Insects and Pests of Field Crops: Dry Edible Bean Insects and Pests

| Corn | Soybeans | Forages | Cereals | Dry Edible Beans |
| Spring and Winter Canola | Other Crops | Soil Management |
| Soil Fertility and Nutrient Use | Field Scouting |
| On-Farm Stored Grain Management | Weed Control |
| Insects and Pests of Field Crops | Diseases of Field Crops | Appendices |

Pub 811: Agronomy Guide > Insects and Pests of Field Crops > Dry Edible Bean Insects and Pests

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Table of Contents

• Introduction
  • Table 13-7, Dry Edible Bean Insect Symptoms in the Field
• Potato Leafhopper
• Defoliating Insects
• Bean Leaf Beetle
• Mexican Bean Beetle
• Western Bean Cutworm
• Tarnished Plant Bug

Introduction

This section describes insects and pests that affect only dry edible bean crops. The insects and pests listed below affect dry edible bean as well as other crops

Bean leaf beetle page
Potato leafhopper
Seedcorn maggot
Western bean cutworm
Wireworm

Table 13-7, Dry Edible Bean Insect Symptoms in the Field, shows insects and pests that could be causing the symptoms in the field.

Table 13-7. Dry Edible Bean Insect Symptoms in the Field

	Insects and Pests
Symptom	Wireworms	Seedcorn Maggot	Slugs	Potato Leafhopper	Mexican Bean Beetle	Bean Leaf Beetle	Western Bean Cutworm	Tarnished Plant Bug
Gaps in the stand: Tunnelling into cotyledon, embryo or hypocotyl	x	x	x1
Holes in leaves
Ragged holes in leaf (looks like hail damage)			x
Leaves have been skeletonized					x
Round holes in leaf						x
Leaves distorted or discoloured
Margin of leaves yellow or appear scorched, leaves puckered				x
Flower blasting or young pod drop								x
Pod/Seed feeding insects
Holes or scars on the surface of the pods						x
Entry hole into the pod, holes in the seeds in the pod							x
Hard dark spots on pods and seed, seeds may have picks or dimples								x
1Slime trail noticeable.

 

Potato Leafhopper (Empoasca fabae)

Potato leafhopper (PLH) is an important pest of dry edible beans. Information about this pest can be found at Potato leafhopper

Defoliating Insects

Research conducted at the Ridgetown Campus of the University of Guelph indicates that prior to flowering, beans are able to tolerate up to 50% leaf loss with minimal loss in final yield. Complete defoliation prior to flowering delayed maturity by 30 days. Lower levels of defoliation did not delay maturity. At later stages, the impact of defoliation is greater. Total losses will be determined by the growing conditions and the ability of the plant to recover. Losing more than one-third of the leaves during flowering or pod fill can greatly reduce yield. See Figure 13-3, Yield Loss vs. Defoliation of Navy Beans.

Figure 13-3. Yield Loss vs. Defoliation of Navy Beans




Source: Schaafsma and Ablett, 1994.

 

Text Explanation for Figure 13-3 - Yield Loss vs. Defoliation of Navy Beans


 

Use Figure 13-2, Defoliation Chart for Soybean Leaf-Feeding Insects, as a guideline to determine if the threshold has been reached.


Text Explanation for Figure 13-2, Defoliation Chart for Soybean Leaf-Feeding Insects

Bean Leaf Beetle (Certoma trifurcata)

Bean leaf beetle is an important pest of dry edible beans. Information about this pest. .


Mexican Bean Beetle (Epilachna varivestis)

Description: Mexican bean beetle is the only member of the lady beetle family in Ontario that eats plants. All the other lady beetles are beneficial predacious insects. The adult beetles are oval in shape, approximately 6 mm (1/4 in.) in length with 16 small black spots on their coppery-red backs, resembling a lady beetle Plate 99.

Plate 99. Mexican bean beetle adult. The beetles have 16 small black spots on their coppery-red back. Larvae have black-tipped spines along their back.



The heads of the Mexican bean beetle, however, are the same coppery-red colour as their backs, whereas lady beetle heads are typically black and white. Adults will darken with age to an orange-brown colour. The larvae are yellow and have 6 rows of long, branching, black-tipped spines along their backs.


Life History: This pest over-winters as adults in grassy fencerows and wooded areas. The adults emerge in May and begin feeding on young bean plants. Eggs are laid on the underside of the bean foliage. Larvae hatch, and young larvae feed in clusters. As they mature, larvae will scatter more. Feeding continues for approximately 1 month before larvae attach themselves to the plant and pupate. Adults emerge approximately 2 weeks later. There are 1-2 generations per year.


Damage: Mexican bean beetle is less of a problem in very hot, dry summers. Early-maturing bean varieties may be grown with little or no injury. Both the adult and larvae feed on the leaves, flowers and pods, but most injury is concentrated on the leaves by the larvae. First symptoms are large holes. As feeding continues, the entire leaf is consumed except for the leaf veins, causing the leaves to look skeletonized. Damage is usually localized.


Scouting Technique: Examine 10 plants at five locations across the field. Monitor border rows. Determine the percentage of defoliation present using Figure 13-2, Defoliation Chart for Soybean Leaf-Feeding Insects, as a guide.


Action Threshold: Substantial yield loss does not take place until up to 35% defoliation occurs before bloom and 15% after bloom. If border plants show evidence of Mexican bean beetle, a border spray may be necessary.

Management Strategies:Depending on when the beetles enter the field, insecticide seed treatment may provide some protection against early-season feeding. Foliar insecticide is only recommended if pest populations and damage are at threshold, because insecticide will kill the natural enemies as well. Control weeds along borders and fencerows to expose adults in their over-wintering sites. Several natural enemies keep this pest under action thresholds.

Western Bean Cutworm (Striacosta albicosta)

Western bean cutworm is an important pest of dry edible beans. Information about this pest.

Tarnished Plant Bug (Lygus lineolaris)

dry edible beans, canola, sunflowers

Description: Tarnished plant bug (TPB) adults are approximately 5 mm (1/5 in.) in length, mottled, yellowish-to-reddish-brown in colour and have a small triangle shape on their back Plate 100. The nymph stage does not resemble the adults but can be misidentified as aphids, though they lack the cornicles ("tailpipes") that aphids possess. Nymphs are yellowish-green, wingless and lack the distinctive triangle-shape on their back. Older nymphs develop four small black dots on the thorax and one on the abdomen.

Plate 100. Tarnished plant bugs are mottled, yellowish- to reddish-brown, and have a small triangle shape on their back.

Life History: TPB have several host crops but tend to move into canola and dry edible beans when alfalfa is being cut. They over-winter as adults in the leaf litter and plant debris within fields, woodlots, fencerows and ditch banks. Once temperatures warm up, adults migrate to other host crops to feed and lay eggs. Several generations occur within the summer. It is usually the later generations that enter the edible bean crop once other host crops are no longer suitable for feeding. TPB tend to be more of a prevalent in hot, dry years.

Damage: The adults and later stages of nymphs are the more damaging stages. TPB have piercing-sucking mouthparts that they use to pierce into the plant tissue and inject saliva that breaks down some of the plant tissue. Feeding on flowers can cause flower abortion. Feeding during pod stages results in scarring, malformation and dimpling or pitting of the pods. Sap may ooze from the feeding sites on the pods, which increases the risk of pod disease development. TPB can also drill directly into the seed, causing pick, reducing seed quality. In sunflowers, TPB injury causes kernel brown spot.

Scouting Technique: Monitor fields weekly during the early-pod and seed-filling stages. Monitor intensely after neighbouring alfalfa fields have been cut. Take 20 sweeps in a 180° arc in 5 areas of the field to determine the average number of adults and nymphs per sweep. TPB prefer pigweed in flower, which can be monitored to help indicate when TPB are present in and around the field. Border rows are apt to have higher populations, so ensure that sweeping takes place.

Action Threshold for Dry Edible Beans: A treatment may be required when an average of one to two tarnished plant bugs per sweep is found during the pod stages.

Action Threshold for Canola: No thresholds have been validated for Ontario, though other jurisdictions recommend spraying canola when two tarnished plant bugs per sweep can be found after petal fall, but prior to pod maturity.

Action Threshold for Sunflowers: One tarnished plant bug adult or nymph per nine heads prior to or at bloom warrant control in fields for confectionary production.

Management Strategies:

• Several parasitic wasps help control TPB. Use a foliar insecticide only when threshold has been reached, because insecticides are extremely detrimental to these parasitoids.
• Spray in the very late evening or early morning when bees are less likely to be foraging in the crop.
• Contact local beekeepers at least 24 hours in advance so that they can move their hives prior to spraying.

Control weeds, particularly pigweed, which can attract TPB to the field.