What effect does powdery mildew have on infected plants?

The correct answer highlights the negative impact of powdery mildew on infected plants. Powdery mildew is a fungal disease that affects a wide variety of plants, causing a white or gray powdery coating on the leaves. This fungal infection reduces the plant's ability to photosynthesize effectively, which can lead to stunted growth. Additionally, the disease can cause leaves to dry out and eventually drop from the plant, further weakening its overall health and vigor.

The other options incorrectly suggest positive effects. Enhanced growth and flourishing leaves do not occur with powdery mildew; instead, the disease results in compromised plant health. The notion that infected plants become hardier or more disease-resistant contradicts the reality that powdery mildew makes plants more susceptible to further stress and other diseases. Lastly, while robust roots might be an indicator of a healthy plant, powdery mildew primarily affects the foliage, so the idea that roots grow deeper and more robust in the presence of this infection does not align with its actual effects on plant physiology.