Effects of herbicides on the population dynamics of weeds in lowland ricefield.

Date

4-1993

Degree

Bachelor of Science in Biology

Major Course

Major in Ecology Genetics

College

College of Arts and Sciences (CAS)

Adviser/Committee Chair

Marissa P. Caldas

Abstract

study on the emergence of weeds throughout the growing season and the effects of both pre- and post-emergent herbicide on emergence, survival and reproduction of some lowland ricefield weeds in their natural habitat was conducted. It also provided some ecologically sound information that can aid in developing weed management strategies. Demographic censusing of weeds was done from December 1991 to April 1992 in lowland rice farm at Bangias, Laguna. Five blocks consisting of four horizontally arranged 1m sq. quadrats and four treatments (control, with N-(butoxymethyl) 2-chloro-2',6'-diethylacetinilide (machete),with 2,4- dicholorophenoxyacetic acid (2,4-D) and with machete + 2,4-D) were used in the analysis. Results showed a generally higher emergence for the weeds in the control compared to the herbicide treatments. This was mentioned to be most likely caused by the pre-emergent herbicide, machete. There was also absence of late emergence in which was speculated to be caused by limited number of viable non-dormant seeds in the soil. Ecological explanations such as canopy overlap, water level and competition was also mentioned. Results also showed a generally higher survival and reproductive success for the species Amania, Sphenoclea and Echinochloa in the control compared to the herbicide treatments. This was the result of the post-emergent 2,4-D herbicide. The survivorship curve for the three species also confirmed the susceptibility of broad-leaf weeds (Amania and Sphenoclea) and sensitivity of grass weed (Echinochloa) to 2,4-D. In terms of success and reproduction however, this strongly demonstrate that the herbicides were able to drastically reduce overall success of both broad-leaf and grasses at least within one single season. However, 2,4-D failed to completely suppress the plants that survived. The failure of both types of herbicides to totally eliminate weed has a tremendous impact on future weed infestation. Despite success (it suppresses a large proportion of the weed), herbicide may however, be rendered ineffective in the long run because their continuous use strongly select existing resistant or tolerant weed genotype, which would eventually proliferate. Long term studies on evolutionary responses of weeds to herbicides therefore strongly recommended. are therefore strongly recommended.

Language

English

Location

UPLB Main Library Special Collections Section (USCS)

Document Type

Thesis

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