Common Barbara Karst Bougainvillea Plant Diseases: How to Identify and Treat

A part of the bougainvillea’s appeal is that they are relatively disease and pest-free plants. It is NOT common for your bougainvillea to be affected by these pests and diseases if you follow BGI’s Rules for Care, and fertilize with Bougain® which contain a significant amount of micronutrients – vital for healthy, blooming bougainvillea. This page contains most (but not all) common pests/diseases that may affect your bougainvillea.

On the rare occurrences that your bougainvillea experiences pest problems or disease, always try the least toxic method of pest control as your first step. If you use chemical pesticides to control insect pests, you will also kill natural predators. If you choose a chemical control, follow directions and guidelines closely and always wear protective clothing and safety gear including a long-sleeved shirt, long pants, neoprene gloves, goggles and a respirator. Chemical pesticides are not recommended for use inside the home.

Known also as greenfly, blackfly or plant lice, aphids are minute plant-feeding insects. Important natural enemies include the predatory ladybugs/ladybirds/ladybeetles, and lacewings. Aphids are tiny, pear-shaped, sap-sucking pests, appearing in the spring to feast on your plants’ tender new leaves. They leave behind a secretion that attracts ants and promotes mold growth. Not to fear; you don’t have to resort to toxic chemicals to save your bougainvillea.

The early symptoms are small reddish-brown leaf spots which usually occur on younger foliage, and cause the leaves to look “rusty”. These enlarge into circular or irregular dark necrotic spots. When environmental conditions are drier and less favorable, leaf spots are slower to develop. Lesions have a tan center surrounded by a dark redbrown margin, and are sometimes bordered by a chlorotic halo. In time, leaf edges may become ragged as the necrotic tissue turns dry and papery. Under conditions of high rainfall or relative humidity the lesions develop quickly and are often black and vein delimited. Infection of developing leaves and bracts results in puckered, distorted growth.

Natural Control Maintaining dry foliage is the primary control measure. Prune branches back and away from each other or, if just starting to grow, allow a large amount of space between them. Branches that are overlapping can’t dry quickly and become more susceptible to leaf spot disease. Remove infected leaves and/or plants from the growing area. Dispose of them immediately to reduce the spreading of infection.

Chemical Control Spray fungicide in the spring if necessary. It will not cure infection that is already there, but it can control the spread of it. In frost-free climates where bougainvillea is perennial, disease incidence drops during cool and/or dry weather.

Yellow or tan spots appear on older leaves may be sign of Magnesium deficiency (common with yellow bougainvillea varieties), or from over-watering.

Plants that are over-watered or subjected to water logged conditions can develop root or stem rot. It’s easily prevented by careful handling and by the application of a broad spectrum fungicide drench during transplanting or planting in the landscape.

Mites; namely Spider Mites

The webspinning two-spotted spider mite occasionally makes their home on bougainvillea. To the naked eye, spider mites look like tiny moving dots. Adult females, the largest forms, are less than 1/20 inch long. Spider mites live in colonies, mostly on the under-surfaces of leaves. The names “spider mite” and “webspinning mite” come from the silk webbing most species produce on infested leaves. The presence of webbing is an easy way to distinguish them from all other types of mites. Mites cause damage by sucking cell contents from leaves. A small number of mites is not usually reason for concern, but very high populations—levels high enough to show visible damage to leaves—can be damaging to plants. At first, the damage shows up as a stippling of light dots on the leaves; sometimes the leaves take on a bronze color. As feeding continues, the leaves turn yellow and drop off. Often leaves, twigs, and fruit are covered with large amounts of webbing. Damage is usually worse when compounded by water stress. Check the undersides of leaves for mites, their eggs, and webbing; you will need a hand lens to identify them. To observe them more closely, shake a few off the leaf surface onto a white sheet of paper. Once disturbed, they will move around rapidly. Be sure mites are present before you treat. Sometimes the mites will be gone by the time you notice the damage; plants will often recover after mites have left.

Natural Control If a treatment for mites is necessary, use selective materials, preferably insecticidal soap or insecticidal oil. Petroleum-based horticultural oils or neem oils are both acceptable. Oils and soaps must contact mites to kill them so excellent coverage, especially on the undersides of leaves, is essential and repeat applications may be required. Mid-season washing with water to remove dust may help prevent serious late-season mite infestations. Regular, forceful spraying of plants with water will often reduce spider mite numbers adequately. Be sure to get good coverage, especially on the undersides of leaves.

Chemical Contol Spider mites frequently become a problem after the application of insecticides. Such outbreaks are commonly a result of the insecticide killing off the natural enemies of the mites, but also occur when certain insecticides stimulate mite reproduction. Naturally controlling mites is the best method.

Thrips are tiny, slender insects with fringed wings that cause discoloration and deformities on bougainvillea and other plants. Other common names for thrips include thunderflies, thunderbugs, storm flies and corn lice. Thrips are generally tiny (1 mm long or less) and are not good flyers, although they can be carried long distances by the wind. Thrips feed by piercing plant cells with their paired maxillary stylets, which form a feeding tube. Due to their small size, cryptophilic behavior, and high rate of reproduction, thrips are difficult to control using classical biological control. Only two families of parasitoid hymenoptera are known to hunt them, the Eulophidae and the Trichogrammatidae.

Whiteflies typically feed on the underside of plant leaves. Whiteflies feed by tapping into the phloem of plants, exposing plants to the whiteflies’ toxic saliva and decreasing the plant’s overall turgor pressure. The damage is quickly elevated as whiteflies congregate in large numbers, quickly overwhelming susceptible plants. Damage is further exacerbated as whiteflies, like aphids, excrete honeydew as a waste product, which promotes mold growth. Whitefly control is difficult and complex, as they rapidly gain resistance to chemical pesticides. A major problem is the fact that the whiteflies and the viruses they carry can infect many different host plants. Use of yellow sticky traps to monitor infestations and only selective use of insecticides is advised.

Fungal and Bacterial Leaf Spot (Pseudomonas and ropogonis)

The early symptoms are small reddish-brown leaf spots which usually occur on younger foliage, and cause the leaves to look “rusty”. These enlarge into circular or irregular dark necrotic spots. When environmental conditions are drier and less favorable, leaf spots are slower to develop. Lesions have a tan center surrounded by a dark redbrown margin, and are sometimes bordered by a chlorotic halo. In time, leaf edges may become ragged as the necrotic tissue turns dry and papery. Under conditions of high rainfall or relative humidity the lesions develop quickly and are often black and vein delimited. Infection of developing leaves and bracts results in puckered, distorted growth.

Defoliation will occur when leaf spotting, blighting or marginal necrosis becomes severe.

Natural Control Maintaining dry foliage is the primary control measure. Prune branches back and away from each other or, if just starting to grow, allow a large amount of space between them. Branches that are overlapping can’t dry quickly and become more susceptible to leaf spot disease. Remove infected leaves and/or plants from the growing area. Dispose of them immediately to reduce the spreading of infection.

Chemical Control Spray fungicide in the spring if necessary. It will not cure infection that is already there, but it can control the spread of it. In frost-free climates where bougainvillea is perennial, disease incidence drops during cool and/or dry weather.

See “Aphids”, “Scale Insects: Parasites, Mealybugs”, and “Whiteflies”

Problem as a result of over-watering, under-watering, low light levels, or cold temperatures.

Yellow or tan spots appear on older leaves may be sign of Magnesium deficiency (common with yellow bougainvillea varieties), or from over-watering.

Plants that are over-watered or subjected to water logged conditions can develop root or stem rot. It’s easily prevented by careful handling and by the application of a broad spectrum fungicide drench during transplanting or planting in the landscape.

Caterpillars; namely the Bougainvillea Looper Caterpillar

The bougainvillea looper is a green or brown caterpillar about 1 inch long. It is also called inchworm or measuring worm. The looper larva mimics stems and branches very well and feeds primarily at night, which is why you may see the damage but fail to find the culprit on the plant. The adult is a moth, a very fast flyer with a wingspan of about 1 inch. The moth does not feed on the foliage. Like the larva, it also is active at night, when it is believed to lay its eggs on the underside of bougainvillea leaves. Go out scouting very early in the morning or at night if you have a good strong flashlight. The bougainvillea looper feeds from the edges of the leaves, which results in severe scalloping of the foliage. Attacks begin on the young tender shoots and leaves before progressing down the stem. The insect will cause significant visual damage to bougainvillea, although this does not apparently result in the death of the plants.

Chemical Control

Bacillus thuringiensis (BT, or Dipel®) and neem-based biological insecticide products should are a good solution and should be effective on the loopers without harming other insects that may biologically control them. Insectical oils and soaps will not control caterpillars such as the looper. Most synthetic insecticides with labels permitting use against caterpillars on landscape ornamentals, such as carbaryl (Sevin®), will likely kill the bougainvillea looper, although these products are often destructive to beneficial insects as well. Spraying insecticides late in the evening is recommended. This is when the bougainvillea looper caterpillars and adult moths are active, and also when the beneficial insects are not likely to be active.

Common Bougainvillea Problems