Patrick J. Minogue

Comparison of Aminocyclopyrachlor to Common Herbicides for Kudzu (Pueraria montana) Management

Abstract Kudzu is an invasive perennial climbing vine characterized by fast growth rates and tolerance to control measures. Repeated applications with high rates of 2,4-D plus picloram provide effective kudzu control, but picloram use is not permitted in certain states due to groundwater pollution concerns. Studies were conducted in Alabama and Florida to compare kudzu control with aminocyclopyrachlor, a new herbicide, to control provided by aminopyralid, clopyralid, metsulfuron methyl, and picloram plus 2,4-D, which are common treatments for kudzu management. Two annual applications of the same herbicide treatment were evaluated for effects on kudzu cover, kudzu volume index, and cover of other vegetation. Aminocyclopyrachlor at 140 to 280 g ae ha−1 (2 to 4 oz ae ac−1) was as effective as the standard 4.48 kg ae ha−1 (4 lb ae ac−1) 2,4-D amine plus 1.2 kg ae ha−1 picloram for kudzu control. There were no differences in kudzu control among the three rates of aminocyclopyrachlor tested. Colonization by graminoids, forbs, and Rubus spp. at 2 yr was greatest for herbicides providing the best kudzu control: aminocyclopyrachlor, and 2,4-D plus picloram. Herbicide treatments were more effective in controlling kudzu at the Alabama location, but repeated annual applications for 2 yr did not completely eliminate kudzu with any treatment at either site. Nomenclature: 2,4-D; aminocyclopyrachlor; aminopyralid; clopyralid; metsulfuron methyl; picloram; kudzu, Pueraria montana (Lour.) Merr., USDA code PUMOL, EPPO code PUELO. Interpretive Summary: The new herbicide, aminocyclopyrachlor, applied at 140 to 280 g ae ha−1 controlled kudzu as well as the standard treatment for kudzu management, 4.48 kg ae 2,4-D amine plus 1.21 kg ae picloram, and generally better than the other common kudzu herbicides metsulfuron methyl, aminopyralid, and clopyralid. Graminoids, Rubus spp., and forbs recolonized plots receiving the most effective treatments for kudzu control. Graminoid (grasses, sedges) cover increased following aminocyclopyrachlor treatments, an important consideration for restoration of infestations where kudzu was planted for erosion control in the region. Annual herbicide applications for 2 yr did not eradicate kudzu, confirming the need for multiple years of treatment or more frequent applications.

REMOVAL OF NITROGEN AND PHOSPHORUS BY EUCALYPTUS AND POPULUS AT A TERTIARY TREATED MUNICIPAL WASTEWATER SPRAYFIELD

Various progenies of Eucalyptus grandis and E. amplifolia, and clones of Populus deltoides, were evaluated for plant removal of nitrogen (N) and phosphorus (P) for 26 months at a municipal waste spray field in north Florida. Tertiary treated wastewater containing 2.73 mg L−1 nitrate N and 0.30 mg L−1 total P was applied using sprinkler irrigation (93.8 m3 ha−1 d−1) to fast growing trees utilized for bioenergy. Eucalyptus amplifolia and E. grandis survived and grew very poorly as the result of severe winter injury in two successive years and were not evaluated for nutrient removal. Survival and growth of P. deltoides demonstrated suitability for phytoremediation, and selected clones were evaluated for biomass and nutrient content. Removals of total N (TN) and total P (TP) were greatest for main stem (36% and 44%, respectively) and foliage (44% and 36%, respectively). Low biomass producing clones generally had higher nutrient concentrations, but high biomass producing clones removed more TN and TP. Approximately 789 kg ha−1 TN and 103 kg ha−1 TP were removed by the highest biomass producing P. deltoides clone, representing 215% of N and 615% of P inputs.

Potential Invasiveness for Eucalyptus Species in Florida

Abstract To assess the potential invasiveness of common eucalyptus species planted for pulpwood, mulch wood or bioenergy crops, field surveys of eucalyptus seedling recruitment were conducted in north and central Florida locations within seed bearing eucalyptus stands and in the proximate plant communities where seed dispersal may occur. Plant communities included non-grazed pasture, intensively site-prepared forestland, abandoned forest road and upland mixed pine- hardwood forest. No eucalyptus seedlings were found in any of the 310 1-m2 survey plots across the two locations. Second, seed addition studies were conducted to determine the relative potential for seedling emergence and survival among Eucalyptus amplifolia, E. camaldulensis and E. grandis added into plots at two seed densities, under disturbed and nondisturbed conditions, in the understory of the eucalyptus stands and in each of the aforementioned proximate plant communities. Overall, the probability of emergence of added seed was very low (P  =  0.0 to 0.0032), and seed density effects were not significant. Emergence was significantly greater in disturbed conditions compared to nondisturbed conditions for seedlings originating from natural seed rain from the eucalyptus canopy in central Florida. The amount of time that seedlings survived was greater for E. camaldulensis compared to the other species but no seedlings survived more than 13 wk. These data indicate that under specific favorable conditions, eucalyptus seedlings may establish within or proximate to planted stands, but the overall level of invasiveness demonstrated by E. amplifolia and E. grandis is low for north or central Florida. The demonstrated role of disturbance in facilitating eucalyptus seedling recruitment suggests that a stable perennial plant community (native grasses) should be established instead of bare soil buffer zones to mitigate spread. Nomenclature: Cabbage gum (Eucalyptus amplifolia Naudin); yellow mallee (Eucalyptus incrassata Labill.); river red gum (Eucalyptus camaldulensis Dehnh.); rose gum [Eucalyptus grandis W. Hill ex Maiden]. Management Implications: Because of its potential for fast growth and high fiber yields, eucalyptus plantations are being established in the southeastern US Coastal Plain as a source of pulpwood, mulch wood and possibly biofuel. Two quantitative study approaches used within seed bearing Eucalyptus amplifolia stands and their proximate native and modified plant communities in north and central Florida found low invasive potential overall. Surveys at the two locations found no eucalyptus recruitment, suggesting limited success for seedling establishment. The subsequent study evaluated the invasive potential of three commercially important eucalyptus species by adding seed at two densities to disturbed (forest litter or vegetation removed to expose mineral soil) and nondisturbed sites. The combined research findings demonstrated that eucalyptus seedling establishment and survival were generally low at the northern and central Florida locations, although greater numbers of seedlings were observed in disturbed conditions, within the eucalyptus stands and for E. camaldulensis as compared to E. grandis or E. amplifolia. Seed addition at 500 or 1000 expected germinants per m2 did result in seedling establishment, but no seedlings survived more than 13 wk. Whereas these results do not support previous weed risk assessment conclusions of high invasion risk for E. camaldulensis, they suggest that caution is warranted regarding the cultivation of E. camaldulensis, especially concerning practices that might increase soil disturbance near eucalyptus stands. The demonstrated role of disturbance in facilitating eucalyptus seedling recruitment suggests that perennial native plant communities should be established instead of bare soil buffer zones. Future research is needed for south Florida where subtropical temperatures favor eucalyptus growth and where commercial plantations are becoming more common.

Exotic Eucalyptus plantations in the southeastern US: risk assessment, management and policy approaches

As eucalyptus cultivation increases in the southeastern United States to provide feedstock for pulpwood, landscape mulch and an emerging bioenergy market, there is concern regarding potential invasiveness. Recently, models to predict the likelihood of invasiveness have produced conflicting results. Our uncertainty about invasion risk and the relative values we hold for environmental and industry protection will influence which management options and policies are pursued. Here we synthesize the essential practices and barriers to potential eucalyptus spread relative to different stages of the invasion process. Additionally, we offer a discussion of social and economic implications of the possible policies and regulatory techniques for mitigating future problems, with an emphasis on the often-recommended precautionary approach. We highlight future research needs and emphasize a landscape level, collaborative adaptive management approach.

Sequential Sulfometuron Methyl Applications in Eucalyptus benthamii Plantations

Abstract A study was conducted to refine herbicide rates for sequential applications of sulfometuron methyl over newly planted Eucalyptus benthamii seedlings in the Coastal Plain of the southeastern United States. Container-grown, 6-wk-old seedlings were planted in July 2011 on a nonbedded agricultural site in Quincy, FL and on a bedded forestry site in Wing, AL. Treatments included a single sulfometuron application at 13, 26, 39, or 52 g ha−1, 2 wk after planting; sequential applications at the same rates, 2 and 8 wk after planting; and a nontreated check. All sulfometuron treatments provided effective control of all vegetation groups at both sites, with the exception of 13 g ha−1 for forbs in Quincy. Sparse weed cover in Wing was eliminated by any sulfometuron treatment. In Quincy, two applications provided better weed control than a single one, resulting in more bare ground and less grass and vines. Bare ground increased with increasing sulfometuron rate from 0 to 26 g ha−1. The 26 g ha−1 rate resulted in 95 and 88% bare ground 6 and 12 wk after the first application, respectively, compared to 62 and 51%, respectively for the nontreated check. All sulfometuron treatments had a small positive effect on Eucalyptus seedling growth at the Quincy site, resulting in greater stem diameter (6.0 to 6.7 mm) than the nontreated check (5.0 mm), despite slight foliar necrosis. At the Wing site, in addition to slight foliar necrosis, sulfometuron decreased final seedling survival, height, and stem diameter (48 to 68%, 77.8 to 81.6 cm, and 8.7 to 9.2 mm, respectively), compared to the nontreated check (99%, 88.3 cm and 11.2 mm, respectively). Two sulfometuron applications at 13 to 26 g ha−1 provided selective weed control at both sites, but further refinement is needed for various Eucalyptus genotypes, soil, and vegetation types. Nomenclature: Sulfometuron methyl; camden white gum, Nepean River gum, Eucalyptus benthamii Maiden & Cambage.

Control of Invasive Japanese Climbing Fern (Lygodium japonicum) and Response of Native Ground Cover During Restoration of a Disturbed Longleaf Pine Ecosystem

Japanese climbing fern (Lygodium japonicum) is an invasive species prevalent through the southeastern United States that grows on, around, and intermingles with native groundcover in a variety of forest ecosystems. Management of this species can be problematic because herbicide control must also ensure minimal impact to native plants, particularly in ecosystems undergoing restoration and recovery from disturbance. We tested 3 herbicides (glyphosate, imazapyr, and metsulfuron methyl) at various rates, alone and in combination, to evaluate their efficacy for fern control and impacts to non-target, native groundcover in a longleaf pine (Pinus palustris) ecosystem subject to dormant season burns and hurricane and salvage logging disturbances. All herbicide treatments reduced Japanese climbing fern cover by 77–98% at 1 yr following treatment, but at 2 yr there was considerable re-growth on imazapyr and metsulfuron-methyl treated plots. Glyphosate applied alone as a 2 or 4% solution provided 91–98% fern control after 2 yr, and there was no significant improvement using combinations of glyphosate with other herbicides. Climbing fern cover increased by 70% in the untreated control. We found a significant correlation between reduction in fern cover and increase in other vegetation, though species composition changed minimally. Species richness at 2 yr after treatment increased by 2–3 species following application of glyphosate alone or in combination, and decreased on the untreated control. We recommend directed spray applications using 2% glyphosate solutions for efficient control. Using this approach on matted fern should result in little detriment to native groundcover, even with this broad-spectrum herbicide.

Selective Herbicides for Cultivation of Eucalyptus urograndis Clones

Competition control is essential for successful eucalyptus plantation establishment, yet few selective herbicides have been identified. Five herbicides, flumioxazin, imazamox, imazapic, oxyfluorfen, and sulfometuron methyl, were evaluated for selective weed control in the establishment of genetically modified frost tolerant Eucalyptus urograndis clones. Herbicides were applied at two or three rates, either before or after weed emergence, and compared to a nontreated control and to near-complete weed control obtained with glyphosate directed sprays. Applications prior to weed emergence were most effective for weed control and, with the exception of imazapic, all resulted in enhanced eucalyptus growth relative to the nontreated control. Among postemergent treatments, only imazamox enhanced stem volume. Among selective herbicide treatments, preemergent 2240 g ha−1 oxyfluorfen produced the best growth response, resulting in stem volume index that was 860% greater than the nontreated control, although only 15% of the volume index obtained with near-complete weed control. Imazapic was the most phytotoxic of all herbicides, resulting in 40% mortality when applied preemergent. Survival was 100% for all other herbicide treatments. This research found the previously nontested herbicides imazamox and imazapic to be effective for selective weed control and refined application rate and timing of five herbicides for use in clonal plantations.

Influence of phosphorus limitations on the growth, nutrient partitioning and physiology of mahogany (Swietenia macrophylla King) seedlings

ABSTRACT The effects of four rates of phosphorus (P) fertilization (0, 0.56, 5.6 and 56.0 mg l−1) in soilless medium on the growth and physiology of mahogany seedlings were examined. The greatest response occurred at the 56 mg l−1 rate, with relatively small differences between other treatments. Biometric parameters increased at the 56 mg l−1 compared to 0 mg l−1 rate except root dry mass. Both the concentration and the total content of P and Kjeldahl nitrogen (N) increased in leaves, stems and roots with P application rate. Foliar concentrations of potassium (K), calcium (Ca), magnesium (Mg), manganese (Mn) and sulfur (S) declined, and boron (B) and copper (Cu) increased with P limitations; zinc (Zn) and iron (Fe) were unaffected. Physiological adaptations of mahogany to P limitations include the preferential allocation of carbon (C) to plant roots, and increases in P utilization efficiency, P acquisition efficiency and the concentration of organic acids in xylem fluid. Root phosphatase activity was not influenced by P fertilization.

Selective Herbicides for Bald Cypress Restoration and Cultivation

Abstract Studies were conducted in 2007 and 2008 to evaluate herbicides having both PRE and POST activity for selective weed control in bald cypress plantings. Five herbicides were applied at two or three rates at two different timings. The first timing was to dormant seedlings without foliage and prior to weed emergence (i.e., PRE). The second timing was to foliated seedlings with established weed seedlings present (i.e., POST). Herbicide treatments included aminopyralid at 70 and 120 g ae ha−1, hexazinone at 420 and 560 g ai ha−1, imazapyr at 140 and 210 g ae ha−1, sulfometuron methyl at 110, 160, and 210 g ai ha−1, and flumioxazin at 290 and 430 g ai ha−1. Herbicide rate had little effect on vegetation control. PRE-applied sulfometuron methyl was most effective, providing nearly complete control of graminoids and broadleaves at 60 d after treatment (DAT). POST-applied treatments were generally less effective, though in the 2008 study imazapyr and sulfometuron methyl resulted in approximately 60% bare ground at 60 DAT. Growth of bald cypress seedlings was enhanced by both PRE- and POST-applied sulfometuron methyl, flumioxazin, or hexazinone and by PRE imazapyr. The best bald cypress growth response followed POST-applied sulfometuron methyl at 210 g ha−1, which resulted in 63 cm3 mean volume index, more than fivefold greater than the nontreated check. Aminopyralid caused severe and lasting seedling injury. POST-applied imazapyr resulted in fasciculation and no growth benefit, despite providing the most efficacious weed control among POST treatments. Survival and growth of bald cypress can be greatly enhanced with a single selective herbicide treatment using sulfometuron methyl, flumioxazin, or hexazinone applied before or following foliation in the spring. Nomenclature: Aminopyralid; flumioxazin; hexazinone; imazapyr; sulfometuron methyl; bald cypress, Taxodium distichum (L.) Rich var. distichum.

Japanese Climbing Fern (Lygodium japonicum) Management in Florida's Apalachicola Bottomland Hardwood Forests

Abstract Japanese climbing fern (Lygodium japonicum) is an invasive vine that has been identified as an economic and ecological threat in forest ecosystems of the Southeast. In two separate studies, we examined the use of directed sprays of glyphosate, imazapyr, and metsulfuron-methyl herbicides, alone and in combination, for control of Japanese climbing fern and for impacts to associated vegetation in mixed bottomland hardwood–cypress forests at two first terrace sites of the Apalachicola River in north Florida. Two yr after treatment, various rates of glyphosate alone generally provided greater percent control (84 to 95%) than imazapyr alone (−25 to 86%) or metsulfuron-methyl alone (−5 to 53%). Combinations of 2% glyphosate and imazapyr and/or metsulfuron-methyl resulted in 81 to 97% control at 2 yr after treatment, with no significant differences among the combination treatments or 2% glyphosate alone. Change in percent cover of associated vegetation groups was not influenced by treatment except for one location where graminoid cover increased 1 yr after metsulfuron-methyl treatment but decreased after imazapyr or glyphosate application. Species richness of dominant understory vegetation remained nearly constant at both locations regardless of treatment. These data indicate that glyphosate alone or in combination with imazapyr or metsulfuron-methyl will provide effective, although not complete, control of Japanese climbing fern, and that directed herbicide sprays minimally impact nontarget vegetation. Nomenclature: