Climate Change’s Impacts on Weeds and Herbicide Efficacy: A Review

ISSN: 2319-7706 Volume 6 Number 9 (2017) pp. 2846-2853 Journal homepage: http://www.ijcmas.com Climate change is a natural and continuous process. But recent relatively rapid change in climate occurs due to anthropogenic activities which makes alarming attention because it contributes largely to global warming by affecting the greenhouse gases (GHGs) and aerosols. GHGs mainly CO2, methane, nitrous oxide CFC11, CFC12, HCFC22and HFC23 with different global warming potential accumulate in atmosphere and increase in concentration over time creating the so called “greenhouse effect”. This effect can alters balance by transmitting incoming solar radiation but absorbing outgoing thermal radiation from surface. Atmospheric CO2 rose from 280 to 387 μmolmol –1 from 1750 to 2007 and expected to reach 600 μmolmol –1 by 2050 and global earth surface temperature is likely to rise in a range of 1.1 to 6.4°C during the 21st century due to the rising CO2 concentration. Weeds are complex in nature and have significant negative effect on agriculture. Chemical weed control becomes major choice/tool because of its economic, easy to use, greater efficacy, due to scarcity of labour and time saving. Climate component viz., light, CO2, temperature, precipitation, humidity, wind, environmental stress etc. affect crop-weed competition and efficacy of applied herbicides. Light stimulates weed seed development and leaf shape. Light is the source of energy for photosynthesis and the rate of photosynthesis determines the rate of phloem translocation of assimilates and subsequent phloem translocation will increase the movement of foliar-applied systemic herbicides. Most crops are C3 and most weeds are C4, and hence weed competition will consequently decrease as CO2 increases, should not be viewed as universal axiom as there are four major C4 crops of economic importance (corn, pearlmillet, sorghum, and sugarcane), and their many important C3 weeds. Increasing CO2 concentration increases the starch concentration in tissue and reduces the protein content leads to less demand of amino acids synthesis which alters the efficacy of ALS inhibitors herbicides. High temperature shortens the growth phases, stimulate stomata conductance and lowers the viscosity of cuticular lipids leads to increase permeability and diffusion of herbicides through the cuticle. Warmer temperature also reduce uptake of herbicides due to rapid drying of droplets. Increasing temperatures may mean an expansion of weeds into higher latitudes or higher altitudes.. Increased cuticle thickness and leaf pubescence in response to drought, will also reduce herbicide entry into leaves. At higher humidity leaf retention time of herbicides mainly hydrophilic increases. Blowing wind may cause spray drift or dry up the spray droplet. So there is need to pay special attention and to study the impact of climate factors on weed life, crop-weed competition and herbicide efficacy so that adaptation and mitigation strategies can be developed for changing climate. K e y w o r d s Climate changes, Natural process, Greenhouse effect, Environment. Accepted: 26 August 2017