This summer I lined my pond edges with limestone. Before I put the limestone down, I covered the ground with a heavy landscape cloth in the hopes of controlling any grass or weeds from growing up through the limestone. It didn't work. I now have a lot of grass / weeds coming up in the limestone. It's nearly impossible to cut with the weedeater. What can I spray on the limestone that will kill the grass / weeds without killing my fish??

Any of the herbicides made up of glyposate that are used for emergent plants will do the trick. Even Roundup found locally will not hurt your fish although it is not specifically for aquatic application and allegedly is bad for frogs. I have not found that to be the case on my ponds. The Great Blue Herons are more of a threat than the Round up to the frogs for me.

Aquastar is an approved 53.8% glyphosate for use around aquatic enviroments, it is non-selective and used to be sold under the brand name Rodeo. It works great on cattails too.

http://www.cygnetenterprises.com/product/aquastar.htm

Thanks everyone, I appreciate the info. Sounds like roundup will be the easier chemical to get.