SORGHUM CROP DISEASESA PRESENTATION TO IPM COURSE/FFS

PARTICIPANTS BY

MR. 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