Vol. 15—1961 - NorthEastern Weed Science Society

559.
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treated at the 5.0 p~a. rate and control was judged to be 100%. The demarcation
between the treated and untreated portions of the ponds was distinct,
indicating that the inflow to the ponds had prevented diffusion of the herbicide
above the boundaries of the plots.
Decomposition of f. crispus progressed very slowly in the plots treated
at 1.0 ppnl•. By the end of one month some slight regrowth was noted. The
maximumcontrol achieved in these plots was 65%. There was no significant
difference observed in the effectiveness of the two forms of the herbicide-­
granular and liquid.
All four ponds in these tests overflowed into a commonreceiving pond of
1/8 acre surface area. This receiving pond in turn supplied the inflow to a
series of four 1/10 acre ponds identical to Ponds #2, 3, 4, and 5. When the
Endot~ applications were made on June 16 to the numbered test ponds, the receiving
ponds below were similarly infested with weed growth. About a month
later it was noted that the 1/8 acre receiving pond and also the series of 1/10
acre ponds below had become relatively free of weed growth. Although control
was confined only to f. crispus it was not necessary for the hatchery personnel
to manns.Hy remove vegetation from these ponds for the duration of the summer.
In tests initiated on July 21, 1960, two 1/10 acre ponds received total
treatments of Endothal at the rate of 3.0 ppm. Pond #6 was treated with the
granular preparation and Pond #7 with the liquid. With the exception of small
areas at the intake ends of these ponds, 100%control of ~. crispus was realized
in three weeks.
By the end of September all treated ponds that received a constant, although
small, inflow of water contained regrowth of~. crispus ranging from 5% for those
treated at 5.0 ppm. to an average of 40%for those treated at 1.0 ppm. It was
calculated that a complete change of water occurred in these ponds in approximately
six days.
The very effective control of f. crispus realized in the aforementioned
untreated receiving ponds suggested that Endothal might be effective in controlling
this plant in trout rearing raceways carrying a substantial flow of
water. A raceway approxirrLately one-half mile long located at the Benner Spring
Fish Resea~ch Station was made available for such a test. This race~ay averaged
14 ft. in ~idth. The depth graded from 1.5 ft. at the intake end to 3.0 ft. at
the outlet. The flow was reduced to a measured volume of 3J2 gpm. A section
380 ft. long at the head of the raceway was treated with Endothal granular at
5.0 ppm. At the end of one week close examination of the plants showed that
damage to f- crispus ~as confined to the extreme terminal portion of the stems.
This damage was observed from about the midpoint of the treated section to several
hundred feet belo~ the treated area. On September 16, about one month
after the date of treatment, the raceway was free of ~. crispus for a distance
of 1300 ft. or roughly one-quarter mile. Partial control extended down an additional
600 ft. Also, only partial control ~as obtained in a 100 ft. section
immediately below the intake. Algae and commonwater weed, also abundant in the
raceway, ~ere apparently not affected by the herbicide.
Although all ponds and raceways used in the Endothal tests contained fish
life, no fish kill or indication of distress was observed at any of the application
rates tested.