CORN CROP DISEASESA PRESENTATION TO IPM COURSE/FFS PARTICIPANTS
BYMR. ALLAH DAD KHAN
PROVINCIAL COORDINATOR IPM KPK FOR MINFAL PAKISTAN
SEED AND SEEDLING DISEASES
SYMPTOMS:
Disease damage may appear similar to some environmental stress, but general and specific symptoms can help with diagnosis.
General effects: reduced emergence, slow growth and stunting in a random or circular pattern, wilting, chlorosis/yellowing, post-emergence damping-off.
Specific symptoms of seed and root infections include: rotted seed and seedlings before or after emergence; red/yellow discoloration of leaves; complete or partially rotted roots with firm or soft, brown-reddish- to gray lesions or decay; discolored and soft coeleoptile; death of leaf tips; wilting; and sunken,discolored lesions on mesocotyl.
Leaf spots and streaks can also occur, resulting from anthracnose and Stewarts wilt infections
SEED AND SEEDLING DISEASES
PATHOGEN INVOLVED:· DISEASE MANAGEMENT:PLANT Some common genera of `fungal'
pathogens that cause one or more of the symptoms noted above are Stenocarpella (Diplodia), Pythium, Rhizoctonia, Fusarium, Colletotrichum, and Penicillium.
Two bacterial pathogens that can affect corn seedlings are Erwinia [=Pantoea] (Stewart's Wilt) and Pseudomonas (holcus spot).
The source of these pathogens is soil, infested residue remaining from previous years crops, or infested seed.
Nematodes can also damage corn seedlings, especially in sandy soils.
into soil greater than 50-55°F.
Use seed treated with fungicides. However, these chemicals are most effective for about 2 weeks after planting depending on soil water content and temperature.
The primary fungicidal seed treatments used are of two main groups
FUSARIUM STALK ROT
SYMPTOMS
Similar to Diplodia and Gibberella stalk rots
Inner stalk will have a light pink discoloration, but no black specks (fungal fruiting bodies) will be present in or on the stalk
Ears may be small and lower nodes may be shredded or break
Eventually, the stalks may die and lodge
FUSARIUM STALK ROT
PATHOGENS INVOLVED DISEASE MANAGEMENT
Fusarium moniliforme, F. proliferatum, and F. subglutinans (a fungus)
These fungi are found wherever corn is grown
Overwinters in crop residue
Use hybrids that are resistant to other stalk rot diseases.
Minimize all crop stresses
Control insects Use proper plant
population
BACTERIAL STALK ROT
SYMPTOMS
Symptoms are similar to those of Pythium stalk rot
One or more of lowest internodes will turn tan to brown and become water soaked, soft, or slimy and there may be a foul odor
Upper leaves wilt and a soft rot can occur at the base of the whorl, and this may spread rapidly down the plant and cause lodging
BACTERIAL STALK ROT
PATHOGEN INVOLVED DISEASE MANAGEMENT
Erwinia chrysanthemi pv. zeae (bacterium)
Wide host range, including monocots as well as dicots
Infection sites are stomata, hydathodes, or the wounds of leaves or stalks
Overwinters in stalk residue on the soil surface line
May be transmitted by larvae of the maize borer
Incorporate soil debris with fall plowing
Avoid flooding and excessive overhead irrigation
ANTHRACNOSE STALK ROT
SYMPTOMS
Symptoms usually most apparent just before crop maturity
Uniform or blotchy, shiny, black color on the outer stalk
Inner stalk may also be black and systemically infected, or may not have any discoloration
Several internodes of the plant may be rotted and easily crushed with finger pressure
The plant above or below the ear may die and lodging may result.
ANTHRACNOSE STALK ROT
PATHOGEN INVOLVED DISEASE MANAGEMENT
Colletotrichum graminicola (a fungus)
It is the same that causes the Anthracnose leaf blight disease
The only common stalk rot pathogen that can cause a leaf blight disease
Overwinters in corn residue
Use disease resistance hybrids
Maintain balanced fertility
Reduce plant stress Control the corn borer
CHARCOAL ROT
SYMPTOMS
Symptoms may first appear similar to Fusarium, Diplodia, & Gibberella stalk rot
A key sign of charcoal rot is gray or black discoloration in the inside the rind due to the presence of many tiny, black sclerotia (can be seen with hand lens)
Plant may die and lodge
CHARCOAL ROT
PATHOGEN INVOLVED DISEASE MANAGEMENT
Macrophomina phaseolina (a fungus)
Has a very wide host range that include sorghum and soybean.
Infects soybeans more often than corn in the Midwestern U.S.
The pathogen overwinters on host crop residue
Use hybrids resistant to Diplodia and Gibberella stalk rot.
Minimize early senescence of stalk tissue
Reduce moisture stress
DOWNY MILDEW OF MAIZE
SOUTHERN CORN LEAF BLIGHT
SYMPTOMS:
Common lesions are elongated, tan lesions between veins on leaves
Different isolates of this pathogen will cause lesions of different sizes
Race O causes long, tan, lesions that have brown borders on leaves.
Lesions will develop differently on various inbreds and hybrids
SOUTHERN CORN LEAF BLIGHT
PATHOGEN INVOLVED: DISEASE MANAGEMENT:
Cochliobolus heterostrophus (=Bipolaris maydis) (a fungus)
Overwinters in corn residue Especially prevalent in areas with a
warm, humid climate Three races known of this pathogen:
race O, race T, and race C Race T and race C are known to be
specifically virulent to corn with cytoplasm male-sterile T and cytoplasm male-sterile C, respectively. Since the switch from cytoplasm male sterile T to normal cytoplasm corn, race T is not considered to be a threat.
Use of resistant hybrids Crop rotation Tillage may be helpful