Every year, dry bean growers wrestle with insects and the impact they have on yield and quality. Some of the pests arrive early in the season, some of them come later. Some do damage above ground while others do their business under ground.
On this episode of RealAgriculture’s Edible Bean School, OMAFRA canola and edible bean specialist Meghan Moran shines a light on the big yield robbers in edible beans and offers tips on how growers can identify and best manage these pests.
When it comes to insect damage, Moran says above ground pests that come later in the season tend to have a greater impact on the quality of the beans, but there can be situations where below-ground pests cause significant damage.
“I’ve certainly seen fields with significant seedcorn maggot damage that needed to be replanted,” she notes “The majority of fields have CruiserMaxx seed treatment so there is some protection against soil-borne insects and early-season insects.”
Moran breaks the edible insects into two categories — chewers and suckers. She says chewing insects can cause defoliation of the plants which may impact yield, but this is less common than other insect problems. She adds that bean plants can handle up to 35 per cent defoliation prior to flowering and 15 percent during or after flowering.
Below-ground pests lead to a plant stand reduction, which may or may not lead to replanting or yield reduction. The most common chewers that grower see are bean leaf beetle, western bean cutworm, corn borer, and Japanese beetle.
Chewers may cause yield loss by completely removing pin pods and small developing pods. They may chew up whole beans in the pods, which causes some yield loss; or they may just take a small bite out of a bean, creating a quality issue. Chewers may also cause quality issues by leaving a hole in pods where diseases can enter and damage quality — some beans actually change colour or become discoloured when exposed to oxygen.
Sucking insects have a stylus or syringe-like mouthpart that they poke into the plant tissue and feed by sucking. These insects may feed on leaves and cause damage that leads to yield loss, or they may feed directly on pods and beans which causes damage and loss of quality, including misshapen, shrivelled or discoloured beans.
Suckers include potato leafhoppers which inject a protein that blocks the plant’s vascular tissue. This causes the leaf edges to become yellow and puckered, with a characteristic yellow “V” shape beginning at the tip of the leaves. When severe, the leaves appear burned or necrotic, a condition typically referred to as “hopperburn.”
In the video, Moran and host Bernard Tobin discuss the growing season and identify some key pest growers need to look out for. They also review thresholds and identify how to best control the pests to minimize yield and quality impact.
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