Advances in Weed Management (2015) SS Rana and MC Rana Department of Agronomy, Forages and Grassland Management College of Agriculture, CSK Himachal Pradesh Krishi Vishvavidyalaya, Palampur-176062 (India) Advances in Weed Management SS Rana and MC Rana 2015 DEPARTMENT OF AGRONOMY CSK Himachal Pradesh Krishi Vishvavidyalaya Palampur-125004 Copyright 2014 SS Rana , Sr Scientist, and MC Rana, Prof, Department of Agronomy, Forages and Grassland Management, Coll ege of Agriculture, CSK Himachal Pradesh Krishi Vishvavidyalaya, Palampur- 176062. No part of this pub lication may be reproduced, stored in a retrieval system, or transmitt ed, in any form or by any means, electronic, mechanical, photocopying, recording, or otherwise without the writt en permiss ion of the authors . Citation Rana SS and MC Rana. 2015. Advances in Weed Management . Department of Agronomy, College of Agriculture, CSK Himachal Pradesh Krishi Vishvavidyalaya, Palampur , 55 pages. PREFACE Weeds are probably the most ever-present class of crop pests and are responsible for marked losses in crop yields. Of the total losses caused by pests, weeds have a major share (30%). They reduce the crop yield and deteriorate the quality of produce and hence reduce the market value of the turn out. Therefore, management of weeds in all agro-ecosystems is imperative to sustain our crop productivity and to ensure the food security to the burgeoning population. There has been a long-felt need for a teaching manual on Advances in Weed Management. This manual is a precise account of various theoretical aspects of weed management presented in a simple language suitable for Agron 606 students. The manual provides useful information on crop-weed competition, weed shifts, mode of action of herbicides, selectivity of herbicides, climate and phytotoxicity of herbicides, fate of herbicides in soil, residue management of herbicides, adjuvants, herbicide application techniques, herbicide resistance, herbicide antidotes, herbicide interactions, transgenic herbicide resistance crops, herbicide development and registration procedures, bioherbicides, allelochemicals and herbicide bioassays . With all these varied aspects covered in the manual, we hope this will fulfill the requirement of a much needed standard document on Advances in Weed Management not only for the students but also for the teachers, scientists and others involved the field of weed management. The authors would welcome additional information and suggestions from students and teachers to improve the manual. S.S. Rana MC Rana CONTENTS SN Title Page 1 Crop-Weed Competition 1 2 Weed Shifts 15 3 Mode of Action of Herbicides 21 4 Selectivity of Herbicides 38 5 Climatic Factors and Phytotoxicity of Herbicides 50 6 Fate of Herbicides in Soil 58 7 Residue Management of Herbicides 68 8 Adjuvants 75 9 Herbicide Application Techniques 90 10 Herbicide Resistance 100 11 Herbicide Antidotes 109 12 Herbicide Interactions 118 13 Transgenic Herbicide Resistance Crops 126 14 Herbicide Development 131 15 Bioherbicides 159 16 Allelochemicals 163 17 Herbicide Bioassays 175 Appendix –I (Structures of Herbicides) i-xii Advances in Weed Management Crop-weed competition Competition is struggle between two or more organisms for a limited resource (Water, nutrient, light and space) that is essential for growth. The Oxford English Dictionary defines competition as “action of endeavouring to gain what another endeavours to gain at the same time; the striving of two or more for the same object; rivalry”. To compete comes from the Latin word competere, which means to ask or sue for the same thing another does. Competition in biology, ecology, and sociology, is a contest between organisms, animals, individuals, groups, etc., for territory, a niche, or a location of resources, for resources and goods, mates, for prestige, recognition, awards, or group or social status, for leadership. It is opposite to cooperation. It arises whenever at least two parties strive for a goal which cannot be shared or which is desired individually but not in sharing and cooperation. Competition occurs naturally between living organisms which co-exist in the same environment. For example, animals compete over water supplies, food, mates, and other biological resources. Humans compete usually for food and mates, though when these needs are met deep rivalries often arise over the pursuit of wealth, prestige, and fame. Competition is also a major tenet in market economy and business is often associated with competition as most companies are in competition with at least one other firm over the same group of customers, and also competition inside a company is usually stimulated for meeting and reaching higher quality of services or products that the company produces or develops. Competition occurs in virtually every ecosystem in nature. This type of relationship develops when more than one organism in an environment requires the same thing in order to survive. When food and shelter are plentiful, there is no competition. It only takes place when there is not enough to go around. Competition often results in the survival of the fittest. According to Bunting (1960), competition has different shades of meaning for the agronomist and plant physiologist. In his view, physiologists think of competition as for something, usually nutrients, water or light. Agronomists and weed scientists while agreeing, add that competition also exists between plants (Donald 1963). Many definitions were reviewed by Milne (1961). 1. Mather (1961): “Competition implies the presence of one individual as an effective part of other’s environment and a similarity of need or activities so their impact on each other is prospectively detrimental.” 1 Advances in Weed Management 2. Aspinall and Milthorpe (1959): “the interaction between plants and environment. The plants during growth modify the environment around them and the modified environment in turn influences the growth of the constituent plants.” 3. Bleasdale (1960): “Two plants are in competition with each other when the growth of either one or both of them is reduced or their form modified as compared with their growth or form in isolation.” 4. Milne (1961): “Competition is the endeavour of two (more) animals to gain the measure each wants from the supply of a thing when that supply is not sufficient for both (or all).” 5. Birch (1955): “ Competition occurs when a number of animals (of the same or of different species) utilize common resources the supply of which is short, or if the resources are not in short supply competition occurs when the animals seeking that resource nevertheless harm one or the other in the process.” 6. Clements et al (1929): “Competition involves the reaction of a plant to the physical factors that encompass it and of the effect of these modified factors upon adjacent plants. For Clements et al., competition is a purely physical process.” In the exact sense, two plants – no matter how close, do not compete with each other so long as the water content, the nutrient material, the light and heat are in excess of the need of both… Competition occurs when each of two or more organisms seeks the measure they want of any particular factor or things and when the immediate supply of the factor or things is below the combined demand of the organisms. This definition makes competition different from the broader term interference, which includes competition and allelopathy. Crop-weed association Association of weeds with a particular crop is due to the following factors 1. Morphological similarities: Morphological similar weeds are difficult to control both by mechanical and chemical methods. For example plants of Echinochloa crusgalli which resembles with that of rice are often uprooted with rice nursery and well grown plants of this weed transplanted with rice are not controlled with any herbicide recommended in the crop. 2 Advances in Weed Management 2. Seed shedding behavior: Majority of weed plants complete their life cycle before the harvest/maturity of the crop(s) in which they are associated. The seeds which are shed in the field during one season, become the source of infestation during the coming years. About 90 to 95% seeds of problematic weeds such as Phalaris minor , Avena ludoviciana , Echinochloa crusgalli , Ischaemum rugosum and Trianthema portulacastrum are shed in the field. This seed shedding behavior is one of the main reasons of association of a particular weed with a specific crop when sown on same field regularly. 3. Escape removal through sieving: The seeds of few weeds are of the same size as of the crop grains/seeds and these cannot be separated out even by thorough sieving. These seeds are sown in the field along with crop seeds. The size of few weed seeds like Convolvulus arvensis , Rumex spinosus , Avena ludoviciana etc are of the same size as of wheat grain and these cannot be removed even with thorough sieving. The crop infested with these weeds should not be kept for seed production purposes. 4. Congenial environment: The association of weeds not only depends upon crop but it is also influenced by cropping sequence. For example field having infestation of wild oats in wheat crop can be eliminated if brought under rice – wheat rotation at least for 2-3 years. The wild oat seeds being porous absorb water and loose viability with continuous standing water. The continuous wet conditions eliminate wild oats but may give favour to Phalaris establishment due to congenial environmental conditions created with the cultivation of rice. 5. Germination in flushes: The weed seeds which have the tendency to germinate in many flushes are very difficult to control both with mechanical or chemical methods. The flush of weeds which appear after the adoption of weed control measures, produce seed and such type of weeds are rather permanently associated with the crop in spite of adoption of best weed management practices. For example, Phalaris minor seeds germinate in many flushes in wheat crop and due to this character it is very difficult to control this weed.