Yellow Leaves on a Polygala Myrtifolia

Root and Collar Rot

• Researchers at Spain's Universidad Politecnica de Valencia and Britain's Royal Horticultural Society examined a root and collar rot outbreak in Spanish myrtle-leaf milkwort. Their study, published in the British Society of Plant Pathology's 2005 "New Disease Reports," isolated a type of Cylindrocladium fungus as the pathogen responsible for the infection. They identified the fungus as C. pauciramosum, the same species that had infected P. myrtifolia plants in Italy. The disease caused yellowing, wilted leaves and black lesions on the plants' roots and collars.

Cucumber Mosaic Virus

• Researchers at Italy's University of Catania identified the cucumber mosaic virus in potted P. myrtifolia plants at a Sicilian nursery. The plants exhibited CMV's characteristic symptoms, yellow-mottled, deformed foliage and lack of blooms, according to the findings in the December 2002 "Plant Disease." Other indications of CMV include stunted growth and irregular bloom color. CM Infected aphids feeding on their leaves, parasitic dodder plants, grafting to infected stock and contaminated tools all spread the virus to healthy myrtle-leaf milkworts. The virus invades plant cells and hijacks its reproductive processes to produce more viruses. Because CMV is systemic, cuttings from an infected plant also carry the disease.

Cylindrorcadium Root Rot Control

• Cylindrocladium thrives in humid climates at temperatures between 75 and 80 degrees F. Excessively fertilization and overhead watering from above both raise a Polygala myrtifolia's risk of contracting the fungus. Controlling the disease begins with removal and disposal of the most seriously infected plants and all leaf litter. Sprays of copper-, chlorothalonil-, thiophanate methyl-, triflumizole- or mancozeb-based fungicides help protect healthy plants from infection. Always apply any chemical treatments according to the manufacturers' directions.

Cucumber Mosaic Virus Control

• As a viral disease, cucumber mosaic virus doesn't respond to fungicides. Control means preventing infestations of leaf-feeding aphids. These insects contract the disease by feeding on infected plants. For a brief period -- no more than a few hours -- they then transmit the infection to healthy ones. The typically wingless insects appear in large colonies on a plant's foliage undersides and stems. Clearing vegetation away from a shrub and laying down reflective, aluminum-covered construction paper mulch discourages aphids. Using insecticides against an existing population has no CMV-preventive value.