further improvements in the root systems of corn did not occur when a second application of metalaxyl was done 30 days after the crop was sown. Application of metalaxyl once increased corn yield by 12.6% while the weeds in the experimental field reduced corn yield by 19.7%.