Is this fungus white and power-like? If so it could be powdery mildew. Try cutting off the infected flowers and do not get the foliage or flowers wet when you water. Do not let the soil dry out either, as this makes them more susceptible to disease. Once the dry summer weather arrives, the problem should go away. Give the plants plenty of air circulation by clearing away any weeds or nearby plants. Keep growing, Marianne Binetti