By TIM ALEXANDER
Illinois Correspondent

URBANA, Ill. — Goss’ wilt and Physoderma brown spot are showing up in some Illinois cornfields, plant experts from the University of Illinois are warning farmers.

Goss’ wilt, a bacterial disease, is showing up in at least eight counties (Sangamon, Knox, Livingston, Bureau, Edgar, Shelby, Woodford and Piatt), according to Suzanne Bissonnette, director of the UoI Plant Clinic. Bissonnette reported during the last two weeks of July, numerous field corn leaf samples in central Illinois as well as the northern part of the state showed “dramatic” symptoms of Goss’ wilt.

Goss’ wilt preys on wounded corn plants that are vulnerable to infection after experiencing hail, high winds or heavy rainfall. Fields planted corn-on-corn are susceptible to the disease, as are fields containing large amounts of corn stover, those hosting weeds such as green foxtail and shattercane and fields that have been host to Goss’ wilt during previous growing seasons.
According to UoI plant pathologist Carl Bradley, Goss’ wilt was found only sporadically in Illinois prior to this summer. Though a few reports were received last year, the disease appears to be more widespread this season, he stated.

Infected leaves may present large, freckled, tan or gray lesions running the length of the leaf. Plant wilt is the primary result of infection from Goss’ wilt. There is no in-season control option available to producers for combating it.

“The best method of controlling Goss’ wilt is to plant corn hybrids with high levels of resistance,” Bradley advised farmers.
Small, round or oblong spots on corn leaves occurring in bands could signal an infection by the pathogen Physoderma maydis, or Physoderma brown spot, Bradley announced in an Aug. 3 news release issued by the UoI College of Agricultural, Consumer and Environmental Sciences.

“This disease can be confused with purple leaf sheath, because symptoms also can occur on the leaf sheath as dark purple circular lesions. However, if no lesions on the leaves are present, then the leaf sheath symptoms likely are caused by purple leaf sheath,” he wrote.

Just as with Goss’ wilt, there is no effective in-season treatment available to producers to combat Physoderma brown spot. An application of foliar fungicide at this stage of the growing season would probably not be beneficial, Bradley stated. Most cornfields are at a stage, however, when leaf whorl is no longer present, reducing the likelihood of new infections.

Bradley advises farmers who own fields with severe symptoms of Physoderma brown spot to rotate to a non-host crop the following year and plant “the most resistant hybrid available” when returning the field to corn.

He and Bissonnette urge farmers who think their plants may be infected with Goss’ wilt or Physoderma brown spot to collect leaf samples and send them to the Plant Clinic. More information is available online by visiting http://web.extension.illinois.edu/plantclinic

Two “potentially devastating” pathogens affecting double-crop soybean fields have been recently identified, a researcher for the Illinois Soybean Assoc. (ISA) reported.

Jason Bond, Southern Illinois University professor of plant pathology, encountered “significantly accelerated infestations” of Rhizoctonia solani and Southern root knot nematode in southeastern Illinois in late July, prompting Bond and the ISA to urge all soybean farmers to scout their fields for these and other diseases that rob yield.

“The intense heat we’ve experienced over the past few weeks has exacerbated the damage caused by Rhizoctonia solani and Southern root knot nematode in late-planted soybeans,” Bond stated Aug. 4. “Now is the optimal time for producers to scout recently planted fields to diagnose stand issues, especially if the field recently received rain. The problem areas will stand out for another week or two.”

He added the Southern root knot nematode pathogen is prone to attacking sandier areas in a field, with affected plants exhibiting severe “galling” on their roots. The fungus Rhizoctonia solani, however, is not limited to selected soil types. Affected plants will show symptoms including “brick red” lesions on stems and swollen hypocotyls. “Sometimes, the seedlings have slightly twisted stems,” Bond added.

Farmers wishing to submit samples of suspicious plants should cal the SIUC research team at 618-453-4309 or email jbond@siu.edu