Vol. 16—1962 - NorthEastern Weed Science Society

The vigorous regrowth of quackgrass is related to the large number of dormant
buds that are present on the r!;lizomes in an in;f'ested area. Weight of dry
quackgrass rhizomes averages about 0.4 gm per foot.' If an area contains $000 Ib
of the dry rhizomes per acre, this is equal to about 130 feet of rhizome per sq
ft. The nodes on rhieomes average no more than 1 inch apart. Therefore, it is
safe to assume that in excess of 1500 buds exist on the rhizomes in each sq !t
of infested soil. Quackgrass standl1 seldom exceed '::tSOshoots per sq ft. From
this it is apparent that 90 percent or more of the bilds on the rhizomes retn8in
inactive until circumstances are favorable for their development. This reservoir
of dormant bUds is a major hazard, for wheneyer. a stan~ of shoots is destroyed,
some of the dormant buds Will be activated' and will very soon res13ta -
blish the plant. . .
The rhizomes Of qua.ckgrass contain a number of carbohydra.tes of which trit1c1n
is probably present in greatest concentration. Total available carbj'hydrates,
vary from about 30 to $0%of the dry rhizom~tweight according to Pinckney
(12), Schirman and Buchholtz (1.4) and LeBaron and F~rtig (7). If one aSflWnesan
average concentration of availa9le carbohydrates of ,40~ and a total dry ma~ter
content of $000 lb/A, it appears that a reserve of 2000 lb/A of readily av~lable
carbohydrates is stored in the rhizomes. Such,li!large reserve, along with
the abundant supply of inactive bu4s, is ample reason why the growth of quackgr8J.ss
is vigorous and w!:lythe regrowth occurs with such persistence. .
The trends in total carbohydrate reserves during the year in quackgrass do
not show the fluctuations that are found in many hel;'baceous plants. The work
of Pinckney (12) and Schirman and Buchholtz (14) show;s that only minor var;Lations
in reserve level occur during the year. LeBaron and, FeX'tig (7) found a substantial
reduction in fructose content of the rhizomes djl.;r'ingthe winter, but their
data are not fully comparable to the others cited, for it is based only on ,the
content of fructose found in th~. tissue. Since there appeare to be no marked
depression in total carbohydrate level during the seaeon, there is no most favorable
time at which control measures directed at reducing the carbohydrate
content may be initiated.
Stoa, et aL, (15) was one of the first to comment,that the carbohydrate
reserves of quackgrasa could be reduced by continual and consistent defoliat10n.
Dexter (2) showed that organic reserves were reduced more readily after fertilization
with nitrogen~ Defoliation by some tillage 9peration is no doubt effective,
but it is inconvenient and requires the majqr portion of a season to
produce the desired results. Alternative methods involving use of herbicides
now'appe'ar l!I)re promising.
Buchholtz (1), M~ggitt (8) and Fertig (3) have all reported on the superior
control of quackgrass obtained withatrazine and other triazine herbicides.According
to Schirman and Buchholtz (14) and LeBaron and Fertig (7) control results
from the drastic reduction in carbohydrate reserves in the rhizomes following the
treatment. !tappears that respiratory activity is maintained at a high l,-r'lll
after trea'\;ment even t.hough photosynthesis is interrupted. The result is ~_.faster
rate of depletion than can be accomplished by consistent defoliation or,m .
other known method. D~pletion appears to proceed more rapidly when the t~,
growth of the quackgrass is allow-edto remain intact for a month or more following
treatment than.when it is removed. This is reasorulble for the presence:of
the top growth increases the total respiratory activ,Lty of the plant. j, '
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