Vol. 51—1997 - NorthEastern Weed Science Society

102
ULFENTRAZONEAND HALOSULFURON:HERBICIDALEFFICACY
AND SAFETYTO WOODYORNAMENTALS
Todd L. Mervosh and John F. Ahrens'
ABSTRACT
Ou studies of the herbicidessulfentrazoneand halosulfuronwere expandedin 1996to
includead itionalexperimentson woody ornamentalspecies.
In e secondyear of an experimentat Windsor,CT, sulfentrazone(0.125 to 0.5 lb/A) and
halosulfur n (0.031 to 0.125Ib/A) were sprayedon June 6, 1996over the top of activelygrowing
Japanese w (Taxus cuspidatay;globe arborvitae(Thuja occidental is), Eastern hemlock(Tsuga
canadensi ), creepingjuniper (Juniperus horizontalis), and rhododendron(Rhododendron
catawbiene 'Roseum Elegans'). The onlyinjuryobservedin plots treated with sulfentrazonewas
rate-depen ent damageto young hemlockneedles,whichrecoveredfullylater in the season.
Halosulfur n caused severechlorosisand stuntingof new growth of yew and rhododendron,and
to a lesser xtent injuredarborvitae. At 16 weeks after treatment, yews were stunted20 to 50%
and arbo itae 10to 30% relativeto untreated plants, but rhododendroninjuryhad diminished.
Hi her rates of sulfentrazone(0.375 to 1.5lblA) and halosulfuronat the aboverates were
appliedin pril over the top of dormant uprightJapaneseyew (Taxus cuspidata var. capitata)
and globe orvitae. Sulfentrazonecausedno visibleinjuryto either species,but both yew and
arborvitaewere injured(chlorosisand stunting)by halosulfuron. In other experiments,
sulfentraz ne (0.375 to 1.5lb/A) appliedin April over the top of dormantJapaneseyew, Eastern
hemlock, reepingjuniper, and activelygrowingforsythia(Forsythia x intermedia 'Lynwood' )
caused se ere injuryto forsythiaand lesser damageto hemlock. In an experimentin Vermont,
dormant ser fir (Abiesjraseri) tolerated a May applicationofsulfentrazone (0.25 to 1.0Ib/A)
and a July pplication6 weeks after bud break, but the sametreatmentsapplied3 weeks after bud
break in J ne caused substantialinjuryto fraser fir. In a containerexperiment,sulfentrazone
(0.375Ibl ) appliedin late October severelyburned foliageof newlypotted dwarfmugo pine
(Pinus mu '0 'Mughus') and dwarf Albertaspruce (Picea glauca 'Conica' ).
B h sulfentrazone(0.125 to 0.5 lblA) and halosulfuron(0.031 to 0,125lblA) provided
excellent sidualcontrol of annualsedge (Cyperus sp.). In various experiments,sulfentrazone
provided cellentpreemergenceor earlypostemergencecontrol of carpetweed(Mollugo
verticilla ), purslane (Portulaca oleracea), commonlambsquarters(Chenopodmmalbum),
common oundsel (Senecio vulgaris), and northern willowherb(Epilobium glandulosum),
moderate uppressionof annualbluegrass(Poa annua), horseweed(Conyza canadensis), and
yelloww dsorrel (Oxalis stricta), and littleto no control oflarge crabgrass(Digitaria
sanguinal's), prostrate spurge (Euphorbia supina), narrowleafhawksbeard(Crepis tectorum),
common hickweed(Stellaria media), and pearlwort (Sagina procumbens). Halosulfuron
suppresse or controlledspurge, horseweed,woodsorrel, and chickweed,but had littleto no
activity0 annualbluegrass,crabgrass,carpetweed,purslane,lambsquarters,and hawksbeard.
1 Assist AgriculturalScientistand EmeritusWeed Scientist,The ConnecticutAgricultural
Experim t Station, ValleyLaboratory,Windsor,CT 06095.