The Biology and Control of Beach Vitex (Vitex rotundifolia) and Common Reed (Phragmites australis)

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Title: The Biology and Control of Beach Vitex (Vitex rotundifolia) and Common Reed (Phragmites australis)
Author: True, Sarah Louise
Advisors: Dr. Robert Richardson, Committee Chair
Dr. Joseph Neal, Committee Member
Dr. David Jordan, Committee Member
Dr. Kurt Getsinger, Committee Member
Abstract: Beach vitex [Vitex rotundifolia (L.f.)] is a perennial woody shrub native to Hawaii and countries of the Pacific Rim. Beach vitex thrives on coastal sand dunes and was introduced into the southeastern United States for use as an ornamental and dune stabilizing plant. Today, however, it is considered a noxious weed and invasive species due to its aggressive spread and competition with native flora and fauna. Field and greenhouse studies were conducted from 2006 through 2008 to evaluate the efficacy of selected herbicides and mixtures on beach vitex. In one experiment, beach vitex control at 1 month after treatment (MAT) was greatest with glyphosate and glyphosate plus imazapyr (73% to 84%) and at 12 MAT, control increased to 90 and 94%, respectively. Control with triclopyr mixtures was less than 36% at 1 MAT and less than 11% at 12 MAT. In a second experiment, at 1 MAT glyphosate, imazapyr, and metsulfuron controlled beach vitex 66 to 82%. Control with aminopyralid, imazamox, and penoxsulam was less than 50%. At 8 MAT greatest control was observed with glyphosate and imazapyr (83 and 90%, respectively). Control levels with other treatments were significantly lower at 19 to 52%. In a greenhouse study at 3 weeks after treatment (WAT), control was 37 to 68% with glyphosate and 41 to 76% with imazapyr. At 5 WAT, control was 34 to 87% with glyphosate and 48 to 95% with imazapyr. Dry weight was 4.47 to 5.00 g in glyphosate treatments and 3.50 to 6.18 in imazapyr treatments as compared to the nontreated dry weight of 6.93 g. The absorption and translocation of glyphosate in beach vitex was evaluated with cut stem and foliar applications. Plants were treated with a prepared 14C-glyphosate solution and harvested at 6, 24, 48, 92, and 196 hours after treatment (HAT). In beach vitex cut stems, time of harvest was not significant indicating that all absorption and translocation occurred within the first six hours after treatment. The greatest amount of herbicide recovered remained in the stump (348,408 DPM). A moderate amount translocated to the first root section (14,572 DPM) and a minimal amount translocated to root segments greater distances from the stump (1,657 and 617 DPM for second 10 cm of roots and end roots, respectively). In foliar treatments, the greatest recovered herbicide remained in the treated leaf at 17,828 DPM. Recovered 14C-glyphosate in other plant parts did not differ and ranged 1,222 to 4,300 DPM. At 6 and 24 HAT, 2,081 to 2,825 DPM were recovered. Greater amounts of 6,432 to 9,661 were recovered at 48 to 196 HAT. Translocation of the applied herbicide was generally low with both application methods. Another invasive plant common to coastal areas of the southeastern United States is common reed [Phragmites australis ((Cav.) Trin. ex Steud.)]. Often referred to as Phragmites, this perennial emergent aquatic grass is spread worldwide. Field studies were conducted in 2006 and 2007 to evaluate efficacy of selected herbicides on Phragmites. At 12 to 16 WAT, Phragmites was controlled at least 93% with imazapyr at either 1.25 or 2.5% v/v, and at least 73% with glyphosate at the same rates. At 47 to 66 WAT, control by glyphosate and imazapyr was equivalent and at least 88%. Phragmites was controlled with triclopyr at initial ratings (at least 79%), but control was less than 13% at 47 to 66 WAT due to extensive regrowth. Control with 1.25% v/v imazamox did not exceed 51% and control with 0.45% v/v penoxsulam did not exceed 23% at any rating.
Date: 2009-04-28
Degree: MS
Discipline: Crop Science

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