Soybean Pests

Last updated on February 23, 2014





Weed control controlling weeds via cultivation and chemicals is usually the most reliable procedure

Prior to Round-up Ready technologies:

  • Chemicals alone usually apply chemicals at least twice: pre-plant and pre-emergence
  • preemergence and postemergence more feasible now than prior to the mid1980's due to the advent of new postemergence herbicides
    • poast grassy weeds fusillade grassy weeds
    • basagran broadleaf weeds
    • roundup wick system

Round-up Ready fields require 1 to 2 applications

Weed problems in WI

  • Black nightshade berries plug the sieves
  • Smartweeds plug the reel and knock beans down bean plants may hook onto smartweeds on the reel and may eventually fall to the ground
  • Volunteer corn may reduce yields and market grade


Basic Plan for Scouting Soybean Insects in the Corn Belt

  • Crop emergence: early season insects like bean leaf beetle
  • June and July: mid-season defoliators like bean leaf beetle, green clover worm, Japanese beetle. Also sap suckers like two spotted spider mite
  • July and August: late-season defoliators and pod feeders like lean leaf beetle and grasshoppers

Soybean Aphid


Conditions necessary for disease development:

  • Host (susceptible)
  • Pathogen (virulent)
  • Environment (favorable)

Control measures influence all 3 factors

  • Resistant host crop variety has a gene or genes for resistance
  • Control the environment of the pathogen
    • Rotations bury crop residues and eliminate alternate hosts
    • Row spacing
    • Plant density
  • Control the pathogen via chemicals
    • seed treatments: apron vitavax
    • foliar fungicides: benlate (soybeans) topsin
    • soil fungicides: ridomil

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Management effects on disease

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Soybean diseases common in Wisconsin

Summary of relationships among management practices and soybean diseases. Craig Grau, University of Wisconsin

Brown Stem Rot

White Mold

Phytophthora Root Rot

Soybean Cyst Nematode

Seedling Blight

Planting Date


Greater severity and yield loss Greater seedling mortality Greater invasion of roots, unknown yield effect Greater in cool-wet soils
High Plant Population


Greater severity and yield loss



May compensate for seedling mortality

Narrow Row-Width Negates
Greater severity, negates yield advantage Unknown Unknown Unknown
treated seed
No documented effect No documented effect Apron® effectively reduces seedling mortality phase None available Apron®, Rival® effective; respond to no-till and early planting date systems
Crop rotation schemes 2-3 years of nonhost extremely effective. Improves yield of both resistant and susceptible varieties. 2-3 years of nonhost beneficial, but rotation effect improved by planting less susceptible varieties. Limited value 2-3 years of nonhost beneficial. Improves yield of resistant and susceptible varieties. Limited value
No tillage Greater severity and yield loss No-till in nonhost year enhances death of Sclerotinia sclerotia. Greater severity and yield loss Lower SCN population, greater yield Greater severity and yield loss
Soil fertility and tilth Higher K and pH, and supplemental N, reduce severity and improve yield High fertility, dense canopy result in greater severity and yield loss. Additional N results in greater severity and yield loss Minimal effects. High K may be beneficial Compaction results in greater severity and yield loss
Weed management Modest suppression by Pusuit® herbicide Significant suppression by Cobra®. Disruption of sclerotia by atrazine. Disruption of sclerotia by cultivation. Unknown Suppression of SCN reproduction by Blazer® herbicide. Preemergent herbicides suspected of reducing seedling vigor resulting in greater seedling mortality.

Phytophthora root rot

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Usually occurs in poorly drained areas of a field
  • Infects roots and stems, usually early in the growth of the soybean plant
  • Infected plants turn light green due to root infection, plant growth is uneven, lower stems turn brown, and leaves eventually wilt and die
  • There are at least 27 known types or races of prr in Wisconsin
Control measures for Phytophthora root rot
  • identify race(s) present: can do this in Wisconsin by submitting samples to a UW extension office
  • grow a variety that is resistant to the race(s) present
  • cultural practices improve soil drainage rotate with cereals minimize soil compaction if cultivating, ridging soil around the base of plants may help
  • this stimulates new root growth from lower stem
  • chemical treatments (apron and ridomil)

Brown stem rot

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Widespread in northern soybean growing area of the Midwest (Illinois, Iowa, Minnesota, Wisconsin)
  • difficult to identify because it usually develops late in the season
  • inside of lower stem turns brown
  • leaves die prematurely, often confused with early maturity
  • disease is spread in crop residue
Control measures
  • rotate with a cereal
  • resistant varieties

Pod and stem blight

Infects stems and pods of plants as they near maturity

  • small black spots (pycnia) on stems and pods
  • spots are in rows on stems
  • spots are scattered on pods

Disease is seedborne and also overwinters on residue


  • plow refuse under rotations plant seed from disease
  • free fields because infected seed often has low germination most soybean diseases don't have a major effect on seed quality, but pod and stem blight does.

White mold

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Soybean Rust

Soybean Cyst Nematode

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