Plant Disease Management Handbook

Cause Stemphylium botryosum (sexual Pleospora tarda) a fungus that overwinters in affected leaves and other plant debris. The disease is favored by warm wet conditions.

Symptoms Small, pale yellow spots, translucent, with reddish brown centers. Severe spotting may kill leaves. The reduced leaf surface on severely affected plants may result in smaller corms.

Cause Fusarium oxysporum f. sp. gladioli, a soilborne fungus that survives in soil and plant debris for many years as chlamydospores. It can survive in the absence of gladiolus for many years. Population levels are highest in the top 8-inches of soil and the disease is favored by high soil temperatures. Spores infect roots then mycelia travels up the roots and crosses the basal plate.

Cause Curvularia gladioli (formerly Curvularia lunata), a fungus that has been reported from Oregon on gladiolus The disease is favored by warm, wet conditions. Optimum fungal growth is from 75 °F to 85°F; infection occurs after a 13-hour dew period. Leaf spots may show up 4 to 5 days after infection. The fungus can survive on infected corms or in soil at least 3 years. Many cultivars are fairly resistant, but Picardy is very susceptible.

Cause Botrytis gladiolorum, and possibly B. cinerea, fungi. They survive in soil as sclerotia and as mycelium on plant debris. The leaf and flower spot phase of the disease is most prevalent in northern Washington, where weather often favors fungal buildup on flowers and old foliage late in the season. High humidity and leaf wetness are needed for infection and sporulation.

Cause Burkholderia gladioli pv. gladioli (formerly Pseudomonas gladioli pv. gladioli), a bacterium. Unlike other gladiolus corm rot diseases, scab does not kill the affected plants. Unless very severely affected, corms produce normal flower spikes. The bacteria are widespread and may be introduced into a planting on infected corms or may have survived from a previous planting.

By M. Putnam

By M. Putnam

Cause The soilborne fungus-like microorganism Phytophthora cactorum. Spores are produced on infected foliage and in roots. Spores are spread via water splash, surface water runoff, and movement of equipment and workers through the beds. Spores also survive up to at least a year in decayed plant material. The fungus-like microorganism can infect foliage and move down into roots, although direct root infections are more common.

Cause The root-knot nematode, Meloidogyne hapla, does not penetrate to the interior of the root, but remain just beneath the surface. Galled roots are reduced in value.

Symptoms Leaf symptoms are typical of nonspecific stress such as generalized chlorosis, slight stunting, and premature reddening or yellowing.

By M. Putnam

Cause Soilborne fungal and fungus-like microorganisms such as Rhizoctonia solani, Pythium sp., and Phytophthora sp. They are widespread in soil and can be very destructive under cool, moist conditions.