In the second week of October, we had a one-to-three trifoliate seedling alfalfa field in Tulare County with plants dying on the north end. The surviving seedlings had leaves with holes and ragged edges. No insects were observed on what remained of the foliage and none could be found in the soil. Returning to the field in the warm afternoon, we walked further into the field where there was less damage. This time as we walked we observed small, dark insects moving quickly on and off the plants. However, when we stopped to look closely we couldn’t see them on the plants. Then we used a sweep net to sweep in front of us as we walked and collected dozens of pale striped flea beetles in the net. The adults are just 3/16 inch in length and move fast.
Adult pale striped flea beetle, about 3/16 inches long (Photo:UC IPM)
Some seedlings were killed and significant damage was visible on the foliage of remaining plants at that end of the field. UC IPM guidelines don’t list flea beetles as a pest of alfalfa, but flea beetles are listed as occasional pests on seedlings of some other crops and, according to their IPM guidelines, many insecticides control them. In 30 years I had never seen this pest and I am curious to know how common they are in alfalfa. Please let me know if you have seen them on alfalfa, or any other crop, in the central San Joaquin Valley.