SPOTTED ALFALFA APHIDS IN NEW STANDS

Aphids on seedling stands can quickly devastate plants. As few as 1-2 blue or spotted aphids per stem should be considered an economic threshold on seedling stands. On established alfalfa, 5-10 may be considered economic.   

Aphid activity is difficult to detect in short alfalfa when it is windy. Plants that take on a blue, stunted appearance should signal a problem. Careful scouting dry areas of fields may reveal aphids at the soil surface. Thorough application of an aphicide may help save some plants; however, in areas where symptoms are already pronounced, damage may be irreversible. Such areas may ultimately suffer some stand loss.   

If insecticides are needed, then one thorough application of Lorsban should suffice. Be certain to follow all label directions and apply material when conditions are favorable for control.   

If dealing with a taller stand of alfalfa and sweeping the plants is possible, then take 20 sweeps at five locations. Count and calculate the number of aphids per sweep and also count the lady beetles and aphid lions per sweep. If aphid numbers have not yet exceeded the economic threshold (See OSU Fact Sheet No. 7184), and numbers of predators do exceed 5-10 per sweep, populations of aphids may be kept under control without spraying.