The tender mandevilla vine produces trumpet-shaped pink flowers that measure up to 4 inches across. During the summer months, it sports a profusion of flowers, but it also continues to produce blooms lightly throughout the year. A native of Brazil, the mandevilla grows in U.S. Department of Agriculture zones 9 to 11. Usually relatively healthy, the vine can succumb to a number of fungal and bacterial diseases.
Botrytis Blight and Fusarium Stem Rot
Botrytis blight and fusarium stem rot both affect the stems and roots of the mandevilla vine. Both fungal diseases cause similar symptoms. The fusarium stem rot causes the mandevilla vine to display yellow and brown leaves. Entire twigs and branches wilt and die. The roots and stems of the plant begin to show signs of rotting. Botrytis blight often becomes most problematic after cool, wet weather. The mandevilla vine's foliage shows signs of wilting with brown tissue areas. The leaves and buds often display a gray mold. Sunken areas of rot develop on the plant's stems and roots.
The fungus Colletotrichum gloeosporioides, known as anthracnose, causes lesions on the leaves and roots of the mandevilla vine. The leaves often display brown spots that measure over 1 inch in diameter. Cercospora fungus, another type, causes leaf spots that appear circular and black.
Pseudomonas leaf spot occurs from a bacteria. The bacteria causes irregular circles of yellow and brown to occur on the plant's foliage. And corynespora or pseudomonas savastonoi, both fungal infections, cause leaf spots. The disease occurs in sub-tropical and tropical locations. The fungus causes small spots of yellow and black on the mandevilla's leaves. The spots quickly enlarge to engulf the entire leaf. The leaf eventually turns yellow and falls from the vine.
Crown gall, also called olive knot, eventually kills the mandevilla vine. Caused by the bacteria Agrobacterium tumefaciens, the disease causes round tumor-like growths at the stem's base. The galls often measure over 1 inch in size. The plant's growth becomes deformed and stunted as the disease progresses. The galls render the plant's root system unable to absorb water or nutrients. The bacteria usually enters the mandevilla vine through wounds sustained during cultivation. No cure exists for infected plants. Remove them and burn the plants to prevent the bacteria from spreading to healthy plants.
Prevention and Treatment
Prevent botrytis blight by keeping the plant's foliage dry when irrigating. Treat both botrytis blight and fusarium stem rot with fungicides. Remove severely diseased plants and destroy them. Preventative fungal drenches may help prevent healthy mandevilla plants from becoming infected. Keep leaf spot disorders from occurring on the mandevilla vine by avoiding overhead irrigation and overcrowding. Use fungicides to treat the leaf spots. Follow the directions on the fungicide's label when applying.