Mandevilla vines are members of the Mandevilla genus, once called Dipladenia. This genus includes about 100 species, most of which prefer warm climates and plenty of sun. In cooler regions, they can be taken indoors during the winter or grown as annuals. When provided with good drainage and sun, this plant is relatively low-maintenance and a strong grower. However, some mandevilla vines may suffer from yellowing leaves, a condition called chlorosis.
Leaf Spot Infection
According to the National Gardening Association, mandevilla vines may suffer from yellow leaves with black or brown spots if they have a bacterial or fungal infection of the leaves. This disease may be spread by bugs, garden tools and even splashed water. Control leaf spot infections by removing infected leaves when the weather is dry and there is no moisture to spread the infection. Remove any fallen leaves from the base of the mandevilla immediately. When possible, water these plants at soil level, instead of overhead. Fungal leaf spots may be treated using fungicide applications. No chemical treatment for bacterial leaf spot is available.
Mandevilla plants require regular, thorough watering and soil that stays a little damp. However, too much water or poorly draining soil that traps moisture around the roots can damage the plant and prevent it from transporting nutrients into the leaves. Eventually, the leaves turn yellow and fall off. Keep mandevilla plants in rich, well-drained soil with a high percentage of sand and humus. Don't allow the soil around the vine to stay soggy for long periods of time. Very wet conditions can also encourage fungal root rot, which permanently damages the roots and can kill a mandevilla.
These plants prefer significant amounts of sunlight and can suffer from leaf chlorosis when kept indoors for the winter. Whenever possible, keep overwintering mandevilla vines in direct sunlight or the brightest location available. Reduce watering and fertilisation and keep the ambient temperature cool to encourage the plant to go dormant. It may lose some leaves, but will return to good health in spring.
Mandevilla vines need fertiliser about once every two weeks, especially if kept in pots. When the soil lacks the nutrients these plants need, their leaves may turn yellow. Inappropriate soil pH or too much of one nutrient can also cause nutritional deficiencies and yellowed leaves, since these conditions block the plant's ability to absorb certain minerals, such as iron. Test soil pH and nutrient levels, then amend the soil as needed.
Moving mandevilla vines planted outdoors to a pot for the winter can damage their roots, causing a condition known as transplant shock. The plant may wilt, develop yellow leaves or suffer from leaf loss. This problem may go away after a few weeks or it can persist, eventually even killing the plant. Move mandevilla vines carefully, maintaining as much of the existing root system as possible. Prune off yellowed leaves and care for the plant gently until it recovers.