Predicting Tomato Spotted Wilt Predicting Tomato Spotted Wilt Virus on tobacco in North Virus on tobacco in North

CarolinaCarolina

A. L. Mila

Dept. of Plant Pathology

TSWV symptoms on tobacco

Thrips: the culprit

Frankliniella fusca

TSWV epidemiology on tobacco

• Wide range of hosts

• (>500 spp.,>50 families)

TSWV incidence in NC

2.12.82.9

3.53.9

1.240.48

6.30.70.71

10.08

0 2 4 6 8

199819992000200120022003200420052006200720082009

Question:

What is next season’s expected TSWV risk

TSWV in NC (1993-2007)

Severe TSWV epidemics (8 counties)

TSWV epidemic in 2002 and then occasionally (12 counties)

TSWV in “trace” (38 counties)

What can a grower do?

Imidacloprin (such as, Admire Pro: 0.8 oz/1000 pl)AND Actigard (0.5 oz – 1 oz/50,000 pl drench OR 10 – 25

ppm float water)

Chemical control in the greenhouse

Untreated control

Actigard 25 ppm [float water]

Actigard: 4 weeks after transplant

Wake co. 2006

Actigard: 6-7 weeks after transplant

Untreated controlActigard 25 ppm [pretra]

Wake co. 2006

Question:

Which fields will have > 25% TSWV?

What can a grower do?

• Imidacloprin (such as, Admire Pro: 0.8 oz/1000 pl)

AND (if TSW incidence > 25%) • Actigard (0.5 oz – 1 oz/50,000 pl drench OR 10 –

25 ppm float water)

Two questions to answer:

• Question - pre-season risk

What is next season’s expected TSWV risk?

• Question - in-season riskWhich fields will have > 25% TSWV?

TSWV in NC (1993-2007)

Severe TSWV epidemics (8 counties)

TSWV epidemic in 2002 and then occasionally (12 counties)

TSWV in “trace” (38 counties)

A total of 489 cases 58 counties 14 years (1993 – 2007)

Objectives

• Determine if any weather factors are predictors of TSWV risk at the county level

Time: September before transplant to August (harvest)

Weather factors: Total precipitation, days with rain, degree days, and average air temperature

Pre-season risk - Results

Precipitation and temperature of Dec – Feb most significant explanatory weather factors

Parameter Estimate

Total Precipitation (December) -0.007

Total Precipitation (January) -0.014

Total Precipitation (February) -0.008

Sum of monthly average temperature (December, January & February)

0.14

* Magnitude of effect different for counties

Pre-season risk – “county effect”

►Correction between counties?

(Structured heterogeneity)

► Other missing factors?

(Unstructured heterogeneity)

Investigate the “county” effect: Bayesian disease mapping

yi ~ Bin (ni, pi) (likelihood)

pi = f (T, Pr) + Ui + Vi

Structured (autocorrelation)

“Auto-regression function”

Unstructured

N (0, σ2)

• Structured heterogeneity? NO

• Unstructured heterogeneity? YES

Pre-season risk – “county effect”

Sampson co.

TSWV incidence

Pro

bab

ilit

y o

f T

SW

V i

nci

den

ce

Validation (2008 – present)

Predicted Pre-season riskNorth Carolina - 2008

County Station Predicted

Craven Havelock 14 – 22Duplin Mount Olive 4 – 9 Sampson Clinton 13 – 26Lenoir Kinston 4 – 11 Pitt Ayden 1 – 4 Johnston Clayton 0.6 – 3.5Wilson Sims 0 – 1

Reported

14

8

2

10

2.3

4

1

Predicted Pre-season riskNorth Carolina - 2010

County Station Predicted

Craven Havelock 1 – 14 Duplin Mount Olive 1 – 5 Sampson Clinton 0.5 – 10 Lenoir Kinston 1 – 12 Pitt Ayden 0 – 3 Johnston Clayton 0 – 0.5 Wilson Sims 0 – 1

Conclusions

• Winter weather good predictor of TSWV risk for upcoming season

* Importance of spring weather was not discussed…

Pre-season risk on the web

Expand effort - 2009

• Pre-season risk

(Georgia, North Carolina, South Carolina and Virginia)

• In-season risk

(Georgia, North Carolina, South Carolina)

• K. Cherry

• J. Radcliff & M. Browne

• NC Tobacco Agents

• NC Tobacco Research Commission

• Tobacco Education & Research Council

Acknowledgements