Unit 1: Corn Diseases

Unit 1: Corn Diseases Corn Smut Caused by fungus: Ustilago maydis Most widely recognized corn disease Symptoms: Complete barrenness in most plants Result: Reduced grain development ~30% yield loss

Unit 1: Corn Diseases Appears as galls on both the ear and stalk White at first, but develop into dark lesions w/ dark spores inside whitish membrane Galls break and scatter spores Found on: Ears Near midrib of the leaf Nodal buds on the stem More likely to attack vigorous growing plants Not poisonous to livestock

Unit 1: Corn Diseases Smut organism lives in the soil Treatment: Seed disinfection or treatment is ineffective, except to prevent spread to new fields Treatment: Crop rotation Don’t spread manure smut infested manure on fields Many resistant hybrids

Unit 1: Corn Diseases Head Smut Galls on ear and tassels Entire destruction of these structures Mostly affects Southwestern & Pacific Coast states Also caused by fungus living in the soil, or on seed Galls dispense spores just as corn smut

Unit 1: Corn Diseases Control: Rotate field out of corn for 2 years Used treated seed to prevent infestation into other fields Most field corn hybrids resistant, sweet corn varieties are susceptible

Unit 1: Corn Diseases Root, Stalk, & Ear Rot Effects: Reductions in field stand Reductions in plant vigor Chlorosis Barrenness General blighting of the plant Rotting of the ear

Unit 1: Corn Diseases Stalk Rot Caused by fungal infestations: Ear rot: Gibberella, Fusarium, Aspergillus, & Pythium spcs. Root rot: Pythium, Gibberella, Diplodia spcs. Stalk rot: Fusarium, Gibberella, Diplodia Stalk Rot Genetic resistance not available

Unit 1: Corn Diseases Problems tend to occur under certain conditions Symptoms prevalent when plant is stressed Stresses: High N w/ low K High moisture mid to late season after dry early season High moisture stress early in season & during grain fill High leaf disease pressure Insect damage Select hybrids resistant to the above stresses & have good soil fertility

Unit 1: Corn Diseases Ear rot Can continue growth and damage after corn is harvested Mold damage to corn when moisture of grain in storage is >14% Rot and darkening of the corn embryo (called Blue Eye) Nearly all organisms are carried on decaying corn residues or in the soil

Unit 1: Corn Diseases Root rot Some also carried on the seed Molds are typically evident on the ear Can also observe dark bodies on outside or inside of old stalks Root rot Develops on infested kernels Crown roots rot, weak plants die Subcrown roots appear dry, brown instead of healthy white

Unit 1: Corn Diseases Little evidence that root rot fungi advance up the stalk Most serious under dryland conditions Stalks will die and fall Prevention: Use disease-free treated seed Plant at proper soil temperature Balance soil nutrients Plant resistant hybrids

Unit 1: Corn Diseases Leaf Diseases Chemical seed disinfectants are effective Captan, metalaxyl, fludioxonil Increase yield, stand, vigor Leaf Diseases Northern Corn Leaf Blight Infection of the lower leaves Boat-shaped, grayish lesions Spread to other leaves in cool, damp weather Can cause leaf death

Unit 1: Corn Diseases Southern Corn Leaf Blight Treatment: Use resistant hybrids Has caused losses mostly in the East & South Significant damage as far West as NE Southern Corn Leaf Blight Usually not considered a problem Major infestation in 1970 w/ major losses throughout corn belt Needs warm, moist weather to flourish Lesions form on leaf, ear shanks, husks Can infect the ear

Unit 1: Corn Diseases Gray Leaf Spot Problem since 1925 from Atlantic states to eastern corn belt Cool temps w/ prolonged overcast days Lesions can be confused w/ other blight diseases Mature lesions are rectangular restricted by leaf veins Signified by yellow halo Lesions can join causing blight of large portion of the leaf

Unit 1: Corn Diseases Stewart’s Wilt Goss’s Wilt Found throughout the Corn Belt Carried by the corn flea beetle Symptoms: Long, water-soaked lesions that can extend the length of the leaf Leaves turn necrotic Goss’s Wilt Water-soaked lesions forming next to leaf veins Stalks can be discolored

Unit 1: Corn Diseases Next time— Quiz! Affected plants can be stunted and die at any stage Bacterium overwinters in corn debris near soil surface and in the seed Next time— Quiz!