28 February, 2018
As we move towards the pointy end of the season, many growers are finally seeing some useful rainfall and cooler weather. Unfortunately, a cool change at this time of season can increase the risk for Verticillium wilt, Fusarium wilt and boll rots. If potassium uptake has not been sufficient, premature senescence is also possible at this time of year.
Avoiding a misdiagnosis
It’s easy to confuse the symptoms of Verticillium wilt, Fusarium wilt and premature senescence. Stem cuts can be used for indicative assessment but may be subjective, the best way to assess the infected plants is to refer suspected samples to a plant pathologist. Please contact your local CottonInfo REO to determine the appropriate pathologist and address for submitting sample. A diagnostic form can be downloaded HERE.
Temperature highly influences the incidence and severity of Verticillium wilt, while high nitrogen and low potassium are other factors which favour this disease. As a soil pathogen, Verticillium wilt can be spread over wide areas in soil attached to boots, vehicles and farm equipment, as well as through irrigation water. It is therefore critical to reduce the spread by practicing the principles of “come clean, go clean”.
Premature senescence is chiefly caused by insufficient potassium within the plant. Many factors can predispose a cotton crop to premature senescence but predicting a response to potassium is often difficult. Often by the time physical symptoms are observed it is too late to respond, hence early season leaf testing is useful.
Crops with high boll loads may be more susceptible. Varieties such as Sicot 714B3F and Sicot 707B3F may be predisposed to premature senescence due to their ability to rapidly accumulate a boll load. Wet weather is also likely to increase the incidence of boll rots in the lower canopy, with losses of 5% to 30% observed in severe circumstances.
For more comprehensive information on detecting, sampling and managing any of these disease impacts, check out the recent Facts on Friday newsletter on the topic.
By Chris Teague – Extension & Development Agronomist, Border Rivers and Balonne.
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