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Uncommon Diseases Of Corn Observed L


ast week, Goss’s wilt and Physo- derma brown

spot were detected in separate corn leaf samples submitted to the University of Illinois Plant Clinic. Although both dis-

eases have been observed in Illinois in past years, they are not typically found in the state every year. Goss’s wilt. Goss’s wilt is caused by

the bacterium Clavibacter michiga- nense subspecies nebraskensis. This disease is most likely to be observed in areas of the state that have re- ceived hail, high winds, and heavy

available to protect

against Goss’s wilt infec- tion or to reduce disease spread within a field. Fo- liar fungicides are not ef- fective


controlling it. The primary method of con- trol is planting corn hybrids with high lev- els of resist- ance

with your seed dealer

(check for

Top Photo: Corn leaf with Goss's wilt symptoms.

Bottom Photo: Symptoms of Physoderma

Goss’s wilt rat- ings). Fields affected this season should be tilled after harvest to bury affected residue and rotated

on a corn leaf Photo courtesy of Nancy Pataky, University of Illinois Plant Clinic

Symptoms of Goss’s wilt may be confused

with those of other foliar diseases, including Stewart’s wilt, northern corn leaf blight, and Diplodia leaf streak.

rainfall. Symptoms appear as large tan to gray lesions on the leaves, with dark spots, often referred to as freckles, within the lesions. Some plants may wilt, as the pathogen can infect the xylem. In some cases, darkening of the vascular tissue can be observed in affected plants if a cross-section is cut through the stalk. Symptoms of Goss’s wilt may be

confused with those of other foliar diseases, including Stewart’s wilt, northern corn leaf blight, and Diplo- dia leaf streak. Proper identification is important, so suspicious samples should be sent to the UI Plant Clinic. No in-season control options are

to a nonhost crop, such as soybean, next season. Physoderma brown spot.

Physoderma brown spot is caused by the pathogen Physoderma maydis. It is rarely observed in Illinois but has been seen on occa- sion in the past, especially when excessive rainfall has been received during the early growth stages of the corn crop. Symptoms ap- pear as small round to ob- long brown spots on the leaves, which may occur in bands. Free moisture must be present for infection by this pathogen to occur,

and once corn plants reach the de- velopment point where the leaf whorl is no longer present, the likelihood of

2010 Wheat Variety Test Results Now Available For Most States



esults from the 2010 University of Kentucky

Small Grain Variety Test are available at /WheatVarietyTest. Links to all state va-

riety testing programs can be also be accessed at this site. The 2010 wheat growing season

ended with Kentucky farmers harvest- ing 270,000 of the 420,000 acres of soft red winter wheat planted. A statewide average yield of 63 bushels per acre was recorded for a total production of 17 million bushels. The 150,000 acres not harvested for grain were used for forage production and cover cropping. Flood- ing in May contributed to fewer acres being harvested for grain and lower yields in some areas of the state. In 2010, eighty-three wheat entries

16• MidAmerica Farmer Grower / August 6, 2010

from seed companies were evaluated across Kentucky at 7 test locations. In addition to evaluating wheat varieties for differences in grain yield potential, the UK wheat variety tests also evaluate characteristics, such as test weight, heading date, plant height, winter har- diness, lodging and disease reaction. Additional specialized tests were con- ducted to measure wheat varietal dif- ferences in post-grain harvest straw yields, differences in wheat forage bio- mass yields and barley variety perform- ance at a single location. A thorough evaluation of variety char-

acteristics allows growers to select a group of top yielding varieties and then base varietal selection on secondary traits important to their production sys- tem, such as maturity date, disease re- sistance, plant height, forage or straw yield potential. Because weather, soil, and other en-

vironmental factors may alter varietal performance from one location to an- other, tests are annually conducted at

new infections decreases consider- ably. According to fungicide labels, only Headline and Headline AMP list Physoderma brown spot as a target disease. It is unlikely that severity of Physoderma brown spot in Illi- nois would be high enough to war- rant a foliar fungicide application. The best management practices are to rotate to a nonhost crop the following year and plant a resist- ant hybrid, if available.

multiple locations throughout the state. It is best to have multi-year data at multiple locations from which to draw conclusions. Single year data from one test location should not be used for va- riety selection. The University of Ken- tucky offers a statewide summary of varietal performance across all tests, over a one, two or three year period. Va- rieties that perform well across loca- tions and years are more likely to perform well under future growing con- ditions. Variety selection is an important com-

ponent of profitability, both to maximize productivity potential and to utilize sec- ondary characteristics important to the production system and management practices used. Most states have variety testing programs to offer growers free, unbiased, reliable information for vari- ety selection.

∆ BILL BRUENING: Research Specialist,

Plant and Soil Sciences, University of Kentucky


tant Professor/Crop Sciences, Uni- versity of Illinois

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