Crop-weed relationship

Belz RG (2007) Allelopathy in crop/weed interactions - an update. Pest Manag Sci 63 308-326 Belz RG (2008) Stimulation versus inhibition - bioactivity of parthenin, a phytochemical from Parthenium hysterophorus L. Int Dose-Response Soc 6 80-96 Belz RG, Vehni ED, Duke SO (2007) Dose/response relationships in allelopathy research. In Fujii Y, Hiradate S (eds) Allelopathy new concepts and methodologies. Science Publishers, Enfield, NH, pp 3-29... 

Frankenberger, Jr., and Muhammad Arshad Handbook of Weed Management Systems, edited by Albert E. Smith Soil Sampling, Preparation, and Analysis, Kim H. Tan Soil Erosion, Conservation, and Rehabilitation, edited by Menachem Agassi Plant Roots The Hidden Half, Second Edition, Revised and Expanded, edited by Yoav Waisel, Amram Eshel, and Uzi Kafkafi Photoassimilate Distribution in Plants and Crops Source-Sink Relationships, edited by Eli Zamski and Arthur A. Schaffer Mass Spectrometry of Soils, edited by Thomas W. Boutton and Shinichi Yamasaki... 

Teasdale JR, Mohler CL (1993) Light transmittance soil temperature, and soil moisture under residue of hairy vetch and rye. Agronomy J 85 673-680 Teasdale JR, Mohler CL (2000) The quantitative relationship between weed emergence and the physical properties of mulches. Weed Sci 48 385-392 Teasdale JR, Pillai P (2005) Contribution of ammonium to stimulation of smooth pigweed germination by extracts of hairy vetch residue. Weed Biol Manag 5 19-25 Teasdale JR, Beste CE, Potts WE (1991) Response of weeds to tillage and cover crop residue. Weed Sci 39 195-199... 

Much research is needed on the quantitative effects on crop yields of interference by most of our serious weeds, and on the relative contributions of allelopathy and competition to the total interference by each weed species. Crop-crop relationships need to be investigated much more thoroughly to determine which crops can follow others with the least inhibitory or most stimulatory effects. More emphasis should be placed on investigations of stimulatory allelopathlc effects, because these effects have been largely Ignored in the past. Possible autotoxicity should be investigated also to determine if it is unwise to cultivate the same crop continuously without rotation. 

Why weeds reduce crop yields cannot be adequately answered. Considerable data have accumulated which relate duration of weed presence and weed density to crop yield. However, such data provide little explanation for why crop yields are reduced. The objectives of this paper are to 1) provide an overview of the time relationship of competition for growth factors and of allelopathy as factors in crop yield reduction and 2) suggest a direct feedback effect on reproduction in response to light as a possible third direct factor in explaining effects of weeds on crop yield. 

Table 11. Relationship Between Percent Weed Control and Crop Yield, North Central Region, 1983 and 1984...

QulzalofOp-Ethyl. 2-[4-[<6-Chloro-2-quinoxa-tinyl oxy)phenoxy]propanote acid ethyl ester ethyl 2-[4-(6> chloro-2-quinoxalinyloxy)phenoxy]propiOnate quinofop-ethyl DPX-Y 6202 NCI 96683 NC 302 Assure Targa Pilot. C1(H C1NjOj mol wt 372.81. C 61.21%. H 4.60%. Cl 9.51%, N 7.51%, O 17.17%. Post-emergence herbicide for control of grassy weeds in broad-leaved crops. Prepn and herbicidal activity Y. Ura et al., Ger. pat. 3,004,770 (1980 to Nissan). C.A 94, 103421h (]9S1). Prepn and structure-activity relationships G. Sakata er aJ.. /. Pestle. Sch 10, 61... 

Based on the structure-activity relationships shown in Tables I-IV, further investigations were initiated to determine if crop selectivity could be found while maintaining activity on grass weeds. These efforts focused primarily on probing... 

This chapter aims to give an insight into the discovery of the triketone class of herbicides and their continuing development. A very qualitative picture of structure-activity relationships will be discussed and currently commercialized triketones, in terms of their use, weed spectrum, crop selectivity, environmental and toxicological profiles, and manufacture will be described. This chapter also contains an overview of the major companies activities in the field in the last two decades, focusing on compounds that are likely to be brought to the market, or were putatively close to development. 

Another group of toxins called the AAL-toxins was fotmd to have a structural relationship to the fumonisins, since they have only one tricarboxylic acid (TCA) moiety. AAL-toxin TAi (265) and TA2 (266) (Fig. 5.2) are produced by the fungus Alternaria alternata f. sp. lycopersici and can lead to phytotoxic effects on several crops such as tomatoes and weeds (200). Due to the toxic effects of long alkyl-chain pyridinium compounds, this new class of fumonisins is of high interest (201). 

What follows this introduction to plant-plant interactions (Chapter 1) are three additional chapters. The first chapter (Chapter 2) describes the behavior of allelopathic agents in nutrient culture and soil-microbe-seedling systems under laboratory conditions. Simple phenolic acids were chosen as the allelopathic agents for study in these model systems (see justifications in Section 2.2.6). The next chapter (Chapter 3) describes the relationships or lack of relationships between weed seedling behavior and the physicochemical environment in cover crop no-till fields and in laboratory bioassays. Here as well the emphasis is on the potential role of phenolic acids. The final chapter (Chapter 4) restates the central objectives of Chapters 2 and 3 in the form of testable hypotheses, addresses several central questions raised in these chapters, outlines why a holistic approach is required when studying allelopathic plant-plant interactions, and suggests some ways by which this may be achieved. 

To characterize how cover crop residues in no-till systems affect early emergence of broadleaf weeds and to establish and characterize potential relationships between early broadleaf weed seedling emergence and the physical and chemical environments resulting from the presence of cover crop residues. 

At this point some comments regarding the modification of the soil physical and chemical environments by cover crops and weed seedling emergence appear appropriate. In spite of the fact that covariate, correlation and principle component analyses did not identify any significant relationships between seedling emergence and bulk soil physical and chemical characteristics (e.g., soil total phenolic acid. 

To Characterize How Cover Crop Residues in No-Till Systems Affect Early Emergence of Broadleaf Weeds and to Establish and Characterize Potential Relationships Between Early Broadleaf Weed Seedling Emergence and the Physical and Chemical Environments Resulting from the Presence of Cover Crop Residues (Section 3.4.3)... 

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