eating of the stalk underground

Any of you guys experienced outdoor plants being eaten from the inside out? I know something is wrong when the plant starts wilting badly like it has no water. After a day its basically dead and sometimes the plant falls over.
Could be a 2' tall plant or a 10'
The plant after i pick it up is mostly or completely eaten through the stalk below ground level, usually an inch or 2. Ive noticed mostly its ants and some termites as well.
Ive had ants strip the stalk above ground eating it before.
Ive used Seven ant killer a month ago to no avail, ive used ortho and also some liquid bug spray and soaked the area. Nothing has worked so far.
Not sure its termites or the ants. Both have been horrible this year.
Thinking about using Diatomaceous earth Around the plants but the problem is below ground. Anybody experienced this and solved it? Had a 8' tall girl scout cookie drooping badly today. So its the next victim

I have never heard of ants eating plants. Ants would be attracted to other bugs and pests that could cause damage to plants and maybe why the ants are present in large numbers, because there is something else there causing plant problems? My first thought for you is to look into beneficial nematodes if it is a pest of some sort underground and not a fungus/disease.

Termites are eating your roots and stalk, and the ants are eating the termites.

When i see ants near my plants its a sign they are trying to set the scene for aphids so the ants can then feed on there shit they leave behind.....totally different to your situation though

Any good termite remedies that work?

Put diatomaceous earth into your soil.

Greenthumbskunk said:

Any good termite remedies that work?

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You're gonna have to use a treatment made specifically for termites.

Google is best friend here to find termite killer.

I may be wrong, but I don't think it's very common to have this problem of termites eating through wood stalk of canna plants. I would dig underground and investigate and find the exact enemy you face before doing anything.

Could it be some kind of potato bug or borer? Both are known to chew their way through plants.

You gotta dig up one and see what's going on..Here, we have root worms and root maggots.. So it could be anything..
Investigate!

Gophers? Or some other root eating mamal? Gophers have done this to me before