Field Trials of,Dichloro-Diphenyl-Trichloroethane (D.D.T.) Against the Raspberry Beetle (Byturus Tomentosus Fabr.)

Summary

Crops of early leek cv. Prelina were grown in four experiments at Wellesbourne and in Cornwall from 1995 to 1997. Treatments applied included time of sowing, plant raising temperature, transplant type and covering regime. There was no effect of plant raising temperature on marketable yield or on the percentage of flowering plants. It is suggested that with cv. Prelina it is particularly the conditions during early field growth that affect the ability to flower. Larger plants at transplanting, resulting from earlier sowing or the use of peat blocks, increased the percentage of flowering plants but effects of fleece cover were variable, depending upon how close temperatures were to the optimum for vernalization, which was shown to be close to 78C. It is suggested that rather than planting early, with subsequent air temperatures near to the optimum for vernalization, which will result in high levels of bolters, it would be better to delay transplanting. Plants can then be maintained at a raising temperature that is higher than the optimum for vernalization and transplanted when there is a strong probability of air temperatures being higher. Simple models have been developed to predict first, the rate of increase of leek diameter and secondly, the rate of flower stalk extension, so that it will be possible to predict when the crop will be large enough to harvest and when flowering stalks will become unacceptably long.     

Landscape characteristics of disturbed shrubsteppe habitats in southwestern Idaho (U.S.A.)

We compared 5 zones in shrubsteppe habitats of southwestern Idaho to determine the effect of differing disturbance combinations on landscapes that once shared historically similar disturbance regimes. The primary consequence of agriculture, wildfires, and extensive fires ignited by the military during training activities was loss of native shrubs from the landscape. Agriculture created large square blocks on the landscape, and the landscape contained fewer small patches and more large shrub patches than non-agricultural areas. In contrast, fires left a more fragmented landscape. Repeated fires did not change the distribution of patch sizes, but decreased the total area of remaining shrublands and increased the distance between remaining shrub patches that provide seed sources. Military training with tracked vehicles was associated with a landscape characterized by small, closely spaced, shrub patches.Our results support the general model hypothesized for conversion of shrublands to annual grasslands by disturbance. Larger shrub patches in our region, historically resistant to fire spread and large-scale fires because of a perennial bunchgrass understory, were more fragmented than small patches. Presence of cheatgrass (Bromus tectorum), an exotic annual, was positively related to landscape patchiness and negatively related to number of shrub cells. Thus, cheatgrass dominance can contribute to further fragmentation and loss of the shrub patch by facilitating spread of subsequent fires, carried by continuous fuels, through the patch. The synergistic processes of fragmentation of shrub patches by disturbance, invasion and subsequent dominance by exotic annuals, and fire are converting shrubsteppe in southwestern Idaho to a new state dominated by exotic annual grasslands and high fire frequencies.