Vol. 16—1962 - NorthEastern Weed Science Society

5. llslapon and other chlorine,ted organic !lciQs,iS:well as MIl, reduoed wot
growth of ~8Ckgress drastically, but did not IlI8terially reduce bid
dormancy is otten cited as the mechanism involved. A IIIOreexact evaluation
"-" ot the response atter treatment with the chlorinated aliphatic acids is that
bud activity is in fact maintain"', but thet the shoot growth is sharply
reduced.
The dsstruction of shoot growth after trea_not, with dalapon interrl1pts
photosynthetic activity and some reduction in carbohydrate occurs, but at a
rate MUChslower than in the case of plants treated:'wit,h atruine or amitrol
because the respiratory activity!s lower. The residue of dalapon in the
soil and in" the tissue is dissipated rather quickly and after a period of
several, months partial regrowth .-y occur. This regrowth develops from
buds that have remained inactivewb1le the dalaponwes present. Shoots that
do devebp are apt to grow vigorously because of the relatively high carbohydrate
reserve that has been lIl8inte1ned in the rhizome.
The bud response followi~t~tment withMli is somewhat siJnilar to that
observed with dalapon. Zick (16)' snd i1eyer (9) both found that bud activity
was not altered lnaterially, but that the shoot growth was greatly reduced.
Maximumresponses occur only under conditions that fmr absorption ofb
chemical. Applications of MHdo not destroy t,h.' folia,ge so carbohydrates
continue t~ accumulate. The maintenance of,th~ shoote also serves to maintain
a considerable degree of apical dominance. Eventually inactive buds on the
rhizome are releued and when t!lis occurs, teg;rowtb, is abundant and vigorous.
21
1. Quackgrass is a widely distributed and persistent weed in the northern
states and ilj. Canada. The plant spreads zoap:l.dlNb1 both seeds and ridzomefragments.
' The rhizomes are abundant in t,he surface soil and "
normally maintain a total available carbohydrate content of 40% or I1lOre
during the year. This, along with an abut1-dant'lUpply ot inactive bU~ ,
on the rhizomes, assures vigorous and persi,stent,regrowth after de!o]J;ation.
2. Qusckgrass plants treated wi.th,atrazine show marked reductions in the
'total available carbohydrates in ,the rhizomes. The speed of carbo~te
reduction 'is accelerated by maintBining shoot growth on treated plants
and by adding nitrogen when a def~ciency ot ~e element occurs.! major
r.esponse ot quackgrass to ,am1trol also in-volvesthe depletion of carbohydrate
in the rhizomes. Amitrol may not persist in the active form
in the tissue long enough to deplete the resel"VQ to the lethal point.
3. The activity of vegetative buds en quackgras's rhizomes is reduced or
limited by (1) temperatures above 25 C,(2) w1dec.rbon-nitrogen ratios
in the rhizome tissue dUring late spring, and enapical dominance of
shoots or terminal buds.
4. '!'he growth substances inql.l8ckgrass mq be .~ lliaterid other than IAA
for this cotnpoimdhad no detectable effect on the activity of vegetative
buds. TIBiI.IOOdJ.1'i.edpolar transport of bud irJhj:biting tectors while
NAAand various herbicides inhibi t~ or, el1ilQ.nated bud ecti vi ty.