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From the Pests of Ornamental Series
Fusarium Yellows, Wilt, Bulb Rot and Basal Rot
Description: A gradual yellowing of the tips of the oldest leaves is first noticed with a checking in the rate of leaf elongation (stunting). The spike, including the florets, may also be stunted and faded in color. At the base of the plant (near the mother corm), a blackening of the root bases, extending into the corm is seen. The yellowing of the leaves at first may be confined to one side of the leaf, but eventually the entire leaf is affected. Browning and death of the entire plant follows. Wilting of the young spikes may result in a crooked stem just below the flower. Curving of the leaves or spike is also observed near the ground.
If the corm is cut in half, a brown discoloration of the corm is seen. The corms begin to decay in the core and then infection spreads out from the core and finally to the surface at the nodes.
Scab (Neck Rot)
Description: Under wet conditions, and especially in heavy, poorly-drained soils, numerous very tiny, reddish-brown, slightly raised specks are seen first on the leaves (easily confused with thrip damage). These specks are numerous at the fleshy base of the leaf. In wet weather, elongated dead areas (soft and watery) occur when these specks or spots run together.
The soft rot causes the plant above ground to fall over. A shiny, varnish-like ooze is generally seen on leaves in humid weather.
Circular sunken spots with raised margins are seen on the corms, especially at the base.
A shiny, vamish-like ooze is seen over the surface of these spots. The scabby areas do not extend far into the flesh of the corm and may be removed leaving a depression. On the husks, elongated spots or lesions are dark brown to coal black. Holes are left with a rough coal black margin.
Septoris Leaf Spot and Corm Rot (Hard Rot
Description: Circular, small, brown or purple-brown spots are seen on the leaves. Later the spots are dark brown with a lighter center containing black bodies.
Young plants, crowded in rows or beds, are sometimes so badly infected that large numbers may be killed.
Sunken, irregular-shaped, shallow, dark-brown to black areas of decay or hard rot occur on the corm. The corms almost rot entirely.
Sclerotinia Dry Rot
Description: Soil moisture is very important in development of this disease. In wet seasons it may be very serious and is more prevalent in heavy, poor-drained soils. Young plants and those grown from small corms are most susceptible to dry rot. The fungus attacks the leaves and stem (at or below the soil line) and roots. The core of the corm shows no discoloration as that found in corms attacked by the fungus Fusarium. The lesions or spots on the corms are sunken and dark brown to black with raised lighter-colored margins. Large, irregular areas are formed by the spots running together.
A varnish-like ooze is not associated with these spots as in Scab. The husks may be either completely discolored or show isolated brown spots. Small black bodies are found on husks (just above their point of attachment to the corm), corm lesions, and on dead leaves and stems (below the soil line).
Botrytis Leaf Spot
Description: Small, brown, round spots with light brown centers and defined margins occur on leaves. If these spots merge together, they are elongated and irregular. A zone of pale yellow may be seen around the larger spots.
Stemphyllum Leaf Spot
Description: Small, round yellow spots with red or brown dots in the centers occur on both sides of the leaf (especially toward the leaf tip). Premature yellowing, failure to bloom, and entire destruction of plants may result under severe infection.
Curvularia Leaf Spot
Description: Oval, brown spots occur on leaves, stems, and petals. In damp weather, masses of black powdery spores are seen on the spots. Dead spots are surrounded by dark brown rings outlined by yellow leaf tissue.
The greatest damage is on the stems and florets of the spike making them unworthy as cut flowers.