Linda Benedict, Singh, Raghuwinder, Hollier, Clayton A. | 9/10/2014 12:50:09 AM
Clayton A. Hollier and Raghuwinder Singh
Goss’s wilt is a bacterial corn disease new to Louisiana. During the 2013 growing season, it was observed in northeastern Louisiana and reported for the first time. Its previous range was Nebraska to Indiana and from southern Minnesota to the panhandle of Texas, but it had never been detected in the Deep South.
Goss’s wilt is a bacterial disease caused by Clavibacter michiganensis subsp. nebraskensis. Field symptoms were found in mid-June in East Carroll, Madison, Tensas and West Carroll parishes. Classical foliar and stalk symptoms were observed with the greatest damage occurring in the center of 50- to 75-foot diameter circles, while less severe symptoms and, therefore, less damage occurred at circles’ edges.
This disease can have two distinct phases: a leaf blight phase and a systemic wilt phase.
Leaf blight is the most commonly observed symptom, but it is easily confused with other diseases and abiotic disorders. Corn plants with Goss’s wilt exhibit long, large, tan lesions in the centers or on the edges of leaf blades. The margins of these lesions may have a water-soaked appearance. Black flecks, or freckles, can be observed within the lesions. These flecks can be large and cannot be rubbed off plant tissue. Early in the morning or after a rain, symptomatic leaves exhibit a bacterial ooze, or exudate, on lesion surfaces. Dried bacterial exudate is shiny, especially in direct sunlight. During dry weather, Goss’s wilt symptoms are easily confused with drought stress or leaf scorch from chemical burn. Leaf blight symptoms can also be misidentified as nutrient deficiency, chemical injury, Stewart’s wilt (caused by a different bacterial organism) or northern corn leaf blight.
In the systemic wilt phase of the disease, infected plants may exhibit drought stress symptoms and wilt or die prematurely. In this phase of the disease, infected vascular tissue will have orange-to-brown discoloration, which is caused by bacteria moving within the plant’s xylem tissue.
Confirmation of Goss’s wilt can be made by the LSU AgCenter Plant Diagnostic Laboratory.
The bacterium that causes Goss’s wilt survives the winter primarily in infected crop residue and, to a lesser extent, on the soil surface. Research from several states indicates that under more arid conditions, the pathogen can only survive for 10 months on the residue at the soil surface. The bacteria enter any part of the corn plant through wounds, such as those caused by hail and heavy winds. Wind-driven rain can spread the bacteria. Although the bacteria can enter wounds created by insect feeding, insects are not known to transmit the bacteria.
Preventing disease development is important in reducing economic losses from Goss’s wilt. Hybrids with partial resistance to the disease are available, and producers that have experienced Goss’s wilt problems should check with seed dealers to find out more about the availability of resistant varieties.
Adopting production practices that diminish disease pressure will also reduce economic losses. Rotating out of corn production for one year will allow crop residue to break down and reduce bacterial populations. Tillage and other practices that encourage residue decomposition will also reduce the amount of bacteria present to infect the following corn crop. Good weed management techniques are necessary to control grass weed species that can serve as a source of the disease.
Goss’s wilt is caused by bacteria, so fungicides will not prevent or manage the disease. Copper products have been used to control bacterial diseases in other crops; however, these are not economically viable options for large, field-scale use in corn production. The best management strategy for Goss’s wilt is to use a combination of the previously discussed management practices to minimize economic losses.
Clayton A. Hollier is a professor and Raghuwinder Singh is an assistant professor in the Department of Plant Pathology & Crop Physiology.
This article was published in the summer 2014 issue of Louisiana Agriculture Magazine.