19[7] Maize rust[EDFS

This leaflet is produced by the Ministry of Agriculture & Livestock, Solomon Islands, with support
from IPPSI: Improved Plant Protection in Solomon Islands, a project financed by ACIAR, the
Australian Centre for International Agricultural Research, Canberra. Authors: Helen Tsatsia, MAL &
Grahame Jackson, TerraCircle Inc.

Extension Fact Sheet 42:

Maize rust

Common name: Rust of maize

Scientific names: Puccinia polysora is recorded from Solomon Islands, but there is
another rust, P sorghi, that has not been recorded. P sorghi is found in Australia and
elsewhere. Often the two rusts occur together, requiring microscopic examination to
tell them apart.

Hosts: The rust infects maize and sweet corn. It is recorded on some grasses and
relatives of maize in other countries; it has only been recorded from maize in
Solomon Islands.

Damage

The disease is usually of minor importance. Most spots occur on the older leaves;
these dry and die earlier than those that remain uninfected, but the rust comes late in
the growth of the plant, after the seeds have been filled. Maize varieties have been
selected for resistance to this rust.

Biology and Life Cycle

The spots, produced in large numbers on both sides of the leaf (photo, left), and also
on the stem (photo, right), are round to oval, up to 2 mm; they are brown, releasing
large numbers of powdery spores. They burst open, and the spores are spread by wind
over long distances. The spores germinate in water on the surface of the plants and

infect through natural openings (stomata). Warm, humid weather, such as occurs in
Solomon Islands, favours the development of the disease.

Detection and inspection

The rust usually appears late, after the appearance of the male flower or tassel. If the
leaf is held against the light, the spots can be clearly seen. There is a dark centre
surrounded by a yellow margin.

Management

Cultural control:

Cultural control is important. The following should be done:

•  Destroy volunteer plants as the rust can only survive on living plants;
•  Plant maize during the drier times of the year;
•  The rust can be seed borne, but the spores survive for only 2 months, so infection

from seeds is not usually a risk.

Resistant varieties:

There are resistant hybrids of maize and sweet corn.

Chemical control:

The use of fungicides against this disease is not recommended as the effect on yield is
probably minor and their use would not be economic. If needed, copper and
mancozeb would be effective.