What causes milfoil to die off in summer?

[casts_by_fly]

Hi All,

 

Last year the lakes around here had significant milfoil, to the point that I had to buy a light punching setup in prep for this year.  As spring rolled out the milfoil was growing up in all of the expected areas.  Over the past week though (and maybe longer- i have a 3-week gap in getting out before then), 3 of the lakes in the area all have dying or dead milfoil.  Entire weed beds and large coves that were nearly full are empty.  Where the weeds remain in place, they are brown and dead.  The fish want no part of the dead weeds.  Water temps are similar to last year (80-84 right now).  One of the lakes is about 3' low, but in what is now 5' of water and used to be 8' the weeds are dead (and 2 months ago they were pretty thick).  I know that 2 of the 10 or so local lakes were sprayed back in June, but they are the same watershed/stream.  The others are independent (one is township owned, two are state park, etc).  So what could cause grass generally, and native milfoil specifically, to die off this time of year?

 

I know I've got my work cut out for me in some places if there is no grass.

 

thanks,

rick

 

[fishballer06]

Lack of oxygen, too much sunlight reaching the bottom of the lake, spraying, can all kill of aquatic vegetation. 

[softwateronly]

I've seen summer boat traffic kill water clarity which in turn will start a die back, but not as drastic as what you're describing.  I'd be leaning toward man made issues too.

 

scott

[casts_by_fly]

For more details which I should have put originally, the lakes are a mixture of manmade and natural.  None have significant water traffic- they are all a mix of 9.9 and electric only lakes.  So a couple of them get fished fairly hard but some do not.  Water clarity varies by lake.  The one that's down 3' right now normally has 2' visibility.  The one we fished tuesday is normally 6' visibility or so.  Tuesday's lake I could see the township and lake house residents banding together for a spray, but there were no signs (which I think are required by law).  I also fished it 5 weeks ago and there was plenty of grass.  The lake that's 3' low is a state park lake and is experiencing an algal bloom starting up so I thought that might be a cause, but its the only one of these lakes with that problem.

 

I'm starting to think that the reason might not be the same for all of the lakes but I don't know.  Too many lakes and too few commonalities among them.  I might need to go for a drive and look at a couple other lakes around to see what's happening.

[T-Billy]

Last year the lake closest to me had the most weed growth I've seen in it since the 80's. This year it has far less. Sometimes the milfoil hangs in there late into summer, some years not so much. Don't know the reasons, amount of flooding, sunlight, water clarity, disolved O2, all the above? But growth varies wildly year to year in some lakes.

[Tennessee Boy]

I would bet it was sprayed.

[Choporoz]

3 minutes ago, Tennessee Boy said:

I would bet it was sprayed.

They sprayed my lake two months ago and I had no idea until the weeds died after about a foot of growth.  They're coming back nicely now.

  This is my first year on the lake.  Late last summer, the grass was awesome.  Rarely emergent, well defined lines...consistent depths for outside edges....  I was pretty worried when they suddenly died back, but I'm ok now...lol.  Could well be that they spray every year, and I just had no idea.  

 

[casts_by_fly]

last night I went to a lake a fished over a month ago and surprise- the milfoil was bright green and looked freshly grown.  The eelgrass was the same.  I'm thinking maybe last year I started fishing a couple of these lakes in July so I didn't see the early growth and subsequent die back.  I need to see some more lakes right about now and see what we're looking at.  And, maybe go fish the big lake that I was fishing a lot in June/July last year to see if it had a dieback also this year.