Insects and Pests of Field Crops: Dry Edible Bean Insects and Pests
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Agronomy Guide > Insects
and Pests of Field Crops > Dry Edible Bean Insects and Pests
Table of Contents
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
Table 13-7, Dry Edible Bean Insect Symptoms in the Field, shows insects and pests that could be causing the symptoms in the field.
Potato leafhopper (PLH) is an important pest of dry edible beans. Information about this pest can be found at Potato leafhopper
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.
Source: Schaafsma and Ablett, 1994.
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 is an important pest of dry edible beans. Information
about this pest. .
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.
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
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
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 is an important pest of dry edible beans. Information about this pest.
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.
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.
Control weeds, particularly pigweed, which can attract TPB to the field.
For more information:
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