Rotting frogbit - causes/cure?

[chris.m]

Hi all,

I've got a problem with the frogbit in my tank. To be more precise the plant is salvinia natans (at least I think that's what it is).

I've had it in the tank since starting it up six months ago and it was fine and going strong for the first two or three months. After that growth got weaker, with leafs staying much smaller than before, albeit with new leafs still constantly developing. Also, relatively older leafs invariably develop blackish and/or brown spots, form holes and eventually die off - see photo below.

Tank is under T5 lighting with an 8h photoperiod and heavily planted with crypts, mosses and other plants. Used ADA green brighty Step 1 during the first three months and then switched to Step 2 - 3ml per day. All other plants appear healthy and without any deficiencies.

Any ideas what could cause this and how to fix it?

Chris

 

[Kristoph91]

That happened to mine on a small shrimp tank.

I removed the cover glass on the tank and the plant never rotted again, but stopped growing as fast!

Don't know if it was humidity that caused it or what.

 

[chris.m]

Hmmm, that's interesting and sounds like a plausible explanation for your set-up. However, I've never been using a cover on my tank.

So I'm wondering if it could be related to some other cause. A lack of nutrients in the water column, although my other plants seem fine. Or some sort of small bug or disease that's eating it.

I've even been thinking if it could not be some sort of sunburn or drying out effect. I've got a tank-mounted light with two T5 tubes. Distance between the light and the water surface is only about 10 cm, and it's only the oldest leafs that die, even before fully maturing.

Chris

 

[Ady34]

Hi Chris,
i dont know for sure what is wrong with your silvania, but a while ago i had an issue with aphids which apparently can cause a mold on the leaves which deteriorates the plant. I dont know if you have any aphids on your plants, it doesnt look like it, but heres a link to that thread, Darrels (dw1305) post has the information honeydew and its effects http://ukaps.org/forum/viewtopic.php?f=21&t=21554. My plants also were reproducing, but the older leaves tended to be the ones effected, probably through contact with the aphid eggs. It looked a very similar effect.
Also more recently i suffered a slowing in growth rates and decline in silvania plant health, which has now improved with correct dosing of ferts. Floaters tend to be good indicators of low nutrition as they have good access to c02 so unlike underwater plants which tend to fail through c02 issues, floaters tend to fail through poor fertilisation.
You do state however that the rest of your plants are doing well, so ferts seem less likely to be the issue, especially given that the plants are reproducing. If you arnt suffering from any aphids then i dont know what could be the cause.
Hope this helps a little in eliminating causes if nothing else
Cheerio,
Ady.

 

[spyder]

Floaters tend to be good indicators of low nutrition as they have good access to c02 so unlike underwater plants which tend to fail through c02 issues, floaters tend to fail through poor fertilisation.
You do state however that the rest of your plants are doing well, so ferts seem less likely to be the issue, especially given that the plants are reproducing.
Cheerio,
Ady.

This would be my line of logic thought too. I have no clue to the contents of various ADA ferts so can't comment there. Logically, even if other plants are fine, with the access to unlimited Co2, the floaters fert uptake could possibly exceed what is being provided. Over the 6 months of the tanks life, plant mass has most likely increased somewhat so nutrient demands therefore must have increased.

Switching ferts could be related as most floaters are usually regarded as "nitrate sponges" and used to help mop up nitrates. I'd check nitrate contents of the ferts you are, and was using.

I'm having the same issue in my low light shrimp tank that rarely gets any ferts.

 

[Gill]

have had the same issue with my frogbit and salvinia. Found that it was aphids that had got into the tank, and infestation of springtails. removed the affected plants and kept using a baster to wash them into the tank for the fish to eat.

 

[chris.m]

Hi,

thanks a lot to all of you for your excellent and very useful feedback.

I've checked on aphids, but could not find any of the traces you describe. So I'll follow up the nutrients trail and see if a change in dose and/or fertilizer helps (although I'd be reluctant to add nitrates as I do have relatively high levels to start with from my tap water).

For the moment I have removed all but the most healthy looking parts of my salvinia and we'll see how things are after my three week holiday which starts tomorrow (with our trusted cleaning lady looking after the tanks every other day or so; even so still nervous to leave).

Cheers

 

[mark4785]

I have kept similar plants (Amazon frogbit) and frequently got periods of this brownish slimy growth. I simply spent 10-20 minutes removing the brown parts and ensured unaffected frogbit did not make contact with any remaining brown segments as it appears to contaminate other plants. As for the cause, I think too much water movement is the culprit.

I know i'm generalising from frogbit to your species of floating plant, but i'm not sure what else results in similar issues.

 

[dw1305]

Hi all,
Yes, it is Salvinia, which is pretty trouble-free, although having said that I've had both aphids and condensation marks on mine, as "Ady34" suggests.

Because of the look of the leaves, I think it is a low nutrient effect, and probably nitrogen (N) or potassium (K). If you look the leaves are light green, and it definitely the older leaves that are affected. This means it is a nutrient that is mobile (plants can export it from the old leaves) and involved in protein (chlorophyll) synthesis.

This is the Wikipedia page for potassium deficiency in plants <http://en.wikipedia.org/wiki/Potassium_deficiency_(plants)>, and this is the image:

It also says:

often, potassium deficiency symptoms first appear on older (lower) leaves because potassium is a mobile nutrient, meaning that a plant can allocate potassium to younger leaves when it is K deficient.....Plants require potassium ions (K+) for protein synthesis and for the opening and closing of stomata, which is regulated by proton pumps to make surrounding guard cells either turgid or flaccid. A deficiency of potassium ions can impair a plant's ability to maintain these processes....

Which all looks good for your plants being potassium deficient.

However rather than trying to work out what nutrient is missing, I'd use the "Duckweed Index" <http://www.ukaps.org/forum/viewtopic.php?f=17&t=14400> fertilization method. Despite the fact that you have a lot of nitrate in your tap water, I would still initially add some potassium nitrate (KNO3) (39 +14 + 48 = 101, so 39%K, 63% NO3, 14%N), as plants need about x10 more nitrogen and potassium than they do of any of the other nutrients. If this doesn't show a response you can either go straight for a complete fertiliser mix (from one of our sponsors), or you could try "Epsom Salts" (MgSO4.7H2O) , as this sort of deficiency symptom can also be caused by low magnesium levels, or a very high calcium/magnesium ratio.

I'm a great believer in "an ion, is an ion, is an ion", which means there is very little point in buying nutrients from ADA etc, and any source of reasonable purity fertiliser (soluble grade) will do the job just as well, but not every-one agrees.

There is a bit more discussion in this thread, some of it unfortunately unintentionally comic towards the end. Have a look at "Plantbrain" (Tom B's) contribution. <http://www.ukaps.org/forum/viewtopic.php?f=11&t=14594&p=214154&hilit=supernova#p214154>

cheers Darrel