Ice versus insects
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EmailEditor’s note: This article is from the archives of the MSU Crop Advisory Team Alerts. Check the label of any pesticide referenced to ensure your use is included.
Every year, there are a few calls about mysterious insect damage that turns out to be frost or hail damage. Here are a few quick tips that add up to damage from ice versus insects.
Distribution of damage in space. The damage is found at the same level across the entire field. In contrast, insect damage is often patchy, worse in some areas than others, or concentrated along edges or in areas of poor crop growth.
Distribution of damage in time. Leaves with damage are of a similar age (hit at same time with hail or frost), while new growth is not affected. In contrast, with an active insect infestation, you would expect at least some new growth to be damaged. In some cases (for example, aphids), insects actually concentrate on juicy new growth.
Damage to neighboring crops and weeds. The same type of damage is found on larger weeds in the field, on plants along the edge of the field, and in neighboring, especially different, crops. This indicates a widespread event affecting many plants, i.e., weather-related.
Lack of consumption. After a hailstorm, leaves may be tattered, torn and ripped, but leaf tissue itself is not necessarily missing. The tattered leaf can often be "reconstructed" by aligning the tears. With frost damage too, the leaf is initially intact, not missing parts. In contrast, feeding by defoliating insects removes leaf tissue.
Lack of bugs or signs. No insect pest is found, or at least consistently found, associated with the damage. There is also a lack of shed skins, frass (bug poo), slime trails, or other signs that insects or slugs were present.
Café gossip. The talk in the coffee shop is about a big thunderstorm or a cold morning, not about critters.
Dr. DiFonzo's work is funded in part by MSU's AgBioResearch.
