ProCrop

Economic Thresholds (PLH per 10 sweeps) for PLH (Potato Leaf Hopper)
 on Traditional Alfalfa*

*For PLH-tolerant varieties, multiply each PLH threshold by 10.

Notes: These PLH #s refer only to adult stage; if nymphs are also present, this is an indication of an actively reproducing infestation, with high risk of continued/future damage to the current crop. Sweep net is not very accurate as a nymph sampling tool. Use the sweep net only for adult counts; and simply note presence or absence of nymphs.

Notes: When integrating the above information in making a treatment decision, for traditional or tolerant alfalfa, also note the degree of visible damage (i.e., initial signs of stunting as noted by shorter inter-node length, or early signs of yellowing).

Notes: First-year seedings of PLH-tolerant varieties should continue to be scouted and treated using conventional thresholds, due to inherent added susceptibility of young seedlings vs. older stands.

Notes: Table 1 (Iowa State) vs. Traditional Minnesota thresholds: The Minnesota thresholds provided in various publications (range from: 0.5 2.0/sweep) are in agreement for the thresholds shown in Table 1, for the columns at $16-18 insecticide cost/ac. IF a grower's cost will be less than $16/ac, the thresholds will therefore be lower (takes less pest damage to cause economic loss.

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