Vol. 54—2000 - NorthEastern Weed Science Society

HERBICIDE EVALVA nONS IN CHRISlMAS TREE PLANTINGS OF FIR (ABIES spp.)
J. F. Ahrens and T. L. Mervosh'
ABSTRACT
The needforherbicidealternativesforChristmastrees led us to evaluateseveral
herbicides during 1998 and 1999, with emphasis on fir tolerance before and during active growth
in the spring. Accordingly,repeatedexperimentswereconductedat The Connecticut
AgriculturalExperimentStationin Windsor,CT andwith cooperatinggrowersin Somers,CT
andWoodbury,VT. Soil typeswere sandyloamsor silt loarns. Herbicidesprayswere applied
with a Co,-pressurized backpack sprayer in 20 gallA over the top of or on the lower two-thirds
of thetrees. Herbicidesevaluatedin one ormoreexperimentsincludedatrazine90DF plus
simazine 90DF, hexazinone 75DF, thiazopyr 2L, azafeniden 80DF and the sulfonylurea
herbicides thifensulfuron-methyI25DF, chlorimuron-ethyI25DG, sulfometuron-methyl 7500,
prosulfuron 57WDG, and MaN 37503 75WDG. Rates are listed in oz a.i.lA or Ib a.i.lA.
Hexazinone at 0.5, 1.0, or I.51b1A and sulfometuron-methyl at 0.375 and 0.75 ovA
applied 2 weeks before planting fraserfir (Ables fraserty caused no injury. However, hexazinone
at 1.0 and 1.5 lblA applied to establisbed fraser fir before bud break caused slight to muderate
necrosis. Sulfometuron-methyl at 0.1875 to 0.375 ovA did not injure dormant fraser fir and
caused only slight, tolerable chlorosis on fraser fir during active growth. Thifensulfuron-methyl
at 0.25 or 0.5 ovA plus 0.25% X-77, and chlorimuron-ethyl at 0.125 or 0.25 ovA plus 0.25% X­
77 causedno injuryto dormantfraserfirandslight,tolerable chlorosisin Juneon actively
growing fraser fir. Prosulfuron at 0.1425 or 0.285 ovA plus 0.25% X-77 applied during active
growthof fraserfirinearlyandmidJunein VT causedmoderateto severe chlorosison sprayed
foliage. However, sprays of prosulfuron in CT at 0.285 or 0.57 ovA without surfactant resulted
in only slight chlorosis on fraser fir before or after bud break.
MON 37503 at 0.5 or 1.0 ovA applied before bud break did not injure newly planted
Canaan fir (Ables halsamea VaT. phoneTolepsis) in CT nor established fraserfir in VT.
Thiazopyr at 0.5, 1.0, or 2.0 IblA before bud break did not affect established Canaan fir in VT
but injured newly planted Canaan fir in CT. Thiazopyr applied just before or at bud break at 0.5
or 1.0 IblA did not injure balsam fir (Abies balsamea) or fraser fir in CT following two
applications in two years. Azafeniden applied at O.5lblA during active growth caused more
injury to fraserfir than did 1.5lblA applied before bud break. During active growth, injury to
fraserfir from azafeniden at O.5Ib1A was similar to injury from atrazine (21b1A) plus simazine
(2Ib/A). Neither treatment injured fraser fir before bud break. New growth of balsam fir also
was sensitive to azafeniden, whereas newly planted or established Canaan fir tolerated up to 1.5
lb/A before bud break. At 0.5 lblA, azafeniden gave excellent preemergence and postemergence
controlof large crabgrass(Digitaria sanguinalis). Herbicideswith postemergenceactivity
clearlywere saferto coniferswhenappliedto dormantfoliage thanwhenappliedto new needle
growth.
rweed ScientistEmeritusandAssistantScientist,TheConnecticutAgriculturalExperiment
Station, Valley Laboratory, Windsor, CT 06095.
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