Vol. 15—1961 - NorthEastern Weed Science Society

Control
of the Pondweed. Potamogeton crlSpus,
in both Flowing' and Static Situations with Endothal l
J. Curtis Simes, Regional Fishery Manager
Pennsylvenia Fish Commission
An extremely heavy infestation of aquatic vegetation in the earth-bottomed
ponds and raceways at the Pennsylvania Fish Commissions' Pleasant Gap Fish
Hatchery has for many years made it necessary for hatchery workers to conduct
periodic manual weed control operations. Normally b,y early June the small bass
rearing ponds are completely filled with growths of c~ly-Ieaved pondweed, ~­
mogeton crispus; commonwater weed, Anacharis canadensis; duckweed, ~ ~;
and several species of filamentous algae. The water supply for the hatchery
comes from a large limestone spring. Total hardness of this water·averages
about 100 ppm.
In recent years quite a number of promising new herbicides have been tested
/
/ in these hatchery ponds in an attempt to find a more efficient and less costly
weed control procedure. During 1960, the herbicide Endothal was tested at application
rates of 1.0, 3.0, and 5.0 ppm. in both partial and complete treatments
in small ponds ranging from 1/20 to 1/10 acre in surface area. Both the liquid
and granular forms of the herbicide were used for comparative purposes •
. .
.Pond #1, a narrow raceway-type
pond with no inflow or outflow and a surface
area of 1/20 acre, received a partial treatment with Endothal liquid on June 16,
1960. The te.st plot, comprising 20% of the total pond volume and located at the
midpoint of the pond, was treated at an application rate of 3.0 ppm. Water temper~ture
within this pond averaged 65 0 F. One week later f. crispus, the dominant
plant species in this and most of the other ponds, had begun to decompose
and sink below the surface within the test plot and to the one end of the pond
in the direction of the prevailing wind. By the end of one month complete control
of f. crispus was evident in all portions of Pond #1. Periodic checks,
continued to the end of September, revealed that no significant control was
obtained on water weed, duckweed, or filamentous algae. Regrowth of curly-leaved
pondweed was first noted in early August but by the end of September it had not
reached the 5% level. Based on total pond volume the application rate required
to effect complete control of f. crispus, under the conditions prevailing here,
would appear to be less than 0.6 ppm.
Ponds #2, 3, 4 & 5 are identical and are arranged side by side in a series.
Each one has a surface area of 1/10 acre and during the testing period each one
received an inflow of water which averaged 10 gpm. The lower one-third of each
pond ~as treated with either Endothal liquid or granular at rates of 1.0 or 5.0
p~n. ~~l applications were made on June 16, 1960, at which time the water temps:'at:cL'e
in these ponds ranged between 55 0F. and 60oF. At the end of one week
p. S£~~~ had begun to decompose and recede from the surface in the plots treated
at. the 5..0 ppm. rate. In the plots treated at 1.0 ppm., f. crispu~ was slightly
crowned but relatively little decomposition had occurred. Two weeks after the
applications were made, f. crispus had completely disintegrated within the plotu
lEndothal, the disodium salt of J,6-endoxohexahydrophthalic acid, WAS provided
for this study by the Pennsalt Chemicals Corporation.