Biology and response of Echinochloa colona (L.) link to fluazifop-butyl

Three pot experiments were conducted in Batac, Ilocos Norte [Philippines] to investigate the growth and reproductive capacity of Echinochloa colona; study its competitive ability in cotton supplied with varying nitrogen levels; and identify the growth stage that can be effectively controlled by fluazifop-butyl. Growth of E. colona followed a sigmoid curve. Tiller and flower production started at 23 and 54 days after seeding [DAS], respectively. There were 17 tillers and 15 panicles produced per plant. Each panicle produced 8 spikes, each spike producing 30 seeds. E. colona produced as much as 3,600 seeds in a life cycle. Increase in height, leaf production, nitrogen content, and seed output of E. colona were observed as nitrogen level was increased from 35 to 105 kg/ha. E. colona plants that grew with cotton were shorter; produced shorter panicles, fewer tillers, panicles, spikes, and seeds; and exhibited earlier tillering, flowering and panicle production than in monoculture. Height of cotton, number and weight of bolls also increased at high levels of nitrogen. Boll production was reduced by 54.5% when E. colona competed with the crop for the whole season. Crop yield reduction was due to decreased nitrogen content, shorter cotton plants with fewer and smaller bolls. Significant interaction of nitrogen levels and culture occurred on leaf production at 47 and 54 DAS, plant height from 19 to 54 DAS, on tiller and panicle production, panicle length, number of seeds per spike of E. colona and boll production and nitrogen content of cotton. E. colona was most susceptible to fluazifop-butyl when applied at four- and eight-leaf stages of growth. Chlorosis followed by necrosis of the leaves were the visible injury symptoms. The compound was highly selective to cotton. Tolerance of the weed to the chemical increased with maturity. Application of fluazifop-butyl at 4- to 8-leaf stages (13-22 DAS) resulted in excellent control of E. colona, taller cotton plants with more and heavier bolls. Herbicide application at peak tillering and panicle initiation stages resulted in poor control of the weed and shorter cotton plants