Plant Pathology and Microbiology Publications Plant Pathology and Microbiology 2-1993 Terms and Concepts for Yield, Crop Loss, and Disease Thresholds Forrest W. Nutter Jr. Iowa State University, [email protected] Paul S. Teng International Rice Research Institute Matthew H. Royer United States Department of Agriculture Follow this and additional works at: http://lib.dr.iastate.edu/plantpath_pubs Part of the Agricultural Science Commons, Agriculture Commons, and the Plant Pathology Commons The ompc lete bibliographic information for this item can be found at http://lib.dr.iastate.edu/ plantpath_pubs/63. For information on how to cite this item, please visit http://lib.dr.iastate.edu/ howtocite.html. This Article is brought to you for free and open access by the Plant Pathology and Microbiology at Iowa State University Digital Repository. It has been accepted for inclusion in Plant Pathology and Microbiology Publications by an authorized administrator of Iowa State University Digital Repository. For more information, please contact [email protected]. Terms and Concepts for Yield, Crop Loss, and Disease Thresholds Abstract The initial report (14) of a subcommittee of the APS Plant Disease Losses Committee dealt with terms and concepts relating to the measurement of disease intensity to obtain accurate and precise quantitative information on the relationship between disease intensity (stimulus = X) and yield or yield loss (response = Y). In addition to standardizing the terms and concepts for the measurement of disease intensity, members of the full committee identified a need to clarify and standardize terms and concepts pertaining to yield, crop loss, and disease thresholds. A second subcommittee was formed to accomplish this task. This report describes concepts concerning reference points for yield and crop loss as well as a hierarchy for threshold terms, then presents a list of terms and definitions to standardize terminology for crop loss assessment. Disciplines Agricultural Science | Agriculture | Plant Pathology Comments This article is from Plant Disease 77 (1993): 211, doi:10.1094/PD-77-211. Rights Works produced by employees of the U.S. Government as part of their official duties are not copyrighted within the U.S. The onc tent of this document is not copyrighted. This article is available at Iowa State University Digital Repository: http://lib.dr.iastate.edu/plantpath_pubs/63 Special Topic Terms and Concepts for Yield, Crop Loss, and Disease Thresholds FORREST W. NUTTER, JR., Associate Professor, Department of Plant Pathology, 351 Bessey Hall, Iowa State University, Ames 50011; PAUL S. TENG, Coordinator for PPM, International Rice Research Institute, Box 933, Manila, Philippines; and MATTHEW H. ROYER, Chief Operations Officer, Biological Assessment and Taxonomic Support, APHIS-PPQ-OS, USDA, 6505 Belcrest Road, Hyattsville, MD 20782 The initial report (14) of a subcom­ need (Fig. 1). "Maximum attainable the production level achieved when mittee of the APS Plant Disease Losses yield" is the theoretical yield that could producers utilize pest management pro­ Committee dealt with terms and concepts be achieved if the crop was grown under grams currently recommended for a crop relating to the measurement of disease optimum environmental conditions, or cropping system, yet several factors intensity to obtain accurate and precise along with the use of all available crop (environment, weeds, diseases, insects) quantitative information on the relation­ protection tactics to also alleviate the are still limiting yield. The difference be­ ship between disease intensity (stimulus effects of biotic pests. Genetic yield tween actual and attainable yield is the = X) and yield or yield loss (response potential-not biotic pests or environ­ method used by the Food and Agricul­ = Y). In addition to standardizing the ment-is the primary factor that limits ture Organization (FAO) to report crop terms and concepts for the measurement the maximum attainable yield. "Attain­ losses (4). Most, if not all, pest manage­ of disease intensity, members of the full able yield" is the yield obtained at a ment practices are aimed at closing the committee identified a need to clarify and specific location when all available crop gap between actual and attainable yield. standardize terms and concepts pertain­ protection tactics are used to alleviate In a PLANT DisEASE editorial, Cook (5) ing to yield, crop loss, and disease thresh­ the stresses caused by biotic pests. Thus, eloquently argued against the use of the olds. A second subcommittee was formed attainable yield is site-specific and is the term "crop loss." He described a situation to accomplish this task. This report yield obtained when biotic pests are in which a grower achieved a yield of describes concepts concerning reference alleviated but environmental (abiotic) 90 buf acre (grower yield), while replicate points for yield and crop loss as well as factors such as soil fertility, water avail­ plots in the same field fumigated with a hierarchy for threshold terms, then ability, growing degree days, etc., may Telone C to eliminate Pythium spp. and presents a list of terms and definitions still be limiting yield. Attainable yields parasitic nematodes yielded 128 bu/ acre to standardize terminology for crop loss are commonly achieved in well-managed (attainable yield). By FAO's definition, assessment. experimental plots. this difference in yield is an estimate of The cost of deploying all available pest crop loss and represents measurable con­ Reference Points for Assessing management tactics to achieve attainable straints to production. This estimate of Yield and Crop Loss yield may be higher than the return loss corresponds to the as yet unavoid­ Estimates of loss are a prerequisite to expected from the sale of the crop and/ able losses caused by plant pests and the rational development of any agricul­ or may harm the environment because pathogens. If these constraints were tural research program that has plant of excessive inputs. In contrast, "eco­ alleviated, the plant genotypes would protection as a component (1,6,9,17,20, nomic yield" is the achievable yield that realize yields closer to attainable levels. 23). Reliable estimates of loss facilitate provides the highest net return on Thus, "crop loss" is a function of one the objective identification of the relative expenditure. If the cost of utilizing a new or more biotic factors, each of which may importance of biotic pests (2,3,7,10,15). disease management technology exceeds be contributing to a reduction in yield, Consequently, limited resources (federal, the expected return, the technology is not whereas "yield loss" is the reduction in state, or private) can be assigned on a likely to be adopted. "Actual yield" is yield caused by a single pathogen or pest. priority basis to optimize returns from a given effort. Accurate information con­ cerning losses is also needed by growers -----~Maximum Attainable and plant protection specialists to develop Yield decision thresholds for determining when cost-effective control measures should be deployed (7,14,22). The need for reliable ------Attainable Yield crop loss assessment methodology (to develop reliable decision aids) assumes Factor A added importance given the current Factor B worldwide concern about improving or Crop Loss maintaining environmental quality by 1 Factor C reducing the use of pesticides (18). Economic Yield Factor D Several reference points for yield must be characterized before plant protection programs can be prioritized according to ------Actual Yield Journal Paper No. J-14955 of the Iowa Agricultural and Home Economics Experiment Station, Ames. Project No. 3116. Accepted for publication 9 September 1992. ------~Primitive Yield © 1993 The American Phytopathological Society Fig. 1. Reference points for crop loss assessment. Plant Disease/February 1993 211 "Primitive yield" is the yield achieved In addition to injury, damage must in monetary terms if the crop is to be when no disease or pest control tactics also be measured quantitatively if we are sold. Before monetary loss can be esti­ are utilized. The difference between to establish quantitative relationships mated, the amount of damage must be primitive yield and actual yield repre­ between injury (X) and damage ( Y). For multiplied by a price factor. Because the sents improvements in crop protection example, the yield or yield loss response prices of commodities are variable, the presently achieved by the deployment of (damage) may be measured as a reduc­ expected price may be used in calcula­ accepted pest management practices. For tion in volume per unit area harvested tions or a risk-rated system can be used example, in the southeastern United (bu/ acre = L3 I L2), by a reduction in in which probabilities are assigned worst­ States, peanuts grown in the absence of mass per unit area harvested (kgfha = case and best-case price scenarios. For any fungicide commonly yield 40-70% N/L2), and/or by changes in quality, example, a "median" rating is assigned less than peanuts managed with fungi­ such as increased protein content in to the midpoint of prices 'that divides all cides to control foliar diseases. The use barley (% protein = N IN X 100) or possible outcomes. One-half of all pos­ of fungicides has helped to increase the reduced oil content in soybeans (% oil sible outcomes should fall below the actual yield realized by growers, thereby = N / N X 100). The development and median value and one-half should