Further evidence was accumulated indicating that the peach replant disease decreases in severity as the interval increases in time between removal of the old orchard and the planting of new trees. The ameliorating effect of the interval may be related to the decline of Pratylenchus penetrans (Cobb, 1917) Sher & Allen, 1953. In experiments, increased growth of peach was associated with the control of P. penetrans by nematocides and P. penelrans was found to be the first nematode to attack newly developing peach roots. The populations of P. penetrans within such roots increased rapidly, then gradually declined. Generally, ectoparasites appeared later, increased relatively slowly, and occurred infrequently until late in the second growing season. The soils of all commercial peach nurseries in Ontario contain P. penetrans and the nematode may be transported in the roots of nursery stock.

Peach production in Ontario is largely restricted to the Niagara Peninsula and Essex County, areas that are separated by some 200 miles but have a similar climate. The peach replant problem has been much more serious in Essex County than in the Niagara Peninsula. A survey of mature peach orchards showed that Pratylenchus penetrans (Cobb, 1917) Sher & Allen, 1953, is considerably more prevalent in peach soils in Essex County than in the Niagara Peninsula. In both areas, orchards that had a previous history of the replant problem had three to four times greater soil population of P. penetrans than those with no such history. Soils of finer texture were shown to limit the populations of P. penetrans, and the relatively low numbers of this nematode in the Niagara Peninsula appear to result from the influence of the finer soils prevailing in that region. The effect of different soil-particle sizes on the build-up of P. penetrans may explain the distribution of the peach replant problem in Ontario.

No abstract

Ascogaster carpocapsae Vier. was not known to have spread naturally over the mountain barriers into the apple growing districts of British Columbia, and it was considered that the introduction of this species might aid in the control of the codling moth (Cydia pomonella Linn.) which has become a serious pest in that area during recent years.