Cogongrass: Research results from competition and herbicide studies C. Ramsey, USDA-APHIS-PPQ-CPHST National Weed Management Lab Fort 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/m 2 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. 2003Nov. 2005

Field study descriptions 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

Herbicides Tank mix Imazapyr (Chopper) kg ai ha -1 (48 fl oz/ac) Triclopyr (Garlon 4) – 1.68 kg ai ha -1 (48 fl oz/ac) Surfactant – Timberland 90 – 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 ) Liquid extracts – reduced rice germination by 11 – 15%, reduced rice height by 22% ( Casini et al ) Italian ryegrass foliar biomass - 60 to 29% of untreated - residues 0.25 to 8% wt/wt

April 28, 2003 MVC plot July 7, 2003 MVC plot Allelopathy

Loblolly height growth – 3 GSAP

Conclusions Stem volume index – 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 study objectives 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 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 GlyPro 8.96 –

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 study objectives 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 –Replanted on Feb. 9, 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”