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Q and A: Failing Phlox

Follow these tips on what to do about spotty and moldy phlox.

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Q: Every year I get a terrible something on my phlox. The leaves look spotty at first, then moldy. Some turn brown and others a sick yellow. Please help!

A: It's disheartening to keep losing a favorite plant in the same way. Summer phlox (Phlox paniculata) is prone to a variety of fungal and bacterial problems that are often exacerbated by the weather. Of these, the most prevalent — and most serious — is powdery mildew; others are leaf spots and verticillium wilt. The first symptoms of powdery mildew are usually powdery white spots on the leaves. Warm, humid weather seems to invite the disease.

Other culprits of yellowing — and later, browning — foliage can be spider mites, which tend to hit phlox when the weather is hot and dry. The first signs of spider mites are tiny yellow dots on the leaves.

If your plants have been infected with powdery mildew, rake up all the fallen foliage and throw it and any dead plants in the trash (don't compost). Then next spring, plant varieties that are resistant to powdery mildew: 'Blue Boy', 'Darwin's Joyce', 'David', 'Delta Snow' and 'Eden's Crush' are among those that are resistant — meaning, they're not immune to it, but the disease should be fairly limited. Make sure you water the plants at their base; overhead watering (as with regular storms and showers) can create the conditions for powdery mildew. Most gardeners find that spraying their phlox every couple of weeks with a fungicide labelled for powdery mildew is a must. As for mites, if you catch them early enough, insecticidal soap can help control them. Also, making sure that the plant gets regular water and fertilizer can help it withstand the effects of the mites.

Good luck! Summer phlox isn't a low-maintenance plant but its long-lasting and beautiful blooms are unrivaled.

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