This is the most serious disorder affecting gladioli. The fungus that causes this disease can survive in the soil for years. The foliage on infected plants turns yellow or brown, and a rot covered with greyish mould spreads out from the leaf bases. The corms are particularly at risk during storage in moist conditions, when a spongy, dark rot develops so that the centre often drops out completely.
The fungus also affects acidantheras and causes leaf spotting in freesias. To reduce the likelihood of the disease reappearing, there are a number of things you can do. But they will only improve your chances; they won’t guarantee you a disease-free garden, no matter how careful you are.
– Growing plants showing symptoms of core rot should be dug up and burned.
– Do not replant gladioli at same site for at least three years – and more than five for safety. You could try gladioli in another part of the garden, but only if you can ensure that you don’t carry infection from the old site to the new on your boots or tools.
– Follow the old garden advice that every bulb or corm should be handled gently, especially when it’s being lifted for winter. Before storage, soak the corms in a solution of fungicide such as benomyl or thiophanate-methyl for about 30 minutes.
– During the winter, keep the corms in cool, dry, well-ventilated conditions out of direct sunlight. Check the corms weekly for signs of the disease, and destroy any affected corms.
– Even if years later you decide to replant gladioli in the old site, before you do so. soak your fresh stock for 30 minutes in a solution of benomyl or thiophanate-methyl.