Disease surveys in November and March of each season have been undertaken on a regular basis since 1983. The results of these surveys indicate the relative importance of those diseases which are present and provide an indication of the effects of various cultural and environmental factors on disease development. Disease surveys also present an ideal way to monitor the effects of disease control strategies as they are implemented. Verticillium wilt is the most widespread and important disease of cotton in Australia with the potential to reduce yields by 20-25% in some fields when weather conditions are favourable. Seedling disease is always present and effective control is important so that the costs and problems associated with replanting can be avoided. Mycorrhizas have been shown to be important in the early season growth of cotton in some areas. The purpose of these studies was to develop recommendations to growers for the more effective control of verticillium wilt and seedling diseases and to develop a better understanding of the importance of mycorrhizas so that cropping strategies to maximise early season growth of cotton seedlings can be developed. The increasing importance of Black root rot, the recent occurrence of Fusarium wilt and the significant epidemics of altemaria leaf spot in Pima cotton have also demanded attention.

OBJECTIVES: 1. To study sampling and control practices for mirlds in irrigated and dryland cotton. * development of more accurate sampling techniques *insecticide trials to improve control *development of economic thresholds 2. To assess the importance of local alternate hosts in producing populations of green mirids that attack cotton. * assess mirid invasion of cotton from nearby lucerne and safflower *assess whether mirids invade cotton on weather fronts from distant sources

The aim of this study was to complete the development of a mirid feeding bioassay to facilitate screening and characterization of proteinaceous toxins. The types of protein toxins that are available for screening influenced the assays that were developed. Acute toxins, such as the scorpion neurotoxin, can be assayed using adults and scoring for monality or paralysis. However, there is a very limited nwnber of these acute toxins available. Much more numerous and available are inhibitors of digestive enzymes, lectins and similar proteins that are likely to have a more subtle effect on mirid feeding, growth and development. Assessment of the deleterious effect of these proteins necessitated the development of a feeding bioassay using nymphs.

The aims of the CRDC project CSE 29C were: - to optimise the design of recombinant Helicoverpa viruses with increased insecticidal activity (Activities 1 and 2 of the overall program above), - to develop suitable large-scale production systems (Activity 4) and - to assess the potential impact recombinant viruses may have upon the environment (Activity 5). Timescales for the overall program are shown in Figure 1. Objectives for each year of the CRDC project

Vertosols are the main soil type on which cotton is grown in Australia. Eighty percent of irrigated cotton is grown in retained hill. However, from time to time the hills may need realignment which requires knocking dawn the old hills and fanning new furrows and hills. As a result, new hills can be relocated over old wheel tracks, causing a compacted zone beneath the hill in the root zone, thus impeding root growth. The very nature of the Vertosols lends themselves to self repair under repeated wet/dry .cycle. An attempt has been made in this study to investigate the effect of wet/dry cycles in repairing the structure of a compacted Vertosol from a commercial cotton farm in the Darling Downs of Queensland

A growth disorder of cotton ( Gossypium hirsutum) occurs in irrigated cracking clay soils in cotton growing regions of northern New South Wales. Observations of early season cotton growth were made at l 00 m intervals along transects in fields that showed gradients in severity. Ordination analysis of physical and chemical properties of the soil distinguished three groups of sites (A, B, and C) which corresponded to patterns of yield and early season growth. Early season growth and arbuscular mycorrhizal colonisation of cotton at group A and B sites was much slower than at group C sites. Group B sites showed a recovery of yield later in the season while group A sites did not. Group A and B soils had lower pH, finer texture and higher P, Zn, Mn and exchangeable Mg, K and Na than group C soils. Thus, paradoxically, the greatest stunting occurred in the more fertile soils with putatively more favourable pH for cotton growth. Shoot growth also decreased with increasing manganese availability, soil clay content and soil water holding capacity. The stunting of seedlings at an early stage was not consistent with some potential physical and chemical causes of stunting, including sodicity, compaction, manganese toxicity and waterlogging. Cotton had a high relative field mycorrhizal dependency in group C soil (up to 92% at six weeks after sowing). A series of bioassays in pots showed that slow mycorrhizal development in group A soils was not due to a reduction in the number of propagules of mycorrhizal fungi. Cotton was less dependent on mycorrhizal fungi in group A soils (15 to 20 % ), which partly accounted for the lower levels of colonisation, but the soil microflora also inhibited mycorrhizal development. Sterilisation of group A soils consistently eliminated root browning, a symptom of the disorder, and increased cotton growth in pots and in the field. This was despite the negative effects of sterilisation on P and Zn nutrition due to the elimination of mycorrhizal fungi. Fungi, viruses and nematodes were discounted as possible pathogens. Soil borne bacteria were shown to be causal because (i) cotton growth was increased by the application of streptomycin and penicillin, (ii) bacteria were observed in and streaming from browned cotton roots and (iii) bioassays showed that a species of fluorescent Pseudomonas isolated from cotton roots was pathogenic to cotton. Variation in cotton growth within fields could be accounted for by the additive effects of nonbiological and biological properties of the soil, including both beneficial and pathogenic microorganisms

Two fields of cotton on two nearby farms in the Macquarie Valley of NSW which had different histories of weed management were studied to determine if weed seeds were being introduced via irrigation water. The experiment was set up as a randomised block design with five rows on each fann studied. At the beginning of each irrigation, traps constructed from wire gauze with holes of approximately 1.5 mm diameter were placed over the outflow end of each of the siphons feeding the selected rows. At the beginning of the season soil samples were taken from the furrows of the selected rows to determine the size of the weed seed bank in each field prior to irrigation.

A paper was presented at the fourth international Trichogramma and other egg parasitoid conference titled 'Evaluating egg parasitoids for integrated pest management in Australian raingrown cotton.' Highlights of papers presented at the conference and of discussions with researchers are presented below

The comparative advantage1 of cotton production was examined for three production systems in the United States and four production systems within Australia. Operating expenses, income, operating margin and machinery fixed costs are presented. Tax, social structure, subsidies and capital investment differences are also discussed. Sensitivity analysis was conducted varying the exchange rate and crop yields. Conclusions were drawn on the competitive advantages of investing in cotton production in Australia versus the US

Objectives of visit: To attend the 13th Conference of the International Soil Tillage Research Organization (ISTRO) and present paper entitled "Effect of soil preparation method and cotton-based cropping system on seedbed soil properties in a Vertisol". To have discussions with scientists conducting research on sustainable tillage and cropping systems. In the short-tenn their comments will be utilized in improving and analyzing on-going trials of cotton-based rotation systems on "permanent beds" funded by the Cotton Research and Development Corporation (CRDC) as Project DAN 83C.