Physoderma Brown Spot
- Physoderma brown spot lesions occur mainly on the leaf, but may also occur on leaf sheath, stalks, outer ear husks and tassels
- As disease progresses, small lesions may coalesce to form larger affected areas
|Leaf lesions are fairly small, oblong to circular and yellowish or brown, while
lesions on leaf midrib are often purplish to brown.
- Eyespot disease caused by Aureobasidium zeae can look similar to Physoderma brown spot
- Eyespot is a leaf disease with small, yellow, mostly round lesions
- Main difference - lesions of eyespot do not usually occur in the banded pattern across leaf
- On the leaf blade, young Physoderma lesions can also resemble those caused by rusts, such as early southern rust (see arrow below). A higher magnification lens can help distinguish these diseases
|Eyespot infection (left) and southern corn rust (right)
Facts on Physoderma Brown Spot
- Fungal disease caused by Physoderma maydis
- Generally of minor importance in the U.S.
- Localized outbreaks may occur in years when weather favors disease development
- Overwintering fungal structures, sporangia, survive in infected corn tissue or soil
- Sporangia germinate to produce infective zoospores under conditions of moisture and light
- With the right conditions of water, light and temperature when leaves are in the whorl, infections often occur on a diurnal cycle
|This diurnal (daytime) cycle of infection often results in the banded pattern
of lesions seen on leaves.
- Crop rotation, as the fungus survives in infected crop residue
- Tillage to encourage breakdown of crop residue
- Specific management for this disease is not typically required, as the occurrence is sporadic and the effect on yield should be minimal
- Pioneer does not rate its hybrids for resistance to this disease