Closely spaced plants, overcast cloudy weather, and flower drop from overhead hanging baskets encourage Botrytis blight on New Guinea impatiens, garden impatiens, geraniums and other greenhouse crops. The fuzzy grayish-brown spores, seen in this photo, are easily spread on air currents and by water splash. Botrytis is best managed by combining proper sanitation practices with environmental controls.
Remove and destroy infected plants and plant debris. Control weeds. Water early in the day so foliage dries rapidly. Improve air circulation and light penetration by plant spacing and horizontal air flow (circulating fans). Reduce humidity by heating and venting the greenhouse several times in the evening and in the morning. Fungicides appropriate for Botrytis include26 GT, 26/36, Compass, Cleary's 3336, Botran, Decree, Daconil, Dithane,Heritage, Exotherm Termil, Sextant, Protect DF, and Medallion. Check label for host appropriateness. Resistance to Cleary's3336, 26 GT, and Sextant has been reported in Botrytis populations. Always alternate fungicide applications between materials with different modes of action to prevent resistance development.