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Determine Whether Leaf Feeding on Soybeans is a Big Deal or Not

Determine Whether Leaf Feeding on Soybeans is a Big Deal or Not

One question is 'who done it?' The bigger question is whether it matters.

Cody Kerr looked at the feeding damage on this leaf and answered two questions fairly quickly. Kerr is a sales rep with DeKalb who serves northern Ohio. He is a farm boy from Franklin County, Ind.

"The feeding between the veins indicates that it was likely caused by a beetle like bean leaf beetle," he says. Japanese beetles tend to make a more-rounded, larger hole in the leaf, at least sometimes."

Beetles at work: Bean leaf beetle likely fed on this plant. However on a whole-plant basis, foliage loss is minimal and treatment based on this amount of damage would not be warranted.

He also noted that while seeing holes in a leaf or a leaf with lost tissue between the veins is unsightly, it takes a lot of it to cause a problem and justify insecticide treatment. That's because it's the percentage of the damage on the foliage of the whole plant, not just one or two leaves, that matter. The plant typically has enough leaves to still capture sunlight for photosynthesis if part of a leaf or two is destroyed by insects.

When the damage occurs does make a difference. These soybeans are in the reproductive stage. It takes a lower percent of damage at this stage to justify treatment than when the plant is in the vegetative stage. That's because the plant needs a large factory to produce the materials needed to fill pods with plump soybeans.

The 2014 the Purdue University Corn & Soybean pocket Field Guide, available in paper-book, pocket-size or as an app for an iPad, gives a good indication of how much damage it takes before you should become concerned and decide to treat a field.

The leaf shown here is probably showing somewhere between 5% and 10% damage. However, since most leaves on the plant are not damaged at all, the overall percent defoliation is obviously far below the level whey you would become concerned.

A 10% loss of foliage at the R4 to R5 stage where pods are forming could cause a 2 to 4% yield loss. Again, however, that's 10% of the entire plant, not a single leaf. At R4 to R5 40% defoliation could cause 9 to 11% yield loss.

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