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pressure. In wet years, alfalfa has “wet feet,” making it more difficult for the plant to start to grow. “Wet feet” combined with weevils feeding on the plant could actually create more problems for growing a healthy plant at first cutting. It’s very rare to not have to spray for wee- vils. Maybe a younger field can do without, but generally, after a stand is 2 years old, treatment for weevil is necessary in the San Joaquin Valley. In the past, chlorpyrifos, or Lorsban, was the go-to product for weevil treatment. Currently, Warrior mixed with malathion is the main treatment used for controlling weevils. Increasingly, there is a push for softer chem- istries, but Egyptian weevils aren’t easy to kill because they are inside the plant. This makes them difficult to treat, as many of the chem- icals are contact chemicals, and the weevil needs to feed on it.
Egyptian weevils are a problematic pest in alfalfa in established versus seedling fields. They basically have one generation that cycles through and aren’t an issue the rest of the sea- son. The first cutting when the weevil nymph is feeding is when damage occurs. Later cuttings, when the adults are feeding, don’t affect the plant the way nymph feeding does. Weevil activity starts in mid-February through late March. Weevil nymphs look like a worm nymph and feed on the tips of the alfalfa. They can do extensive damage if left untreated because they can slow plant growth and prevent the plant from flourishing. The leaves become stringy, and the weevils leave holes in the leaves. Weevils feed on the top of the plant. But they are in the layers of the new growth of the leaf, making them difficult to see. Heat will bring the weevils sooner, but even with cooler weather, there is always weevil
PEST CONTROL ADVISOR
How do you prevent weevil damage in alfalfa?
Cameron Jones, Nutrien Ag Solutions, Stockton
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March 8, 2023 Ag Alert 17
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