Answer: There are many different possible causes for this to happen. One is a spray toxicity, meaning a reaction if you have recently sprayed them. Another is water/heat stress, especially common with newly planted roses -- keep the soil evenly moist like a wrung out sponge. Fungal problems related to overhead watering and poor air circulation plus high humidity can cause flower problems. Thrips can cause the edges of the petals to brown as well, and would be appearing at this time of year. There are also some micronutrient issues that can cause browning but the above would be more common. You might want to consult with your local county extension to see if they can help you diagnose it more specifically, and based on knowing that decide what to do. If it is something that requires a chemical control, they will have the most up to date information on what to use and how/when is best to apply it for maximum results.
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