Control of Cogongrass in Forests and Natural Areas

Transcription

1 Control of Cogongrass in Forests and Natural Areas 2016 Aquatic Weed Control Short Course Coral Springs, FL Pat Minogue, Ph.D., R.F. Associate Professor of Silviculture University of Florida

2 Cogongrass infestation in the southeastern United States points of introduction

3 Cogongrass (Imperata cylindrica) Among world s 10 worst weeds, 500 million acres One of Florida s worst weeds, more than 1 million acres Displaces nearly all native vegetation Alters natural ecosystem Severe wildfire hazard Flowers in spring

4 Recognize Cogongrass Off-center mid vein, serrated leaf margin Segmented rhyzomes

5 Cogongrass Biology Adaptive - poor soils, drought, fire Disturbance increases spread Persistent in low light conditions Rhizomes (roots) can be 60% of biomass Wind-dispersed seed, viability variable

6 Herbicide Treatments in Forests Burn prior to treatment to promote new foliage growth, better herbicide effectiveness Apply in late summer, early Fall 3 qts/a Accord plus oz Arsenal AC 3 4 qts/a Accord where desirable hardwoods trees are present UF Forestry Research, Walton Co. MULTIPLE treatments are needed Need to re-establish native vegetation

7 Control of Cogongrass in Southern Pine Forests Two study sites in the Alabama Coastal Plain 22 Herbicide treatments compared to non-treated Re-treatment tested in split plots September vs. October Application Timing Glyphosate rates: 1.5, 3, 6, 12 lb ae/acre Imazapyr rates: 0.25, 0.5., 1.0, 2.0 lb ae/acre Application volume 10, 20, 40 GPA for 3 lb glyphosate lb imazapyr tank mix Minogue, P.J., J.H. Miller, and D.K. Lauer Use of glyphosate and imazapyr for cogongrass (Imperata cylindrica) management in Southern pine forests. Southern Journal of Applied Forestry 36:19-25.

8 Satellite view of cogongrass infestations

9 Application Timing Percent control of cogongrass 2 years after retreatment New Infestation Appl. Timing Glyphosate Imazapyr Gly + Ima Average September 56 a 50 a 75 a 59 a October 36 b 47 a 55 b 45 b Old Infestation Appl. Timing Glyphosate Imazapyr Gly + Ima Average September 50 a 74 a 67 a 64 a October 43 a 64 b 58 a 55 b Minogue et al South. J. Applied Forestry 36:19-25

10 Glyphosate Rate Response 100 New infestation 100 Old infestation 80 control(%)=100 x sin 2 ( rate) 80 control(%)=100 x sin 2 ( rate) Control (%) control(%)=100 x sin 2 ( rate) 20 control(%)=100 x sin 2 ( rate) Glyphosate Rate (kg ae/ha) Glyphosate Rate (kg ae/ha) One application Retreat after 1 year Minogue et al South. J. Applied Forestry 36:19-25

11 Imazapyr Rate Response New infestation control(%)=100 x sin 2 ( rate) Old infestation control(%)=100 x sin 2 ( rate) Control (%) control(%)=100 x sin 2 ( rate) 20 control(%)=100 x sin 2 ( rate) Imazapyr Rate (kg ae/ha) Imazapyr Rate (kg ae/ha) One application Retreat after 1 year Minogue et al South. J. Applied Forestry 36:19-25

12 Application Frequency Percent control of cogongrass 2 years after treatment or retreatment New Infestation Frequency Glyphosate Imazapyr Gly + Ima Single 29 b 30 b 48 b Retreatment 62 a 67 a 80 a Old Infestation Frequency Glyphosate Imazapyr Gly + Ima Single 33 b 61 b 55 b Retreatment 60 a 77 a 70 a Minogue et al South. J. Applied Forestry 36:19-25

13 Comparison of glyphosate and imazapyr for cogongrass control Herbicide 1 X All Rates 1 X All Rates Lb ae/acre New Infestation Old Infestation 3 lb Glyphosate (Percent Control) b 45 a 35 b 47 b 0.5 lb Imazapyr 3 lb Gly lb Imaz 39 b 48 a 66 a 69 a 65 a a -- Minogue et al South. J. Applied Forestry 36:19-25

14 10, 25, 40 GPA Application Volumes 3 lb ae Glyphosate lb ae Imazapyr 100 New infestation 100 Old infestation Control (%) Application Volume (l/ha) Application Volume (l/ha) One application Retreat after 1 year Minogue et al South. J. Applied Forestry 36:19-25

15 Summary Herbicide efficacy increased linearly with increasing glyphosate or imazapyr rates (using greater than labeled rates) but eradication was not achieved. On average, application in September provide better control than in October. Repeated September applications of 2 lb ae/a imazapyr gave the best control (88-90%). Control with the combination of 3 lb glyphosate and 0.5 lb imazapyr did not differ between 10, 25 and 40 GPA application volumes.