Presentation on irrigation and soil oxygen

Presentation on the Boyce Cotton comparative analysis

For season 2004-2005, sixty-one percent of cotton aphid populations were Pirimor resistant but Intruder, Actara, Thiodan and Pegasus susceptible. Two-spotted mite was Agrimec, Comite and Pegasus susceptible. Intrepid resistance was detected in 43 and Talstar 57 percent of mite stains. Curacron resistance in two-spotted mite was ubiquitous and often at high frequencies. At the time of writing testing for season 2005-2006 was incomplete but Pirimor resistance seemed less than in season 2004-2005. Intrepid resistance was still detected in 67% of the two-spotted mite strains although the product was not available for use in cotton. We conclude that the resistance management strategy for cotton aphid and two-spotted mite should remain 'as is' for season 2006-2007.

The detrimental effect of aphid feeding on plant growth has been reported from various crops around the world (Atakan and Ozgur, 1996; Hille Ris Lambert, 1970; Kimmins, 1986; Lowe, 1967; Miles, 1987). We first studied the effects of aphid feeding on cotton and dry matter production in 1999/2000. Prolonged feeding by heavy aphid populations significantly decreased cotton and dry matter production and raised questions about how aphids caused these effects. Contamination of leaves by honeydew, salivary effects and assimilate removal could all be factors. We also noticed that aphid infested plants often grew poorly, even before the level of honeydew production was very high, and speculated that perhaps aphids also affected the photosynthetic rate of cotton. Since it is known that the removal of leaf sugars (such as occurs during aphid feeding) can increase the concentration of sugars in the leaf and thereby give negative feedback to photosynthesis (Blechschmidt-Schneider, et al., 1989; Franck, et al., 2006), we decided to consider this factor first. Our subsequent work investigated any relationships between aphid populations and plant photosynthetic response; how many aphids would be required to elicit a response; and the duration of the response to become measurable.

Key points *Cotton aphid uses a wide range of hosts in winter when cotton is not available. * Farm gardens provide a habitat for cotton aphid especially when conditions are dry. Aphids sampled from such sites show resistance to traditional chemical controls. * Aphids maintain chemical resistance within populations by reproduction by cloning. * Reducing the abundance of aphid hosts on farm through winter, especially weeds, may help reduce abundance on cotton. A list of key hosts is provided.

The use of carbon isotopes as a 'natural marker' of Helicoverpa has proven very useful in this regard (see below). This short paper presents some preliminary results of carbon isotope analyses that we have conducted using both H. armigera pupae collected within a range of different crops and reared to adulthood, and mating moths collected within Bt crops. The research is a follow on from a preliminary study by G. Fitt and P. Gregg (unpublished data) who first recognised the potential for using carbon isotope signatures for identifying the plant host origins of Helicoverpa moths in Australia. Others (e.g. Gould et al 2002) have used the technique to identify plant host origins for other moths overseas.

The objective of this study was to determine what if any biological activity occurred in H. armigera adults and larvae when exposed to extracts from a leguminous plant from Africa, herein referred to as Plant Y.

Black root rot (caused by Thielaviopsis basicola), is an important seedling pathogen in the cotton industry in Australia (Nehl et al. 2004). The disease develops in the early part of the season (3-5 weeks after sowing), under favourable weather conditions, especially low soil temperatures (16-20 DEGREES C). All production areas in NSW and Queensland currently have the pathogen. There are currently no practical eradication methods and prevention, by farm hygiene, is vital. The pathogen produces large quantities of thick-walled spores (chlamydospores) that persist in the soil over long periods. Movement of contaminated soil via farm machinery and vehicles has a significant contribution to transferring the pathogen within and between farms. Several leads are currently under investigation for developing better disease control, including the impact of crop rotations on spore concentration and disease, the use of novel biofumigation (green manure) crops, and the relationship between soil types and disease severity. A further avenue of research is the use of synthetic chemicals, such as acibenzolar-S-methyl (Bion, Syngenta Crop Protection), which act to induce resistance to the pathogen prior to the pathogen attacking the plant. This enhanced form of resistance is referred to as systemic acquired resistance (SAR).

Black root rot is a seedling disease caused by the soilborne fungal pathogen Thielaviopsis basicola. It is a significant threat to cotton and other crops in Australia, especially in cooler areas and seasons. The pathogen, T. basicola, produces thick walled spores that can survive in the soil for years (Figure 1). Although it was first detected in NSW in the 1980s it quickly spread by movement of the spores attached to foot-ware or machinery wheels. In just over a decade it has come to affect more than half of the cotton farms in southern Queensland and New South Wales. Regular disease surveys of cotton fields in NSW have shown an increase of incidence from 22% of fields inspected in NSW in 1995 to over 60% of farms surveyed in NSW in the 2000/2001 season and it was estimated that the incidence of black root rot in 2004 have reached 95% of the fields regularly surveyed in northern NSW (Allen and Lonergan 1997; Allen 2002; Nehl and Allen 2001

The severity of diseases caused by species of Fusarium is often increased by high rainfall and cool temperatures (Neal, 1947; Sharma and Sharma, 2003; Wang et al., 1999; Young, 1947). Wet conditions are commonly encountered early in the cotton growing season in parts of Australia. Wang et al. (1999) found that disease caused by Fov on cotton seedlings, in the glasshouse, was most severe within a temperature range of 18 - 23C and was decreased at higher temperatures, suggesting that cooler climatic conditions would favour the development of Fusarium wilt in the field. Similar temperatures are experienced in the early part of the season in Australia. If sowing can be delayed without leading to yield loss, the period of exposure of the crop to cool wet conditions that favour infection of seedlings by Fov may be decreased. We studied the impact of delayed sowing on the severity of Fusarium wilt of cotton in three seasons on a farm near Moree, Australia.