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Plantwise Technical Factsheet

sugarcane downy mildew (Peronosclerospora sacchari)

Host plants / species affected
Saccharum officinarum (sugarcane)
Zea mays (maize)
List of symptoms/signs
Growing point  -  mycelium present
Inflorescence  -  twisting and distortion
Leaves  -  abnormal colours
Leaves  -  fungal growth
Leaves  -  necrotic areas
Leaves  -  shredding
Stems  -  dieback
Stems  -  distortion
Stems  -  mycelium present
Whole plant  -  dwarfing
Symptoms
Sugarcane

Symptoms on sugarcane may differ, depending on when infection occurs (Mukerji and Holliday, 1975). When diseased setts are used, the young plant may die or become generally stunted, and discoloured. Infection at a later stage causes pale green to yellow longitudinal stripes which increase in length after each leaf unfolds. The stripes may become a chlorotic mottling, later necrotic with oospores lying between the veins.

Later infections cause abnormal stem elongation ('jump up canes'); stems are weak, have more internodes and fewer shorter leaves which may not unfold. Shredding is observed, caused by the disintegration of leaf tissue.

Maize

Maize infected at a very early growth stage causes stunting and death.

Local lesions lead to systemic infection. Initial lesions which are small, round, chlorotic spots on the leaves, appearing two to four days after infection. Systemic symptoms appear as pale yellow to white stripes or streaks at the base of the third to sixth oldest leaves. Several streaks may form in each leaf and may extend the length of the leaf.

On the leaves of some varieties or on older leaves, streaks may be narrow and discontinuous. On late-infected or mildly infected plants, streaks may disappear as plants approach maturity. White, downy, or powdery masses of conidia and conidiophores appear on both leaf surfaces as well as the leaf sheaths and husks. This downy growth is usually produced at night at moderate temperatures (25°C), especially when dew is present.

Plants may be distorted with small, numerous, poorly-filled ears and improperly formed tassels. Ear shanks may be elongated. Sterility may also occur.
Prevention and control
Cultural Control and Sanitary Methods

In view of the epidemiological knowledge of sugarcane downy mildew, it has been recommended that control measures include removal of infected maize and other hosts within at least 42 m of newly sown seed (outside the range of conidial dissemination); rogueing of any infected plants from adjacent fields; sowing at the same time within an area to prevent cross-infection during different stages of growth; removal and burning of infected plants to prevent the provision of sources of primary infection; and using seed only after drying to 13-14% moisture (Lal et al., 1977; Mikoshiba, 1983; Payak, 1975).

Host-Plant Resistance

Resistant maize hybrids have given give good control of sugarcane downy mildew (Lal et al., 1973; Schmitt and Freytag, 1977; Sun, et al., 1976).

In sugarcane, the variety ROC20, released in April 1994, was selected from the cross 69-463 X 68-2599 made in 1983 has been found to be highly resistant to P. sacchari. In Taiwan, disease patterns due to infection by P. sacchari in seven sugarcane varieties grown in Huwey (sporadic disease), Hsinying (severe) and Pingtung (marginal damage) were compared from survey records for 1965-78. Varietal resistance was conditioned by environment. The resistance rating based on records was similar to that based on field tests. In the resistant varieties F156, F161 and F146, disease development depended primarily on the region in which the variety was planted, while in the resistant varieties F160, F167 and NCo310, environment was the more important (Schmitt and Freytag, 1977).

Chemical Control

Due to the variable regulations around (de-)registration of pesticides, we are for the moment not including any specific chemical control recommendations. For further information, we recommend you visit the following resources:

Impact
Periodic epidemics of sugarcane downy mildew have occurred in Taiwan. Between 1960 and 1964, 70% of the fields of one variety were affected (Payak, 1975; Sun et al., 1976). It is not as severe in other south-east Asian countries or in Australia. The damage to maize crops is usually greater than that to sugarcane (Payak, 1975, Sun et al., 1976). In Fiji, sugarcane downy mildew at one time caused major losses sugarcane growing areas, but these were reduced to very low levels by the release of resistant cultivars coupled with an intensive system of disease control (Daniels et al., 1972).

In 1965-78, P. sacchari infection of sugarcane and maize and host factors were compared in Taichung (nonepidemic), Huwey (sporadic), Hasinying (main damage) and Pingtung (marginal damage) geographical regions of Taiwan. Disease factors were intensity, extent, frequency, and duration. The host factors were: planting acreage of sugarcane and maize, the ratio of the two crops; ratio of disease-conducive cultivars planted and disease potential index of the sugarcane population; ratio of susceptible and resistant maize, and the practice of maize interplanting. A good correlation was found with the ratio of disease-conducive sugarcane, the disease potential index of the sugarcane population and disease incidence on sugarcane. A failure to find a correlation between disease on sugarcane and the maize host population may be due to inadequacy of historical data. The host factors accounting for the different levels of disease intensities in the different regions were also discussed (Poon et al., 1982).
Related treatment support
 
External factsheets
CIMMYT Plant Pest and Disease Factsheets, Centro Internacional de Mejoramiento de Maiz y Trigo (CIMMYT) (International Maize and Wheat Improvement Center), English language
Pestnet Factsheets, Pestnet, English language
PlantVillage disease guide, PlantVillage, English language
BSES Factsheets, BSES Limited, English language
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