Corn Dis Rev. 4/15 Corn Seed Diseases

Disease Cause Symptoms Control

SEED ROTS Pythium spp., a. Seed Rots - seed rots before 1. Sow injury-free seed of AND Fusarium spp. germination. resistant varieties. SEEDLING and several b. Damping-off and seedling 2. Plant seed in warm, fairly o BLIGHTS others blight. Soft rot of stem near moist soil (above 12.8 C): ground. proper seedbed preparation; c. Seedling Wilt - gray correct placement of fertilizer, discoloration starting at the herbicide, and other leaf tips. pesticides. d. Root Rots - water-soaking, 3. Use seed-protectant fungicides, browning and sloughing of e.g. fungicide components in rootlets. Acceleron, CuriserMaxx, etc.

Corn Stalk Rots and Root Rot

Disease Cause Symptoms Control

o CHARCOAL Macrophomina Attacks seedlings or plants 1. Soil temperatures above 37 C ROT phaseoli approaching maturity. Brown are favorable for disease. water-soaked lesions on roots 2. In irrigated areas, charcoal rot later turning brown. Causes can be minimized by premature ripening, shredding and maintaining moist soils. breaking at crown. Very small 3. Balanced soil fertility; avoid black sclerotia on vascular stands high levels of N and low levels give interior of stalk a charred of K. appearance. 4. Reduce plant population.

GIBBERELLA Gibberella zeae Shredding of pith tissue, usually a 1. Full-season hybrids are STALK reddish coloration of pith. generally more resistant. ROT Softening and discoloration of 2. Balanced fertility, high N and exterior of lower internodes. low K increase disease Sudden onset of gray-green color severity. of leaves of early infected plants. 3. Lower plant populations.

DIPLODIA Diplodia maydis Diseased stalks are weakened 1. Same as Gibberella Stalk Rot. STALK and break readily. Occasionally ROT minute black pycnidia, the fruiting bodies of the fungus, form in the fall just beneath surface of lower internodes. Pith may be disintegrated and discolored.

FUSARIUM Fusarium Same as with other stalk rots. No 1. Same as Gibberella Stalk Rot. STALK moniliforme distinct coloration of the pith sets ROT stalks apart of different diseases.

ANTHRACNOSE Colletotrichum Unlike other common stalk rots, it 1. Same as Gibberella Stalk Rot. STALK graminicola may rot several internodes of the ROT plant. Most easily recognized late 2. Control of corn borer can be in the season by the shiny black important, as the fungus is color on the outer stalk, which known to enter through its may be uniform or blotchy. feeding sites. Internal stalk tissues are often blackend or discolored, and stalks can be easily crushed.

3 Corn Dis Rev. 4/15

Corn Ear Rots

Disease Cause Symptoms Control

DIPLODIA Diplodia maydis Husks of early-infected ears appear bleached or 1. Early harvest. EAR ROT (syns. Diplodia straw-colored. Lightweight ears usually stand 2. Proper storage; zeae and upright with inner husks adhering tightly to one below 18% Stenocarpella another on the ear because of mycelial (mold) moisture initially maydis) growth between them. Black minute pycnidia for ears, 15% for may be scattered on husks, floral bracts and shelled grain. sides of kernels. Ears infected later in growing 3. Crop rotation season may show no external symptoms, but and fall tillage of when ears are broken, a white mold is found residue can growing between kernels whose tips are reduce disease discolored. Infection usually begins at ear base. levels.

FUSARIUM Fusarium A salmon-pink to reddish-brown discoloration 1. Same as KERNEL moniliforme first appears on caps of individual kernels or Diplodia Ear Rat. OR groups of kernels scattered over ear. A powdery EAR ROT or cottony-pink mold growth develops on infected kernels. Fungus commonly becomes established around channels made by earworms or corn borers. Disease favored by dry, warm weather.

GIBBERELLA Gibberella Characterized by a reddish mold that appears at 1. Plant resistant EAR ROT zeae the tip and grows down the ear. Seldom does the varieties. OR fungus colonized the entire ear. If infected early, 2. Balanced fertility, RED ROT entire ear may rot and be covered with a pinkish high N and low K increase mycelium that causes the husk to tightly adhere to the ear. Husks and ear shanks may be covered disease severity. 3. Lower plant with superficial, blue black perithecia. populations.

PENICILLIUM Penicillium Occurs primarily on ear injured mechanically or 1. Reduce EAR ROT oxalicum by insects. A powdery, green or blue-green mold mechanical and OR occurs on and between kernels, usually at ear insect damage. BLUE EYE tip. 2. Harvest as soon as possible. 3. Dry corn when above 15% moisture for shelled corn.

Corn Storage Rots

Disease Cause Symptoms Control

SEVERAL Aspergillus spp. Storage rots may develop on ear or 1. Reduce moisture as rapidly KINDS OF Penicillum spp. shelled corn in storage, causing a as possible to 13% and STORAGE reduction in feed and market value. aerate to maintain a ROTS Aspergillus flavus produces a poison uniform temperature of 4 to o toxic to man and animal. Invasion of 10 C throughout the bulk. whole kernels in bins results in 2. Chemical storage additives discoloration, heating, caking and are effective if used before mustiness. rots occur.

4 Corn Dis Rev. 4/15

Corn Leaf Diseases

Disease Cause Symptoms Control

NORTHERN Exserohilum NCLB is recognized by long elliptical 1. Some varieties may CORN turcicum gray-green or tan spots on leaves (2.5 to have some LEAF (syns. 15cm). Lesions first appear on lower resistance. BLIGHT Helminthosporium leaves, as season progresses until 2. When practical (NCLB) turcicum) nearly all leaves are covered. Often fungicides may be spores are arranged in concentric zones applied to leaves so that a faint targetlike pattern in when lesions are first lesions is evident. Kernels are not found. attached. Disease is retarded by dry weather.

SOUTHERN Bipolaris maydis Lesions are generally parallel-sided, 1. Use resistant CORN (syns. grayish tan and range in size from varieties. LEAF Helminthosporium minute chlorotic flecks up to 3 cm. 2. When practical yellowish-green halos surround leaf BLIGHT maydis) fungicides may be lesions. The new race attacks all parts (SCLB) applied. of corn plant. 1. Plow under infected GRAY Leaf spots of this disease usually appear Cercospora leaves in the fall. LEAF several weeks after silking as long, zeae-maydis 2. Practice rotation. SPOT narrow, tan lesions contained within vein 3. Use resistant varieties margins, ranging up to 1/2 by 2-3 cm. . Lesions become gray and can eventually 4. W hen practical fungicides coalesce across the entire leaf. may be applied.

ANTHRACNOSE Colletotrichum Symptoms vary greatly based on 1. Plow under crop LEAF BLIGHT graminicola variety, age of leaf, and environment. residue in the fall. Small, water-soaked leaf spots that are 2. Rotate. oval to elongated can appear at any 3. Avoid susceptible growth stage. Spots can become tan varieties. later and black acervuli may develop.

Corn Rusts

Disease Cause Symptoms Control

COMMON Puccinia sorghi Oval to elongate cinnamon-brown pustules 1. Plant resistant varieties CORN scattered over both surfaces of leaves. As 2. Apply timely fungicide RUST corn matures pustules become brownish applications when black. Pustules may appear on any practical above-ground parts of plant. Pustules break through epidermis early in their development. This is one characteristic that differentiates this rust from Southern Corn Rust.

SOUTHERN Puccinia Pustules are definitely lighter in color, 1. Plant resistant varieties CORN polysora smaller and more circular than those of 2. Apply timely fungicide RUST common rust. Epidermis remains intact applications when over postules for a longer time than practical common rust, but eventually ruptures.

5 Corn Dis Rev. 4/15

Corn Virus and Mycoplasma-Like Diseases

Disease Cause Symptoms Control

MAIZE Maize Dwarf Similar to corn stunt. Shortening of upper 1. Use resistant DWARF Mosaic Virus internodes that imparts a "featherduster" varieties. MOSAIC (MDMV) appearance to plants. Leaves have a finely 2. Eradication of (MDM) stippled mottle or mosaic of light and dark johnsongrass in field. (Corn Stunt) green on youngest leaves. As plants 3. Destruction of the mature, mosaic disappears and leaves aphid vector is not become yellowish green and frequently feasible from a show blotches or streaks of red. Severely practical standpoint. infected plants are barren or show poor seed set. Symptoms are most severe on plants infected early.

MAIZE Maize Chlorotic Fine chlorotic striping associated with small 1. Plant tolerant CHLOROTIC Dwarf Virus visible veins. Chlorotic stripes may extend hybrids. DWARF (MCDV) for some distance and are parallel to veins. 2. Plant early to avoid (MCD) As plants age, leaves may take on a leafhoppers. yellowish and reddish discoloration. 3. Eradicate Stunting is very pronounced. Horizontal johnsongrass. splitting of leaf margins may occur. Transmitted by leafhopper Graminella nigrifrons.

CORN Mycoplasma-like Small circular to elongated, chlorotic spots 1. Control leafhoppers, STUNT organism (Not a develop at base of young plants. Often corn stunt agent is (Not found virus) these coalesce and become elongated transmitted by five in Tennessee) stripes that may be discrete or diffused. leafhopper Chlorosis, redding of leaves, proliferation of species. ear shoots and suckers and pronounced 2. Use resistant reduction in internode length are varieties. characteristic symptoms. May be confused with Maize Dwarf Mosaic.

Corn Smut Disease

Disease Cause Symptoms Control

COMMON Ustilago maydis Conspicuous galls are first covered 1. Avoid injury or susceptible SMUT with white membrane. Galls are varieties. powdery black inside with masses of 2. When practical, remove spores. Galls occur on any part of galls before they break plant and can be almost any size and open. shape. 3. Rotate when possible. 4. Avoid injury from herbicides.

6 Corn Dis Rev. 4/15

Sorghum Diseases

Disease Cause Symptoms Control

SEEDLING Fusarium sp., Pre-emergent death of seedlings Use seed treatments, BLIGHT Pythium sp., accompanies by water-soaked and crop rotation with non- Helminthosporium sp. rotted seedling tissue. Post- grass crops. Use high- emergent unthrifty seedlings or quality seed. Control death of seedlings accompanies by nematodes and soil rotted roots, stems, etc. insects.

ANTHRACNOSE Colletotrichum Leaf spots that are circular to oval Plant resistant varieties. graminicola which can be as large as 1" in Treat seed and use crop diameter but usually smaller. rotation. Early planting Young lesions are reddish to purple may escape some and appear as small dots. Mature damage. lesions have distinct dark purple When practical margins with lighter colored fungicides may be centers. Lesions often more applied. distinct along midrib. Infects other parts also. Symptoms first appear as small ZONATE Gloecercospora Purchase disease-free spots red to brown in color LEAF SPOT sorghi seed. Treat seed. accompanied by water-soaked Forage sorghum is more tissue. Semi-circular to circular susceptible than grain bull's-eye spots later occur. These sorghum. spots range from small spots to 3" When practical or more in diameter. Rings of fungicides may be purple and brown appear applied. alternately. small red GRAY LEAF Cercospora Leaf spots start as spots Plant resistant SPOT sorghi that enlarge to form narrow, varieties. Treat seed rectangular lesions delimited by and use crop rotation. veins. Lesions may coalesce to form When practical longitudinal stripes or irregular blotches fungicides may be and possibly cause leaf death. Lesion applied. color can vary from dark red, purple to straw colored. Lesions may have a grayish cast due to sporulation.

HEAD Caused by several Seeds, glumes, and rachis parts Plant resistant MOLD fungi blemished by purple spotting or varieties. No other presence of pink, red, brown, or control at present green mold growth. time.

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