Trey Price - pprice@agcenter.lsu.edu - @ppp_trey Potential Issues with Cover Crops and Diseases in Louisiana Production Systems January 23, 2018 Trey Price - pprice@agcenter.lsu.edu - @ppp_trey 318-235-9805

How does disease occur? No Disease

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

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

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

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

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.

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

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

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

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

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

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

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.

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.

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