I didn’t see these on my bougies in Santa Barbara either. Go out scouting very early in the morning or at night if you have a good strong flashlight. Growing Bougainvillea in Gardens. Root rot, Botrytis, black spot and other fungal pathogens can all cause rosemary to turn black. I purchased several big Barbara Karst Bougainvillea from Golden Nursery in San Mateo, CA. The … The reason rosemary leaves turn black is because of fungal disease which is caused by damp soil around the roots or high humidity. Rosemary is native to the Mediterranean where it grows in sandy or stoney soils that drain quickly and thrive in full sun with infrequent rainfall or watering. Leaves are ovoid to elliptic-lanceolate, may be variegated, and vary considerably in size between varieties. hi , i have an avocado plant which is about 6 month old and it was fine and growing perfect but the older leaves which grown while it was still in the water started to get weak (like loosing color and brown, dry tips). Head’s up: Those black droppings are a sign caterpillars are in the house! Asked November 1, 2014, 11:22 AM EDT. Generally, bougainvillea plants are hardy in U.S. Department of Agriculture plant hardiness zones 9 and above. Bougainvillea flower drop can be caused by temperatures that are lower than those the plant is used to. Why Do Plant Leaves Turn Black?. Lawns. Bougainvillea are thorny, evergreen summer bloomers, but their orange, yellow, crimson or purple flowers are actually modified leaves called bracts. Plant leaves turn black for a number of reasons, including environmental factors and bacterial infections. Like the larva, it also is active at night, when it is believed to lay its eggs on the underside of bougainvillea leaves. Although there are many species of Bougainvillea, most plants in the ornamental trade today are hybrids of three horticulturally important species: B. glabra, B. spectabilis, and B. peruviana. Barbara Karst Bougainvillea flowers and leaves turning brown, drying, and falling off, need expert g - Knowledgebase Question. The bougainvillea looper feeds from the edges of the leaves, which results in severe scalloping of the foliage. San Bruco, CA . Question by jhh4 July 15, 2005. In some cases the plant is salvageable. Read on for information about how to grow a bougainvillea. These are the 2 which I have seen on my bougainvilleas & have experience with: Leaftier Caterpillar. leaves turning black.