Tomato leaf curl virus disease (TLC) was checked by frequent and early applications of Anthio, Folimat, Malathion and Phosdrin against the aleyrodid vector, Bemisia tabaci. Conversely, up to two-fold increases of fruit yield resulted from such applications of the insecticides. Though seed-bed or field applications, separately, gave satisfactory results on occasions, treatments of the plants in the seed-bed and the field were often both essential. Field observations during the experimental period, over four consecutive seasons, showed peak infection rates within the first 8–12 weeks of tomato planting. There were marked inter-seasonal fluctuations of disease incidence, ranging from < 50 to 100 per cent. There was no clear correlation between spread of the disease and the wind direction. Epidemiological behaviour of the disease is discussed in relation to its chemical control.

The effects of rainfall on yield of rainfed grain sorghum in a rotation experiment have been investigated over six years. There was a positive association between yield and rainfall during May and from the beginning of July to the first half of September, but a negative association at other times of the year. Total rainfall in August and September, and the annual total, were positively related to yield, while the totals of June and July were inversely related. Variation in monthly rainfall accounted for up to 86 per cent of the variation in yield, while the total rainfall in August and September accounted for up to 96 per cent.

The application of lime to natural pastures in Rio Grande do Sul, Brazil, did not increase herbage yields, but nitrogen fertilizer, alone and in combination with phosphorus fertilizer, enhanced dry matter productivity significantly. Dry matter yields of the natural pasture were more than doubled at the highest fertilizer rate, though the botanical composition of the sward was only modified slightly by various lime and fertilizer treatments.

Mild manual defoliation of pigeon pea plants had little effect on pod numbers, pod weights, or number of seeds per pod in two experiments. The effects of severe defoliation depended on timing and differed between pigeon pea cultivars. Late severe defoliation reduced pod numbers in both experiments, but early and intermediate severe defoliation also differed in their effects. Some physiological implications of these results are suggested.

The growth of plants is controlled by the availability of photosynthesized carbohydrates. Since both rainfall and sunshine are needed for photosynthesis an empirical expression is proposed which relates vegetative growth to the product of rainfall and bright sunshine hours over a specified period. Tea is a crop in which the yield is entirely vegetative and harvested throughout the year. Laycock's data for tea yields from constant treatment plots in Malawi show that yield was strongly correlated with the product of rainfall per month (R) and average daily hours of sunshine per month (S) for the previous month (r=0·972). The graph of yield vs RS for the previous month gives a straight line passing through the origin. This empirical weather parameter RS appears suitable for the study of vegetative harvests.

Two cocoa progenies, T85/799×T17/359 and E1:C43/291×T63/967 (Series IIB hybrid), were compared for degree of infestation by 17 insect species comprising a Coccid, an Aphis, a Mirid and six ants. A significantly greater proportion of trees of the second variety was infested by the mealybugs Planococcus citri Risso and Pseudococcus hargreavesi Laing, by the Lecaniid scale Gascardia sp. nr. zonatus Newst., by the aphis Toxoptera aurantii Boys, by attendant ants Camponotus spp., and Crematogaster spp., and by the ant Polyrhachis laboriosa F. Smith. Because of differences in habitat requirement between the four Hemiptera, it is postulated that it is more likely that the response is due to a physiological difference between the two progenies than to a purely environmental difference.

The main axis of a Principal Components Analysis, based on measurements of width and depth of canopy of two cocoa progenies was shown to be an index of canopy size and the second axis an index of shape. Mean scores of the progenies T85/799×T17/359 and E1:C43/291×T63/967 (Series IIB hybrid) on these axes showed that their canopies did not differ significantly in shape, but that the canopy size of Series IIB trees was on average greater than that of T85/799×T17/359. Regression lines of log numbers per tree of Planococcus citri Risso against canopy size of the two progenies were parallel, indicating that for a given canopy size P. citri was 2·3 times more prevalent in trees of Series IIB than in T85/799×T17/359. A similar analysis with the combined numbers per tree of seven mealybug species showed that they were 1·9 times more prevalent in Series IIB than in T85/799×T17/359 trees of the same size.

Bulbs of 20 onion cultivars were stored at 30°C and assessed for rotting and sprouting. No evidence of heritable resistance to high-temperature rotting was found, but the suppression of sprouting by high temperatures appeared to be a common character of onion cultivars.

The response of groundnut plants to CCC was investigated by applying concentrations of 0, 500, 1000 and 1500 ppm three times as a foliar spray. CCC at 500 ppm gave more kernels, and heavier yields of pods, kernels and oil, than 1000 or 1500 ppm or the control treatment. Application of CCC resulted in a greater percentage of shell and of moisture in the whole pod than in the control.

Work was conducted in Alexandria and Sakha districts, Egypt, to study the influence of planting dates and seeding rates on yield of seed cotton, yield components and fibre properties of Egyptian cotton, Menoufi variety, during 1970–1972. Four planting dates were studied, together with four seeding rates. The number of lost plants decreased as planting date was delayed, and the highest yield of seed cotton resulted from the third date of planting (20–23 March) using hand-drilling. Neither planting dates nor seeding rates had significant effects on most of the other characteristics studied.

Responses of nodulating and non-nodulating isolines of Clark and Harosoy to applications of N were studied, to evaluate the suitability of symbiosis versus N fertilization for soybean. Nodulating lines did not respond to N when they were either effectively inoculated or raised on a field which had been under inoculated soybean in the past. On a field brought under soybean for the first time, uninoculated Clark and Harosoy needed 300 and 235 kg. N/ha. respectively to give maximum yields. Symbiosis proved better than N fertilization for the N nutrition of soybean.

Performance of Short Kaura, a photosensitive Nigerian sorghum, was compared at Samaru in ten sowings in 1972. Except for a two-week interval between the fifth and sixth sowings, all sowings were at weekly intervals from 12 May to 21 July. Total dry weight and grain yield decreased with delay in sowing after 26 May at the rate of 1700 kg.ha.−1 week−1 and 360 kg. ha.−1 week−1 respectively. Each week's delay in sowing after 12 May shortened the total growth cycle by 5·9 to 6·0 days, with 77 to 78 per cent in the vegetative phase, 7 to 8 per cent in the head development phase and 14 to 16 per cent in the grain filling phase. Although the date of head initiation seemed to be determined by photoperiod, sowing date also had a small but definite effect.