Pond Boss Forums AQUATIC VEGETATION Identifying plants Friends pond weed problem.

A Friend purchased a new place with about a half acre pond on it and the attached weeds are growing pretty heavy in it. He came to me for advice to which I said I have know idea but I know a place where they know everything. That being said he has put 5 grass carp in in the spring and said they don't seem to be making a difference and was wondering if there was a good chemical treatment. As always Thanks in advance for any and all help.

I think you have water primrose.
http://www.fosc.org/WaterPrimrose.htm

The grass carp if effective will need to grow or be larger to consume the more fibrous water primrose. In the meantime you may be able to chemically control it with some spot sprayings of
Chemical Control Options
The active ingredients that have been successful in treating water primrose include 2,4-D (E), diquat (E), triclopyr (E), glyphosate (E), imazamox (E), and imazapyr (E). E = excellent, G = good

This site says http://aquaplant.tamu.edu/management-options/water-primrose/
Biological Control Options
There is no known biological control for water primrose, although goats are known to forage on many types of emergent vegetation.