Jeffrey F. Derr

Common Reed (Phragmites australis) Response to Mowing and Herbicide Application

Abstract Common reed is an invasive species that has overtaken wetland habitats in the eastern United States and can spread into roadsides, turf, and ornamental sites. The postemergence grass herbicides used in nursery crops and turf, clethodim, fenoxaprop, fluazifop, and sethoxydim, did not control common reed. Dithiopyr, MSMA, and quinclorac also did not control this weed. Glyphosate applied at 2.24 kg ai/ha (2.0 lb ai/ac) was more effective in preventing regrowth of common reed than glufosinate at 1.12 kg/ha (1.0 lb ai/ac). Mowing every 2, 4, or 8 wk controlled common reed 93, 81, and 69%, respectively, by the end of the growing season, but only reduced regrowth by approximately 55% the following May. Applying glyphosate at 2% v/v either 1 mo after a mowing or 2 wk prior to mowing reduced common reed regrowth the following May by approximately 90%. Applying glyphosate without mowing provided similar common reed control the following spring compared to glyphosate combined with a single mowing. Common reed regrew in all treated plots 1 yr after study initiation, indicating that control treatments must be repeated if common reed is to be eradicated from a site. Nomenclature: Clethodim; dithiopyr; fluazifop; fenoxaprop; glufosinate; glyphosate; MSMA; quinclorac; sethoxydim; Common reed, Phragmites australis (Cav.) Trin. ex Steud

Response of Japanese Stiltgrass (Microstegium vimineum) to Application Timing, Rate, and Frequency of Postemergence Herbicides1

Japanese stiltgrass is a nonnative invasive grass that occurs in a variety of habitats and is widely distributed throughout the eastern United States. In natural areas such as forests, herbicide options that selectively control Japanese stiltgrass while preserving native herbaceous and woody vegetation may be desired. The efficacy of three selective postemergence herbicides (fenoxaprop-P, imazapic, and sethoxydim) applied early season, midseason, or late season on monoculture understory stands of Japanese stiltgrass in forests was examined in an experiment conducted at a site in North Carolina and a site in Virginia from 2002 to 2004. The herbicides, averaged across application timings, controlled Japanese stiltgrass at the end of the growing season 83 to 89% and seedhead production 79 to 94% compared with nontreated plants. Seedling emergence was reduced in the spring of 2004 by 89, 70, and 78% by fenoxaprop-P, imazapic, and sethoxydim, respectively, applied in 2003. In another experiment at the North Carolina site in 2002 and 2003, fenoxaprop-P or sethoxydim applied twice (4 wk apart) at half-registered rates controlled Japanese stiltgrass. This study demonstrates that land managers have multiple POST herbicide and application timing, rate, and frequency options for Japanese stiltgrass control. Nomenclature: Fenoxaprop-P; imazapic; sethoxydim; Japanese stiltgrass, Microstegium vimineum (Trin.) A. Camus #3 MCGVM. Additional index words: Invasive plant, annual jewgrass, bamboograss, flexible sesagrass, Japanese grass, Marys grass, Nepalese browntop. Abbreviations: 1X, maximum use rate.

Preemergence and Postemergence Control of Japanese Stiltgrass (Microstegium vimineum)1

Preemergence (PRE) and postemergence (POST) herbicides registered for large crabgrass control were evaluated for control of Japanese stiltgrass, an invasive, nonnative C4 annual grass. Benefin plus oryzalin, dithiopyr, isoxaben plus trifluralin, oryzalin, oxadiazon, pendimethalin, prodiamine, or trifluralin applied PRE controlled Japanese stiltgrass 87% or greater 8 wk after treatment. Benefin plus trifluralin, metolachlor, or napropamide applied PRE were less effective (78, 39, and 59% control, respectively). Single POST applications of clethodim, fenoxaprop-P, fluazifop-P, or sethoxydim controlled Japanese stiltgrass 50 to 88%. These herbicides applied twice provided 82 to 99% control. Single POST applications of glufosinate controlled Japanese stiltgrass 82 to 85%, whereas two applications provided complete control. Single POST applications of glyphosate were just as effective as two applications in controlling Japanese stiltgrass. Dithiopyr, MSMA, and quinclorac applied POST were ineffective on Japanese stiltgrass. All PRE and POST herbicides tested were equally or more effective on Japanese stiltgrass than on large crabgrass, with the exception of metolachlor applied PRE and dithiopyr or quinclorac applied POST. Nomenclature: Benefin; clethodim; dithiopyr; fenoxaprop-P; fluazifop-P; glufosinate; glyphosate; isoxaben; metolachlor; MSMA; napropamide; oryzalin; oxadiazon; pendimethalin; prodiamine; quinclorac; sethoxydim; trifluralin; Japanese stiltgrass, Microstegium vimineum (Trin.) A. Camus #3 MCGVM; large crabgrass, Digitaria sanguinalis (L.) Scop. # DIGSA. Additional index words: Annual jewgrass, bamboograss, flexible sesagrass, invasive plant, Japanese grass, Marys grass, Nepalese browntop. Abbreviations: DAT, days after treatment; POST, postemergence; PRE, preemergence; WAT, weeks after treatment.

Response of Four Improved Seeded Bermudagrass Cultivars to Postemergence Herbicides during Seeded Establishment

Herbicides and herbicide prepackaged mixtures registered for use on established bermudagrass turf may cause significant injury to recently seeded bermudagrass cultivars, delaying full establishment. Research was conducted to evaluate the use of 12 herbicide treatments applied at onset of uniform stolon development (4 to 8 wk after seeding) to recently seeded ‘Princess 77,’ ‘Riviera,’ ‘Savannah,’ and ‘Yukon’ bermudagrass cultivars. In general, Yukon was more susceptible to herbicide injury than other cultivars. Atrazine at 1.1 kg ai/ha injured all cultivars 55 to 59% 14 d after initial treatment (DAIT), which lead to reduced bermudagrass cover 21 DAIT. Triclopyr + clopyralid at 0.63 + 0.21 kg ae/ha, respectively, injured Savannah and Yukon greater than other broadleaf weed herbicides (2,4-D + mecoprop + dicamba or 2,4-D + clopyralid + dicamba). Foramsulfuron did not injure or reduce bermudagrass cover of any cultivar evaluated at any rating date. The only adverse effect of trifloxysulfuron was a reduction in Riviera and Yukon ground cover at 21 DAIT. MSMA applied sequentially and quinclorac treatments did not injure or reduce ground cover of Savannah or Princess 77. MSMA applied sequentially and/or quinclorac injured and reduced ground cover of Riviera and Yukon; however, both cultivars completely recovered from MSMA or quinclorac injury by 42 DAIT. Nomenclature: clopyralid, 2,4-D, dicamba, foramsulfuron, mecoprop, MSMA, triclopyr, trifloxysulfuron, quinclorac; common bermudagrass, Cynodon dactylon (L.) Pers. #3 CYNDA, ‘Princess 77’, ‘Riviera’, ‘Savannah’, ‘Yukon.’ Additional index words: Seeded establishment, stolon development, turfgrass tolerance. Abbreviations: DAIT, days after initial treatment; NTEP, National Turfgrass Evaluation Program.

Pendimethalin Movement Through Pine Bark Compared to Field Soil

Preemergence herbicides are commonly applied to nursery containers for control of annual weeds in the production of ornamental plants. Pine bark is a popular container growing medium because it is inexpensive, drains well, is easy to transport, and supports acceptable nursery crop growth. However, little is understood about leaching of herbicides through pine bark. The downward movement of these herbicides through container media may inhibit root growth in sensitive nursery crops and also reduce herbicidal efficacy. Four experiments were conducted at two different irrigation volumes to evaluate depth of pendimethalin movement in packed columns of pine bark and field soil. After 17.5 cm of water was applied over 7 d, pendimethalin moved downward into the 6 to 9-cm depth in 100% pine bark, whereas no movement was detected below the 0 to 3-cm depth in a Tetotum loam soil, as determined by a large crabgrass bioassay. Doubling the irrigation volume to 35 cm of water applied over 14 d did not significantly increase pendimethalin movement in pine bark or field soil. However, it did decrease pendimethalin persistence in the top 0 to 3-cm depth in pine bark. The pine bark had a higher cation exchange capacity than did the field soil. However, the physical characteristics of pine bark, a large volume of void space and low bulk density, resulted in higher hydraulic conductivity rates than in field soil. These factors may be the principal reasons that pendimethalin leached to a greater extent through pine bark than the field soil. Nomenclature: Pendimethalin; large crabgrass, Digitaria sanguinalis (L.) Scop.

Common Reed (Phragmites australis) Response to Postemergence Herbicides

Abstract The invasive biotype of common reed has taken over wetlands and can spread into roadsides, turf, and ornamental sites. Additional control options are needed for managing this biotype in noncrop areas and other sites. In container trials, fosamine, glyphosate, and imazapyr all provided excellent control of common reed. Triclopyr suppressed common reed, with increasing rates improving the growth reduction. Chlorflurenol, primisulfuron, and sulfosulfuron did not suppress common reed growth. In field trials, glyphosate and imazapyr were more effective than fosamine, providing 82 and 93% control, respectively, the following April after either June or September applications. The optimum window of application for glyphosate may therefore include both summer and fall applications, wider than the commonly accepted window of only fall treatments. Fosamine provided greater suppression of common reed when applied in September (68% control) compared to June applications (43% control). Nomenclature: Chlorflurenol; fosamine; glyphosate; imazapyr; primisulfuron; sulfosulfuron; triclopyr; common reed, Phragmites australis (Cav.) Trin. ex Steud.

Broadleaf Weed Control with Sulfonylurea Herbicides in Cool-Season Turfgrass

Abstract Broadleaf weeds are common and troublesome pests in cool-season turfgrass species such as tall fescue, Kentucky bluegrass, perennial ryegrass, and creeping bentgrass. Broadleaf weeds are primarily managed in these grasses through POST applications of growth regulator herbicides in the phenoxy, benzoic acid, and pyridine chemical classes. There are disadvantages to use of these chemicals, including nontarget plant damage and limited residual control. Certain annual broadleaf weeds can be controlled through application of isoxaben or a PRE crabgrass herbicide, but these herbicides do not control emerged broadleaf weeds. There are advantages to use of sulfonylurea herbicides, including PRE and POST control of annual and perennial weeds, a different mode of action, and these herbicides have low vapor pressure, reducing the potential for offsite movement. There are disadvantages to the use of sulfonylurea herbicides, including limited spectrum of broadleaf weed species controlled and limited tolerance in cool-season turfgrass species. The primary sulfonylurea herbicides used in cool-season turfgrass are chlorsulfuron, halosulfuron, metsulfuron, and sulfosulfuron. There have been specialized uses for primisulfuron and tribenuron-methyl. Nomenclature: Chlorsulfuron; halosulfuron; metsulfuron; primisulfuron; sulfosulfuron; tribenuron-methyl; creeping bentgrass, Agrostis stolonifera L.; tall fescue, Festuca arundinacea Schreb.; perennial ryegrass, Lolium perenne L.; Kentucky bluegrass, Poa pratensis L.

Detection of Fenoxaprop-Resistant Smooth Crabgrass (Digitaria ischaemum) in Turf

Greenhouse studies verified that smooth crabgrass from a golf course tee in southern New Jersey was resistant to fenoxaprop-P, although smooth crabgrass from a nearby untreated rough was susceptible to this herbicide. Fenoxaprop-P-resistant plants were injured, however, when fenoxaprop-P was applied at levels above the maximum use rate for turf. Fenoxaprop-P applied postemergence at 0.76 kg ai/ha, four times the maximum rate, reduced shoot weight of the resistant biotype by 35%, whereas application of 1.52 kg/ha, eight times the maximum rate, reduced shoot weight by 64%. Large crabgrass and the susceptible biotype of smooth crabgrass were controlled by fenoxaprop-P applied at 0.1 kg/ha. Fenoxaprop-susceptible and -resistant biotypes of smooth crabgrass had a similar response to MSMA, dithiopyr, and quinclorac applied postemergence. The fenoxaprop-P–resistant smooth crabgrass biotype was controlled by the cyclohexanedione herbicides sethoxydim and clethodim, but the aryloxyphenoxypropionate herbicides fluazifop and quizalofop reduced shoot weight by only 15 to 66% depending on herbicide and rate. Nomenclature: Clethodim; dithiopyr; fenoxaprop-P; fluazifop-P; MSMA; quinclorac; quizalofop; sethoxydim; large crabgrass, Digitaria sanguinalis (L.) Scop. #3 DIGSA; smooth crabgrass, Digitaria ischaemum Schreb. Ex Muhl # DIGSU. Additional index words: Herbicide resistance, postemergence grass herbicides, turfgrass. Abbreviations: ACCase, acetyl-coenzyme A carboxylase; APP, aryloxyphenoxypropionate; CHD, cyclohexanedione; smooth crabgrass (R), fenoxaprop-P–resistant smooth crabgrass; smooth crabgrass (S), fenoxaprop-P–susceptible smooth crabgrass; WAT, weeks after treatment.

The status of weed science at universities and experiment stations in the northeastern United States

Weed science is an important component of pest management. Weeds cause approximately 12% loss in United States crop production, reduce crop quality, poison livestock, and adversely affect human health, recreation, and transportation. Herbicides comprise approximately 65% of pesticide expenditures, whereas insecticides and fungicides each comprise less than 20%. The total effect of weeds, including crop losses and costs of control, in the United States was estimated in 1994 to be

Controlling Bamboo (Phyllostachys Spp.) with Herbicides

20 billion annually. A survey was prepared and mailed to weed scientists at universities and experiment stations in the northeastern United States to determine the number of faculty positions and course offerings devoted to weed science. There are approximately five times as many entomologists and more than three times as many plant pathologists as weed scientists at universities in the northeast. There are more than six times as many graduate students currently in entomology and more than four times as many in plant pathology compared with weed science. Few undergraduate courses in weed science are taught, and most universities have no graduate classes in weed science. There are almost seven times as many undergraduate entomology courses and more than twice as many plant pathology courses as weed science classes in this region. There are more than 17 times as many graduate entomology courses and more than 15 times as many plant pathology courses compared with weed science graduate classes. There are no departments devoted solely to weed science in the northeast, whereas entomology and plant pathology departments are both common. Most universities have little to no faculty assigned to aquatic, forestry, noncrop weed control, weed ecology, or laboratory trials, and numbers assigned to agronomic and horticultural crop weed management are limited. Additional university resources are needed if weed science research, teaching, and extension efforts are to meet the priority needs in weed management. Additional index words: Entomology, faculty positions, graduate classes, graduate students, plant pathology, undergraduate classes. Abbreviation: FTE, full-time equivalents.