By John Brien, CCA, AgriGold Regional Agronomist
Goss’s Wilt is one of the most devastating and feared leaf diseases a corn grower can experience.
There have been several “reports” of finding Goss’s wilt in Ohio corn fields in 2011, but no confirmed cases to AgriGold’s knowledge. All the cases have been a case of misidentification. Even though there are no cases of Goss’ Wilt in Ohio, nor does AgriGold believe there will be for several years, some background information and how to identify the pathogen should help extinguish any false rumors and/or fears.
Goss’s Wilt was first observed in Nebraska more than 40 years ago. For much of that time, the disease seemed to be content in Nebraska but beginning in 2008 it began to march eastward into Iowa, Illinois and Indiana. Since that time Goss’s Wilt has continued to grow exponentially in the I-states, most notably Iowa and Illinois.
The pathogen that causes Goss’s Wilt overwinters in crop residue and serves as the primary inoculum source. As the young plants are damaged by wind, hail or heavy rain the bacterium enters into the plant via a wound and can cause two types of symptoms. The most common symptom is water-soaked lesions that appear on the leaf and glisten in the sunlight. Goss’s wilt lesions tend to have wavy or bleeding margins between healthy and diseased tissue. The foliar lesions can progress and kill large areas of the canopy thus significantly reducing the photosynthetic capacity of the corn plant. The other, less common symptom occurs when the xylem tissue within the stalk becomes discolored and slimy causing the plant to conduct water less effectively.
Yield losses have been documented from both the wilt and leaf blight phases of the disease, however it has been difficult to quantify. The reason for the difficulty is that timing plays a major role in how much yield is negatively impacted by Goss’s Wilt. If a corn plant is infected early in the growing season versus late in the growing season, there is a higher chance for significant yield loss. Also if weather conditions continue to be favorable, high humidity along with warm temperatures of at least 80°F, there will be more yield loss that will be associated with Goss’s Wilt. Therefore if the disease moves onto the corn plant late and/or the favorable weather conditions are short term, little or no yield loss will be associated with Goss’s Wilt.
The two most common measures to control disease are tillage and crop rotation. Tillage has been shown to help reduce the occurrence of Goss’s Wilt, but does not completely eliminate the pathogen. Research has shown that pure cultures of the bacterium did not survive long in bare soil; however, the bacterium was able to survive for up to 10 months in the surface on corn residue. When the residue was buried the pathogen was still found in the stalks after 10 months but at reduced levels. Using tillage methods that bury infected residue should reduce the survival of Goss’s wilt and the rate of new infections.
Crop rotation is the next defense against Goss’s Wilt. The bacterium that causes Goss’s wilt is enhanced in fields of continuous corn. Rotating to a non-host crop such as wheat or soybeans will allow time for the infested residue to further break down and inoculum levels to decrease. Areas like southern Iowa and Northern Missouri do not have Goss’s wilt occurring at a very high rate because the majority of acres in these areas are rotated and not continuous corn. Both tillage and crop rotation will help decrease the severity of Goss’s wilt but do not guarantee complete freedom from the disease showing up.
The best method to control Goss’s Wilt is by selecting resistant hybrids. Many seed companies have made it a priority over the last couple years to select and advance hybrids with improved Goss’s Wilt tolerance. AgriGold has been a leader for germplasm resistant to Goss’s Wilt. AgriGold’s research station in Kearney, NE was where we first began to rate our germplasm years ago. As the disease has moved eastward our research stations in Ames, IA and Champaign, IL have increased their selections as well. Currently our research personal are inoculating select experimental trials with the Goss’s Wilt bacterium when the corn is 12-inches tall. To properly inoculate the plants, researchers simulate hail by creating a wound to the plant and then apply the bacterium at 2 different times, 1 week apart. The hybrids are then evaluated in late summer and their tolerance levels recorded. AgriGold also uses its agronomy team to record and fine tune each hybrids rating across our marketing area.
Currently AgriGold uses a 1-10 scale to rate for Goss’s wilt. The lower the rating the more susceptible the product is to Goss’s wilt. Many of Family B hybrids rate very tolerant to Goss’s wilt and hardly show any presence of the disease even under high pressure. While our Family F’s tend to be more susceptible to Goss’s Wilt. AgriGold has been working to identify hybrids in the Family F genetic pool with good to high tolerance.
2011 has proven too many corn growers that Goss’s wilt is here to stay. The rate and area of growth in 2012 is unknown but fully expected to expand to the East and South. The extent of yield loss on the infected acres will drastically depend on the timing of the infection and the timing of the weather after infection. As of right now, there are no fungicides/bactericides documented to cure or stop infections of Goss’s wilt. Therefore looking for other avenues to control and/or manage Goss’s Wilt will be important in 2012.