Diseases of Cotton XI project aimed to increase Australia’s biosecurity preparedness through

early detection by completing annual disease surveillance on commercial cotton farms,

recording the presence/absence of exotic cotton diseases and establishing Australia’s capacity

to screen for exotic strains of bacterial blight.

Seedling diseases continue to threaten the productivity and sustainability of cotton production

in Australia. Seedling disease occurs when cotton is invaded by a number of soil-borne fungi

including Pythium and Rhizoctonia spp. Continued independent evaluation of effectiveness

of seed treatment fungicides and combinations against seedling disease is needed. These

trials provide the most up to date information on new and existing seed treatments available.

The cotton industry spends millions of dollars on seed treatments each season. It is important

that the effectiveness of current fungicides (including the industry standard) and potentially

new treatments are continually evaluated. Including different chemicals and noting the

results also indicates the dominant pathogens present during each season. For example when

stand counts have been high under Apron (Metalaxyl) treatments, this can indicate that the

dominant pathogen was likely Pythium spp. Alternatively when stand counts are high under

PCNB treatments, this can indicate that Rhizoctonia was the likely dominant pathogen.

Biofumigation is the term used to describe the natural suppression of soil borne pests and

diseases using plants containing high levels of glucosinolates (GSLs) in their tissue such as

Brassica crops. Glucosinolates are naturally occurring sulphur compounds that provide

plants with protection. When these plants are incorporated into the soil, tissue is disrupted

and the glucosinolates are broken down by the plant enzyme Myrosinase to produce

phytochemicals called isothiocynates (ITCs). The ITCs are biocidal to a range of organisms

and have the potential to suppress pest and disease organisms. In previous biofumigation

experiments at Australian Cotton Research Institute (ACRI), treatments included canola,

vetch, chickpea and fallow. The biofumigation trial in this project continued the research

from Diseases of Cotton X. The biofumigation crops included vetch, Doublet fodder radish,

biofum blend (40% Doublet Fodder Radish, 50% Carinata Brassica and 10% Achilles white

mustard) and a fallow treatment. Different Brassicas release different quantities of ITCs,

therefore it is important to include more than one variety when assessing crops for

biofumigation potential.

The long term disease survey data has shown an increase in Verticillium wilt in NSW over

recent years. Cotton varieties resistance to the pathogen that causes Verticillium wilt is

temperature sensitive. Consequently varieties that are resistant at 25-27oC are susceptible at

20-22oC. Preliminary examination of some fields in the long term data had shown that fields

with a high incidence of black root rot early in the season also had high incidence of

Verticillium wilt later in the season. Discussions with leading pathologist Dr Stephen Allen

about his experiments and observations also indicated there may be an interaction. The long

term data provides an excellent opportunity to look for potential interactions between

pathogens and incidence/severity of disease.

The NSW pathology team worked in close collaboration with QDAFF pathologist Dr Linda

Smith and also UNE researcher and senior lecturer Dr Lily Pureg studying the pathogens that

cause black root rot and Verticillium wilt in cotton. NSW DPI assisted with collecting and

supplying pathogen cultures to both Linda and Lilly. NSW DPI continued to work closely

with CSIRO (planting off site trials), CSD Dr Stephen Allen with disease surveys and disease

enquiries and Dr Nilantha Hulugalle in assessing his field trials for disease.