Diplodia Ear Rot
Symptoms of Diplodia Ear Rot
- Early infected plants have tan spots on husks or bleached husks that are obvious from a distance.
- Husks on severely infected plants dry down well before the rest of the plant.
- White mycelial infection progresses from base of ear to tip.
|Pycnidia, black fungal fruiting structures, may be present on kernels, cob
or husk (below)
- Extensive mycelial growth causes ears to remain erect and husks to bind tightly to ear.
- Rotted seed may germinate prematurely (vivipary).
- Later-infected plants are less damaged and may show no obvious symptoms on husks.
- Mycelial growth may be limited to white growth between kernels and on the cob.
Facts on Diplodia Ear Rot
- Caused by the fungus Stenocarpella maydis, previously known as Diplodia maydis.
- Wet weather during grain fill and upright ears with tight husks promote Diplodia.
- Can cause ear rot, stalk rot and seedling blight.
- Corn is only known host.
- Wet weather plus moderate temperatures allow infection to occur if spores are present from early silking until two to three weeks after silking.
- Diplodia is highly dependent on quantity of infected, unburied corn residue (stalks, cobs and kernels).
Impact on Crop
- Reduced grain quality and reduced yield due to lower kernel size and test weight.
- If infection occurs early, some ears may not produce harvestable grain. Less damage results if ear is more developed when infection occurs.
- Fungal growth is most common during milk, dough and dent stages.
- Mycotoxins are not associated with this disease but some animals may reject infected feed.
Management of Diplodia Ear Rot
- Hybrid selection – Hybrids differ in their susceptibility to Diplodia ear rots, but all will show some damage under severe conditions.
- Pioneer’s hybrid ratings range from 4 to 6 for most hybrids (9=resistant), indicating that high resistance is not yet available.
- Pioneer corn breeders continue to screen parent lines and hybrids in multiple environments where Diplodia occurs to improve resistance levels in new hybrids.
- For fields with a history of severe Diplodia ear rot infection, growers should select hybrids with a rating of 5 or higher.
- Select hybrids of varying maturity and stagger planting dates if possible (because weather conditions at silking are key to Diplodia infection, this can help spread risk by spreading silk dates).
- Rotate crops (at least one year out of corn).
- Partially or completely burying corn residue can provide substantial disease control.
- Level of Diplodia ear rot is proportional to the amount of infected corn residue on soil surface.
Harvest and Storage
- Harvest seriously infected fields early and dry grain to below 15% moisture (below 13% for storage through the following summer).
- Cool infected grain below 50 F as quickly after harvest as possible and store at 30 F.
- Clean grain after drying and before storing to remove lighter, damaged kernels, cobs and fines.
- Diplodia development on ears in field can worsen in the bin if grain is not dried properly.
- Screen grain and store the most infected grain separately to help avoid putting the whole bin at risk.