Pests on Soybeans

Two-spotted Spider Mite

• Order Acari   Family Tetranychidae

• Tetranychus urticae

• Distribution: Worldwide

• Description: Small: 0.3-0.4 mm long, broadly joined cephalothorax and abdomen, greenish-yellow to orange in color with two large black spots on both sides of the body.

Two-Spotted Spider Mite

Two-spotted Spider Mite Life History

• All stages are found on plant structures

• Feed mainly on undersides

• Have one 6-legged larval stage and two 8-legged larval stages

• In northern states they overwinter as adults. In warmer places they remain partially active

• On heavily infested plants, females climb up on leaves to be dispersed via wind

Two-spotted Spider Mite Life History

• There are multiple generations per year

• Females produce up to 300 offspring in first month of egg laying

Two-spotted Spider Mite Damage

• Often recognized by evidence of feeding and not actually by seeing the mites

• Feed mainly on leaf undersides

• Small yellow or white spots appear on leaves (stipples)

• reduction in photosynthetic activity

• Extensive feeding results in yellow/brown leaves that eventually drop off

Two-spotted Spider Mite Damage

Two-spotted Spider Mite Management

• Two natural enemies: predaceous phytosiid mites and a fungal pathogen (Neozygites floridana)

• In soybeans, control of spider mite outbreaks is primarily through chemical application

• Initial monitoring for the mites should begin along the field edges, where infestations should be first evident

Bean Leaf Beetle

• Order Coleoptera  Family  Chrysomelidae

• Cerotoma trifurcata

• Origin: Native, especially abundant in the eastern U.S.

• Description: adults 5mm long. Elytra yellow with black dots and marginal stripe. Black triangle behind the prothorax. Larvae are white and cylindrical with a black head

Bean Leaf Beetle

Bean Leaf Beetle Life History

• Adults leave overwintering habitats in April and move into alfalfa fields

• When soybeans emerge, they move into the soybean fields

• Females lay eggs in soybean fields (130-200 eggs/ female)

• Larvae feed on roots and nodules

Bean Leaf Beetle Life History

• Mature larvae build an earthen cell and pupate

• 1 to 2 generations/year in the north and 3 generations/year in the south

Bean Leaf Beetle Damage

• Larvae feed on roots, root hairs, and nodules

• Adults defoliate. This can be recognized as small round holes between major leaflet veins

• Most defoliation is early season

• Adults may feed on pods, causing seed vulnerability. Can be recognized by shrunken, discolored, and moldy seeds

Bean Leaf Beetle Damage

Bean Leaf Beetle Management

• Plant soybeans as late as possible within the recommended planting period of a certain variety

• Estimate population levels with regular sampling and consultation of economic thresholds

• Application of pesticides if necessary

Potato Leafhopper

• Order:  Homoptera   Family: Cicadellidae

• Empoasca fabae

• Distribution: native. widely distributed in eastern North America

• Description: Adults are small, 3.5m long. Wedge shaped, and pale green in color. Females have bladelike structure = ovipositor

Potato Leafhopper

Potato Leafhopper Life History

• Overwinter near Gulf of Mexico

• Immigrating adults first appear in alfalfa and other crops when migrating north until soybeans emerge

• Adults females insert eggs into soybean plants (2-3 eggs/day)

• One or more generations can occur on soybean during a single growing season

Potato Leafhopper Damage

• Use mouthparts to tap into the plant’s phloem tissues

• Distorted leaf veins

• Leaves often yellow-brown in color, a.k.a.  “hopperburn”

• Plant growth often stunted by leaf damage

Potato Leafhopper Damage

Potato Leafhopper Management

• Approx. economic threshold is 5 leafhoppers/plant in early season and 9/plant in late season

• Soybean varieties with dense pubescence provide a mechanical barrier that makes it difficult for leafhoppers to feed or have successful oviposition

Mexican Bean Beetle

• Order: Coleoptera  Family: Coccinellidae

• Epilachna varivestis

• Origin: Native to Mexico

• Distribution: Found in Central America, Mexico, U.S., Quebec and Ontario

• Description: Adult is oval shaped, orange-red color with 8 black spots per elytron. Larvae are yellow-orange with six rows of branched spines

Mexican Bean Beetle

Mexican Bean Beetle Life History

• Adults overwinter in plant debris or under rocks near soybean field

• Adults emerge in spring when temperatures increase above 50F (10C)

• Females lay between 700 and 1000 eggs over approximately 40 days

• 4th instars attach to internode of leaf and pupate (5-10 days)

Mexican Bean Beetle Damage

• They damage several legume species

• Adults and larvae defoliate the plants

• Adults may also feed on stems and pods

Mexican Bean Beetle Damage

Mexican Bean Beetle Management

• Greatest potential for economic loss is during the reproductive stages of soybean

• Defoliation levels above 15% in determinate and indeterminate cultivars can require management. Defoliation must exceed 35% once full pods are present in order to be of economic significance

Grasshoppers

• Redlegged and differential grasshoppers are sporadic, yet serious pests of soybean

• Consecutive years of drought often result in the build up of damaging population numbers

• Infestation generally starts along the edges of a field

Grasshopper

Grasshopper Damage

• Feeding is primarily on leaves before pods are available

• Leaf and pod feeding both occur once pods are formed, consuming often the whole pod (including seeds)

• If seeds remain, the feeding may make them more vulnerable to fungal infection

Grasshopper in Soybean Field

Grasshopper Management

• Biological control of high grasshopper densities is often accomplished with particular fungal spores

• Often insecticides are used

• Economic Thresholds: 30-45 nymphs/sq. yard and 8-14 adults/sq. yard

Seedcorn Maggot

• Seedcorn maggot is a common soybean pest

• Often problems in recently disturbed fields with organic matter, such as manure

• Damage more likely when conditions are cool and wet

Seedcorn Maggot Injury

• Larvae feed on both germinating soybean seeds and cotyledons

• Plants have variable emergence, or no emergence due to seed feeding

• Larval feeding can damage the growing tip of the soybean plant, causing y-shaped tops

Seedcorn Maggot Damage

Seedcorn Maggot Management

• Chemical seed treatment is often used in fields with lots of organic ground matter

• Delaying of seed planting