1. Trey Price - pprice@agcenter.lsu.edu - @ppp_trey
Potential Issues with Cover Crops and Diseases in Louisiana Production Systems
January 23, 2018
Trey Price -

2. How does disease occur?
No Disease

3. Growth/Reproduction*
Plant Disease Cycle
Infection*
Host recognition
Invasion
Penetration
Colonization*
Inoculation*
Growth/Reproduction*
Secondary Inoculum*
Incubation
Symptoms*
Primary Inoculum*
Overwintering*
Dormancy

4. Disease Cycle – Inoculum Sources
Infested plant debris
Infected seeds
Infected transplants
Infested soil
Airborne spores
Weeds
Alternate/Alternative hosts
Insects (vectors)

5. Where do diseases occur?
Fruit
Leaves
Stems
Stalks
Crown
Roots
Above ground
Below ground

6. Potential cover crops used in LA?
Wheat, Rye, Oats, Triticale
Radish (“Brassica”)
Winter Peas
Vetch
Clover
Others?
Retain/Increase Nutrients
Reduce Erosion
Conserve Soil Moisture
Increased Organic Matter
Improve Soil Quality/Health
Suppress Weeds

7. How do these cover crops change environmental conditions?
No tillage system
Moisture retention at planting
Lower soil temperature
Optimum conditions for many seedling diseases are cool, moist conditions
Possible concern = increased seedling disease incidence.

8. Corn Seedling Diseases
Caused by many fungi
Favored by cool, wet conditions
Pythium spp. caused significant losses in 2014
Rhizoctonia solani can be a problem
Seed treatments may be effective in problem areas, rarely impact yield
In-furrow options

9. Potential Detrimental Effect of Cover Crop – Corn Seedling Diseases
Cereal rye cover may increase Pythium spp.
Depending on species
Recommend burndown at least 2 wks before planting (Pythium spp. decrease with time after burndown)
Expect increased seedling disease with late burndown
Possible increase of Fusarium spp.
Some of these pathogens also go to soybean
Cover crop placement may be important in this situation
Acharya et al. 2017, Bakker et al. 2016

10. Soybean Seedling Disease Management
Rhizoctonia solani, Pythium spp., Phytophthora spp., Fusarium spp., and others
Cool, wet conditions soon after planting
Seed treatments are effective
Most of the time, seed treatments do not result in significantly preserved yield

11. Potential Beneficial Effect of Cover Crop – Soybean Seedling Diseases
Cereal rye and/or Brassica cover may decrease Rhizoctonia solani
Multiple studies showing allelopathic effect of Brassica species
Also lower Septoria brown spot severity following cereal rye
Wen et al. 2017

12. Cotton Seedling Diseases
Fungicide seed treatments very effective
Most beneficial under stressful conditions…
Poorly-drained soils
Cool weather
Poor seed quality
Proper planting date
Appropriate soil temperature
Long range forecast calling for warm temperatures

13. Mixed Effects of Cover Crop – Cotton Seedling Diseases
No effect of stale seedbed on Rhizoctonia spp.
Potential for increased Pythium spp. in stale seedbed
No effect on Rhizoctonia spp. With legume covers (hairy vetch/crimson clover)
Increased Pythium spp. with legume covers
Potential reduction in Thielaviopsis basicola with legume covers
Coyler and Vernon, 2005
Rothrock and Kirkpatrick, 1995

14. Are cover crops exposed to field crop pathogens?
Short answer = YES
Many foliar pathogens over winter in plant debris
Many pathogens are persistent in the soil
Many field crop pathogens have broad host ranges
Possible concern = increased chances of pathogen reproduction and increased inoculum during cash crop growing season.

15. Take Home… Disease Triangle (host, pathogen, environment)
No till systems = ↑ moisture, ↓ temperature
No till systems = may or may not favor pathogens
Cereal rye hosts some of the same pathogens as corn and soybean
Cereal rye and Brassicas may reduce disease in other cases
Cover crop placement may be key in some cases
Some cover crops may have allelopathic effects
Most “base” fungicide seed treatments likely will be adequate
Overall…very little is known of the influence of cover crops on seedling diseases, foliar diseases, etc. in our production systems.

16. Thanks to all Collaborators!
Agents
Producers
Consultants
Industry
Dan Fromme
Scott Washam and Crew
Clayton Hollier
Todd Yelverton
Charlie Overstreet
Boyd Padgett
John Stapp
Dustin Ezell
Karla Emfinger
Todd Spivey
Josh Copes
Sebe Brown
Myra Purvis
Jerry Bartleson
Paul Washam
Warren Ratcliff and Crew
Darrell Franks and Crew
Daniel Stephenson
Donnie Miller
Rick Mascagni
Steve Harrison
Kelly Arceneaux
Vinson Doyle
Teddy Garcia
Louisiana Soybean and Grains Research and Promotion Board