调查 | 从萎蔫萧瑟到层林尽染，京城红叶为何晚红一周？

Core Viewpoint - The article discusses the delayed color change of autumn leaves in Beijing, attributed to unfavorable weather conditions and plant diseases, with a notable improvement observed by the end of October [1][5][6]. Group 1: Weather Conditions - The optimal conditions for leaf color change include low temperatures and strong sunlight, which were lacking earlier in the season due to high temperatures and prolonged rainy weather [6][7]. - As of October 31, the weather began to clear, providing favorable conditions for the leaves to change color [6][10]. Group 2: Leaf Color Change Timing - The best viewing period for red leaves in Beijing is projected to be from late October to mid-November, with a one-week delay in color change compared to previous years [5][10]. - The peak viewing period for the iconic Fragrant Hills is from October 25 to November 15, with an expected 80% color change in certain tree species [5][10]. Group 3: Plant Health Issues - Observations indicate that some yellow leaves appear unhealthy, potentially due to two main diseases: powdery mildew and wilt disease, which affect the health and color of the leaves [9][10]. - The wilt disease is caused by a soil-borne fungus that has persisted in the soil for years, affecting the newly planted trees in Beijing [9][10]. Group 4: Diversity of Autumn Foliage - The article highlights that autumn foliage in Beijing is not limited to red leaves; various colors such as yellow, brown, and purple are also present, showcasing a rich diversity of plant species [10][12]. - Parks like the Olympic Forest Park and others feature a variety of colorful leaves, including ginkgo and white wax trees, contributing to the vibrant autumn scenery [12][13].