Regular disease surveys have highlighted the changing status of cotton diseases over time and

provided valuable insights into the factors affecting their distribution and severity.

• The disease surveys provided overwhelming evidence that seedling mortality is not related to the

incidence or severity of black root rot but increases with increasing latitude

• The observed incidence of black root rot has decreased in the past three seasons, most likely as a result

of climatic conditions and drought-enforced fallows but has increased rapidly in the Lachlan and

Murrumbidgee Valleys.

• The rate of reporting of new cases of Fusarium wilt, now totalling 81 farms in NSW, has declined in

recent years, potentially due to farm hygiene, greater deployment of less-susceptible varieties and drier

conditions in spring.

• Fusarium wilt has been observed on 41% of the set of farms surveyed annually in NSW and is

spreading at a steady rate of increase among those farms

• The incidence of Verticillium wilt decreased recently in the Namoi Valley, probably due to greater use

of resistant varieties, although the disease is still observed in 45 to 60 % of fields surveyed annually

across NSW

• An apparent decline in boll rots over recent years probably reflects both the drought and the expansion

of the surveys into southern NSW, where summer rainfall is low.

Experiments were conducted to develop and/or evaluate control strategies for control of

seedling disease, black root rot and Fusarium wilt:

• High seed vigour index, while decreasing seedling mortality, was not related to seedling growth;

seedling mortality was not related to seed mass

• The fungicide DynastyTM consistently performed as well as, and sometimes better than, the standard

fungicides

• Seed treatment with fertilisers and other non-fungicidal products, were not effective in controlling

seedling disease, nor was Bion® in most cases except in crops with Fusarium wilt, suggesting that

Bion® may activate resistance against F. oxysporum f.sp. vasinfectum as a seedling pathogen.

• Seed treatment with Bion® activated resistance against Fusarium wilt and black root rot of cotton,

although its efficacy was variable

• In-furrow application of the fungicide azoxystrobin was very effective in controlling seedling disease in

some seasons at some locations.

• Delayed sowing decreased the period of exposure of cotton to conditions that favour black root rot and

seedling disease, even when cool and wet conditions coincided with the late sowing.

• Pre-plant and at-planting herbicides had no effect on the severity of black root rot or growth of seedling

cotton

• In comparison to continuous cotton, nine years of bare fallow did not eliminate arbuscular mycorrhizal

fungi (AMF) in the soil, although re-colonisation by AMF probably occurred, as the black root rot

pathogen, T. basicola, also colonised the fallowed plots in the absence of plant hosts.

• During bare fallows of up to four years at Bourke, AMF survived in sufficient numbers for normal

development of mycorrhizas in cotton

• AMF were not affected by transgenic cotton varieties

• Seed treatment with a plant flavonoid reputed to increase mycorrhizal development in the field was

phytotoxic at the recommended rate and no conclusion about mycorrhizal effects could be drawn.

• Evaluation of a commercial inoculum, putatively containing mycorrhizal fungi, showed that no

mycorrhizal fungi were present in the product.

Results of these experiments and observational studies have been incorporated in strategies

for integrated disease management and disseminated to the cotton industry by way of

publications, media releases, field days and meetings with growers and consultants.