There are many kinds of root rot, so it is a dicey thing to recommend a certain product, but here are a few things that might be effective:

Water less often~ This is the first thing to do, no matter what other treatment you use, and sometimes, it is effective even all by itself.

Streptomyces lydicus~ That is a fungus that eats other fungi, including a wide variety of root rot fungi. It may be hard to find, but it is fully safe and organic. The brand that I am most familiar with is Actinovate.

Captan fungicide~ Still available in the States, but I don't know about anywhere else. Also kills a wide variety of root rots, but some strains are becoming resistant. It's not recommended for large areas due to water table contamination.

Subdue fungicide~ More effective than Captan, but it requires an applicators license to buy, at least in the States. I don't know for sure, but that requirement implies higher toxicity.

I only had this happen once in a humid warm conservatory here in the Uk and moving the arum to a drier air, but keeping its roots damp solved the problem, with the help of fungicide to start with! Arum lillies - all varieties - like moist, and even wet, soil around their roots, with gritty free drainage, so very useful in mild areas for planting around edges of ponds etc. Not sure about air quality where you are, but arums can be susceptible to high humidity, affecting the main plant - leaves develop spots of fungus, flowers rot, and stems collapse. They like a drier air and moist free-draining roots! If this sounds like what you have then cut off all shoots and burn, then when new shoots appear spray with fungicide fortnightly until flowers appear. Take care of disease residue in the soil - maybe re-plant in new gritty soil?

thanks for advice will give them a try , im sure u can tell im new around here :-D

Gardening is learning something new each day. You are only 'new' as you put it on this particular point. I daily find a 'new' thing, as I know many others do - except one member at a local garden centre who is the fountain of all knowledge, whom I never seem to be able to surprise or stump!!

I just realized something--if you are talking about Zantedeschia species, they go dormant during the summer in hot-summer climates. Sometimes the process of falling asleep can resemble rotting, or watering more to try to keep them awake can actually rot them. Did they look like the photos of "Arum Lily" in GoYpedia, at the bottom of the page?

Tugbrethil Thats them for sure ,so they do this in summer ok ,what a relief.It has been very hot here in SA, they are falling asleep but also going brown .I was digging in some compost and found a white sludggy thing that i assumend was root rot thats when pannic set in :-0 ,thanks so much.

Avkq47 thanks i feel that every gardening nursery should have someone with that kind of knowledge . I saw last night that my roses have black spots ,any advice ?

Good to hear, though that white sludgy thing sounds suspiciously like a rotted rhizome. Remember to keep them a little on the dry side while they sleep. or they will rot for real.

Hello - yes, Rose Clear is good. Apply out of direct sunlight, ie early morning or late evening, if your days are sunny, or on any overcast day, and every fortnight. Do not spray on wilted roses - water them well first. I also spray or remove any diseased leaves that have fallen to the ground, and mulch every autumn. You could also try a good tonic at the start of their next growing season, which being our opposite is probably now for you. Don't spray any open blooms - just the leaves, stems and ground below. Also, feed your roses when they start to flower, to encourage strong and healthy plants more capable of fighting disease.

thanks for advice :-)