mel turner mturner at
Sat Apr 1 15:44:52 EST 1995

In article <3lfl14$r7d at> agpcrv at writes:
>mturner at (mel turner) writes:
>> agpcrv at writes:
>>>I am making this enquiry for a friend who is farming in a dry region of 
>>>South Africa. His dam is overgrown with Azolla to the extent that the
>>>entire water surface has been covered. Does anyone have any experience 
>>>with eradicating this water fern?
>>>Any help would be much appreciated
>>If it is really Azolla and not Salvinia (better known as a serious  aquatic 
>>pest), the farmer may actually benefit from allowing it to grow, periodically 
>>skimming off the excess and using it as "green manure"--- Azolla has a 
>>symbiotic relationship with nitrogen-fixing cyanobacteria (Anabaena azollae) 
>>and thus can be used to enrich soil.

>Thanks very much for your reply. I saw the plants about 2 years ago and was
>informed by the farmer that they were Azolla. He may have been misinformed,
>and since I cannot distinguish between the 2 genera myself, if you know of a
>simple way to tell them apart, we would be interested to check them out.
>If they are Azolla I am sure he would want to utilise them for compost. However,
>if they are Salvinia, is there an effective, less labour-intensive method than
>dragging, to get rid of them. He has a concern that the plants will suffocate
>his fish as well as silt up the dam.

Azolla species all have tiny, moss-like, branching leafy shoots with minute 
leaves.   Salvinia has much larger (ca. thumb-nail size) leaves (rounded-oval 
in shape but generally  folded sharply along midrib, the upper/inner surface 
with remarkable water-repellent "eggbeater-shaped" hairs that  trap air for 
floatation.    Only  Azolla has true roots, (Salvinia instead has finely 
dissected submerged leaves).  I think there is a lot of literature out there 
on controlling Salvinia, but skimming and composting still seems like a good 
idea regardless of species.   

     As someone else posted,  Salvinia would be using the excess (farm 
runoff?) nutrients from the pond water, whereas Azolla would in addition be 
able to fix atmospheric nitrogen.   Someone with say, a rowboat, a long &  
fairly fine-mesh net, and assitants on shore should be able to skim large 
areas of pond surface fairly quickly, and the effect would be to remove large 
amounts of excess nutrients from the water that could then be returned to the 

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