Group 0 Early - Weed Science at the University of Illinoisweeds.cropsci.illinois.edu/extension/Other/WeedEmergePoster.pdf · Winter annuals normally complete emergence prior to planting

Winter annuals normally complete emergence prior to planting of corn or soybeans.Examples: Horseweed (marestail), white cockle, field pennycress, shepherd’s purse.

Group 1Emergence beginsseveral weeks priorto corn planting.

GDD < 150

Group 4Emergence beginsafter cornemergence.

GDD > 350

Group 3Emergence beginsat end of cornplanting season.

GDD = 250-400

Group 2Emergence beginssoon before or atcorn planting.

GDD = 150-300

Group 0Emergence occurs infall or early spring.

Common cocklebur

Giant ragweed Common sunflower

Woolly cupgrass

Lambsquarters Penn. smartweed

Giant foxtailCommon ragweed Velvetleaf

Yellow foxtail Black nightshade Wild proso millet

Large crabgrass Fall panicum Waterhemp Morningglory sp.

North Central RegionIntegrated Pest Management Program

Leopold Center for Sustainable Agriculture

Funding provided by:Iowa State UniversityUniversity Extension

University of Illinois

University of MinnesotaExtension Service

This poster is a joint project of:University of WisconsinCooperative Extension

United States Department ofAgricultureAgricultural Research Service

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Late

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Knowing when weeds begin to emerge canimprove weed management by helping todetermine when to scout fields and implementcontrol tactics. Although the initial emergencedate for weeds varies from year to year, theemergence sequence of different weeds is fairlyconstant. Each group below includes weedsthat begin to emerge at similar dates. Most weeds

emerge over a prolonged time period, so weedsfrom earlier groups may still be emerging whenlater groups begin to emerge. The GDD (base48) information is an estimate of heat unitsrequired to reach 10% emergence. However,weed emergence is influenced by several otherfactors than air temperature, including cloudcover, soil type and moisture, and crop residue.

For some species, the majority of emergenceoccurs in a short time period (2-3 weeks),whereas other species may emerge over aprolonged period (8-10 weeks).

The duration of emergence for species is indicatedby the color background where its name appears.

LongMediumShort

Integrated Pest ManagementIPM-64