We grow roses, and we are having serious problems with Botrytis developing after just 4 days in a vase. Could you recommend a postharvest treatment solution that would be effective? We are currently using Teldor®. (S.M.)
Botrytis is the most serious postharvest fungal problem in roses, and it appears you are running into a problem of a strain of Botrytis that is resistant to the Fenhexamid (Teldor®) fungicide.
The disease spreads by spores that are formed in the greenhouse on diseased material, often dead or dying prunings and other plant residue, so perhaps the most important control measure is good sanitation in the greenhouse. Don't leave any plant materials on the ground in the greenhouse, and immediately remove any infected stems or buds. A greenhouse fungicide regime that rotates among effective chemicals is also an important strategy. Postharvest dips are commonly used. If Teldor® is no longer effective, perhaps you should try a different fungicide? A couple of years ago we wrote a paper on the use of low concentrations of sodium hypochlorite which was very effective as a postharvest dip in preventing development of Botrytis in roses. I'd certainly test that as well. There is zero chance of the fungus developing resistance to sodium hypochlorite.