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.

• Seedling mortality was low during the 1990’s but increased dramatically in 2000, 2001

and 2002, largely due to cool wet conditions during spring.

• The risk of seedling disease increases with increasing latitude; the southern regions of

NSW are particularly prone with up to 60% seedling loss observed in some fields.

• NSW is currently experiencing an epidemic of black root rot of cotton. Black root rot was

observed on all of the farms surveyed regularly in the Macintyre, Gwydir, Namoi and

Macquarie Valleys, and in 78% of fields and 39% of plants within those farms. The

disease was detected in the Murrumbidgee Valley for the first time in 2003.

• The distribution of continued to increase. Fusarium wilt has been reported

on a total of 75 farms in NSW and was observed on 30% of the farms surveyed regularly

by NSW Department of Primary Industries.

• In NSW, adoption of less-susceptible varieties is ahead of the incidence of Fusarium wilt

• Transects of an infested field in the Macquarie Valley suggested that Fusarium wilt may

progress much more quickly in cooler cotton growing regions.

• Verticillium wilt was observed at very low levels, although its incidence has increased in

the Namoi Valley, probably due to a period of declining use of resistant varieties.

• Many farms do not have black root rot, Fusarium wilt or Verticillium wilt and farm

hygiene should be practiced to minimise further spread.

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

seedling disease, black root rot and Fusarium wilt:

• Delaying the date of sowing as late as possible within the planting window can avoid

conditions that favour seedling disease and black root rot.

• Planting should be timed to coincide with the onset of periods in which the mean soil

temperature will be 16°C during the first week from sowing and delayed after preirrigation

until soil water content is at the lower end of the range that is adequate for

seedling establishment, in a given soil

• Different seedling pathogens vary in dominance from field to field and year to year; the

fungicide treatment DynastyTM consistently performing as well as the standard fungicides.

• Seed treatment with acibenzolar-S-methyl consistently activated resistance against

Fusarium wilt of cotton but not Verticillium wilt.

• A practical method for application of acibenzolar-S-methyl to cotton seed was developed,

using 6 mg/kg seed incorporated in the standard seed treatment fungicides, with no

phytotoxic effects and an extended, active shelf life.

• Vetch, mustard and canola were increased the severity of Fusarium wilt and should not be

used as biofumigation crops on farms with Fusarium wilt

• The peak activity of the black root rot pathogen and seedling pathogens are mutually

exclusive, providing further evidence that T. basicola does not kill cotton seedlings

• Mycorrhizal fungi survived in substantial numbers after long bare fallows of 28 and 35

months in fields at Bourke and after a bare fallow of four years at Narrabri

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.