Fusarium rot and gray mold of freesia flowers

The appearance of this disease is incidental. Symptoms can be detected shortly after seedling emergence, or later, throughout the entire growing season of the crop. Affected plants show stunted growth; leaves wilt prematurely, turn red, then yellow, and die. A rotting area appears at the base of the shoot. Sometimes the infection also affects the corm; its vascular tissue becomes rusty-brown, and general rot develops gradually. Infected corms look normal at the time of harvesting but rot during storage, especially at insufficiently low temperatures. The pathogen can persist in seeds, corms, and soil. All commercial freesia cultivars are susceptible to Fusarium rot.

Control. After the disease appears, the soil must be steamed or treated with chemicals, although it is more expedient to perform continuous disinfection, as a slight Fusarium rot infection may go unnoticed and develop to the level of an epiphytotic in a short time. Before planting, corms should be carefully inspected for infection, and diseased specimens should be removed. To control the disease after planting, irrigation with a suspension of captan or benomyl can be performed. It is also recommended to submerge corms in a benomyl solution immediately after harvesting and again before planting.
Fig. 14.1. Right — severe infection of freesia seedlings with Fusarium rot, left — healthy plants.
Fig. 14.2. Fusarium rot of freesia corms. Left — healthy corm, center — initial stage of the disease, right — mother corm and cormels severely affected by rot.

Gray mold and flower spotting (Botrytis cinerea)

When affected by this common disease, red spots up to 4 mm in diameter appear on freesia petals. Flowers become diseased at any stage of development and after cutting. Furthermore, the pathogen colonizes damaged leaf tissues and sometimes causes plant death by forming a stem constriction right at the soil surface. On affected leaves and stems, the disease is easily identified by the abundant growth of gray mold. Gray mold reaches an epiphytotic level when there is a large amount of wilting tissue in the planting and during prolonged periods of high relative humidity of the air.

Control. By careful irrigation and as frequent ventilation as possible, the humidity of the microclimate in the planting should be maintained at a minimum level. Removing dead plants and wilting leaves will help suppress the development of the disease on the crop. Controlling relative humidity is of particular importance during the flowering period, as it helps protect flowers from spotting. The most effective chemical control method is high-volume spraying with iprodione, vinclozolin, or treatment with iprodione aerosol.

Viral diseases

Viral diseases of freesia: symptoms and transmission pathways

Bean yellow mosaic. When affected by the bean yellow mosaic pathogen, leaves of some freesia cultivars remain asymptomatic, while chlorotic and then necrotic mottling appears on the leaves of others. With severe infection, plants are characterized by extreme dwarfism. On flowers of red and blue cultivars, spotting and streaking develop; they are smaller in size, deformed, with shortened petals that expose the pistil and stamens.

The non-persistent bean yellow mosaic virus is transmitted by aphids. The spread of the infection during the crop growing season is not always accompanied by symptoms, but the pathogen enters the corms and becomes very harmful to plants the following year.

Freesia mosaic. Mosaic virus of freesia does not produce symptoms on leaves, but flowers of affected plants become mottled, although they do not deform. The pathogen is also non-persistent and is transmitted by aphids.

Necrotic leaf lesions and protection methods

Leaf necrosis and severe leaf necrosis. Symptoms of necrosis often appear on the fourth leaves of plants grown from corms and on the second leaves when grown from cormels. Chlorotic spotting and streaking begin at the leaf tip and spread across the entire blade. Affected leaves become gray-brown, then necrotic. Symptoms do not develop on flowers and corms.

Severe necrosis begins with the first leaf and develops rapidly, causing similar but more pronounced symptoms than simple necrosis. Sometimes plants die before flower formation; if they do appear, the color of the petals turns out to be altered. Necrotic spots are visible on the corm, gradually covering it entirely.

When symptoms of severe necrosis develop, signs of freesia mosaic infection also appear, but only with sequential infection by these pathogens (first necrosis virus, then freesia yellows virus). The mosaic virus itself does not cause such severe symptoms. The exact cause of leaf necrosis has not been established, and attempts to transmit the infection to healthy plants have also been unsuccessful.

Control. There are no cultivars of freesia resistant to viral diseases; the only methods of protection against viruses are as follows:

• growing freesia from seed (freesia viruses are not transmitted via seed);
• careful selection of planting corms;
• constant control of aphid vectors.