Climate Change’s Impact on Field Crop Diseases

Daren MuellerIowa State University Extension

Pests and climate

• Changing weather affects corn and soybean growth and development

• Weather also can affect • plant pathogens

• beneficial and harmful insects

• weed species

Hatfield et al., 2008. Agriculture. In: The effects of climate change on agriculture, land resources, water resources, and biodiversity. A Report by the U.S. Climate Change Science Program and the Subcommittee on Global Change Research. Washington, DC., USA, 362 pp

How do changes affect disease?

Plant

Pathogen Environment

Changes in environment

• Climate trends− Increasing temps

−More extreme weather events

−More rainfall in parts of Midwest, especially heavier rainfalls

• Main challenges−Drought

− Flood

Diseases and climate

• Temperature and moisture are the two most important factors affecting diseases

• Disease outbreaks can be directly related to extreme weather events• Sudden death syndrome

• Charcoal rot

• Physoderma brown spot

Sudden death syndrome

• Now the #1 soybean fungal disease

• Root rot disease that causes foliar symptoms

• More problematic after heavy rainfall in reproductive stages

• Yields within patches reduced from both root rot and foliar symptoms

Charcoal rot

• More problematic in hot, dry seasons

• Patches vary in size

• Yields within patches reduced significantly

“With predictions of more extreme weather events in the future, including drier growing seasons, it is expected that the incidence and severity of charcoal rot will continue to increase in the North Central region.”

--Kiersten Wise at Univ. Kentucky

Physoderma brown spot

• Increasing problem across the Midwest

• Seedlings most susceptible

• Infection usually occurs within the whorl

• Spores need light and moisture to germinate

• Saturated soils and free water early in season favors disease

Changes in agronomic practices

• Earlier planting

• Narrow row spacing in conjunction with higher populations

• Environmental considerations − Reduced tillage

− Cover crops

− Improved water management Practices can affect:• Canopy closure (microenvironment)• Soil moisture• Amount of and survival of pathogens• Overwintering populations of insects• Attractiveness of crop to insects• Weed pressure

Winter rye cover crops and corn seedling disease

No rye (control)3 DBP 8 DBP 17 DBP

DBP – Days before planting corn that winter rye cover crop killed

Acharya et al., 2017. Plant Dis. 101:591-600.

Effect of rye termination on corn seedling disease

Co

rn s

eed

lings

wit

h d

isea

se (

%)

Days before (DBP) or after (DAP) planting corn when rye sprayed with herbicide

Acharya et al., 2017. Plant Dis. 101:591-600.

3 DBPRoot rot, stunted, less

vigorous seedlings

No cover cropHealthy roots and vigorous seedlings

Effect of rye termination on corn seedling disease

Acharya et al., 2017. Plant Dis. 101:591-600.

• Increase in foliar fungicide use

• More seed treatments options

• Seed treatment issues associated with honeybees

• Herbicide resistant pests

• Bio-based pesticides

Changes in pest management practices

How do changes affect disease?

Plant

Pathogen Environment

Changes in diseases

• Some are new/invasive• Bacterial leaf streak

• Tar spot

• Some have diminished• Stewart’s wilt and corn flea beetle

• Some have increased• Foliar pathogens more commonly

associated with the south (e.g., southern rust, frogeye leaf spot)

• Virus diseases

T. Jackson-Ziems

Frogeye leaf spot

• Can be found in all soybean growing areas, but historically more of a problem in southern regions

• Average loss in Midwestern states− 1996-2000: ~460,000 bushels/year ($0.04/ac)

− 2014-2018: ~15.7 million bushels/year ($2.06/ac)

• Now a main target of foliar fungicides across the U.S.

Insects and climate

• Temperature is an important factor affecting insects

• Consequences of increased temperature for:• Thrips positively respond to

heat and drought; increased accounts of thrips in 2012 and 2013

• Soybean aphid reproduction responds negatively to high temperatures

Soybean virus disease outbreaksVirus Primary vector

1996 – 2000

Bean pod mottle virus Bean leaf beetle

Soybean mosaic virus Soybean aphid

2013 – 2017

Soybean vein necrosis virus Thrips

Tobacco ringspot virus Thrips

Tobacco streak virus Thrips

How do changes affect disease?

Plant

Pathogen Environment

Changes in host plants

New traits

• Yield enhancement

• Nitrogen use efficiency

• Herbicide-resistance

• Pathogens and insect pests resistance

• Drought/heat tolerant

• Cold/frost tolerance

• Improved feed efficiency

• Improved fatty acid profile

• Improved protein content

• Breeding efforts continually improve resistance against diseases and tolerance against abiotic stresses such as temperature and water.

• Complemented with biotechnology to provide further improvements.

Changes in host plants

• Any release of new traits may introduce genetics more susceptible to diseases− Breeding focus should include

protection against multiple diseases, pests and stresses

− Need to study interaction of host plant with environment in the presence of disease

• New crops?− Possible example: mung bean is more

drought tolerant than some crops and is one of the protein sources for plant-based burgers

CropProtectionNetwork.org

Average white mold incidence of Roundup

Ready 2 Xtend® (RR2X) and Roundup

Ready 2 Yield® (RR2Y) soybean varieties

averaged over three Wisconsin locations in

2017 where white mold was the major yield-limiting factor.

Summary

Climate change

Agronomic practices

Pest management

practices

New crops and/or

geneticsTechnology

Economics

Insect pests and

diseases

Daren Mueller@dsmuelle

For more information on field crop diseases

Crop Protection Network

CropProtectionNetwork.org