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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

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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 be closing the gap between actual and use of precise and accurate measure­ above. Thus, there would be one chance attainable yield. Soilborne pathogens, ments of X and Y, coupled with infor­ in two of a price better than the median however, continue to limit production mation concerning the value of the crop outcome and an equal chance of a less levels achieved by growers. These patho­ ($/bu, $fib, etc.) provides a means for favorable outcome. A "worst" rating is gens, coupled with the effects of weeds, researchers to develop a number of refer­ assigned to unfavorable prices that insects, and nematodes, continue to ence thresholds for improved decision would be experienced only about once cause a gap between actual yield and making to better manage plant patho­ in 40-50 years of farming. A "pessimis­ attainable yield, although the magnitude gens and pests (16-18). Thus a chain of tic" rating is assigned to unfavorable of this gap fluctuates from year to year. quantitative information is needed along outcome at the one-sixth probability with appropriate linkages: injury­ level. Thus, there would be one chance Terms and Concepts damage-monetary loss-economic in six of an outcome as bad or worse for Crop Loss damage threshold. than the pessimistic rated level. The be about half­ "Crop injury" is defined as the visible These linkages are needed because pessimistic rating should and the worst or measurable symptoms and/ or signs injury data per se are insufficient to way between the median "best" rating is assigned to caused by plant pathogens or pests, and develop thresholds. Injury is not the same rating. A prices that would be exceeded "crop damage" is defined as any reduc­ thing as damage. Injury (X) assessed at favorable 40-50 years of tion in the quantity and/ or quality of time (1) must be interpreted to project only about once in rating is yield that results from crop injury (20). damage at some future point in time farming. An "optimistic" outcomes at the Plant pathology evolved into its own (usually harvest). This linkage (equation) assigned to favorable probability level. science not because plant pathogens is known as the "damage function." The one-sixth simplicity, let us cause injury, but because injury often partial regression coefficient (slope ofthe For the sake of price for barley results in damage and damage results in equation) that relates injury to damage assume that the median best, optimistic, loss of revenue or direct loss of a food is known as the "damage coefficient." is $3.00/bu and that prices are $4.00, source (9,12,19,20,24). Injury (disease There may be more than one damage pessimistic, and worst respectively. intensity) can often be measured quanti­ coefficient if injury affects quality as well $3.50, $2.50, and $2.00/bu, are com­ tatively by specific units of measure as quantity of yield. For example, barley When these price coefficients coefficient (dimensions). For example, disease inci­ spot blotch, caused by Cochliobolus bined with the damage tbe monetary loss per acre, as dence has the dimensions N/N, since sativus, has been shown to reduce not (-32.4), be determined (Fig. incidence is defined as the number of only yield quantity (bu/ acre) but also affected by price, can that the price coefficient infected sample units divided by the total malting quality by increasing protein 2). It is evident loss and, there­ number of sample units assessed (14). content and by decreasing kernel plump­ greatly affects monetary greatly affects the economic Disease severity may have the dimen­ ness ( 13). Barley protein content in excess fore, also Loss functions for sions N/L2 (number of lesions per unit of 13.5% (dry weight basis) is heavily damage threshold. quality can also be leaf area), N / N (number of lesions per discounted or rejected for use by malt­ damage in terms of of the number of units sample), or L2fL2 sters (22). High protein is undesirable included to improve estimates by plant pathogens (visible diseased leaf area/ total leaf area). because high-protein barley germinates direct losses caused the price per As an alternative to measuring disease unevenly and tends to require longer and pests. For example, by intensity to analyze disease and pest­ steeping time. A reduction in the per­ bushel for malting barley decreases in pro­ induced losses, several researchers have centage of plump kernels (weight of 1.3¢ for each one-tenth increase injury result in proposed that the integrals of healthy kernels remaining on a 2.38 mm X 1.91 tein. Should disease barley (green) leaf area duration or healthy em slotted sieve after shaking for 30 sec protein levels above 13.5%, the for use by the (green) leaf area index (square meters of per total weight of the sample X 100) crop may be rejected bushel green leaf tissue per square meter of! and) may also be discounted at the buying malting industry and the price per paid for feed barley. would have a better relationship to yield point. The damage coefficients for could fall to the level the per­ (8,11,21). Nutter (11) found a good rela­ reduced barley yield quantity, increased Moreover, each I% decrease in reduces tionship between green leaf area index protein content, and reduced percent centage of plump kernels also (GLAI) and yield in several crops and plump kernels as affected by spot blotch the price per bushel by an additionall.6¢. exist, that a hand-held, multispectral radiom­ severity are: yield reduction (bu/ acre) = Thus, several loss functions may considered when eter could be used to accurately and -32.4 (disease severity), protein content and these should be mon­ rapidly estimate GLAI. Solar "radiation (%) = + 1.02 (disease severity), and attempting to determine the total This informa­ interception" (magejoules per square percent plump kernels = -39.0 (disease etary loss from damage. meter by green leaf area) and "radiation severity). Although there is a linear tion will directly affect the development thresholds. use efficiency" (grams per megajoule) are relationship between injury and damage of economic damage variables used in crop growth simulation in these examples, the relationship models to account for the effects of path­ between injury and damage may or may Threshold Terms and Concepts information, it ogens and pests on crop growth and not be linear for other pests and crops. Without quantitative thresh­ yield. Radiation interception generally is The next linkage point is the "loss would not be possible to develop programs a function of G LAI. function," which relates damage to loss olds for use in plant protection

212 Plant Disease/Vol. 77 No. 2 (7, 16,17 ,23,24). Quantitative units of with the resolution to detect a level of the economic damage threshold would measure provide a means for researchers the pathogen or pest that is below the be the amount of injury causing $15.00 to develop thresholds that can be used "warning threshold," which is the patho­ damage per acre. If the price per bushel to help producers make more prudent gen or pest density or injury level below of barley is $1.50, this would be an injury disease and pest management decisions. the "action threshold" and alerts a (disease severity) level of approximately In a hierarchy of thresholds (Fig. 3), the grower to prepare for action. The action 0.35 or 35% (Fig. 2). If the price per "perception (detection) threshold" is threshold is the pathogen or pest density bushel of barley is $4.00, the economic defined as the lowest pathogen or pest or injury level at which action must be damage threshold would be approxi­ population density or injury level needed taken to prevent the pathogen or pest mately 0.15 or 15%. Since decision to detect a pathogen or pest. Sample population from exceeding the "damage thresholds are based on both injury and design (random, regular, stratified ran­ threshold," which is the lowest pathogen price, we prefer the term "economic dom, sequential, etc.), sampling pattern or pest or injury level at which some damage threshold" to "economic injury (X, W, diamond, etc.), and sample size damage is projected. The action taken threshold." as well as distribution of the pathogen to prevent a pathogen or pest population Damage thresholds are rarely static or pest in the crop affect the detection from exceeding the damage threshold and are often affected by the "expected threshold. If an entire population of often costs the grower, and this amount yield," which is an estimate of the antici­ plants (a census) were inspected for the of money is converted to its equivalent pated level of production made by the presence of a disease, then even a single amount of damage and added to the grower or farm manager (22). Zadoks lesion may be detected. However, in­ damage threshold to determine the (23) described the use of "sliding" dam­ specting every plant in a population of "economic damage threshold." For age thresholds for wheat as affected by plants is rarely practical. Therefore, a example, if the cost of aerial application various pathogens and pests. In general, sampling protocol must be developed of a fungicide to barley is $15.00/acre, damage threshold values increase as a crop approaches maturity. Thus, as the growing season progresses, the amount 120 of injury required to cause economic $3.50 damage 110 also increases. Zadoks (23) also noted that soil type (and other abiotic 100 factors) can affect damage thresholds. If $3.00 ,..., quality is an important factor affecting w 90 0: price, as with most fruits and vegetables, 0 < 80 $2.50 then the damage threshold on these crops 0: w may be close to zero. ll.. 70 ..... $2.00 Terms and Definitions "-' 60 Ill Our subcommittee was appointed to Ill 50 0 $1.50 draft a list of terms and definitions per­ -' 40 taining to yield, crop loss, and disease 0 __J thresholds. The first draft was distributed w 30 to committee members at the 1988 >= annual meeting of APS. Suggestions 20 from the full committee were incorpo­ 10 rated into a second draft that was distrib­ uted to committee members at the 1990 annual meeting. Final comments and 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0 suggestions of committee members were DISEASE SEVERITY then incorporated into the terms and definitions listed here. Fig. 2. Effect of barley price ($I bu) and level of disease severity on yield loss ($/acre). critical level: lowest level of disease injury 0% Return (Yield) (or pest inteusity) that, when exceeded, results in yield loss(= damage thresh­ 100% Loss old); it is sometimes possible to empiri­ cally establish, under a well-defined set of experimental conditions, the min­ economic damage threshold imum injury or pest intensity levels that will result in crop damage (see cost of control ~ also threshold, damage) damage threshold crop: population of plants grown to pro­ vide food, fiber, medicinals, seed, fuel, action threshold or other products crop damage: any reduction in the quan­ tity and/ or quality of yield that results warning threshold from injury crop injury: visible or measurable symp­ perception (detection) threshold toms and/ or signs caused by pathogens or pests crop loss: a reduction in value and/ or financial return due to damage; often 0% Loss measured as the difference between 100% Return (Yield) actual yield and attainable yield due to the effects of one or more pathogens Fig. 3. Hierarchy of thresholds for decision making. or pests (see also loss data, yield; loss Plant Disease/February 1993 213 data, crop) governments, and consumers loss, yield: the difference between actual damage coefficient: the partial regression loss, postharvest: losses resulting from yield and attainable yield for a single coefficient relating injury level (X) to crop damage occurring after the crop pest (see also crop loss) damage level ( Y) (see also damage is gathered from the production site, loss data, crop: data sets documenting function; loss, function) i.e., damage occurring during trans­ and quantifying the relationships be­ damage function: an equation relating port, storage, processing, and/ or tween one or more pathogens (or pests) injury (or pathogen or pest population marketing of the salable product and the crop losses they cause (see also density) to yield or yield loss during loss, potential: regional or site-specific loss data, yield) a specific period of crop development crop losses that may occur in the ab­ loss data, yield: data sets that document economic injury level: classic definition sence of effective control measures; the and quantify the effects of a single coined by entomologists to describe difference between attainable yield and pathogen (or pest) on yield (see also the level of pest attack at which the primitive yield loss data, crop) benefit of control just exceeds its costs; loss, preharvest: losses resulting from maximum genetic yield potential: see the phytopathological equivalent is crop damage occurring before the crop theoretical yield potential; yield, economic damage threshold (see also is gathered from the production site maximum attainable threshold, economic damage) loss, primary: pre harvest and postharvest net crop growth rate: amount of crop harvest index: proportion of crop bio­ losses of plant products due to plant biomass produced per square meter mass that composes a commodity (e.g., diseases (and pests), excluding costs per day; often measured as a function grain, tuber, fruit) in relation to the associated with the deployment of dis­ of radiation use efficiency and radi­ total biomass of a crop ease (and pest) management practices ation interception loss, actual: measured losses that have loss, production: the reduction in units radiation interception: amount of solar already occurred and may still be of yield (bushel, kilogram, ton, etc.) radiation captured by the photosyn­ occurring and may be divided into for a defined geographic area (county, thetic surface of a crop within a defined direct and indirect losses state, region) based on knowledge of unit area, commonly expressed as MJ I loss, consumer's: the losses realized by the mean percent yield loss (or loss m2fday the consumer as price increases in com­ proportion) for a particular pathogen radiation use efficiency: amount of crop modities as a result of direct and or pest as determined by the equation: biomass produced per unit of inter­ indirect (actual) losses occurring at the production loss = [actual yield (of a cepted solar radiation, usually ex­ grower level and/ or during processing, geographic area) divided by (1.0 -loss pressed as g/ MJ storage, transport, and marketing proportion)] minus the actual yield of theoretical yield potential: the maximum loss, crop: see crop loss the geographic area yield obtainable when the level of loss, direct: the losses in quality and loss, regular: an estimation of the level biotic stresses due to pathogens (or quantity of product sustained by the of losses occurring each season over pests) equals zero; usually taken as the grower, including costs expended for a specified period of time y-intercept calculated from regression disease and/ or pest management prac­ loss, rural community: the economic life equations relating increasing injury (or tices; direct losses may be partitioned of the rural community and its depen­ pest) levels (X) with yield response ( Y) into primary and secondary losses (see dent industries as affected by reduction threshold, action: the pathogen (or pest) also loss, indirect; loss, primary; loss, in crop yield and quality (e.g., as in­ population density or injury level at secondary) vested capital decreases, unemploy­ which action must be taken to prevent loss, economic: the difference in financial ment increases) the pathogen (or pest) population from return between maximum economic loss, secondary: losses caused by a reduc­ exceeding the damage threshold yield and actual yield tion in the yielding capacity of future threshold, damage: the lowest pathogen loss, exporter's: produce rendered non­ crops (cumulative effect of soilborne, (or pest) population density or injury salable, usually in bulk product, due seedborne, or tuber-borne diseases in level for which at least some damage to injury or contamination by patho­ annual crops, premature defoliation or is projected (see also critical level) gens (or pests) or their products (e.g., reduced vigor in perennials) sustained threshold, detection: the minimum path­ aflatoxins) at the grower level; this includes the ogen (or pest) population density or loss, farmer's: losses occurring at the costs associated with the deployment injury level required for a disease or grower level; loss of food, income, or of disease (and pest) management pest to be detected in a crop; this capital that impoverishes growers, practices as well as loss of capital in­ threshold is affected by sampling pro­ which may include the cost of disease vested in soil, seed, renovation prop­ cedures (pattern, number, distribution (or pest) prevention and/ or manage­ agation, etc. of pathogens and pests, etc.) ment practices loss, state: government costs to maintain threshold, economic: generic term for the loss, function: an equation used to esti­ plant protection services, education concept whereby damage levels (esti­ mate monetary loss from damage (see and research institutions, and exten­ mated from injury) are used in making also damage function) sion services and subsidies to ensure cost-efficient disease management loss, hidden: the extent to which a fair income to the grower and to decisions "normal" crop falls short of its attain­ stabilize prices, including loss in tax threshold, economic damage: the lowest able yield or return on investment (e.g., revenue due to reductions in plant disease (or pest) population density or early season injury by diseases [or products caused by diseases (and pests) injury level that will cause the damage pests] may result in the production of loss, structural: losses that are unavoid­ threshold to be exceeded by an amount subsequently smaller leaves [reduced able in a given agroecosystem, such equal to the cost of disease (or pest) radiation interception] and therefore as the cost of using resistant germ control measures; the concept has been lower yields) plasm, crop rotation, etc. applied primarily where management loss, indirect: losses arising from the loss, theoretical: the difference between tactics are responsive rather than increased cost of handling, storage, maximum attainable yield and actual preventative processing, and/ or transport sustained yield threshold, perception: see threshold, by various parties as a direct conse­ loss, transitional: losses that occur when detection quence of plant pathogens (or pests); growers change over from one farming threshold, warning: the pathogen (or these parties include the farm opera­ system to another; restricted to loss pest) population density or injury level tor, rural community, exporters, trade of income or interest (see also loss, that is below the action threshold and for wholesale and retail dealers, structural) warns a grower to prepare to act on

214 Plant Disease/Vol. 77 No. 2 the action threshold using all available production and pest yield loss assessment based on crop physiology. tolerance, disease: a measure of the rela­ control technologies to optimize yield; Pages 150-159 in: Crop Loss Assessment and tive yield response of two or more host thus, the crop genotype Pest Management. P. S. Teng, ed. American is the limiting Phytopathological Society, St. Paul, MN. genotypes to increasing injury levels factor on yield production (see also 7. James, W. C., and Teng, P. S. 1979. The quanti­ caused by diseases (see also tolerance, yield, attainable) fication of production constraints associated pathogen or pest) yield, maximum economic: the yield with plant diseases. Pages 201-267 in: Applied tolerance, pathogen or pest: a measure Biology. Vol. 4. T. H. Coakey, ed. Academic based on optimization of the input/ Press, New York. of the relative yield response of two output ratio that gives the highest 8. Johnson, K. B. 1987. Defoliation, disease, and or more host genotypes to increasing financial returns on expenditures (= growth: A reply. Phytopathology 77:1495-1497. pathogen (or pest) population density economic yield) 9. Main, C. E. 1977. Crop destruction-The raison levels (see also tolerance, disease) yield, primitive: the yield of land races d'etre of plant pathology. Pages 55-78 in: Plant Disease. Vol. I, How Disease Is Managed. J. yield: the measurable product of a crop in subsistence agriculture; sometimes G. Horsfall and E. B. Cowling, eds. Academic yield, actual: the site-specific yield defined as the yield obtained when no Press, New York. obtained when crops are grown using disease (or pest) control tactics are 10. Mumford, J. D., and Norton, G. A. 1984. current production practices at the employed (i.e., a nontreated control) Economics of decision making in pest manage­ ment. Annu. Rev. Entomol. 29:157-174. farm level yield, reference: the average yield of a II. Nutter, F. W., Jr. 1990. Remote sensing and yield, attainable: the site-specific yield crop inclusive of all production con­ image analysis for crop loss assessment. Pages obtained when crops are grown using straints for a given region (usually 93-105 in: Crop Loss Assessment in Rice. all available pest control technologies reported International Rice Research Institute, Manila, in units of yield per unit crop Philippines. to minimize biotic stress, i.e., a area) 12. Nutter, F. W., Jr. 1991. Assessing the benefits measure of the genetic potential of a yield, theoretical: the yield obtained associated with planned introductions of crop genotype at a specific site (see under the best growing conditions genetically engineered organisms. Phytopathol­ also yield, maximum attainable) according to calculations based on ogy 81:344-348. 13. Nutter, F. W., Jr., Pederson, V. D., and Pyler, yield compensation: the phenomenon plant and crop physiology or the R. E. 1985. Effect of spot blotch (Cochliobolus whereby injury to individuals in a pop­ maximum theoretical yield as deter­ sativus) on the quality and yield of malting ulation is compensated for by an mined by using crop growth simula­ barley. Brew. Dig. 59:24-28. increased yield response in adjacent tion models 14. Nutter, F. W., Jr., Teng, P. S., and Shokes, F. M. 1991. Disease assessment terms and con­ healthy plants cepts. Plant Dis. 75:1187-1188. yield components: characterization of We acknowledge the following for 15. Ordish, G., and Dufour, D. 1969. Economic the individual plant parts that directly their comments and suggestions in com­ basis for protection against plant diseases. contribute to yield based on frequency, piling this special report: Richard D. Annu. Rev. Phytopathol. 7:31-50. 16. Pedigo, L. P., Hutchins, S. H., and Higley, L. size, and/ or weight (e.g., in barley: Berger, Kira L. Bowen, C. Lee Campbell, G. 1986. 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Phytopathology yield, gap: the quantitative difference 3. Carlson, G. A., and Main, C. E. 1976. 77:393-398. between actual yield and attainable Economics of disease-loss management. Annu. 22. Wilson, W. W. 1983. Price/quality relationships yield as affected by varietal and envi­ Rev. Phytopathol. 14:381-403. in the malting barley market. N.D. State Univ. 4. Chiarappa, L., ronmental influences; a measure of ed. 1981. Crop Loss Assessment Agric. Exp. Stn. Agric. Econ. Rep. 83003. Methods. Suppl. 3. FAO Commonwealth Agri­ 23. Zadoks, J. C. 1985. On the conceptual basis of crop loss cultural Bureaux, Farnham Royal, United· crop loss assessment: The threshold theory. yield, maximum attainable: the yield ob­ Kingdom. Annu. Rev. Phytopathol. 23:455-473. tained when crops are grown under 5. Cook, R. J. 1985. Use of the term "crop loss." 24. Zadoks, J. C., and Schein, R. D. 1979. Epi­ Plant optimal envir.onmental conditions Dis. 69:95. demiology and Plant Disease Management. 6. Gaunt, R. 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Plant Disease/February 1993 215 Salute to APS Sustaining Associates RJR Nabisco, Inc. Contact: Gary M. HeUmann, Bowman Gray Technical Center, llOO Reynolds Boulevard, Winston­ This section is designed to help APS members understand more Salem, NC 27102; 919/741-0735. RJR Nabisco, Inc., is one about APS Sustaining Associates. Information is supplied by of the world's leading consumer packaged goods companies, company representatives. Each month features different compa­ with major interests in tobacco and food products. As one nies. A complete listing appears in each issue of Phytopathology. of the world's largest processors of agricultural products, RJR Nabisco's subsidiaries produce more than 100 leading brands in 29 product categories. It has worldwide manufacturing R hone-Poulenc Ag Company. Contact: Valerie Wolford, operations and markets its products in more than 100 countries. P.O. Box 12014, Research Triangle Park, NC 27709; 919/ For many years, the company has provided substantial support 549-2243. Rhone-Poulenc is a rapidly growing company and funding for agricultural and educational programs, in­ engaged in the discovery, manufacturing, and marketing of cluding major research and extension efforts designed to crop protection chemicals. It is the U.S. affiliate of Rhone­ develop technology and enhance strategies for increased disease Poulenc S.A., the largest chemical manufacturer in France control in plants. and among the I0 largest chemical groups in the world. Current products include the fungicides Aliette, Rovral, and Chipco 26019; herbicides Ronstar, Asulox, Buctril, Weedar, and Rogers NK Seed Company. Contact: Wayne L. Wiebe, 21435 Weedar 2,4-D; plant growth regulators Cerone, Ethrel, Prep, Road 98, Woodland, CA 95695; 916/666-0986. On January and Flore!; insecticides-nematicides Larvin, Mocap, Sevin, I, 1991 , Rogers Brothers Seed Company and Northrup King Temik, and Zolone; and the defoliant Folex. Aliette is a Vegetable Division merged to form one company. Over the systemic material capable of providing bidirectional transloca­ past 100 years each company has developed into a leader in tion in the plant. It is active primarily against Phycomycetes its respective vegetable seed lines. Rogers NK Seed Company, (downy mildew, Phytophthora, and Pythium species). Rovral which combines Rogers large seed line with Northrup King's (Chipco 26019) is a broad-spectrum fungicide that provides small seed line, is one of the largest full-line vegetable seed control of Alternaria, Botrytis, Helminthosporium, Moni/inia, companies in North America. Rogers NK Seed Company has Rhizoctonia, Sclerotinia, Aspergillus, Penici/Jium, Rhizopus, a strong commitment to research. The goal of its research and Mucor. is to develop, produce, and market improved agronomic and vegetable crop cultivars. To help achieve these goals, the company has research stations throughout the United States, Ricerca, Inc. Contact: Suzan H. Woodhead, 7528 Auburn as well as in Canada, Mexico, South America, and Europe. Road, Painesville, OH 44077-1000; 216/357-3752. Ricerca, Inc., is a broad-based technology company that provides R&D services on a contract basis to clients in the agricultural and chemical industries. More than 200 scientists and support Rogers NK Seed Company. Contact: Paul Moser, Research personnel help clients to develop new products, improve exist­ Center, 6338 Highway 20-26, Nampa, ID 83687; 208/466-0319. ing products, and support the registration of products in com­ On January I, 1991, Rogers Brothers Seed Company and the pliance with good laboratory practices. The Plant Disease vegetable seed division of Northrup King merged to form Control Group has the expertise and facilities for large-volume Rogers NK Seed Company, a full-line vegetable seed company primary screening and advanced testing of chemicals against that supplies seed to the processing, fresh market, and garden more than 30 diseases and several nematode species. Specialty seed industries. The major research emphasis is development studies such as rain tenacity evaluations and wood preservative of new varieties and improvement of existing strains. Research assays are available. The Biocontrol Group conducts discovery, at Rogers NK has top priority; its main goal is to increase development, toxicology, and formulations research leading the productivity, quality, and reliability of crops for the benefit to the registration of biocontrol agents of plant diseases, weeds, of the consumer, farmer, and processor. Plant pathology and and insects. The Biological Evaluations Group offers herbicide its application to disease control are important to its success. and insecticide screening and Subdivision J studies. Rogers NK is a member of the Sandoz Seeds group.

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