Rusts—Many species
Rusts are easily recognized by the dry, brown, orange, purple,
reddish, or yellowish spore masses or pustules that form
on the lower leaf surfaces. Rusts infect many plants, including
aster, carnation, geranium, iris, lily, pansy, primrose,
snapdragon, sunflower, and sweet pea. The
upper surface of heavily infected leaves can become spotted
or turn yellow or brown, and infected leaves may curl, wither,
and drop prematurely. Severely
infected plants may be stunted. Some rust species cause
tissue swellings, galls, or cankers, especially on woody
plant parts. These rusts can cause stem dieback and,
rarely, can kill the entire plant.
Solutions
Rust fungi infect under mild, moist conditions. Reduce
infections by minimizing the length of time that foliage
is wet. Avoid overhead watering, which favors rust
spore germination and spread. Alternatively, water
early in the day so that plants dry more quickly. Use
good sanitation. Remove and destroy affected plants
or plant parts as soon as they appear. Prevent excess
humidity, provide good air circulation, and don’t crowd
plants. Some
plants are resistant to rust. Consider using these
to avoid rust problems. Fungicides, including neem
oil, applied at the first signs of
infection can also prevent serious damage from most rust
fungi.
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Sunflower foliage damaged by rust
Rust on rose leaves |
