Vol. 15—1961 - NorthEastern Weed Science Society

541.
By the end of three weeks, the surfaoe of the plots was
partly oleared by the natural deoomposition and sinking of the
vegetation. This olearing prooess oould easily be hastened by
raking and removing the dead plants. The borders of the plots
were preoisely outlined by the flat green pads of the untreated
surrounding area. Even the oorners were aoourately defined.
This would imply that little diffusion of the 2, 4-D had ooourred.
All plots showed the destruotion of Nym~ea and Brasenia. The
two plots reoeiving the largest doses, 20-75 and D=2o-100,
exhibited extreme oonditions. The deoomposition ooourred more
rapidly and more intensely.
As for the submerged plants, it was as always, very diffioult
to make a deoision. In the dredges, many living weeds
(Ohara, Utrioularia and several Potamogetons) were still present.
In faot, the Utrioularia possessed oonspiouous bright green growing
tips. The oarpet of dense vegetation on the bottom was
definitely still present and growing.
The next sampling date was September 15, eleven weeks after
the applioation of the pellets. During late July and August,
the surfaoe of all plots had beoome olear of lily pads and remained
so for the season. The borders and oorners of several
plots were still very preoisely outlined and obvious to even a
oasual observer. In plots where low ooncentration of 2, 4-D had
been used, (0.9 ppm and 1.3 ppm) a aery few new leaves of
NlIDphaea were sprouting in soattere patohes. However, in all the
other plots no regeneration was notioed. In brief, all conoentrations
used were effeotive in olearing the surfaoe of Nymphaea
and Brasenia for the season. .
As for the submerged plants, it oan be said that the dense
carpet of Utricularia and Ohara was diminished and restrained,
but not eradioated. A oomparison with untreated surrounding
areas did show a reduotion in the mass of vegetationwhioh is
held far below the surfaoe of the water, instead of oooupying
every inoh from bottom to surfaoe. The moss Drepanooladus appeared
to be entirely resistant to 2, 4-D granules and showed
no retardation in growth or reduotion in abundance.
It is suggested that the low oonoentrations used were sUffioiently
strong to olear the surfaoe of floating weeds, and
that possibly even lower ooncentrations might well be effeotive
for these speoies.
Since the summer of 1960 was a relatively cool and sunny
period, no extremes of temperature were reoorded either- for the
air or the water. From June 8-September 20 the variation in· the
pond followed the expeoted seasonal trend. Throughout the
month of June the temperature of the water remained constantly
at 7l oF. By July 1, it rose to 74 oF, and increased to 78 0F by
July 20. By September 15, it had dropped to a seasonal 68 0F.