following question was sent to the P&PDL diagnosticians here
at Purdue University:
Question: Over the past year I prepared and planted 5 acres
of a rye grass mix and have seen fine growth. Just recently, over
the past few weeks, I've noticed a yellow/orange discoloration
appearing on the grass. Initially, I thought it was simply due
to a lack of water and subsequent browning of the grass. Today
I realized that it is due to a fine powder that appears rust colored
on my shoes as I walk through the grass. Is this a fungus?--with
spores coloring my shoes? Can you identify what is causing my problem
and recommend a cure? (July 14, 1998)
Question: Last year, I put in a new lawn. It's
doing well, except, recently, it began leaving a rust-colored powder
on my shoes. Is that something that will affect the health of my
Answer: Check out the information
from one of our past "What's Hot" issues: http://www.btny.purdue.edu/PPDL/hot96/What_Was_Hot8-19.html#Rust_in_Turf
The powder is actually millions of microscopic
spores produced by a fungus called rust. There are several different
rust fungi that cause rust. The most common one on Kentucky bluegrass,
annual bluegrass, fescues and ryegrasses is Puccinia graminis.
A separate species, Puccinia zoysia can infect zoysia grass.
Rust becomes a problem when grass plants are growing slowly.
When grass plants are growing fairly rapidly, leaf tissues are
removed by mowing at relatively frequent intervals, and the disease
does not become apparent. With grass plants that are growing slowly,
the fungus has sufficient time (7-14 days) to produce the microscopic
spores in infected leaf tissue. These spores are then wind-blown
or splashed by rain or irrigation to other leaves, where new infections
can occur. Consequently, the disease can become very severe when
certain weather conditions occur when the grass is growing slowly.
Leaf infections occur most frequently when days are dry and windy
followed by heavy dew formation at night. The dry, powdery spores
are easily disseminated by wind currents.
Rust, by itself, rarely kills a grass plant, unless other stress
factors are involved. Rust infected plants are weakened. When the
disease continues into late fall, infected plants may become more
susceptible to winter injury. Young seedlings are highly susceptible,
and proper water and fertility management may be required for early
The rust fungi rarely survive the winter in Indiana. The disease
organisms survive winters in infected tissues in the southern and
southwestern states. Spores of the fungi are wind-borne in spring
and summer from those areas and the disease moves northward into
Indiana and surrounding states, usually in July and August.
Control of rust in the home lawn is best accomplished by fertilizing
and irrigating, as needed, to promote grass growth. Do not promote
excessive growth. Water infrequently, but deeply. Irrigate during
the early part of the day. Irrigate at a time that will permit
complete leaf dryness before dew formation. Watering in the evening
will increase the length of time that free moisture is on the leaves
and will increase the chances of infection. Mow frequently and
collect clippings when possible. Several fungicides will aid in
the control of rust, but multiple applications are generally required,
and you might choose to achieve control via management practices
first. You may find products containing chlorothalonil or mancozeb
being sold under various trade names at garden supply stores or
Information listed is valid only for the state of Indiana.
The information given herein is supplied with the understanding
that no discrimination is intended and no endorsement by the
Purdue University Cooperative Extension Service is implied. Any
person using products listed assumes full responsibility for
their use in accordance with current direction of the manufacturer.
Purdue University is an equal opportunity/equal access institution.