٥ RESTORATION OF NATIVE PLANTS THROUGH CHEMICAL CONTROL OF ALLIGATORWEED AT EUFAULA NATIONAL WILDIFE REFUGE Shannon L. Allen School of Forestry and Wildlife Sciences

ALLIGATORWEED ( Alternanthera philoxeroides )  Perennial herb  Native to South America  Vegetative reproduction  Forms thick, interwoven mats

ALLIGATORWEED  Reduces light penetration  Reduces gaseous exchange  Displaces native plants  Reduces waterway drainage

EUFAULA NATIONAL WILDLIFE REFUGE  Northern portion of Walter F. George impoundment of the Chattahoochee River  2,300 hectares of open water and managed wetlands  Primary objective includes providing food and habitat for waterfowl and other birds.

MOIST-SOIL MANAGEMENT  Maintenance of moist-soil conditions during growing season to:  Promote growth of desirable plant species  Control undesirable plant species  Provide food and habitat

NATIVE WETLAND PLANTS  Sedges ( Cyperus spp.)  Rushes ( Rhynchospora spp.)  Beggar ticks ( Bidens spp.)  Smartweeds ( Polygonum spp.)

HOW DO WE CONTROL ALLIGATORWEED?

OBJECTIVES  Objective 1  Determine the rate and timing of triclopyr and imazapyr application that most effectively controls alligatorweed  Objective 2  Determine the rate and timing of triclopyr and imazapyr application that most effectively restores native wetland plant species

METHODS  Randomized block design  4 blocks (15 m x 40 m)  Kennedy Unit ( n = 2)  Bradley Unit ( n = 2)  24 plots/block  Experimental plots (5 m x 5 m)

 Treatments  2 herbicides  3 application rates /herbicide /herbicide  low, medium, high  3 application dates  April, July, and September 2004 METHODS

HERBICIDE RATES  Triclopyr (935L -ha or 2.4L -plot of water)  Low = 4.8L -ha or 12ml -plot  Medium = 9.6L -ha or 24ml -plot  High = 14.4L -ha or 36ml -plot  Imazapyr (467L -ha or 1.2L -plot of water)  Low = 1.2L -ha or 3ml -plot  Medium = 2.4L -ha or 6ml -plot  High = 3.5L -ha or 9ml -plot Rates within range recommended by manufacturers.

TREATMENT APPLICATION  Herbicides applied with a 2L, CO 2 pressurized backpack sprayer  2.5 m wide, 5-nozzle boom 5-nozzle boom  2 swaths per plot

PLANT SAMPLING  Pretreatment : 1 week before 1 week before application date  Post treatment : 1, 2, 3 weeks, and 1, 2, 3 weeks, and 1, 2, 3 months 1, 2, 3 months  Two subplots (0.5 m x 0.5 m) per plot (0.5 m x 0.5 m) per plot

PLANT SAMPLING  Parameters measured:  percent cover of each plant species  alligatorweed density (#stems/quadrat)  alligatorweed height (cm)

PLANT BIOMASS  October 2004 and 2005  Alligatorweed and native plants collected plants collected in subplots ( n = 2) in subplots ( n = 2) (0.25 m x 0.25 m) (0.25 m x 0.25 m)  Plants sorted by species, dried to species, dried to constant mass, constant mass, and weighed and weighed

STATISTICAL ANALYSIS  Differences in plant biomass between fixed variables herbicides, rates, and application dates were tested with ANOVA using PROC MIXED  Pretreatment percent cover, stem density, or height were not significant covariates

RESULTS Native Plants Alligatorweed

ALLIGATORWEED BIOMASS Variable F Value DF P Value Herbicide4.281,33<0.05 Rate4.562,33<0.05 Application Date ,33<0.001 Herbicide x Rate 0.032,33N.S. Herbicide x Application Date 4.321,33<0.05 Rate x Application Date 2.522,33<0.1 Herbicide x Rate x Application Date 0.492,33N.S.

ALLIGATORWEED BIOMASS April July

NATIVE PLANT BIOMASS Variable F Value DF P Value Herbicide3.481,33<0.1 Rate1.002,33N.S. Application Date 8.881,33<0.05 Herbicide x Rate 0.252,33N.S. Herbicide x Application Date 0.381,33N.S. Rate x Application Date 3.202, Herbicide x Rate x Application Date 0.182,33N.S.

NATIVE PLANT BIOMASS Triclopyr Imazapyr April July

ALLIGATORWEED VS NATIVE PLANTS April July

PERCENT COVER OF ALLIGATORWEED AFTER APRIL TREATMENT Triclopyr Imazapyr

PERCENT COVER OF ALLIGATORWEED AFTER JULY TREATMENT Triclopyr Imazapyr Triclopyr Imazapyr

SUMMARY ) Alligatorweed:  In April, imazapyr controls better than triclopyr  Herbicides control equally at July application  July application controls better than April application  In April, high application rate more effective than medium and low rates  In July, no difference between rates

SUMMARY ) Native plants:  Triclopyr results in greater biomass than imazapyr  In April, high rate results in greater biomass than low rate  High rate in April results in greater biomass than high rate in July

ALLIGATORWEED BIOMASS Variable F Value DF P Value Herbicide0.021,33N.S. Rate3.452,33<0.05 Application Date ,33<0.001 Herbicide x Rate 1.182,33N.S. Herbicide x Application Date 6.211,33<0.05 Rate x Application Date 0.002,33N.S. Herbicide x Rate x Application Date 1.332,33N.S.

ALLIGATORWEED BIOMASS Low Medium High

NATIVE PLANT BIOMASS Variable F Value DF P Value Herbicide0.041,33N.S. Rate1.302,33N.S. Application Date 8.941,33<0.01 Herbicide x Rate 1.032,33N.S. Herbicide x Application Date 7.191,33<0.05 Rate x Application Date 0.082,33N.S. Herbicide x Rate x Application Date 0.182,33N.S.

ALLIGATORWEED VS NATIVE PLANTS April July

SUMMARY ) Alligatorweed:  High application rate controls better than low rate  No difference between herbicides at April or July application  July application of imazapyr better than April application  No difference in control by triclopyr at April or July application

SUMMARY ) Native plants:  No difference between herbicides at April and July application  No difference between April and July with triclopyr application  Greater native plant biomass with July application of imazapyr than April application

MANAGEMENT RECOMMENDATION  To manage for native wetland plants in treatment year:  Apply high rate of triclopyr in April to control alligatorweed and allow greatest native plant biomass

MANAGEMENT RECOMMENDATION  To manage for native wetland plants one year after treatment:  Apply high rate of imazapyr in July for greatest control of alligatorweed and highest native plant biomass one year after treatment

ACKNOWLEDGEMENTS: Committee members : Dr. Gary R. Hepp, Dr. Bob S. Boyd, Dr. James H. Miller, and Dr. Ralph E. Mirarchi Field Technicians : Erwin Chambliss, Frank Allen, Frank and Betty Tee Smith Refuge Staff (Frank Dukes and especially Milton Hubbard) Funding : U.S. Fish and Wildlife Service, BASF, and SePro