Soybean Insects

Justin McMechan, Ph.D., D.P.H Crop Protection and Cropping Systems Specialist Department of Entomology, University of Nebraska-Lincoln

Soybean Insect Pests

Vegetative Reproductive

Prior to Emergence

• Typically show up under cool and wet conditions • Investigate areas with poor emergence or missing plants • Examples: – Seedcorn maggot – Wireworms – White grubs

Vegetative Stage Pests

Bean Leaf Beetle • Overwinters as adult • Lots of color variations • Start on alfalfa and sweet clover • Found on earliest planted soybean • Hides under leaves

Soybean Gall Midge • New species • Larvae can be found at the base of the plant • Can kill soybean plants under heavy infestation • Heaviest infestation on field edge

Vegetative Stage Pests

Legend Soybean Gall Midge = 2018 = 2019 • As of 2020, it has been found = 2020 in 114 counties across five states

Soybean Gall Midge • As of 2020, it has been found in 114 counties across five states • Adults lay eggs on plants once they produce a fissure or are injured

Vegetative Stage Pests

Soybean Gall Midge • As of 2020, it has been found in 114 counties across five states • Adults lay eggs on plants once they produce a fissure or are injured • As larvae feed, stems may turn black at the base

Soybean Gall Midge • Begin scouting 10 days after adults emerge • soybeangallmidge.or g

Vegetative Stage Pests

Soybean Gall Midge • Begin scouting 10 days after adults emerge • soybeangallmidge.or g • Push plants over and look near the soil line

Vegetative Stage Pests

Soybean Gall Midge • Not all orange larvae are soybean gall midge • White mold gall midge – Not a pest of soybean Legend – Feeds on white mold = 2018 – Can be found on different = 2019 parts of the plant = 2020 = White mold – Different field distribution gall midge

Soybean Defoliators

Estimating Defoliation in Soybean

10 random plants

Illustration by Justin McMechan

Remove leaves from top, middle and 10 random 1 bottom of plant Top plants Remove the highest and lowest defoliated trifoliate. Keep remaining leaflet Middle Repeat for middle and bottom

Estimate defoliation and avg. leaves Bottom

Repeat 1 - 4 at 4 more locations and

take an avg. defoliation from 40 leaves Illustration by Justin McMechan

Estimating Defoliation in Soybean

Remove leaves from top, middle and 10 random 1 Top bottom of plant Top plants Remove the highest and lowest 2 defoliated trifoliate. Keep remaining leaflet Middle Repeat for middle and bottom

Estimate defoliation and avg. leaves Bottom

Repeat 1 - 4 at 4 more locations and

take an avg. defoliation from 40 leaves Illustration by Justin McMechan

Remove leaves from top, middle and 10 random 1 Top bottom of plant Top plants Remove the highest and lowest 2 defoliated trifoliate. Keep remaining leaflet Middle 3 Repeat for middle and bottom Middle Estimate defoliation and avg. leaves Bottom Bottom Repeat 1 - 4 at 4 more locations and

take an avg. defoliation from 40 leaves Illustration by Justin McMechan

Estimating Defoliation in Soybean

take an avg. defoliation from 40 leaves Illustration by Justin McMechan

Remove leaves from top, middle and 10 random 1 Top bottom of plant Top plants X4 Remove the highest and lowest 2 defoliated trifoliate. Keep remaining leaflet Middle 3 Repeat for middle and bottom Middle Estimate defoliation and avg. leaves 4 Bottom Bottom Repeat 1 - 4 at 4 more locations and

5 take an avg. defoliation from 40 leaves Illustration by Justin McMechan

Estimating Defoliation in Soybean

5 take an avg. defoliation from 40 leaves 30% vegetative stage Illustration by Justin McMechan Threshold: 20% reproductive stage

Practice! • Do you want to test your skills?

https://severity.cropprotectionnetwork.org/crop/soybeans/soybean-insect-defoliation-training

Defoliator Information

What other information is important to collect? • Insects • Soybean – Species – Stage – Stage – Size of canopy – Abundance – Weather – Actively feeding

• Not all insects cause the same type of injury • Soybean • Pod damage – Stage can be significant – Size of canopy – Weather

Painted Lady Butterfly

• Lay eggs singly on plants • Feed as caterpillars for 2-6 weeks • Pupate for about 7-17 days • Tend to aggregate towards the field edges • 97% of plant consumption occurs in the last two instars

Photos: Iowa State University

Dectes Stem Borer Jim Kalisch, UNL • Small beetle that is native to the North America • Spends most of its time in the main stem as larvae • Girdles plant near soil

surface as plant matures Z. Rystrom

Reproductive Stage Pests

Soybean Aphid • Only colonizing aphid on soybean • Around 15 generations per year

Stinkbugs • Show up around R1 (flowering stage) • Often on field borders • Can damage seeds and pods

Reproductive Stage Pests

Beneficial Insect Stinkbugs Spined Soldier Stinkbug • Show up around R1 (flowering stage) • Often on field borders • Can damage seeds and pods • Not all stinkbugs are pests

Beneficial Organisms • A number of beneficial organisms can be naturally occurring in soybean fields • Spined soldier stinkbug • Minute pirate bug • Lady beetles • Syrphid fly larvae • Entomopathogens

Summary • Insect pests can be found on all different parts of soybean plant • Not all insects are distributed equally across a soybean field • A sweep net is a great tool for collecting critical information • Defoliation in soybean is often overestimated