The tarnished plant bug damage affects leaves and removes the buds off the plants. As the disease progresses, lower leaves curl downward. My five border phlox started having powdery mildew so I sprayed them with Bayers Advanced Fungicide but with all the constant rain the rest of the leaves started having black spots on then and then turned yellow. B) Close-up view of single leaf spot with dark fruiting bodies (pycnidia) visible in center. Grow garden phlox in a sunny location as a border or a backdrop to shorter flowers. Eventually, the roots shrivel and turn brown or black. If left untreated, black spot spreads rapidly and weakens plants severely. The phlox bug’s feeding causes white or light green spots on the leaves and buds. But the soil is not dry. 1 of 3. Black spot leaf disease shows itself first with black spots appearing on the leaf, then with rings of yellow as the spots grow, until the leaf turns entirely yellow and then falls off. Black Spot. I had to cut down one plant. The phlox plant bug (Lopidea davisi) is a reddish orange and black bug that feeds predominantly on phlox. It is a big problem with roses. I have picked some and could mail them to you if you like. The roots of rotting creeping phlox plants display light brown spots and lesions develop on the stems. Powdery, fluffy white spots and blothces on leaves, stems, and flower parts; Tiny black round spheres may be visible within white spots late in the season; Spots typically start on lower leaves but can spread to cover the entire plant; As a soil-borne fungus, it's present at all times, even deep winter. Phlox > Spots on leaves. I have never seen this in my yard before. Leaves are turning yellow and brown, worse on the bottom. My tall garden phlox are diseased. Phlox prefers a moist garden soil and needs adequate ventilation around the … All the phlox plants in various locations in my planting beds have yellow leaves at the base of the plant and expanding up the stems. They are not turning yellow or brown in the veins, but rather in between the veins. Garden phlox is a showy landscape flower with large flowers that decorate a flowerbed during the second half of the summer. Black spot is another common fungal disease. Septoria leaf spot of phlox. (See photo at top.) AND they have black dots. Yellow leaves on phlox usually meant under watering. Leaves eventually begin to yellow around the spots, then become all yellow and fall off. The tips are deformed. A) Seedling showing dark-bordered leaf spots on lower leaves. And the black dots are evenly distributed on the leaves. Powdery Mildew Erysiphe cichoracearum. The disease typically begins as black spots on the foliage. Causes of Creeping Phlox Black Rot. These spots are most prevalent on upper leaf surfaces, and may be up to 1/2" across. There is no powdery mildew present.