Cogongrass: Research results from competition and herbicide

studies

C. Ramsey, USDA-APHIS-PPQ-CPHST

National Weed Management LabFort Collins, CO

Cogongrass history

• Cogongrass – 1912 in Alabama

• 1920’s – forage trials in Texas, Mississippi, Alabama, and Florida

• Worldwide – 1 billion ac infested

• 1979 – 19 counties MS

• 2002 – 50 counties MS

Rhizome reserves

• Biomass = 8.9 tons/ac = 2,000 g/m2

• Rhizomes are jointed• Rhizomes buried below 8

cm can not resprout• Rhizomes able to

reproduce – 2 cm cutting

Defoliation and rhizome biomass

• Defoliation – reduces total nonstructural carbohydrate reserves (TNC)

• One mowing– reduced rhizome biomass

by 22%• Second mowing

– reduced rhizome biomass by 38%

• Second disking– Reduced rhizome biomass

by 66%Willard et al. (1997)

Aerial photos

Oct. 2003 Nov. 2005

Field study descriptions

• 2003 - Cogongrass competition loblolly pine

• 2004 – Herbicide /adjuvant study

• 2005 – Cogongrass – loblolly pine root drench study

Objectives for 2003 competition study

• Competitive effects of cogongrass and native herbaceous vegetation on loblolly seedling growth and survival

Site Preparation

• Loblolly pine plantation located in Pond Creek Unit – International Paper property

• Harvested: 2000• Site Preparation: October 15, 2002• Planted: March 6-13, 2003• Pine measured:

– 10 MAP – 2003– 20 MAP - 2004

Herbicides

• Tank mix • Imazapyr (Chopper) - 0.84 kg ai ha-1 (48 fl

oz/ac)• Triclopyr (Garlon 4) – 1.68 kg ai ha-1 (48 fl

oz/ac)• Surfactant – Timberland 90 – 936.2 ml ha-1

(12 fl oz/ac)• Aerial application on Oct. 15, 2002

Vegetation condition

• No site preparation in cogongrass – Cogongrass competition - CGC

• Site preparation in cogongrass– Mixed vegetation competition - MVC

• Site preparation in native vgt.– Native vegetation competition - NVC

• Weed-free - WF

First year effects on pine biomass

• Competitive effects of cogongrass, native vegetation, and no vegetation on loblolly pine biomass

Allelopathic root exudates

• Cogongrass reduces corn yield by 80 – 100% (Udensi et al. 1999)

• Liquid extracts – reduced rice germination by 11 – 15%, reduced rice height by 22% (Casini et al. 1998)

• Italian ryegrass foliar biomass - 60 to 29% of untreated - residues 0.25 to 8% wt/wt

April 28, 2003April 28, 2003MVC plot

July 7, 2003MVC plot

Allelopathy

Loblolly height growth – 3 GSAP

Conclusions• Stem volume index

– 2004 - WF > NVC > MVC > CGC

• SVI – 98% reduction with cogongrass competition

• Vegetation competition time lag

• Pine diameter detected resource competition for four vegetation conditions

Pine restoration conclusions

• 100% re-infestation of herbicide treated area by the end of second growing season

• Pine establishment window too short for rapid canopy closure

2004 Herbicide/adjuvant studyobjectives

• Determine the effects and interactions of two herbicides and adjuvants on foliar control of cogongrass

• Determine effects and interactions of herbicides and adjuvants on rhizome biomass over time

Study design

• Four blocks

• Outer plot - 5 x 5 m

• Inner plot - 3 x 3 m

• Spray date - Nov. 4-5, 2004

Site preparation

• Cutover site - International Paper property• Harvested – July, 2000• Site Preparation - June, 2001

– Velpar ULW – 5.3 kg/ha (4.7 lb/ac)

• Planted – Jan. 2002• Percent foliar cover and rhizome biomass

– June, 2005 – 7 MAT– Nov., 2005 – 12 MAT

Herbicides

• Study design – 2 x 2 x 2 x 3 = 24 trts

• Imazapyr (Chopper) - 32 and 64 fl oz/ac

• Gly Pro Plus (glyphosate) – 128 and 256 fl oz/ac

• MSO conc – 0, 25, 50% v/v

• Silwet L-77 – 0, 0.12% v/v

• Stimupro – 0.7, 1.4, 2.1% v/v

Herbicide costs

• Chopper– 32 fl oz/ac = $51/acre– 64 fl oz/ac = $102/acre

• GlyPro Plus– 128 fl oz/ac = $19.61/ac– 256 fl oz/ac = $39.22/ac

• MSO = 0, $49, $98/ac• Silwet L-77 = 0, $3/ac

November 6, 2004

Chopper vs GlyPro Plus – 12 MAT

Chopper @ 1.12 - 25 - 0

GlyPro Plus @ 8.96 – 25 - 0

Conclusions

• Foliar – 7 MAT– Chopper = GlyPro (8.9 kg ha-1) > Glypro Plus (4.4 kg

ha-1)

– Adjuvants • No effect at 7 MAT

• Increased control at 12 MAT

• Rhizomes – 7 MAT– Chopper – no effect

– Adjuvants – no effect

Conclusions

• 7 MAT sampling time – too soon to detect foliar or rhizome biomass effects

• Rhizome sampling – 8 replications with screw type auger did not reduce variability

• Improvements for sampling methods– Longer time frame – 12 or 24 MAT– Rhizomes – larger unit size – 20 x 20 x 20 cm

2005 Loblolly pine root drench studyobjectives

• Determine the effects of powdered charcoal and seaweed extracts on loblolly pine seedling growth and survival

Site preparation

• Cutover site - International Paper property• Harvested – July, 2000• Site Preparation - June, 2001

– Velpar ULW – 5.3 kg/ha (4.7 lb/ac)

• Cogongrass application - Nov. 29, 2004• Chopper – 1.12 kg/ha (64 fl oz/ac)• Planted – Jan. 2002

– Replanted on Feb. 9, 2005 - 2 MAT Chopper appl.

Root drenches

• Factorial trt design – 3 x 4 = 12 trts

• Gro-Safe charcoal – 0, 50, 100 g/l

• Stimupro (seaweed extract) – 0, 4, 8, 12% (v/v)

• Premixed in water for overnight

• 1 liter sphagnum peat moss/pine seedling

• 300 ml root drench/ seedling

June, 2005

Conclusions

• Charcoal root drench– No effect on seedling survival– Trend to decrease survival

• Stimupro– Negative effect on seedling survival

Conclusions

• Peat moss – may have improved survival– Did not include a control for peat moss

• Stimupro may have stimulated fine root growth – Increased root uptake– Increased seedling mortality

• Test a larger “split peat moss plug”