Featured Disease
Sugarcane Rust Disease (Puccinia melanocephela)
Sugarcane rust is caused by Puccinia melanocephela, an
obligate parasitic fungus. Changes in varietal susceptibility to
rust have been observed over the years, suggesting the existence
of fungal variants. Since 1978, sugarcane production in Florida
has been threatened by sugarcane rust and the pathogen is now found
almost everywhere sugarcane is grown.
Because the disease has had considerable economic impact, screening
for resistance has become an integral part of Florida sugarcane
breeding programs. Yield loss assessment due to rust is difficult,
but estimates range from a conservative 20% to 40% during severe
infestations.
Identification
Sugarcane rust is mainly a disease of the leaf. The earliest symptoms
are small, elongated yellowish spots that are visible on both leaf
surfaces. The spots increase in length, turn brown to orange-brown
or red-brown in color, and develop a slight chlorotic halo. Lesions
typically range from 2-10 mm in length but occasionally reach 30
mm. They are seldom more than 1-3 mm in width.
Infections are usually most numerous toward the leaf tip, becoming
less numerous toward the base. Pustules, which produce spores, usually
develop on the lower leaf surface. Certain cultivars, however, may
have some pustules on the upper surface.
On a highly susceptible variety, considerable numbers of pustules
may occur on a leaf, coalescing to form large, irregular, necrotic
areas. High rust severities may result in premature death of even
young leaves. Severe rust has caused reductions in both stalk mass
and stalk numbers, thereby reducing cane tonnage.
Control
The best means of control for sugarcane rust is to grow resistant
varieties. However, resistance has not been stable or durable on
certain varieties, presumably because of rust variants. For this
reason, it is highly recommended that growers diversify their varietal
holdings.
Varietal diversification may play an important role in holding
down the overall area-wide disease pressure, thereby reducing the
natural selection pressure for one particular rust variant and preserving
the durability of host plant resistance in current resistant varieties.
Sulfur is the only chemical currently registered for control of
rust on sugarcane.
Studies have shown control of the rust fungus using sulfur is either
not effective or does not offer enough economic return to be used.
No effective biological control has been found to date. Since soil
factors have been identified as being associated with rust infection
levels on sugarcane, avoid growing susceptible varieties in areas
with low soil pH and/or high levels of P and K nutrients.
Sugarcane grown in fields receiving recent applications of mill
mud is typically very prone to rust. If possible, plant these fields
with varieties that have demonstrated, durable rust resistance.
Summarized from Sugarcane Rust Disease' for more information please refer
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