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Pests & Diseases

Diseases and pests diminish crop yields; find out what the current threats are and learn how to battle these yield robbers.


I reported recently on stunted and yellow alfalfa plants that were being reported in Berks, Dauphin and Lancaster counties (see pictures).

Samples were sent to Dr. Deborah Samac, USDA-ARS alfalfa pathologist, in St Paul, Minnesota, and I received back a report that the culprit is "Candidatus Phytoplasma asteris" or more commonly known as “Witches-broom phytoplasma.”

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This key is designed to serve as a guide to identification of the more typical larvae of some of the common insect species found in many alfalfa fields during the mid-to-late season. A 10-power to 15-power hand lens will be most helpful in using this key.

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This article describes some common pests and options for their control.


• Description: The sugarcane aphid is a pale lemon-yellow color and prefers pangolagrass. The greenbug is pale green with a dark green stripe on its back.

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Potato leafhoppers have the potential to hurt alfalfa every year. This is generally a second-cutting and third-cutting pest and has been more common recently.

These small (one-eighth-inch long), bright green, wedge-shaped insects may cause severe damage to alfalfa by injecting a toxin into the plant as they feed. This feeding results in a distinctive yellow or purple triangle shape at the tip of the leaf.

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A natural predator, native insect-attacking nematodes, have proven to overcome the most destructive alfalfa pest in North America, the alfalfa snout beetle. 

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Grasshoppers are a visible, frustrating pest of rangeland and field crops. 

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