The silverleaf whitefly, B-biotype Bemisia tabaci, first detected in Australia in 1999, has

become a major pest on cotton in central Queensland. The silverleaf whitefly is also found,

albeit in low numbers, in most other cotton districts in Australia. The silverleaf whitefly

represents a considerable threat to cotton production in Australia.

The objectives of this project were:

• To monitor whitefly species distribution on cotton.

• To use toxicological, biochemical molecular and genetic techniques to continue

investigate insecticide resistance mechanisms in B-biotype B. tabaci.

• To continue a resistance monitoring programme for B- biotype, B. tabaci.

• To devise and test resistance insecticide management strategies for management of

Bemisia tabaci in Australia.

The project has tracked the expansion of silverleaf whitefly into most cotton areas of New

South Wales and Queensland. Resistance monitoring has exposed serious insecticide

resistance problems in the silverleaf whitefly, including resistance the insect growth

regulators. Studies have demonstrated cross-resistance between the two insect growth

regulators that have been used on cotton in Australia. Resistance mechanism and synergism

studies, however, have provided the means to overcome most resistances in the silverleaf

whitefly. The research project has been an instrumental part of the central Queensland,

silverleaf whitefly, resistance management strategy, which, so far, has prevented “sticky

cotton” problems.

Major Outputs of this project have been:

• Results of this project have given a knowledge of the distribution and abundance of

whitefly species on cotton in Queensland and New South Wales. While the silverleaf

whitefly has expanded into most cotton areas, data show that Greenhouse whitefly,

silverleaf whitefly and native B. tabaci can co-exist on cotton.

• Insecticide resistance levels in the silverleaf whitefly can be very high and resistance is

easily selected for, thus emphasising the need to rotate chemistry. Resistance to the

insect growth regulator pyriproxyfen is of particular concern, because of the industry’s

dependence on use early season, to prevent silverleaf whitefly population build-ups Post

insect growth regulator use, pyriproxyfen resistance levels are so high, as to suggest that

consecutive generations of silverleaf whitefly are receiving pyriproxyfen. It is therefore

likely that the threshold based initiation of pyriproxyfen use, is giving a longer use period

in the area than is desirable. In 2004, post insect growth regulator use, pyriproxyfen

resistance was extreme and coincided with reports of poor control at Emerald.. Piperonyl

butoxide synergism studies with pyriproxyfen, however, showed complete suppression of

resistance and piperonyl butoxide synergism may become a very valuable tool in

prolonging the life of pyriproxyfen on cotton.

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• This project has also developed technology for more effective insecticide synergism in

the field, for the control of resistant silverleaf whitefly. Using our patented concept

(Gunning, R. V and Moores, G. D. Method and Composition for Combating Pesticide Resistance

UK Patent no. 0309773.0, PCT/GB2003/001861),of microencapsulation of insecticides to

delay insecticide release until piperonyl butoxide has effectively inhibited the esterase

enzymes causing resistance, we have been able to overcome resistance. Field trials

demonstrated outstanding control with pyrethroids, against highly resistant silverleaf

whitefly. This resistance control technology can be applied to a number of esterase

mediated resistances in the silverleaf whitefly, such as insect growth regulators,

imidacloprid, the pyrethroids will lead to greatly improved control options for the

silverleaf whitefly.

Fusarium wilt is caused by pathogenic fungi in the genus Fusarium, which infect the roots of susceptible plants and are able to spread throughout the vascular system, stimulating the production of gums and gels that block metabolite and water transport (Beckman, 1987). In resistant plants, infection is restricted to vascular tissue in the lower part of the root system, coincident with the production of antifungal metabolites and the formation of structural barriers to infection (Beckman,1987). The I-2 resistance gene has been introgressed from Lypersicon pimpinellifolium to cultivated tomato (L. esculentum) and protects plants from race 2 (Alexander,1945) of Fusarium osporum f.sp. lycopersici (Stall and Walter,1965; Cirulli and Alexander, 1966). I-2 as been isolated by map-based cloning and encodes a cytosolic protein with an N-terminal leucine zipper, a

putative nucleotide binding site, and seventeen C-terminal 17 leucine-rich repeats (SImons et al.1998). A cytological study involving tomato plants containing an I-2 promoter-gusA construct showed that the pattern of I-2 expression was coincident with the site of pathogen containment in resistant roots (Mes et al., 2000).

Fusarium oxysporum. sp. vasinfectum is found in most countries where cotton (Gossypium spp. ) is grown. The pathogenicity of seven Australian isolates of this fungus has been analysed and no significant resistance was seen in 11 G. hirsutum cultivars, although G. aboreum cv. Roseum was resistant (Davis et al. , 1996). These results are consistent with the observation that most commercial cotton cultivars show relatively poor resistance to Australian races of F.oxysporum f. sp. vasinfectum.

Although Fusarium oxysporum, in is probably a species complex with different vegetative incompatibility groups (Fernandez et al. 1994; Davis et al. 1996) and polyphyletic origins (Skovgaard et al. 2001), it is possible that elicitors may be shared between different formae speciales. Hence, the avirulence factor of F. oxysporum f. sp. Iycopersici race 2 that is recognised by I-2 in tomato might also be present in races of F. oxysporum f. sp. vasinfectum. The availability of genetic, molecular and

cytological data relating to I-2-mediated resistance make I-2 a good candidate (indeed the only candidate) for expression in plants lacking genetic resistance to Fusarium. Many resistance genes function in plants from the same taxonomic family e. g. pepper BS-2 functions in other Solanaceaous plants such as tomato (Tai et al. 1999), and some are also able to recognise their cognate elicitors and trigger a defence response in plants from other taxonomic families e. g. Cf-4 in lettuce (van der Hoorn et al. 2000) and Cf-9 in oilseed rape (Hennin et al. 2001, 2002) or initiate a Iigand

independent response e. g. RPW8 in native tobacco (Peart et al. 2002). Hence, it is possible that I-2 could trigger defence responses in plants outside the Solanaceaous such as cotton. The overall aim of the project was therefore to test the tomato I-2 gene for its ability to confer Fusarium resistance in cotton (Gossypium hirsutum).

During their visit, the US Scientists interacted and shared experiences and

techniques with Dr David Nehl and Dr Om Jhorar of NSW Agriculture, Dr Stephen

Allen from CSD and DrJoe Kochman and DrNikkiSeymour of the QDPl. They were

also able to participate in, and make presentations to, the FUSCOM workshop at

Toowoomba.

Participants in the exercise learnt nematode extraction techniques including

wet sieving, sucrose centrifugation and preservation of samples. The samples were

despatched to the USA for preliminary identification by Dr Terry Kirkpatrick.

Black root rot, caused by a soilborne fungus, was first observed in Australian cotton in 1989. The disease has developed rapidly since then and now occurs in most of the cotton production area in NSW and Queensland. The fungus survives for long periods in the soil as very resilient, dormant spores that are produced abundantly on cotton roots. The severity of black root rot increases in proportion to the number of cotton crops, irrespective of fallows or rotations. The reproductive capacity and toughness of the spores make T. basicola virtually impossible to eradicate. Black root rot is favoured by cool temperatures and the infection of roots is, therefore, most severe at the seedling stage, causing stunted growth. No single control measure gives adequate protection against this pathogen and an integrated disease management approach is required.

The objectives of this research project were to evaluate novel and existing control measures for black root rot, conduct ongoing assessment of the impact of farming systems on black root rot and to consolidate and expand upon the existing disease management strategy for black root rot. A range of potential tools for control of black root rot were evaluated in glasshouse and field experiments. Key findings include:

• Confirmation that in-furrow application of the fungicide benomyl was ineffective in controlling black root rot (as previously indicated for other fungicides)

• Treatment of cotton seed with acibenzolar-S-methyl has potential for control of black root rot as part of an integrated disease management strategy

• The effectiveness of biofumigation against black root rot depends upon good growth, incorporation and breakdown of the biofumigation crop

• Delayed sowing has potential to avoid climatic conditions that favour black root rot and seedling disease and should be an effective control; the use of varieties with high fruit retention should enable delayed sowing without loss of yield potential

• Long-term rotation with non-host crops, such as cereals, has potential to decrease the population density of the black root rot pathogen sufficiently to control disease

• The host range of T. basicola was extended to include several weed species, indicating that effective control of weeds should help to reduce carryover of the black root rot pathogen

The integrated disease management strategy for black root rot has been modified to include the key findings of this research.

Resistance to some carbamate insecticides ( methomyl and carbaryl) in H. armigera is has been known since 1983. But at that time no resistance to thiodicarb (also a carbamate) was identified. However, in early 1993, there were severe H. armigera control problems with thiodicarb in sweet corn and maize crops. These failures were widely distributed across New South Wales and Queensland. Testing at Tamworth showed that these populations were resistant to thiodicarb (approximately 30 fold). In some, the resistance frequency was as high as 80%. 1hiodicarb resistance conferred cross resistance to other carbamates (such as methomyl). While thiodicarb resistant H. armigera were largely confined to the maize and sweetcorn populations, a resistance survey on cotton in early 1993 indicated that a low frequency (-10%) of thiodicarb resistant individuals were also present in the cotton areas of NSW and Queensland

Insecticide resistance continues to be a major problem for the cotton grower. It also is the focus of much of the research into the use and management of transgenic plants. At times, the jargon associated with resistance can be vague or misleading, not only to the cotton grower or consultant but also to specialists in pest management. Terms such as resistance factors, resistance levels and resistance frequencies are all used to connote the seriousness of resistance. The distinction among the three terms is not always clear and they are sometimes used interchangeably

This is a new project that aims to develop diagnostic molecular probes for the most threatening insecticide resistance mechanisms in Australian H. armigera

At the 1992 Australian Cotton Research Conference, we reported on field trials of a prototype Heliothis ID kit that were held during the 1991-92 growing season (Trowell et al., 1992). We described a number of problems revealed by the field trials and outlined the research and development plan we had put in place to overcome them. All those problems were overcome by October 1992 and our second prototype performed very well in trials held during the 1992/93 growing season. Subsequently, the kit was licensed to Abbott Australasia Pty. Ltd. Who christened it the LepTon Test Kit. As is probably well known throughout the cotton growing community, the LepTon Test Kit was launched by Abbott Australasia in October 1993 and has now been commercially available for one full cotton growing season. It plays an important role in the Australian cotton industry's resistance management strategy.

It has now been 11 years since the introduction of the Insecticide Resistance Management Strategy in the 1983/84 season. Continued monitoring of resistance levels in Heliothis armigera during that time has given the following results: