Theodore M. Webster Crop Protection and Management Research Unit USDA-ARS, Tifton, GA

The Perfect Storm?Why an invasive weed (Commelina benghelensis)

threatens agriculture in the Southeast US

Theodore M. WebsterCrop Protection and Management Research Unit

USDA-ARS, Tifton, GA

Georgia Agriculture

• 1988– Corn: 600,000 ac

– Cotton: 350,000 ac

– Soybean: 930,000 ac

– Peanut: 690,000 ac

– Wheat: 575,000 ac

– Total: 4,268,000 ac

• 2003– Corn: 340,000 ac

– Cotton: 1,450,000 ac

– Soybean: 190,000 ac

– Peanut: 540,000 ac

– Wheat: 380,000 ac

– Total: 3,807,000 ac

Cotton acreageas a % of totalsummer crop

acreage

1. Boll weevil eradication2. Glyphosate-tolerant cultivars ~90%

The Perfect Storm?

• Georgia Agriculture: early 1990’s

– Reliance on PRE Herbicides with soil residual activity (fluometuron: 90% acres)

– Only POST graminicides

– Cultivation: 2 to 3 cultivations/season

– Conservation tillage: <1% of cotton acres

The Perfect Storm?

• Georgia Agriculture: current situation

– Reliance Roundup Ready Cotton Cultivars (90%)

– Abandonment of PRE Herbicides with soil residual activity (fluometuron: <10% acres)

– Cultivation: <15% acres

– Reduced tillage on 45% of the acres

Grady County, GAGrady County, GAPhoto by Stanley Culpepper, UGAPhoto by Stanley Culpepper, UGA

Tropical spiderwort Tropical spiderwort in cottonin cotton

Grady County, GAGrady County, GAPhoto by Stanley Culpepper, UGAPhoto by Stanley Culpepper, UGA

Tropical spiderwort Tropical spiderwort in cottonin cotton

After 2 Applications of Roundup

Roundup: <55% control of tropical spiderwort2- to 4 glyphosate applications/seasons

may be the only herbicide applied

Grady County, GAGrady County, GA

Tropical spiderwort Tropical spiderwort in peanutin peanut

s-Metolachlor - Rainfall, CostImazapic - Rotation Restrictions2,4-D - Cotton proximity

• Native to Asia and Africa

• 1928: Introduced to US

• Mid-1930’s: Common throughout Florida

• 1983: Federally Noxious Weed

• 1998: not considered a serious pest in Georgia

• 2001: considered the 9th most troublesome weed in cotton

• 2002: Most troublesome weed facing cotton growers

TROPICAL SPIDERWORTCommelina benghalensis

Tropical Spiderwort Distribution in Georgia:

Survey: Culpepper, UGA Weed Science Survey: Georgia Department of Agriculture

1999Present

in 5Counties

2004Present

in 29Counties

Identification

Alan York, NCSUAlan York, NCSU

Of the 170 Of the 170 CommelinaCommelina spp., it is one of a few spp., it is one of a few that is vegetatively distinct (Faden 1992)that is vegetatively distinct (Faden 1992)

TROPICAL SPIDERWORTTROPICAL SPIDERWORTTip more bluntedTip more blunted

Length:Width Ratio <3:1Length:Width Ratio <3:1

SPREADING DAYFLOWERSPREADING DAYFLOWERTip sharperTip sharper

L:W Ratio L:W Ratio >>3:13:1

Mike Burton, NCSUMike Burton, NCSU

4.34.3

1.01.01.51.51.01.0

Red Hairs at the Red Hairs at the apex of the apex of the

membranous sheathmembranous sheath

Commelina virginicaCommelina virginica may may also have red or white also have red or white

hairs, but it has narrow,hairs, but it has narrow,long leaf blades long leaf blades (4:1 or greater)(4:1 or greater)

Aerial flowers begin forming 8 to 10 Weeks after emergence

Field conditions: 240 Aerial flowers/plant

(Kaul et al. 2002)

Of the nearly 250,000 species of flowering plants…Of the nearly 250,000 species of flowering plants…

… … 36 have underground flowers36 have underground flowers

Underground flowers (within spathes)

2002 Arlene Mendoza

North Carolina State University

Subterranean flowers begin to form by 6 weeks after emergence

Field conditions: 19 Subterranean

flowers/plant(Kaul et al. 2002)

It’s the onlyCommelina spp.

in the U.S.to have spathes

on rhizomes

Four Types of Seeds!Four Types of Seeds!

TropicalSpiderwort

Growth

Time (days after planting)

0 5 10 15 20 25 30 35 40 45 50 55 60 65 70 75

Nu

mb

er o

f tr

op

ica

l sp

ide

rwo

rt s

ho

ots

0

5

10

15

20

25

30

35

40

45

50

55

Between 48 and 69 DAP: Number of Shoots More Than Doubled

Transplanted 5-Leaf Tropical Spiderwort at Day=0; Greenhouse Study

RAPID GROWTH

Time (days after planting)

40 42 44 46 48 50 52 54 56 58 60 62 64 66 68 70

Nu

mb

er o

f tr

op

ical

sp

ider

wo

rt s

pat

hes

0

10

20

30

40

50

60

70

80

Between 40 and 69 DAP:2.5 New Spathes Every Day

Transplanted 5-Leaf Tropical Spiderwort at Day=0; Greenhouse Study

Seeds Viable within 25 days

of flowering (?)

1 to 3 Flowers/Spathe Usually 3 seeds/Aerial Flower

Maheswari and Maheshwari 1955

Emergence Patterns

Growing degree days (Tb = 20 C)

0 100 200 300 400 500 600 700

Cu

mu

lati

ve s

pid

erw

ort

em

erg

ence

(%

)

0

20

40

60

80

100

120

Cotton: planted April 2003

Cotton: planted April 2004Cotton: planted June 2004

Cotton: planted May 2003

No-Crop: Goldsboro, NC 2003

Can we predict tropical spiderwort emergence?

Cotton: April 2003


0 100 200 300 400 500 600 700

Cu

mu

lati

ve s

pid

erw

ort

em

erg

en

ce (

%)

0

20

40

60

80

100

120

Cotton: June 2004


0 100 200 300 400 500 600 700

Cu

mu

lati

ve s

pid

erw

ort

em

erg

en

ce (

%)

0

20

40

60

80

100

120

Cotton: April 2004


0 100 200 300 400 500 600 700

Cu

mu

lati

ve s

pid

erw

ort

em

erg

en

ce (

%)

0

20

40

60

80

100

120

Cotton: May 2003


0 100 200 300 400 500 600 700

Cu

mu

lati

ve s

pid

erw

ort

em

erg

en

ce (

%)

0

20

40

60

80

100

120

20%

65%

Jun

e 17

May 28

29%

82%

Jun

e 24

May 28

27%

46%

July

13

Jun

e15

25%

84%

Au

gu

st 3

July

7

170 GDD 374 GDD378 GDD

220 GDD

386 GDD

182 GDD 166 GDD

390 GDD

Grady County, Georgia

Can We Control Tropical Spiderwort?

Tropical Spiderwort: Hoed 1 week ago

ABILITY TO RESIST CONTROL TACTICSDoes cultivation control spiderwort or sprig it?

Tip Cutting:100%

One Leaf &Two Nodes:

100%One Leaf &One Node:

57%

One Leaf,No Nodes:

0%

Stem -1 Node, No

Leaf: 10%

Cuttings placed in water solution; Root growth evaluated after 3 weeks

ABILITY TO RESIST CONTROL TACTICSABILITY TO RESIST CONTROL TACTICS

Mike Burton, NCSU

3 Weeks After Planting

3 Node Pieces Buried:2.5, 5, 7.5, 10 cm

3 Node Pieces:Sprigged, 1 Node

Above Ground

Hoeing weather…Hoeing weather…Can I minimize my cotton yield loss?Can I minimize my cotton yield loss?

HypothesisHypothesis

• Cotton planting date will affect the Cotton planting date will affect the impact of spiderwort on cotton yieldimpact of spiderwort on cotton yield

• Early-planted cotton will be more Early-planted cotton will be more competitive with spiderwort than late-competitive with spiderwort than late-planted cottonplanted cotton

How long can cotton tolerate the presence of tropical spiderwort

before yield is affected?

WEEDY Duration - Spiderwort competed for:

2 Wks4 Wks6 Wks8 Wks10 Wks

WEED-FREE Duration – Plots Free of Spiderwort for:

2 Wks4 Wks6 Wks8 Wks10 Wks

Cotton Planted:Cotton Planted:• 30 April 2003 30 April 2003

(DP 555 BG/RR)(DP 555 BG/RR)• 18 May 2004* 18 May 2004*

(DP 555 BG/RR)(DP 555 BG/RR)• 13 June 2004 13 June 2004

(DP 424 BGII/RR)(DP 424 BGII/RR)

• Pendimethalin applied PREPendimethalin applied PRE• Center-pivot irrigation as Center-pivot irrigation as

neededneeded• Naturalized population of Naturalized population of

spiderwortspiderwort

960 Worker-Hours in 2004Weed-free intervals maintained

through hand-hoeing

Weed-Free All SeasonWeed-Free All Season 6 Wks Weedy, then Weed-Free

8 Wks Weedy, then Weed-Free8 Wks Weedy, then Weed-Free 10 Wks Weedy, then Weed-Free

22 July 2003

Spiderwort interferencereduced cotton canopy growth

22 July 2003

Weedy All SeasonWeedy All Season 2 Wks Weed-Free Then Weedy2 Wks Weed-Free Then Weedy

4 Wks Weed-Free, then Weedy4 Wks Weed-Free, then Weedy 6 Wks Weed-Free, then Weedy6 Wks Weed-Free, then Weedy

Yield DataYield Data

Growing degree days (Tb=20C)

0 100 200 300 400 500 600

Co

tto

n Y

ield

(%

of

Wee

d-F

ree

Co

ntr

ol)

40

50

60

70

80

90

100

110

Weedy duration after planting, then Weed-FreeWeed-Free duration after planting, then Weedy

Field Study, Grady County, Georgia; Cotton Planted April 30, 2003

WF All Season

2 WYThen WF

4 WYThen WF

6 WYThen WF

8 WYThen WF: 45%

10 WYThen WF

WY All Season


0 100 200 300 400 500 600

Co

tto

n Y

ield

(%

of

Wee

d-F

ree

Co

ntr

ol)

40

50

60

70

80

90

100

110



WY All Season

2 WFThen WY

4 WFThen WY

8 WFThen WY

10 WFThen WY

WF All Season

6 WF Then WY: <10%


0 100 200 300 400 500 600

Co

tto

n Y

ield

(%

of

Wee

d-F

ree

Co

ntr

ol)

40

50

60

70

80

90

100

110


200 GDD200 GDD~3 WAP~3 WAP



95% Yield

Growing degree days (Tb= 20C)

0 100 200 300 400 500 600 700

Co

tto

n y

ield

(%

of

Wee

d-F

ree

Co

ntr

ol)

30

40

50

60

70

80

90

100

110


Field Study, Grady County, Georgia; Cotton Planted May 18, 2004

<20%<20%

Field Study, Grady County, Georgia; Cotton Planted May 18, 2004


0 100 200 300 400 500 600 700

Co

tto

n y

ield

(%

of

Wee

d-F

ree

Co

ntr

ol)

30

40

50

60

70

80

90

100

110


A single weed controlevent initiated between

225 to 238 GDD,Just prior to 6 WAP

Growing degree days (Tb = 20C)

0 100 200 300 400 500 600 700

Co

tto

n y

ield

(%

of

Wee

d-F

ree

con

tro

l)

30

40

50

60

70

80

90

100

110


Field Study, Grady County, Georgia; Cotton Planted June 13, 2004

~45%~45%

Field Study, Grady County, Georgia; Cotton Planted June 13, 2004


0 100 200 300 400 500 600 700

Co

tto

n y

ield

(%

of

Wee

d-F

ree

con

tro

l)

30

40

50

60

70

80

90

100

110





0 100 200 300 400 500 600

Co

tto

n Y

ield

(%

of

We

ed-F

ree

Co

ntr

ol)

40

50

60

70

80

90

100

110


April 30, 2003


0 100 200 300 400 500 600 700

Co

tto

n y

ield

(%

of

Wee

d-F

ree

con

tro

l)

30

40

50

60

70

80

90

100

110


June 13,2004


0 100 200 300 400 500 600 700

Co

tto

n y

ield

(%

of

We

ed

-Fre

e C

on

tro

l)

30

40

50

60

70

80

90

100

110


May 18, 2004

Critical Period of Spiderwort Control

• April ‘03: 200 to 350 GDU• May ‘04: 225 to 238 GDU

• June ’04: 85 to 454 GDU

Continuous spiderwort competition with peanut, 2 WAP

Critical Period of Spiderwort Control in Peanut

Continuous spiderwort competition with peanut, 6 WAP

Effective weed control4 Weeks Later

Weed-free PeanutsWeed-free Peanuts Weedy PeanutsWeedy Peanuts

No peanuts to harvest

What Other FactorsWhat Other FactorsHave Contributed ToHave Contributed ToThe Rapid ExplosionThe Rapid Explosion

of Tropical Spiderwortof Tropical Spiderwortin Georgia?in Georgia?

County Maintained Road County Maintained Road Adjacent to Test SiteAdjacent to Test Site

Grady County, GeorgiaGrady County, Georgia

•How’s it spreading so fast?

•How long has it been here?

•Are we just selecting for it with our current management programs?

1. It’s probably been around for a while

The Amazing Rate of Spread?The Amazing Rate of Spread?

Cotton Gin TrashCotton Gin Trash

2. We’re probably moving it around with cotton lint2. We’re probably moving it around with cotton lint

The secret to it’s success?

Corn planted in March

Corn is too tall for control tactics as Commelina benghalensis begins to germinate

Atrazine has dissipated prior to June

Tropical spiderwort: August

3. Lack of management in corn;3. Lack of management in corn; Spiderwort can complete a Spiderwort can complete a “ “generation” in 42 daysgeneration” in 42 days

Tropical Spiderwort: September

4. No post-crop harvest management4. No post-crop harvest management

TropicalspiderwortIn this boxFor 3 months…

… 10 days after putting this into water 5. Ability to vegetatively persist5. Ability to vegetatively persist under unusual circumstancesunder unusual circumstances

Future Research DirectionsFuture Research Directions

• Develop an accurate predictive model Develop an accurate predictive model for tropical spiderwort germinationfor tropical spiderwort germination

• Evaluate the seedbank longevity of Evaluate the seedbank longevity of tropical spiderworttropical spiderwort

• Determine the primary dispersal Determine the primary dispersal mechanism(s)mechanism(s)

• Characterize the environmental limits Characterize the environmental limits of tropical spiderwort in the USof tropical spiderwort in the US

Acknowledgements:Acknowledgements:• Thomas E. Sklany (Study Coordinator)Thomas E. Sklany (Study Coordinator)• James Davis (Study Coordinator)James Davis (Study Coordinator)• Amy DavisAmy Davis• Steven FulghumSteven Fulghum• Stefanie CrossStefanie Cross• Van JonesVan Jones• Darryl BrynerDarryl Bryner• Charlie HiltonCharlie Hilton• Carroll JohnsonCarroll Johnson• Robert GiddensRobert Giddens• Chad BurkhalterChad Burkhalter• Jacob FeyereisenJacob Feyereisen• Jessica DanielJessica Daniel• Amanda WebbAmanda Webb• Michael SmithMichael Smith

Grower Cooperators:Grower Cooperators:• Mark and Elden WhighamMark and Elden Whigham• Donald ConnellDonald Connell• Jim TenewitzJim Tenewitz

Supported by:Supported by:• Georgia Cotton CommissionGeorgia Cotton Commission• Cotton IncorporatedCotton Incorporated• Georgia Cotton FarmersGeorgia Cotton Farmers

Documents

Theodore M. Webster Crop Protection and Management Research Unit USDA-ARS, Tifton, GA