The Effect of Numerous Herbicides on the Germination of Orobanche aegyptiaca and Striga hermontheca

Abstract

Two hundred and thirty seven chemicals were tested to determine their effect on the germination of Orobanche aegyptiaca and Striga hermontheca. From their activity in these tests and a knowledge of their general properties the following are regarded as being the most promising for the pre-em. control of (1) Orobanche — oryzalin, dichlobenil, chlorthiamid, nitralin and chloramben. (2) Striga — 2, 4-D, MCPA and a range of other phenoxy compounds, chlorfenac, with MON 097, prynachlor, PH 40–21, PRB-8, RU 12068 and U 27658 showing the most interesting activity among the newer compounds.     

The Experimental Application of Insecticides from a Helicopter for the Control of Riverine Populations of Glossina tachinoides in West Africa. II. Calibration of Equipment and Insecticide Dispersal

Abstract

Trials were carried out in Upper Volta to assess equipment for the application of insecticides as aerosol from helicopters for the control of riverine tsetse flies (G. tachinoides). Flying techniques were developed to direct aerosols in the downwash of the helicopter to tsetse breeding sites close to the water's edge. Good penetration of droplets below the riverine canopy was achieved during the late afternoon and early morning when weather conditions were very stable.     

Plant Disease Control

Abstract

Experiments have been carried out in the Ivory Coast to assess the performance of a prototype rapid release system to apply larvicides for the control of S. damnosum, the vector of onchocerciasis. The equipment was fitted to a Pilatus Porter aircraft and was used to apply Abate larvicide to a large river during conditions of low water level. It was shown that the equipment could accurately deliver volumes of larvicide between one and 50 l and that these quantities could be placed exactly along chosen points in the river, provided the aircraft was flown along the direction of the watercourse. Satisfactory control of S. damnosum larvae was achieved at three sites using a dosage rate of 0.05 ppm/10 min of waterflow. However, it was recommended that a dosage of 0.1 ppm/10 min be adopted in future work because some of the more extensive sites treated were underdosed. It was not possible to assess the biological effectiveness of the equipment for treating small rivers, but physical tests were carried out which suggest that the system should be suitable for applying larvicide to rivers as narrow as five metres width. Recommendations were made to improve the reliability of the equipment for use in an operational onchocerciasis programme.     

Grassland community composition drives small-scale spatial patterns in soil properties and processes

The presence and activity of individual plants can affect soil resource availability and microbial processes, and can influence the spatial scale over which soil properties vary. While soils have been found to differ under plants of differing growth form (i.e. grasses vs. trees), few studies have focused on small-scale soil differences under comparably-sized species. Here we investigate how two types of C-3 grasses influence patterns in soil properties and processes at scales of less than one meter in a California grassland. To understand how native perennial grasses differ from invasive annual grasses in their effects on soils, we used cross-semivariogram analysis to quantify the degree and scale of spatial heterogeneity in soil properties and processes in experimentally-seeded grasslands. We then used mapping techniques to correlate spatial patterns of soil properties and processes with the cover of annual and perennial grasses aboveground. We found that many soil properties and processes belowground were spatially-correlated with the aboveground presence of annuals or perennials. Soil moisture became more heterogeneous with increasing amounts of perennial cover, suggesting that perennial bunchgrass individuals take up more water and produce zones of resource depletion in comparison with soils directly under annual grasses. The association of belowground resources and activity with the two types of grass suggests that the historical shift from perennial to annual dominance in California grasslands led to changes in the small-scale spatial structure of soil properties and processes in these systems. These changes may alter ecosystem function and could potentially perpetuate invasive annual grass dominance.