S U M M A R YNine field trials were carried out from 1967 to 1973 on sandy loam soils in Staffordshire and Worcestershire to study the relationship between potato yield and numbers of potato cyst nematodes (Globodera spp.).Three (probably five) of these trial sites appeared to be infested with G. rostochiensis only, whereas both species occurred on the remaining four sites which grew the resistant variety, Maris Piper. Although mixtures of the two species occurred on some plots they tended to have different distributions within each trial site.The results from this work have been analysed, together with those from earlier work in the Eastern Counties on peat and silt soils, over two population density ranges, 0-40 eggslg (5 sites) and 0-160 eggs/g (16 sites). There is no evidence of any difference in the regression of yield on eggslg amongst the five sites in the lower range (b = -0.90 +_ 0.11) nor amongst 15 of the 16 sites in the higher range (b = -0.40 +_ 0-02). Analysis of 10 sites with sufficient data in the 40-160 eggslg range gave b = -0.24 k 0.06. Thus the regression lines are essentially parallel for each of the two ranges, covering several potato varieties, soil textures and different potential yields and suggest that the varieties used are equally tolerant. The losses are 6.25 tfhaf20 eggsfg for the 0-40 eggslg range, 1.67 tlhaf20 eggslg for the 40-160 eggslg range, and 2.75 t/ha/20 eggslg as a mean for the whole range. A maximum loss of 22 t/ha is indicated.Peat soils are less dense than mineral soils but there was no need for adjustment in nematode counts. Losses caused by potato cyst nematodes are better expressed as actual yield losses rather than as percentage decreases.

No abstract

S U M M A R YLongidorus elongatus attacks sugar beet on light sandy soils in the West Midlands. Severely damaged plants may die or recover, producing fanged roots. Up to 335 L. elongatus/zoo g of soil were found around attacked seedling plants and were often visible to the unaided eye on the roots of freshly lifted plants.Five experiments were made and regressions computed of yield of beet, total numbers of plants and numbers of normal and fanged beet on L. elongatus numbers. Between 24% and 50% of roots per IOO L. elongatus/ zoo g were killed or became fanged. Corresponding figures for loss of plant were between 7'5% and 33%. Estimated loss of yield varied between 0.8 and 7.3 tons (2.0-18.3 t/ha)/ acre/Ioo L . elongatus/200 g, the former where the potential yield was high and the latter where poor growing conditions hindered recovery.Large numbers of Trichodorus occurred in two trial sites and there is some evidence of competition between the two genera. Significant negative regressions for Trichodorus spp. were obtained in one trial suggesting a loss of 12% total and 17% normal roots per IOO Trichodorus spp./200 g.

SUMMARY During 1973 the susceptibility to spraing of 12 commercial potato cultivars was tested on land in North. Worcestershire infested with viruliferous Trichadorus nematodes. The wide‐spectrum pesticide phorate reduced spraing in the harvested crop by over 60 per cent compared with untreated plots, bat the order of symptom expression was similar in both treated and untreated plots.

SUMMARY Field populations of Myzus persicae (Sulz.) collected from 30 sites in Yorkshire and Lancashire were tested by total esterase or bioassay techniques for resistance to Organophosphorus insecticides. All the populations examined included some resistant aphids and some populations contained individuals with esterase activity characteristic of very resistant aphids.