Rye and Goss’s Wilt?
Can Winter Rye Increase Goss’s Wilt? 
Some farmers are concerned about winter cover crops being a potential host for Goss’s Wilt. According to Alison Robertson, Iowa State University 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. Schuster reported in a Nebraska Extension bulletin from 1975 that oats, wheat and barley were not hosts of Goss’s Wilt bacterium. Winter rye was not 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 the Goss’s Wilt bacterium but considering the similarities of winter rye to the other small grains that were tested it is unlikely that winter rye is a host for the bacterium.
Create an unfavorable environment for the bacteria……
1) Choose a disease resistant hybrid. Disease susceptible hybrids may be severely diseased and thus ensure large increases in the population of the Goss’s wilt bacterium in your fields. Disease resistant hybrids have less disease and thus the increase in the 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 chose a disease resistant hybrid.
2) Increase corn residue decomposition. The Goss’s wilt bacterium survives at high levels for over 10 months in infested surface corn residue. When infested corn residues are buried within the top 4” or 8” of the soil surface, survival of the bacterium is greatly reduced, as are population numbers of the Goss’s wilt bacterium. If you are over-seeding a cover crop into standing corn you will not be able to do fall tillage. You may think that 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 crop agronomists from around the Midwest, however, have stated that 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.
3) Increase your rotation. Extending your rotation will enable further breakdown of corn residues and may decrease the potential for a Goss’s wilt outbreak.
Can a cover crop increase residue decomposition by “firing” up the biology of the soil?
Cereal rye is not a host and is recommended to break the cycle. Rotating with cereal rye then soybeans is a good practice to reduce Goss. The bacteria normally don’t survive more than 10 months. Mike Plumer, Retired University of Illinois Extension
Increased worm populations from adding a winter cover crop would help decompose corn residues faster. Dr. Tom Kaspar, NLAE
There is lots of anecdotal evidence that brassica and legume cover crops tend to accelerate decomposition of previous crop residue. Dr. Joel Gruver Western Illinois University
We do a lot of cereal rye drilled in 10” rows into cornstalks ahead of soybeans. Just running over the stalks with a no-till drill gets the decomposition process started similar to a light disking. Also done some fields of rye into no-till continuous corn and it is almost always a better environment than just straight no-till into corn. Steve Berger Iowa
The corn stalks may not break down as fast but if the 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 leaving the stalks on top of the ground. Dan Towery Ag Conservation Solutions
No doubt about it and I have anecdotal observations. Put a low Carbon to Nitrogen rye material with high Carbon to Nitrogen cornstalks and the worms and organisms go to work. Super charge the rye with some extra Nitrogen in the spring and the corn residue will all be gone by June. Daniel Davidson Contributing Agronomist Telvent DTN
Therefore should I still use a cover crop?
No study has shown that a winter rye cover crop is a host for the Goss’s Wilt bacterium. Cover crops provide a multitude of benefits from improving soil structure, holding nitrogen and phosphorus on the soil where cash crops will be planted to decreasing weed pressure. In Iowa, over-seeding cover crops by plane has become very popular and is a good strategy for farmers to get their cover crop planting out of the way before harvest. However if you have fields that have had Goss’s Wilt here are some additional things to think about:
1) Start with resistant plants: if Goss’s wilt has been reported in your area, plant only those hybrids that have good resistance to the disease.
2) On fields where Goss’s wilt has occurred, rotate to a non-host crop for a minimum of one year.
3) Include some shorter season Goss’s 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.
For more information contact Sarah Carlson at Practical Farmers of Iowa, 515-232-5661 or sarah@practicalfarmers.org