Goss’s, winter rye lack connection
Some farmers are concerned about winter cover crops being a potential host for Goss’s wilt.
According to Alison Robertson, Iowa State University Extension plant pathologist, Goss’s wilt is a disease of corn caused by the bacterium Clavibacter michiganense subsp.nebraskensis.
Some plants can serve as alternative hosts for the bacterium, namely green foxtail, barnyard grass and shattercane.
• Some farmers worry that winter cover crops are a potential host for Goss’s wilt.
• Goss’s wilt is a foliar corn disease that’s caused by a bacterium, not a fungus.
• No study has shown that winter rye cover crop is host for Goss’s wilt bacterium.
Schuster reported in a Nebraska Extension bulletin in 1975 that oats, wheat and barley were not hosts of Goss’s wilt bacterium. Winter rye wasn’t included in this study. There are no other studies to our knowledge that have been conducted to see if winter rye is a host for Goss’s wilt bacterium, but considering the similarities of winter rye to other small grains that were tested, it’s unlikely that winter rye is a host for the bacterium.
Knocking out bacterium
Below are ways to create an unfavorable environment for the bacterial corn disease.
• Choose a disease-resistant hybrid. Disease-susceptible corn hybrids may be severely diseased, thus ensuring large increases in the population of Goss’s wilt bacterium in your fields. Disease-resistant hybrids have less disease and thus the increase in population of the bacterium within a field is far less than if a susceptible hybrid were planted. To reduce the risk of Goss’s wilt, first choose a disease-resistant hybrid.
• Increase corn residue decomposition. The Goss’s wilt bacterium survives at high levels for more than 10 months in infested surface corn residue. When infested corn residues are buried within the top 4 to 8 inches of the soil surface, survival of the bacterium is greatly reduced, as are population numbers of the bacterium.
If you are overseeding a cover crop into standing corn, you won’t be able to do fall tillage. You may think this could create a scenario of increased disease pressure over time because surface corn residues may take longer to break down than buried residues.
Several agronomists from around the Midwest, however, say continued use of cover crops, especially winter rye, improves soil biology to the point that crop residues decompose noticeably faster when following a cover crop than without.
• Extend your rotation. Extending your crop rotation will enable further breakdown of corn residues and may decrease the potential for a Goss’s wilt outbreak.
Can a cover crop increase the crop residue decomposition by “firing” up the biology of the soil? Increased earthworm populations from adding a winter cover crop would help decompose corn residues faster, says Tom Kaspar, USDA research agronomist at the National Laboratory for Ag and Environment at Ames. There is lots of anecdotal evidence that brassica and legume cover crops tend to accelerate decomposition of previous crop residue.
“We grow a lot of cereal rye drilled in 10-inch rows into cornstalks ahead of soybeans,” says Steve Berger, a farmer at Wellman in southeast Iowa. “Just running over the stalks with a no-till drill gets the decomposition process started similar to a light disking. Also, we’ve planted some rye into no-till continuous corn, and it is almost always a better environment than just straight no-till into corn without a rye cover crop.”
The cornstalks may not break down as fast, but if soil biology is working (it may take several years of proper management for this to occur) and there are more earthworms present, then the residue will break down faster than if you leave the stalks on top of the ground, says Dan Towery, a consultant with Ag Conservation Solutions.
So, should I still use a cover crop? No study has shown that a winter rye cover crop is a host for Goss’s wilt bacterium. Cover crops provide a multitude of benefits. Those include improving soil structure, holding nitrogen and phosphorus on the soil where cash crops will be planted, and decreasing weed pressure.
In Iowa, overseeding cover crops by airplane has become very popular and is a good strategy for farmers to get their cover crop planting done before harvest.
However, if your fields have had Goss’s wilt, here are things to think about:
• Start with resistant plants. If Goss’s wilt has been reported in your area, plant only those corn hybrids that have good resistance to this disease.
• On fields where Goss’s wilt has occurred, rotate to a non-host crop for a minimum of one year.
• Include some shorter-season Goss’s wilt-resistant corn hybrids on fields where you have high Goss’s wilt presence. After corn harvest, use a no-till drill to seed cover crops, which will help cut up and speed breakdown of residue. Or do fall tillage and then plant a cover crop to be able to break up the disease cycle. Increase the soil-to-residue contact to enhance the decomposition process.
Carlson is research and policy director for Practical Farmers of Iowa. For more information on cover crops, contact her at 515-232-5661 or firstname.lastname@example.org.
This article published in the November, 2011 edition of WALLACES FARMER.