Botrytis blight (Botrytis cinerea) is a fungal disease that attacks roses in cool, wet weather. It often begins as small gray-brown flecks on the petals, and these eventually grow to engulf the entire flower in grayish-brown fungus. The brown petals usually fall off the plant, and infected buds fail to open.Click to see full answer. Thereof, why do Rose flowers turn brown?Balling – a condition caused by high humidity or over watering from above the rose. Some roses are more susceptible than others. Blooms only partially open and petal edges begin to turn brown and rot. To determine if balling is the cause of brown-edged petals, feel and smell the bloom.Additionally, how do you keep rose petals from turning brown? Protect your roses from heat and drought stress which can turn petals brown. When temperatures climb over 90 degrees, mist your roses early in the morning to keep them moist. Check the soil frequently to make sure that it does not dry out. Container grown roses may need to be watered up to twice daily. Thereof, why are my rose petals turning brown? Exposure to extreme weather causes rose petals to turn brown at the edges. Although most rose varieties go dormant during the winter, some roses in warmer climates set buds before the last frost. If freezing temperatures arrive unexpectedly, the petals of these rose buds appear stressed and turn brown.What to do when Rose leaves turn brown?Ironically, overly wet soil can also damage the roots. If the leaves of your roses are turning brown, check the soil. If it is very dry, water the bushes more often. If it is very wet and you see standing water, improve the drainage by adding sand to the soil, or by moving your bushes to a raised bed.