I have had pythium issues for a few years. I've tried so many different things and sterilised the hell out of the equiptment and environment. Eventually I decided to try something commercial and decided on propamocarb hydrochloride, marketed as Promess. This is advertised as not being suitable for recirculating and I'm an NFT person, so it may seem like an inappropriate choice of product. However, the pythium damage hits seedlings/cuttings and small plants the hardest, making them stressed, with red petioles and damping off. The leaves show clawing and rusting, giving the impression of nutrient deficiency/overdose. The roots initially look slightly off white and swollen with no further deveopment. Household 5% bleach won't cure it, but does help as a partially preventative control at 1.5ml per 10litres. I've made one single application of Promess at 15ml per 10litres, hand watered sick plants in 1 inch + 3 inch cubes and 5 days later they are 80% bounced back with healthy fresh root growth and pert newly growing leaves. Promess is marketed as a single use semi systemic fungicide (oomycide?). I wouldn't apply in flower or to large plants because of the unknown effects of smoking the compound, although it will be so dilute in dried product. Tests have shown subsequent crops in rotation show no trace at harvest, so it really isn't persistent in soil. It is regularly used commercially for the seedling stage of brassicas such as broccoli, which are obviously for human consumption.
If you have recurrent pythium issues and want to use a chemical application, Promess will work for you.
If you have recurrent pythium issues and want to use a chemical application, Promess will work for you.