Differences in pear varieties, source of scion wood, and kind of rootstock had little effect on the incidence of leaf curl in these tests. Psylla are evidently the vectors of curl and there appears to be little hope of controlling the disease through selection of propagating material, unless psylla are excluded. If not infected in the nursery row, many pear trees may quickly become infected in the young orchard even under the best commercial spray program.

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