The objectives of this study were to: l) determine the role of soil instability and clay translocation in the formation of shiny-faced soil aggregates, 2) determine the roles of clay translocation and vehicular compaction in the formation of subsoil densification in cracking clays used for cotton production, and 3) examine the effect of aggregate surface fabric on the movement of water and solutes in these soils. The results of this study have extended the results of previous research on cracking clays to show that the past practices used in long-term irrigated cotton growing have resulted in substantial deep subsoil densification down to depths of 200 cm, and that such deep subsoil densification is likely to be widespread in these soils. This project has also identified that the cause of the deep subsoil densification in irrigated cracking clay soils used for cotton production is vehicular compaction (as a result of heavy axle loads) rather than clay translocation as has been previously suspected. The results indicate that the present trends and recommendations towards the use of lower axle loads and permanent bed systems in cotton production in Australia are very appropriate for these soils. The scanning electron microscopy study on the fabric of these soils has provided an understanding of the fundamental nature of this soil characteristic and provided a more rational basis for the measurement and subsequent interpretation of this soil characteristic. For example, the results of this project indicate that that dull ped fabrics cannot be taken to infer that structural instability in the form of clay mobilisation and translocation has not taken place in these soils. The fabric studies clearly show that there are clay coatings on the structural surfaces within these soils: the solute movement work indicates that at moisture contents below that where the large pore space is coated by conductive films of water, the presence of such clay coatings leads to preferential flow.

The effects of rotation crops and their management on soil properties, and irrigated cotton productivity and profitability were evaluated from 1993 to 1996 in some typical cracking clays (V ertisols) of the Namoi and Macquarie valleys of New South Wales. The project consisted of 3 field experiments: (a) an experiment on tillage systems and rotations (intensive tillage or minimum tillage sown with continuous cotton, and minimum tillage sown with a cotton-wheat sequence which were imposed in 1985, on which three rotations: cowpea-cotton, continuous cotton and fallow-cotton were superimposed in 1993) located at the Australian Cotton Research Institute near Narrabri; (b) a rotation crop management experiment (wheat+l40 kg ha-1 N-cotton, unfertilized wheat-cotton, and winter grain legume-cotton sequences where the legume grain was either harvested or incorporated) located near Wee Waa; and ( c) a rotation crop management experiment [high input (99 kg N and 17 kg P ha-1, irrigated) wheat-cotton, low input (16 kg N and 17 kg P ha-1, rainfed) wheat-cotton, rainfed field pea-cotton, summer fallow-cotton, low input wheat-dolichos-cotton, low input wheat-dolichos +24 kg P & 73 kg K ha-1-cotton, and continuous cotton sequences] located near Warren. (The low input wheat-dolichos/P+K fertilizer-cotton sequence was replaced by a faba bean-cotton sequence in 1995). Soil properties which were monitored to a depth of 0.6 min every site included organic matter fractions, plastic limit, strength, shrinkage indices derived from shrinkage curves, exchangeable Ca, Mg, Kand Na, pH, nitrate-N and electrical conductivity. Profile water content and water extraction to 1.2 m, nutrient uptake, crop vegetative growth, cotton lint yield and fibre quality were also quantified. Economic rerorns were evaluated by comparing gross margins for rotation crop-cotton sequences.

Objectives: A). To establish the uptake and partitioning patterns of potassium in cotton. B). To establish the most suitable predictor of deficiency amongst soil, leaf blade, leaf petiole and leaf petiole sap potassium; including the most appropriate potassium test. C). To establish appropriate methods of within season amelioration of potassium deficiency.

Aims: * Determine the economic impact of thrips on cotton and evaluate new means of control. * Evaluate the range and possible mechanisms of plant resistance to thrips and mites. * Investigate host preferences of thrips and manipulation of hosts to increase thrips predation. * Investigate further the impact of thrips on mites through predation, induced resistance and effects on plant quality. * Refine action thresholds for the control of two-spotted spider mites on cotton. * Evaluate the efficacy of new acaricides and investigate novel technologies for controlling mites. * Determine resistance levels in mites to acaricides and factors influencing development of resistance. * Evaluate the effect of early season insecticides on mites and their predators.

The goals of this research were: 1. measure the soil stresses and deformations due to "edge of bed" operations, and measure the changes to soil physical properties (infiltration, aeration, strength) that result. This was to be pursued in collaboration with the anticipated rotation experiments led by Cooper and the structure project led by Koppi; 2. correlate the field performance of operations with soil conditions, in order to detennine optimum conditions for operations; 3. transfer the conclusions via SOILPAK, the Australian Cotton Grower and Grower Conferences

This project had two major aims consistent with the overall goal of controlling Verticillium wilt in cultivated cotton (Gossypium hirsutum). The first aim was to employ molecular genetic techniques to differentiate between isolates of the fungal pathogen Verticillium dahliae in order to develop a better understanding of the epidemiology of Verticillium wilt disease in cotton. The second aim was to produce molecular genetic fingerprints of the wilt-tolerant cotton cultivars currently being developed by the CSIRO to assist in the identification and tracking of potential genes for disease resistance in the plant breeding program.

aims of this study were to: obtain base-line data against 12 pesticides and to conduct an initial evaluation of the current resistance status of field-collected cotton aphid strains. To that end laboratory studies were required to establish base-line data for Australian cotton aphid. Susceptible strains of cotton aphid were established and breed in purpose built cages. When sufficient numbers of aphids were available they were assayed against a range of established and potential pesticides to establish base line-data. Once generated, the base-line data was used to screen a number of field-collected strains for resistance.

To develop resistance management strategies for organophosphates (OP's) carbamates, insect growth regulators (IGR's) and new insecticide groups, such as the pyrroles based on a sound understanding of resistance mechanisms 2. To evaluate the importance of a newly discovered pyrethroid resistance mechanism and develop low cost, rapid biochemical techniques for the detection of pyrethroid, carbamate and organophosphate resistance.

Pyrethroid resistance levels in Helicoverpa armigera have continued to escalate slowly to around 80-90% but endosulfan resistance has stabilised at about half that level. Resistance to the partial resistance breaking pyrethroid bifenthrin has increased slightly but on average, resistance levels to this product are about half those to the other conventional synthetic pyrethroids. Profenofos resistance is still low in all areas except for an incipient problem in central Queensland. Via tolerance curve analyses indicate the emergence of elevated levels of pyrethroid resistance mechanisms. These ire synergisable by alternative mfo (mixed function oxidase) inhibitors to Pbo (piperonyl butoxide) and are overcome by synergophore pyrethroid analogues such as Series Two and prallethrin but not by esterase inhibitors nor by a non-ester pyrethroid analogue (silafluofen). This indicates the possible development of new isomorphs of P450 monooxygenases (mfos) synergised by alternate chemical classes of mfo inhibitors such as the propynyl ethers but not fully synergisable by Pbo. Laboratory studies indicated some potential synergists for field evaluation (ethion, malathion, phosmet) but most compounds tested were ineffective, including profenofos, trichlorfon, phoxim, azamethiphos and other esterase and glutathione inhibitors. Cyclodiene resistance did not give cross resistance to the avennectins. Baseline susceptible data and discriminating doses were evaluated for three classes of new insecticides; spinosad, the pyrrole chlorfenapyr and the avermectins (abamectin and emamectin benzoate). Abamectin was identified as a potential new replacement for endosulfan for early season Helicoverpa punctigera control. Helicoverpa punctigera resistance levels to both endosulfan and pyrethroids have remained low. )

A Heliothis NPV formulation, GemStar, showed promise as a basis for successful selective, non-chemical insect control on cotton. Trials were conducted with the virus as a stand-alone insecticide on dryland cotton at Dalby, Q. by D. Murray (QDPI), and in conjunction with Envirofeast on irrigated cotton at Moree by R. Mensah, (NSW Agriculture). On dryland cotton at Dalby, Qld, yields were equivalent to those with conventional chemical control at one of the two sites. The virus failed to contain a heavy infestation of Heliothis in February 1996, but neither did conventional insecticides. In an IPM programme on cotton with lucerne strip cropping at Moree involving 4 Envirofeast sprays followed by 3 sprays of the virus combined with Envirofeast and a clean-up chemical spray, yields were similar to those obtained with a conventional insecticidal regimen. Predator numbers were higher in the Envirofeast/GemStar plots than in other "soft11 treatments", Envirofeast/endosulfan or Envirofeast/Bt endosulfan, suggesting that any disruption to predators by GemStar was at a low level. Bioassays indicated that GemStar maintained its potency during on-farm, refrigerated storage. Levels of infection achieved on cotton were variable but the overall average was about 55%. This suggests that the use of the virus should be integrated with other Heliothis control measures. Thresholds frequently exceeded 2 larvae per row metre without undue damage to the crops, suggesting that this biocontrol system provided greater flexibility in control response than with chemical insecticides. This aspect requires further investigation to determine appropriate thresholds.