Download Common Rust of Corn

Common Rust of Corn
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Common corn rust is a fungal disease that generally affects corn after tasseling.
Weather conditions such as moderate temperatures, frequent rain events, and high relative humidity
significantly impact the development and spread of the disease.
Fields should be scouted for common rust to identify early infection and potentially help manage the
disease.
Life Cycle
Common rust is caused by the fungus Puccinia sorghi
and occurs in temperate to sub-tropic areas. The
pathogen overwinters in the southern United States and
Mexico. In the summer, storms and winds blow the fungal
spores north, into the Corn Belt.
Favorable Conditions
Young leaves are more susceptible to infection with
common rust than older leaves. Once spores land on leaf
tissue, three to six hours of moisture is required for spores
to germinate and infect. Disease development is favored
by moist conditions caused by rainfall, dew, or high
relative humidity (95% or greater), and moderate
temperatures between 60° and 77° F1.
for economic yield loss is fairly low. However, if infection
occurs early in the season when plants are at early
vegetative growth stages (V3 to V7) and weather
conditions are
• Disease is favored by temperafavorable for disease
ture between 60o-77o F
development, the
and RH ≥ 95%.
potential for economic
• Small, < 1/4 inch long, pustules.
yield loss increases.
Yields can be
• Found on both leaf surfaces.
decreased about 0.5%
for each 1% of the leaf
area infected at reproductive, grain filling growth stages
Because corn products differ in their level of resistance to
common rust, the rate of disease development may be
Symptoms
Symptoms on leaves begin as light yellow spots about the
size of a pinhead. In about 7 days these chlorotic flecks
develop into reddish brown pustules. Pustules are found
on the upper and lower surface on the leaf, in contrast to
pustules of southern corn rust, which are mostly found on
the upper leaf surface. These pustules then rupture to
reveal the presence of small, cinnamon-brown, powdery
spores (Figure 1 and 2). The pustules become darker
brown to black later in the season. Pustules are often
found in bands or patches, indicating that infection
occurred while the leaf was in the whorl. Because
pustules rupture the leaf surface, severely infected plants
may show symptoms of moisture stress during hot, dry
weather, even when soil moisture is adequate2.
Effect on Yield Potential
Common rust usually appears to some degree in the
southern United States and Corn Belt every year. If
infection occurs late enough in the season, the potential
www.stewartseeds.com
Figure 1. Common rust on a corn leaf.
Figure 2. Common rust on a corn
leaf with cinnamon-brown, powdery,
circular to elongated pustules.
Common Rust of Corn
different for each product that is grown. Late-planted
corn is more likely to have higher levels of infection since it
will likely have young, more susceptible leaves during the
time when spores first arrive from overwintering locations.
Management Options
The best management option is growing corn products
that are resistant to common rust. Resistance to common
rust can be due to specific genes or general plant
resistance. General plant resistance includes a reduced
number and size of pustules and increased latent period
between infection and spore production.
Fungicides can effectively control common rust.
Fungicides are most effective against rust if initial
applications are made while there are only a few pustules
present per leaf. Use of fungicides is fairly common in
sweet corn and seed corn production. Fungicide usually
are not needed in field corn because plants are past the
most susceptible, vegetative growth stages when rust
spores arrive. However, when corn is planted later than
normal and wet weather (rains, heavy dews) occurs
frequently during vegetative growth stages, fungicide
control of rust may be economical on field corn.
Fungicide are most effective if started very early in the
disease life cycle. Two applications may be required to
prevent rust development under extremely conducive
conditions. Scouting each corn field on a regular schedule
will help determine if fungicide applications should be
considered. If significant levels of common rust are
present on the lower leaves prior to silking and the
forecast is for cool, humid or wet conditions, a fungicide
application may be
Common Rust: Pustules are
beneficial. The
found on both upper and lower
strobilurin and
corn leaf surfaces.
triazole families of
fungicides,
Southern Rust: Pustules are
including Headline
mostly found on upper leaf
AMP®
surface.
fungicide, are
effective at
preventing the spread of common rust in corn and
providing residual protection from other major fungal foliar
diseases such as gray leaf spot, northern leaf blight, and
anthracnose.
Sources:
1
Sweets, L.E. and Wrather, S. 2008. Corn Diseases. University of Missouri Extension.
IPM1001 (Verified 7/11/13)
2
Shaner, G. 2000. Corn Rust—An Epidemic? Purdue University. [Online] http://
www.agry.purdue.edu (Verified 7/11/13)
Additional resources: Compendium of Corn Diseases. APS Press; Lipps, P. et al. Common
corn rust. Ohio State University Extension. AC-0031-01. [Online] http://ohioline.osu.edu
(Verified 7/11/13)
Pataky, S. Differentiating common rust and southern rust. Plant Management Network.
University of Illinois. http://www.plantmanagementnetwork.org/edcenter/seminars/corn/
CommonRust/ (verified 7/16/13).
Pataky, S. Common rust of corn. Plant Management Network. University of Illinois. http://
www.plantmanagementnetwork.org/edcenter/seminars/corn/CommonRust/(verified
7/16/13).
Individual results may vary, and performance may vary from location to location and from year
to year. This result may not be an indicator of results you may obtain as local growing, soil and
weather conditions may vary. Growers should evaluate data from multiple locations and years
whenever possible.
ALWAYS READ AND FOLLOW PESTICIDE LABEL DIRECTIONS. Leaf Design® is a
registered trademark of Monsanto Company. Headline AMP® is a registered trademark of
BASF Corporation. All other trademarks are the property of their respective owners. Stewart
and Design™ is a trademark of American Seeds, LLC. ©2013 Monsanto Company.
CRB07182013.
For additional agronomic information, please contact your local representative