Degree-Day Maps for Management of Soybean Insect Pests in Alabama Bulletin 591 March 1988 Alabama Agricultural Experiment Station Auburn University Lowell T. Frobish, Director Auburn University, Alabama Locations of weather data used for degree-day calculations. I I I r...N..n I 1 m Degree-Day Maps for Management of Soybean Insect Pests in Alabama D. A. Herbert, T. P. Mack, R. B. Reed, and R. Getz ,2 INTRODUCTION T HE was first proposed by Reaumur (9). perature CONCEPT OF relating phenological growth to tem- Commonly referred to as heat unit management (HUM), growing degreedays (GDD), or degree-days (DD), accumulation of daily mean temperatures above a threshold temperature has become an established tool in building of plant, insect, and disease models (5). For example, many insect models employ degree-day equations such as the following for calculating development rates: DD = (x-dt), where DD = degree-days or cumulative heat units required for development, x = mean daily temperature, and dt = lower developmental threshold temperature. Once validated, these models can aid in predicting pest status or plant development. Most insect models are designed for use within a single field or group of fields. This approach ignores population development on a larger scale, such as in an isothermic region within a state. Computer mapping of these regions has been used to aid in understanding insect population development (2). The mapping of isothermic regions would be especially useful for crops such as soybeans, which are grown in most of Alabama. Map'Respectively, Post Doctoral Fellow of Plant Pathology, Associate Professor of Entomology, Academic Computing Specialist III, and Agricultural Meteorologist, National Weather Service. 2 The authors thank Mark A. Schwartz for the calculation of degree-days. Partial funding by Alabama Research Institute Grant 85-504 and USDA Grant 85-CRSR-2-2565 is acknowledged. 4 ALABAMA AGRICULTURAL EXPERIMENT STATION ping degree-days can define "hot spots" within a state where insect pest populations would be most likely to develop at faster rates. Pest management scouts could be asked to concentrate their efforts on detecting high insect pest populations within identified hot spots, thereby increasing the probability of early detection of insect pest outbreaks within and adjacent to those areas. Farmers could also be alerted to the possibility of crop loss so timely pest management tactics could be initiated. In the research reported here, environmental data for Alabama were used to map degree-days for five important soybean insect pests. This report analyzes degree-day maps and indicates where soybean insect pests would be most likely to develop for any of the months studied. METHODS AND MATERIALS Environmental Data Degree-day normals for growing season months of May through October were derived for the 47 Alabama locations monitored by the National Weather Service (see map, inside cover), using a technique developed by Thom (11). This method converts adjusted mean monthly air temperature normals (as defined by the National Weather Service) to monthly degreeday normals. Thom's method permits degree-day computations above and below any threshold temperature. Normal mean monthly air temperature normals were based on 1951-80 data published by the National Climatic Center (8). Compiled average monthly degree-day (AMDD) data were mapped using an 85 vertical cell X 107 horizontal cell grid fit onto a rectangular area enclosing Alabama state boundries. Data values for the grid cell vertices were interpolated from AMDD data using a bivariate spline method (10). Zones were then computed from interpolated values and plotted using contouring software (10). Degree-day Calculations Five economically important soybean insect pests were chosen for degree-day calculations: the corn earworm, Heliothis zea (Lepidoptera: Noctuidae); the soybean looper, Pseudoplusia includens (Lepidoptera: Noctuidae); the velvetbean caterpillar, Anticarsia gemmatalis (Lepidoptera: Noctuidae); the green cloverworm, Plathypena scabra (Lepidoptera: Noctuidae); and the DEGREE-DAY MAPS FOR MANAGEMENT OF INSECTS 5 southern green stink bug, Nezara viridula (Hemiptera: Pentatomidae). Degree-days required for development (shown in the table) were calculated from the literature, assuming an average lower developmental threshold of 15°C (58°F) for all except green cloverworm. A common threshold of 15°C was assumed because it is an average for most species and is used in the recently developed Auburn University Soybean Integrated Management Model (AUSIMM). A lower developmental threshold of 11°C (52°F) was assumed for green cloverworm, based on Hammond et al. (3). RESULTS AND DISCUSSION Egg to adult development of green cloverworm requires 486 degree-days (11°C developmental threshold), see table. Degreeday maps for the green cloverworm indicate that sufficient warming occurs within May for population development in most of Alabama, figure 1. The entire state is conducive to development by June, figure 2, and a second generation of larvae, requiring about 690 degree-days (486 for a first generation and 204 for second generation large larvae), appears to be possible in all but the northeastern-most Appalachian Plateau region. In July, a potential exists for two complete generations in parts of Wiregrass, Gulf Coast, and Coastal Plain regions, figure 3. Development of two generations of green cloverworm is limited in August to restricted areas within Gulf Coast and Coastal Plain regions, figure 4. A second generation of larvae per month is possible in the lower half of Alabama even in September, figure 5. By October, development of green cloverworm appears to be restricted to mainly Baldwin and Mobile counties, figure 6. DEGREE-DAYS REQUIRED FOR DEVELOPMENT OF EGG TO ADULTHOOD FOR SEVERAL INSECT PESTS' Insect Corn earworm.............................. Soybean looper .................. Velvetbean caterpillar.................. Green cloverworm ....................... Southern green stink bug ............ 2 Threshold 15°C 15°C 15°C 11°C 15°C Degree451 435 357 486 423 Source Isley (6) 3 Estimated Johnson et al. (7) Hammond et al. (3) Harris and Todd (4) 'Degree-days were calculated from listed source. Centigrade degree-days. To convert to Fahrenheit degree-days, it is best to use the source articles to recalculate accumulated heat units. 'Estimated by assuming egg, prepupal, pupal, and preovipositional degree-day requirements were similar to those of the corn earworm. Larval degree-day requirement of 187 degree-days was calculated from Boldt et al. (1) i ALABAMA AGRICULTURAL EXPERIMENT STATION Degree-days 420 440 460 480 500 a :520 540 660 580 700 620 640 6i60 700 720 FIG. 1. 11 C threshold degree-day map for May, Alabama. . _ 680 DEGREE-DAY MAPS FOR MANAGEMENT OF INSECTS Degree-days 0 __ 620 640 660 680 _._.. ........ 700 720 ~ 740 _ ........ __ _ ____ 760 780 800 860 880 FIG. 2. 11 C threshold degree-day map for June, Alabama. ALABAMA AGRICULTURAL EXPERIMENT STATION - Degree-days i~ui I _ 760 840 860 880 900 + FIG. 3. 11 C threshold degree-day map for July, Alabama. DEGREE-DAY MAPS FOR MANAGEMENT OF INSECTS Degree-days 740 760 780 800 820 840 860 880 900 + L FIG. 4. 11 C threshold degree-day map for August, Alabama. ALABAMA AGRICULTURAL EXPERIMENT STATION Degree-days 540 560 620 640 660 680 700 .. 720 --- _= _ 740 760 780 800 FIG. 5. 11 C threshold degree-day map for September, Alabama. DEGREE-DAY MAPS FOR MANAGEMENT OF INSECTS Degree-days ___ 220 (Qj - . d Z4 340 360 - 380 40 , 480 FIG. 6. 11 C threshold degree-day map for October, Alabama. Several common soy bean insect pests have 15°C developmental t hresholds, including soybean looper, velvetbean caterllar , corn earworm, and souther n green stink bug. Approximnately 425 degree-days are required for development of' one comp~lete generation for most of these insects, as shown by inJig ind~icates tha~t all could be dataic in the table. Degre-a mappc~ potential p~ests in Alabama as early as May in a southwestern area includling Baldwin, Mobile, lower portions of Washington, C:larke, Monroe, and western Lscambia counties, and in a southeastern zone including Henry, Houston, and Dale counties, figuire 7. Earliest infestations could potentially occur in Baldwin and Mobile counties. InJ] une, figure 8, one complete generation ALABAMA AGRICULTURAL EXPERIMENT STATION Degree-days oil 320 340 pc 360 11ly4 280 1,1a 00 3 20 340 400 FIG. 7. 15°C threshold degree-day map for May, Alabama. of these p~ests c01u1( (lexelop) thi oughout the State, with the exception of' Plateau; a looper lai generation develop in the nort1heaster n-most corIner of' the Appalachian scon0d1 generat ion of corn earworin and soybean ae requir ing ab~out 595 degr ce-day s (425 for a first and 1 70 for second generation lar ge larvxae) could Bald win and Moubile cunit ies. Inl Juniy and August, one c omplete generation of' soyb~eani looper, xvelxvetbean caterpilkia , corn earwxoi I, and sout hemn gr een stink b~ug couIld dev elop) throughout the entire State, figur es 9 and 10. A second gener ation of (01rn eai xx01 n and/or sov bean loopler larvae c ould o ur in Ail of the southei n half as xxell as in the Uppe PICo astal Plain and I en nessee Valley ar eas of . DEGREE-DAY MAPS FOR MANAGEMENT OF INSECTS Degree-days ~ 380 400 40 480 ___500 _ 520 540 560 620 640 660 ;_-_ -FIG. 8. 15"C threshold degree-day map for June, Alabama. JulyN. By Atigtist, little potential should exist in tihe n0o1 herni half of the State for comlpete dievelopmlent of a second generation of larv ae. T he dievelopmlent. of two comip~lete genierat ion s of' coeni earxor l01soybe)anl or looper w ilhin eitlier JuIN O1 August appear s to be im probable. By September, figurIe 1 1, dlevelopmlent of1 ai single generatio01, wx no second ilh larv al genei dtion, woul b0(1e restr ictedi to the lower half of the State. Development of a complete genierat ion of these pests is unllikely in Octob~er, figure 12, b~eca~use even the wai mest areas of Alabamia accumulate < 300 dIegree-(lay s. nort1hern A1.labamda ini ALABAMA AGRICULTURAL EXPERIMENT STATION Degree-days r _. ~ r 520 540 660 680 700 720 640 660 _.. . .. 680 700 720 FIG. 9. 15 C threshold degree-day map for July, Alabama. DEGREE-DAY MAPS FOR MANAGEMENT OF INSECTS Degree-days 520 540 560 600 620 640 660 680 700 720 FIG. 10. 15-C threshold degree-day map for August, Alabama. ALABAMA AGRICULTURAL EXPERIMENT STATION Degree-days P 340 360 380 400 420 440 480 500 520 540 560 580 FIG. 11. 15-C threshold degree-day map for September, Alabama. DEGREE-DAY MAPS FOR MANAGEMENT OF INSECTS 17 '/ '1, A Degree-days / 7 '.7/ If 77 777 7 ,7~ / 80 100 120 140 160 180 200 220 240 260 280 300 l_ FIG. 12. 15°C threshold degree-day map for October, Alabama. 18 ALABAMA AGRICULTURAL EXPERIMENT STATION SUMMARY Temperature is a widely recognized factor regulating insect development. Degree-day equations utilizing temperature data can be calculated from regional, statewide, or within-state zonal weather data. However, microclimate temperatures within crop canopies vary both among crops in a particular zone and within a crop as it matures. These variations can increase or decrease insect development rates, clouding degree-day and generation time calculations. Further, insect populations do not necessarily develop in discrete generations. Differences in individual development rates, prolonged ovipositional (egg laying) periods, and immigration and emigration of adults produce overlapping within-field generations. Degree-day maps developed from macroclimatic zonal data should, therefore, be used as an indication of relative not actual potential for numbers of generations. DEGREE-DAY MAPS FOR MANAGEMENT OF INSECTS 19 LITERATURE CITED (1) BOLDT, P. E., K. D. BIEVER, AND C. M. IGNOFFO. 1975. Lepidopteran Pests of Soybeans: Consumption of Soybean Foliage and Pods and Development Time. J. Econ. Entomol. 68: 480-482. (2) (3) (4) (5) FULTON, W. C. AND D. L. HAYNES. 1975. Computer Mapping in Pest Management. Environ. Entomol. 4: 357-360. HAMMOND, R.B., F. L. POSTON, AND L. P. PEDIGO. 1979. Growth of the Green Cloverworm and a Thermal-unit System for Development. Environ. Entomol. 8: 639-642. HARRIS, V. E. AND J. W. TODD. 1980. Duration of Immature Stages of the Southern Green Stink Bug, Nezara virdula (L.), with a Comparative Review of Previous Studies. J. Georgia Entomol. Soc. 15: 114-124. HIGLEY, L. G., L. P. PEDIGO, AND K. R. OSTLIE. 1986. DEGDAY: A Pro- (6) (7) (8) gram for Calculating Degree-days, and Assumptions behind the Degree-day Approach. Environ. Entomol. 15:999-1016. ISLEY, D. 1935. Relationship of Hosts to Abundance of Cotton Bollworm. Ark. Agr. Exp. Sta. Bull. 320:1-30. JOHNSON, D. W., C. S. BARFIELD, AND G. E. ALLEN. 1983. Temperaturedependent Developmental Model for the Velvetbean Caterpillar (Lepidoptera: Noctuidae). Environ. Entomol. 12: 1657-1663. NOAA, ENVIRONMENTAL DATA AND INFORMATION SERVICE. 1982. Monthly Normals of Temperature, Precipitation and Heating and Cooling Degree Days 1951-80 for Alabama. Climatography of the U. S. No. 81. (9) REAUMUR, R. A. E. DE. 1735. Temperature Observations in Paris during the Year 1735, and the Climatic Analogue Studies of l'Isle de France, Algeria and Some Islands of America. Mem. Acad. Sci., Paris, 1735:545 (in French). (10) SAS INSTITUTE INC., 1985. SAS/GRAPH User's Guide, Version 5 Edition. Cary, N.C. (11) THOM, H. C. S. 1966. Normal Degree Days Above Any Base by the Uni- versal Truncation Coefficient. Monthly Weather Review 94: No. 7. ALBIlL RN I NI1VERSIYY With an agricul- tural research unit int everxV major soil area, Auburn Universitv serves the needs of field crop, livestock. forestry, and horticultural producers in each region in Alabama. Everv citiZen of the State has a stake in this research program, since any advantage from nexv and mo re econom- A 0 1a8 ical ways of produc- ing and handling farm products ci rectly benefits the constaming public. ® Main Agricultural Experiment Station, Auburn. a E. V. Smith Research Center, Shorter. Tennessee Valley Substation, Belle Mina Sand Mountain Substation, Crossville North Alabama Horticulture Substation, Cullman Upper Coastal Plain Substation, Winfield Forestry Unit, Fayette County Chilton Area Horticulture Substation, Clanton Forestry Unit. Coosa County Piedmont Substation, Camp Hili Plant Breeding Unit, Tallassee Forestry Unit, Autauga County Prattville Experiment Field. Prattville Black Belt Substation. Marion Junction The Turnipseed-Ikenberry Place, Union Springs Lower Coastal Plain Substation, Camden Forestry Unit, Barbour County Monroeville Experiment Field, Monroeville Wiregrass Substation, Headland Brewton Experiment Field, Brewton Solon Dixon Forestry Education Center, Covington and Escambia counties 20 Ornamental Horticulture Substation, Spring Hill. 21 Gulf Coast Substation, Fairhope 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19