Degree-DayMaps forManagementof SoybeanInsectPestsinAlabama

Bulletin 591 March 1988Alabama Agricultural Experiment Station Auburn University

Lowell T. Frobish, Director Auburn University, Alabama

Locations of weather dataused for degree-day calculations.

I I I r...N..n I 1 m

Degree-Day Maps for Managementof Soybean Insect Pests

in Alabama

D. A. Herbert, T. P. Mack, R. B. Reed, and R. Getz ,2

INTRODUCTION

T HE CONCEPT OF relating phenological growth to tem-perature was first proposed by Reaumur (9). Commonly re-ferred to as heat unit management (HUM), growing degree-days (GDD), or degree-days (DD), accumulation of daily meantemperatures above a threshold temperature has become an es-tablished tool in building of plant, insect, and disease models(5). For example, many insect models employ degree-day equa-tions such as the following for calculating development rates:DD = (x-dt), where DD = degree-days or cumulative heatunits required for development, x = mean daily temperature,and dt = lower developmental threshold temperature. Oncevalidated, these models can aid in predicting pest status or plantdevelopment.

Most insect models are designed for use within a single fieldor group of fields. This approach ignores population develop-ment on a larger scale, such as in an isothermic region within astate. Computer mapping of these regions has been used to aidin understanding insect population development (2). The map-ping of isothermic regions would be especially useful for cropssuch as soybeans, which are grown in most of Alabama. Map-

'Respectively, Post Doctoral Fellow of Plant Pathology, Associate Professor of Ento-mology, Academic Computing Specialist III, and Agricultural Meteorologist, NationalWeather Service.

2The authors thank Mark A. Schwartz for the calculation of degree-days. Partial fund-ing by Alabama Research Institute Grant 85-504 and USDA Grant 85-CRSR-2-2565 isacknowledged.

4 ALABAMA AGRICULTURAL EXPERIMENT STATION

ping degree-days can define "hot spots" within a state where in-sect pest populations would be most likely to develop at fasterrates. Pest management scouts could be asked to concentratetheir efforts on detecting high insect pest populations withinidentified hot spots, thereby increasing the probability of earlydetection of insect pest outbreaks within and adjacent to thoseareas. Farmers could also be alerted to the possibility of crop lossso timely pest management tactics could be initiated.

In the research reported here, environmental data for Ala-bama were used to map degree-days for five important soybeaninsect pests. This report analyzes degree-day maps and indicateswhere soybean insect pests would be most likely to develop forany of the months studied.

METHODS AND MATERIALS

Environmental Data

Degree-day normals for growing season months of Maythrough October were derived for the 47 Alabama locationsmonitored by the National Weather Service (see map, insidecover), using a technique developed by Thom (11). This methodconverts adjusted mean monthly air temperature normals (asdefined by the National Weather Service) to monthly degree-day normals. Thom's method permits degree-day computationsabove and below any threshold temperature. Normal meanmonthly air temperature normals were based on 1951-80 datapublished by the National Climatic Center (8).

Compiled average monthly degree-day (AMDD) data weremapped using an 85 vertical cell X 107 horizontal cell grid fitonto a rectangular area enclosing Alabama state boundries.Data values for the grid cell vertices were interpolated fromAMDD data using a bivariate spline method (10). Zones werethen computed from interpolated values and plotted using con-touring software (10).

Degree-day Calculations

Five economically important soybean insect pests were chosenfor degree-day calculations: the corn earworm, Heliothis zea(Lepidoptera: Noctuidae); the soybean looper, Pseudoplusia in-cludens (Lepidoptera: Noctuidae); the velvetbean caterpillar,Anticarsia gemmatalis (Lepidoptera: Noctuidae); the green clov-erworm, Plathypena scabra (Lepidoptera: Noctuidae); and the

DEGREE-DAY MAPS FOR MANAGEMENT OF INSECTS 5

southern green stink bug, Nezara viridula (Hemiptera: Penta-tomidae). Degree-days required for development (shown in thetable) were calculated from the literature, assuming an averagelower developmental threshold of 15°C (58°F) for all exceptgreen cloverworm. A common threshold of 15°C was assumedbecause it is an average for most species and is used in the re-cently developed Auburn University Soybean Integrated Man-agement Model (AUSIMM). A lower developmental thresholdof 11°C (52°F) was assumed for green cloverworm, based onHammond et al. (3).

RESULTS AND DISCUSSION

Egg to adult development of green cloverworm requires 486degree-days (11°C developmental threshold), see table. Degree-day maps for the green cloverworm indicate that sufficientwarming occurs within May for population development inmost of Alabama, figure 1. The entire state is conducive to de-velopment by June, figure 2, and a second generation of larvae,requiring about 690 degree-days (486 for a first generation and204 for second generation large larvae), appears to be possiblein all but the northeastern-most Appalachian Plateau region. InJuly, a potential exists for two complete generations in parts ofWiregrass, Gulf Coast, and Coastal Plain regions, figure 3. De-velopment of two generations of green cloverworm is limited inAugust to restricted areas within Gulf Coast and Coastal Plainregions, figure 4. A second generation of larvae per month ispossible in the lower half of Alabama even in September, figure5. By October, development of green cloverworm appears to berestricted to mainly Baldwin and Mobile counties, figure 6.

DEGREE-DAYS REQUIRED FOR DEVELOPMENT OF EGG TO ADULTHOODFOR SEVERAL INSECT PESTS'

Insect Threshold Degree- Source

Corn earworm.............................. 15°C 451 Isley (6)Soybean looper .................. 15°C 435 Estimated3

Velvetbean caterpillar.................. 15°C 357 Johnson et al. (7)Green cloverworm ....................... 11°C 486 Hammond et al. (3)Southern green stink bug ............ 15°C 423 Harris and Todd (4)

'Degree-days were calculated from listed source.2Centigrade 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 re-

quirements were similar to those of the corn earworm. Larval degree-day requirementof 187 degree-days was calculated from Boldt et al. (1)

i ALABAMA AGRICULTURAL EXPERIMENT STATION

Degree-days

420440460480500

a :5205406605807006206406i60

. _ 680700720

FIG. 1. 11 C threshold degree-day map for May, Alabama.

DEGREE-DAY MAPS FOR MANAGEMENT OF INSECTS

Degree-days

620640

__ 660680

_._.. ........ 700~ 720

740_ ........___ 760

____ 780800

860880

FIG. 2. 11 C threshold degree-day map for June, Alabama.

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ALABAMA AGRICULTURAL EXPERIMENT STATION

- Degree-days

i~ui I _ 760

840860880900 +

FIG. 3. 11 C threshold degree-day map for July, Alabama.

DEGREE-DAY MAPS FOR MANAGEMENT OF INSECTS

Degree-days

740760780800820840860880900 +

FIG. 4. 11 C threshold degree-day map for August, Alabama.

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ALABAMA AGRICULTURAL EXPERIMENT STATION

Degree-days

540560

620640660680700

.. 720740760

_ --- _= 780800

FIG. 5. 11 C threshold degree-day map for September, Alabama.

DEGREE-DAY MAPS FOR MANAGEMENT OF INSECTS

(Qj Z4- d .

Degree-days

___ 220

340360

, - 38040

480

FIG. 6. 11 C threshold degree-day map for October, Alabama.

Several common soy bean insect pests have 1 5°C develop-mental t hresholds, including soybean looper, velvetbeancaterllar , corn earworm, and souther n green stink bug. Ap-proximnately 425 degree-days are required for development of'one comp~lete generation for most of these insects, as shown bydataic in the table. Degre-a mappc~ inJig ind~icates tha~t all could bepotential p~ests in Alabama as early as May in a southwesternarea includling Baldwin, Mobile, lower portions of Washington,C:larke, Monroe, and western Lscambia counties, and in a south-eastern zone including Henry, Houston, and Dale counties, fig-uire 7. Earliest infestations could potentially occur in Baldwinand Mobile counties. InJ] une, figure 8, one complete generation

ALABAMA AGRICULTURAL EXPERIMENT STATION

oilDegree-days

320pc 340

36028011 1,1a ly4 003 20340

400

FIG. 7. 15°C threshold degree-day map for May, Alabama.

of these p~ests c01u1( (lexelop) thi oughout the State, with the ex-ception of' the nort 1heaster n-most corIner of' the AppalachianPlateau; a scon0d1 generat ion of corn earworin and soybeanlooper lai ae requir ing ab~out 595 degr ce-day s (425 for a firstgeneration and 1 70 for second generation lar ge larvxae) coulddevelop in Bald win and Moubile cunit ies.

Inl Juniy and August, one c omplete generation of' soyb~eanilooper, xvelxvetbean caterpilkia , corn earwxoi I, and sout hemngr een stink b~ug couIld dev elop) throughout the entire State, fig-ur 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 xxellas in the Uppe PICo astal Plain and I en nessee Valley ar eas of

DEGREE-DAY MAPS FOR MANAGEMENT OF INSECTS

FIG. 8. 15"C threshold degree-day map for June, Alabama.

nort1hern A1.labamda ini JulyN. By Atigtist, little potential should ex-ist in tihe n0o1 herni half of the State for comlpete dievelopmlentof a second gener ation of larv ae. T he dievelopmlent. of two comi-p~lete genierat ion s of' coeni earxor or l01soybe)anl looper w ilhineitlier JuIN O1 August appear s to be im probable. By September,figurIe 1 1, dlevelopmlent of1 ai single generatio01, wx ilh no secondlarv al genei dtion, woul b0(1e restr ictedi to the lower half of theState. Development of a complete genierat ion of these pests isunllikely in Octob~er, figure 12, b~eca~use even the wai mest areasof Alabamia accumulate < 300 dIegree-(lay s.

Degree-days

380~ 400

40

480___500

520_ 540

560

620640

;_-_ -- - 660

ALABAMA AGRICULTURAL EXPERIMENT STATION

r

r

FIG. 9. 15 C threshold degree-day map for July, Alabama.

Degree-days

520_. ~ 540

660680700720640660

_.. .. . 680700720

DEGREE-DAY MAPS FOR MANAGEMENT OF INSECTS

Degree-days

520540560

600620640660680700720

FIG. 10. 15-C threshold degree-day map for August, Alabama.

ALABAMA AGRICULTURAL EXPERIMENT STATION

Degree-days

P 340360380400420440

480500520540560580

FIG. 11. 15-C threshold degree-day map for September, Alabama.

DEGREE-DAY MAPS FOR MANAGEMENT OF INSECTS 17

Degree-days'/ '1, /

A 7

77777

'.7/ 7If ,7~ /

80100120140160180200220240260280300

FIG. 12. 15°C threshold degree-day map for October, Alabama.

l_

18 ALABAMA AGRICULTURAL EXPERIMENT STATION

SUMMARY

Temperature is a widely recognized factor regulating insectdevelopment. Degree-day equations utilizing temperature datacan be calculated from regional, statewide, or within-state zonalweather data. However, microclimate temperatures within cropcanopies vary both among crops in a particular zone and withina crop as it matures. These variations can increase or decreaseinsect development rates, clouding degree-day and generationtime calculations. Further, insect populations do not necessarilydevelop in discrete generations. Differences in individual de-velopment rates, prolonged ovipositional (egg laying) periods,and immigration and emigration of adults produce overlappingwithin-field generations. Degree-day maps developed from ma-croclimatic zonal data should, therefore, be used as an indica-tion of relative not actual potential for numbers of generations.

DEGREE-DAY MAPS FOR MANAGEMENT OF INSECTS

LITERATURE CITED

(1) BOLDT, P. E., K. D. BIEVER, AND C. M. IGNOFFO. 1975. LepidopteranPests of Soybeans: Consumption of Soybean Foliage and Pods and De-velopment Time. J. Econ. Entomol. 68: 480-482.

(2) FULTON, W. C. AND D. L. HAYNES. 1975. Computer Mapping in PestManagement. Environ. Entomol. 4: 357-360.

(3) HAMMOND, R.B., F. L. POSTON, AND L. P. PEDIGO. 1979. Growth of theGreen Cloverworm and a Thermal-unit System for Development. En-viron. Entomol. 8: 639-642.

(4) HARRIS, V. E. AND J. W. TODD. 1980. Duration of Immature Stages ofthe Southern Green Stink Bug, Nezara virdula (L.), with a ComparativeReview of Previous Studies. J. Georgia Entomol. Soc. 15: 114-124.

(5) HIGLEY, L. G., L. P. PEDIGO, AND K. R. OSTLIE. 1986. DEGDAY: A Pro-gram for Calculating Degree-days, and Assumptions behind the De-gree-day Approach. Environ. Entomol. 15:999-1016.

(6) ISLEY, D. 1935. Relationship of Hosts to Abundance of Cotton Boll-worm. Ark. Agr. Exp. Sta. Bull. 320:1-30.

(7) JOHNSON, D. W., C. S. BARFIELD, AND G. E. ALLEN. 1983. Temperature-dependent Developmental Model for the Velvetbean Caterpillar (Lep-idoptera: Noctuidae). Environ. Entomol. 12: 1657-1663.

(8) NOAA, ENVIRONMENTAL DATA AND INFORMATION SERVICE. 1982.Monthly Normals of Temperature, Precipitation and Heating andCooling Degree Days 1951-80 for Alabama. Climatography of the U. S.No. 81.

(9) REAUMUR, R. A. E. DE. 1735. Temperature Observations in Paris duringthe 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 Edi-tion. 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.

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ALBIlL RN I NI1VERSIYY

With an agricul-tural research unit inteverxV major soil area,Auburn Universitvserves the needs offield crop, livestock.forestry, and hor-ticultural producersin each region inAlabama. Everv citi-Zen of the State has astake in this researchprogram, since anyadvantage from nexvand mo re econom-ical ways of produc-ing and handlingfarm products cirectly benefits theconstaming public.

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® Main Agricultural Experiment Station, Auburn.a E. V. Smith Research Center, Shorter.

1 Tennessee Valley Substation, Belle Mina2 Sand Mountain Substation, Crossville3 North Alabama Horticulture Substation, Cullman4 Upper Coastal Plain Substation, Winfield5 Forestry Unit, Fayette County6 Chilton Area Horticulture Substation, Clanton7 Forestry Unit. Coosa County8 Piedmont Substation, Camp Hili9 Plant Breeding Unit, Tallassee

10 Forestry Unit, Autauga County11 Prattville Experiment Field. Prattville12 Black Belt Substation. Marion Junction13 The Turnipseed-Ikenberry Place, Union Springs14 Lower Coastal Plain Substation, Camden15 Forestry Unit, Barbour County16 Monroeville Experiment Field, Monroeville17 Wiregrass Substation, Headland18 Brewton Experiment Field, Brewton19 Solon Dixon Forestry Education Center,

Covington and Escambia counties20 Ornamental Horticulture Substation, Spring Hill.21 Gulf Coast Substation, Fairhope