Mother Nature's answer to the punk subculture's favorite hairstyle, Mohawk-mimicking bird of paradise flowers (Strelitzia reginae) have a one-of-a-kind architectural profile. Their fans of pointed, flame-orange sepals and blue-violet petals rise from beak-shaped, pinkish bracts crowning thick stalks of gray-green foliage. Fall and winter bloomers in U.S. Department of Agriculture plant hardiness zones 9 through 11, sun-loving bird of paradise thrives in coastal conditions. Its rare problems include black leaf spotting associated with insect infestation.
Sooty Molds and Leaf Spots
The black spots blemishing your bird of paradise's leaves aren't symptoms of an actual disease. They're powdery fungal mats germinating from sooty mold spores, and they appear only on plants already hosting one or more varieties of sap-draining insect. Sooty molds don't attack plant tissue. Instead, they consume honeydew, the pests' sugary, syrupy waste. These fungal mats persist as long as their honeydew supply lasts, ruining the plant's beauty. Thick sooty mold interferes with the leaves' sunlight absorption and photosynthesis.
The Insect Connection
When the first black streaking appears on your bird of paradise, examine its stems and leaves to look for any of four sap-sucking culprits. Yellow, green, red, brown or black aphids feed in colonies along stems. Dome-shaped brown and nigra scales have brown or black, headless and legless bodies. Mealybugs are flat, segmented insects covered in powdery white wax. Winged adult whiteflies swarm from the plants when disturbed, but their nearly invisible, orange, yellow or white larvae cling to the leaves. Even if you have difficulty spotting the pests, their sticky honeydew and the ants it attracts are telltale signs of infestation.
The Ant Factor
To protect the honeydew they love to eat, ants join forces with the insects on your bird of paradise. In addition to moving them to new plants for increased honeydew production and building mealybug shelters from bits of plant debris and soil, ants also kill the parasitic wasps, lacewings, beetles and ladybugs that prey on the pests. Help these natural predators do their jobs by spreading slowly acting boric-acid bait around your plant for the ants to transport to their nests. Mix 1 1/4 teaspoons of boric acid powder with 1/2 cup of apple jelly or peanut butter and place the bait in a jar. After puncturing several holes in the jar's lid and sealing it with tape, set it near your plant but hidden from children or pets. The bait should produce results in about a week.
The ants' departure, the return of the invading insects' natural enemies and a few cultural management techniques can eliminate the pests and honeydew from your bird of paradise. Sooty mold deprived of honeydew starves and withers away over time. Avoiding high-nitrogen fertilizer limits the plant's production of tender, new aphid-attracting growth. Hosing down the plants with a forceful jet of water dislodges aphids, whiteflies and scale larvae. Scraping their leaves and stems with a soft toothbrush or plastic scouring pad removes adult scales and mealybugs.
- Monrovia: Bird of Paradise
- University of California Statewide Integrated Pest Management Program: Strelitzia
- University of California Statewide Integrated Pest Management Program: Sooty Mold
- University of California Statewide Integrated Pest Management Program: Aphids
- University of California Statewide Integrated Pest Management Program: Mealybugs
- University of California Statewide Integrated Pest Management Program: Scales
- University of California Statewide Integrated Pest Management Program: Whiteflies
- IPM for Floriculture and Nurseries; Steve H. Dreistadt
- The Royal Botanic Gardens & Domain Trust: Mealybugs Fact Sheet
- Montana State University Extension IPM Center: Ants in the Yard and Garden
- Jupiterimages/Photos.com/Getty Images