Note on the effect of wireworms of the genera Agriotes and Corymbites on crop yields

Experiments were made to illustrate the regular falling off of yield of crops due to increasing wireworm populations under controlled conditions. The genus Corymbites was shown to cause as much damage as Agriotes; Athous was less harmful. The damage caused to various cereals by Agriotes is contrasted.     

THE SPREAD OF VIRUS DISEASES TO SINGLE POTATO PLANTS BY WINGED APHIDS

Young potato plants in pots exposed in the open near plots of potatoes for limited periods at intervals during the summer, became infested with large numbers of winged aphids only during warm, calm and dry weather. Although visited by aphids during May and June, when much of the spread of viruses occurred in nearby potato crops, few of the potted plants became infected. Most potted plants became infected in July when alate aphids were leaving neighbouring potato crops. Widely different proportions of the exposed plants became infected in different years; in two of the three years, many more plants were infected with virus Y than with leaf roll virus.     

THE INFLUENCE OF PLANTING DATE AND MANURING ON THE INCIDENCE OF VIRUS DISEASES IN POTATO CROPS

Field experiments with Majestic potatoes were made over six years at Rothamsted to test the effects of varying date of planting and manuring on the yield of tubers and the incidence of the aphid-transmitted leaf roll and Y (rugose mosaic) viruses. Yield was increased by early planting, and by all the manures, especially dung. Early planting also usually increased the incidence of virus disease. Different manures had different effects on disease incidence; the average results from all comparisons showed the largest increase in incidence of both viruses from the use of dung; sulphate of ammonia increased the incidence of leaf roll, and muriate of potash that of rugose mosaic. Counts in two years showed that aphid populations were highest on the earlier planted potatoes, and were increased by dung, sulphate of ammonia and superphosphate, but were reduced by muriate of potash.