basal rot and tulips

Basal rot is caused by a fungus called fusarium oxysporum spp narcissus, which lives in the soil. (See Dr. Ted Snazelle’s book, “Daffodil Diseases and Pests”, available from ADS.) It might diminish in numbers if there are no host plants, i.e. narcissus. Whether it would vanish completely, I don’t know, but I doubt it. Fusarium oxysporum does have a natural enemy among the fungus family called trichoderma (a.k.a. gliocladium) which also inhabits the soil. I have an area which seemed to have an excess of basal rot, and what I have done is to reinforce the numbers of the trichoderma in the hope that they will counteract the fusarium. I used one of the products sold by The Horticultural Alliance. (Actually, I use trichoderma in all my narcissus plantings.) Alternatively, you might try a fungicide. If you’re not cramped for space, maybe it would be better not to plant daffodils for a few years, but I don’t have that luxury. I don’t know whether there’s a fusarium which attacks tulips, but you might try to google that subject. Nor do I have any idea whether the narcissus type of fusarium might evolve into one that attacks tulips, or vice versa.