Pea aphids, Acyrthosiphon pisum (Harris), were sampled from 1980 to 1983 in field peas, Pisum sativum (L.), in Manitoba. Sweep and foliage samples were taken in commercial fields and plots. Aphids were found in late May or early June soon after the crop emerged, but populations were low throughout June. Populations increased in July, when the crop was flowering and producing pods, and peaked in the latter half of July or early August in 3 of the 4 years, when pods were maturing. Populations decreased rapidly after the peak, as the plants senesced. In 1980, a drought year, aphid densities were low and the populations peaked in the middle of August. From 1981 to 1983, densities exceeded the economic threshold in all commercial fields and all but one of the plots that were sampled.

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A potato breeding population was evaluated for the presence of tolerance and resistance to Verticillium dahliae. Clones were ranked as susceptible or moderately and highly resistant based on symptom expression, and a species-specific polymerase chain reaction (PCR)-based assay was used to determine the Verticillium biomass in the bases of stems. A clone was designated as tolerant if the amount of fungus present in the host tissue was equal to or greater than the collective average amount for all clones in the symptom category above. Tolerant and resistant clones were identified in all trials, but the expression of tolerance was usually unstable across runs. The fungus was detected in some symptomless plants; on the other hand, some symptomatic plants were found to be pathogen-free. These observations emphasize the necessity of accurate quantification of the pathogen biomass in potato during Verticillium resistance breeding programs.

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