Traditionally, maize has been grown
in Asia primarily as a subsistence food crop. In recent years, the per capita
consumption of maize as a food crop has declined while the use of maize as a
feed crop for livestock has increased. Maize yields are especially low in
India, Indonesia and the Philippines
– approximately one-half of the
yield of maize in China, Thailand and Vietnam.
The downy mildew diseases have been
a major limiting factor in production of maize in Asia throughout this century.
Java downy mildew is of great importance in Indonesia, where depending on the
year, 20-80% of the total maize harvests are being lost as a result of downy
mildew damage [1]. Philippine downy mildew is the most serious downy mildew
disease in the Philippines, where the damage usually affects 40-60% of the
total maize yield [1]. Brown stripe downy mildew incidence is greatest in
regions of high rainfall in India and has been reported from most maize-growing
regions of that country with yield losses ranging from 20-90% [2].
Downy mildew infections occur both
as a result of soil borne overwintering spores which infect young plants and
from spores produced by nearby infected hosts such as sugarcane or other
grasses. Once inside maize plants, the fungus moves systemically throughout the
plant. Infected leaves show discolored streaks and have a mildew growth which
becomes a source of spores that spread the disease to other plants. Most of
early infected plants usually die within a month. When cobs are formed, they
are small and poorly-filled. Infected plants have weak and thin stems and poor
root growth.
Research has demonstrated that
systemic fungicides applied as seed treatments and/or foliar sprays provide
excellent control of downy mildew [3]. Yield increases of 8-10% are possible
through seed treatment alone [4]. Research has shown that seed treatment
combined with one foliar spray to control brown stripe downy mildew increased
maize yield by 34% [5]. Seed treatments protect young seedlings from soil-borne spores; as the fungicide is taken up systemically in
the developing seedling, young plants are protected from spores moving into the
crop [6].
Fungicides are widely-used on maize crops in China, Thailand and
Vietnam, but are used on less than 5% of the maize hectares in India, Indonesia
and the Philippines [7] [8]. Recently, as a result of higher maize prices in
India, seed treatments to control downy mildew are being recommended to farmers
[9].
References
1.
Mikoshiba, H. 1983. Studies on the Control of Downy Mildew Disease of
Maize in Tropical Countries of Asia. Technical Bulletin of the Tropical
Agricultural Research Center No. 16.
2.
Putnam, M.L. 2007. Brown stripe downy mildew (Sclerophthora rayssiae
var. zeae) of maize. Plant Health Progress. Published online November 8, 2007.
3.
White, D.G., Ed. 1999. Compendium of Corn Diseases, Third Edition. APS
Press.
4.
Sharma, R.C., C. De Leon and M.M. Payak. 1993. Disease of maize in South
and South-East Asia: problems and progress. Crop Protection. 12(6):414.
5.
Lal, S., S.C. Saxena and R.N. Upadhyay. 1980. Control of brown stripe
downy mildew of maize by Metalaxyl.
Plant Disease. 64(9):874-876.
6.
Williams, R.J. 1984. Downy mildews of tropical cereals. In Advances in
Plant Pathology, Volume 2. Academic Press, London.
7.
AMIS Global web-based market data. 2012. Available at:
www.amisglobal.com.
8.
Gerpacio, R.V., et al. 2001. Maize in the Philippines: Production
Systems, Constraints, and Research Priorities. CIMMYT.
9.
Maize cultivation to be profitable: Tamil Nadu Agricultural University.
The Hindu Newspaper. Published 07.05.2011.
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