Having previously identified poor N recovery as largely a denitrification problem, research began to investigate means of reducing N loss. In theory, denitrification Joss can be reduced by controlling the concentration of nitrate in the soil using nitrification inhibitors (which retard the oxidation of ammonium to nitrate), thus reducing the amount of nitrate available to the denitrification organisms. A recently-completed 3-year project evaluated the ability of nitrification inhibitors to improve N fertilizer recovery.

Various parasitoids of heliothis have been considered in integrated pest management programs throughout the world. Despite the rhetoric that parasitoids have an important role in heliothis management, their niche in Australian cotton fields has yet to be fully evaluated. In this paper we present information from Darling Downs trials where egg and larval parasitoids were released as components of an integrated approach tO pest management.

The aim of the project outlined here is to try and develop the SOLICON techniques that are already being used by soil researchers in order to find a practical technique available to cotton consultants or agronomists (SOLICON 2) that gives an accurate analysis of soil compaction. Here a new, cheaper field technique for acquiring images of soil structure using paint is compared to the existing resin method. The existing method of impregnation (6 & 7) is labour intensive; it talces at least two days of field work followed by at least 2 hrs per sample of laboratory work (reimpregnation, grinding and photography) before the images can be analysed

Management of insect and mite pests attacking cotton crops relies heavily on the use of insecticides. In raingrown crops on the Darling Downs, an average of 8 to 12 insecticide sprays are applied to control the major pests - thrips, mirids and heliothis. In order to reduce the dependence on insecticides in cotton production, alternative management tactics are being evaluated as part of a program towards the development of an integrated pest management package. One of the key elements of our approach was to evaluate parasitoids.

Larvae of one Helicoverpa punctigera and three Helicoverpa annigera strains were stressed by feeding early 3rd instars on artificial diet containing 0.015 mg DiPel 2X (32,000 IU/mg) per ml of diet. The percentage of larvae reaching testing size (that is early 4th instars weighing 30-40 mg) by 10 days from the early 3rd instar (weighing< 5 mg) was 65-75% & 90% for H. armigera & H. punctigera respectively, compared to 99% for the control diet. In addition, those larvae that did survive were about twice as slow to develop from the early 3rd instar to testing size (2.9 & 5.7 days for control and Bt diet, respectively). When larvae reached testing size, they were placed on fresh untreated diet and bioassayed with either fenvalerate, endosulfan or profenofos representing the three major classes of conventional insecticides used against Helicoverpa spp. in Australia

This CRDC-funded project is studying the effect of repeated wet/dry cycles, with drying by rotation crops, on the structure repair of a black, cracking clay. The cotton industry knows that the majority of its soils (cracking clays) respond to wet/dry cycles, to repair structure. Past studies succeeded in showing soil structure repair of the topsoil by repeated wetting/drying where the drying was solely by evaporation. Other field studies have examined the role of rotation crops in drying the soil profile to prevent compaction in subsequent cultivation

The diet incorporation technique has been used to detennine the variability in the baseline susceptible response to Bt in a number of field populations of both Helicoverpa armigera & Helicoverpa punctigera. The commercial Bacillus thuringiensis subspecies kurstaki formulation DiPel 2X (32,000 IU/mg) was incorporated into the standard soyflour/ wheat germ/ agar artificial diet. Newly moulted early third instar larvae were confined on the treated diet in 24 well tissue culture trays for up to 8 days at 25 degrees C. The criterion for assessing mo1tality was the same as for conventional insecticides: no co-ordinated movement when prodded. LCSOs are expressed in mg DiPel 2X per ml of diet.

There have been claims that the addition of lime to irrigated heavy textured clays have improved soil conditions and yields. For soils that already have high levels of free natural lime or high pH there exists theoretical grounds that the practice should be rejected. This project was initiated to record the effects such a practice could have on soil properties, plant growth and yield and to establish if this practice has merit for soils of this nature

Host plant resistance has long been a focus of the CSIRO cotton breeding program. Over the past 8 years we have compared the levels of pest resistance in a variety of cotton cul ti vars which bear either morphological (okra leaf, frego bract), or biochemical factors (high gossypol) for resistance to insects. Some of this work was reported at the last cotton conference (Pitt et al 1992) and elsewhere (Thomson 1987, Wilson and Fitt 1987). As a result of that work, which focussed on resistance to Helicoverpa and mites, several promising lines have been introduced into the CSIRO breeding program. Conventional breeding for pest resistance makes small incremental improvements in the tolerance of varieties to insect feeding. With the advent of genetically engineered cotton the stage is set for quantum leaps in pest resistance, through for example the introduction of the Bt toxin genes. However, this does not mean conventional approaches are no longer useful. Any change which can be made to the plant to make it less atttracti.ve to pests or more tolerant to damage will only enhance the value of genetically engineered traits by providing a stronger, more stable basis on which to manage those genes

The distinctive dark glands covering most of the aelial parts of the cotton plant are well known to growers. These glands contain an oil rich in insecticidal terpenoid compounds and as a consequence are associated with host plant resistance. The glands are a general characteristic of the tribe Gossypiae which, in addition to the cultivated species, includes many wild cottons of no commercial importance. Approximately sixteen wild cottons occur in Australia, probably the best known being Sturt's Desert Rose (Gossypium sturtianum), the floral emblem of the Northern Te1Titory. Whilst this species has been studied in some detail, in particular with respect to its potentially useful glanded plant/glandless seed trait, detailed studies of the chemistry of Australian wild cottons generally, have not been reported. Anecdotal evidence suggests that many of the native species are relatively free of insect infestation in the wild. In association with other work assessing the pest resistance of G. hirsutum varieties, a small plot of wild cottons was grown at Nai.Tabri over the 1993/94 season. The plot was unsprayed and plants were used in bioassays which measured the growth and survival of Helicoverpa larvae throughout the season. Preliminary results of these bioassays are presented here.