The Australian Pesticides and Veterinary Medicines Authority (APVMA) has issued two new minor use permits for the cotton industry to help growers manage foliar diseases. These permits allow for the use of the fungicides Belanty and Merivon to control Target Spot.

According to Samuel Krekeler from the Queensland Department of Primary Industries (QDPI), outbreaks of Target Spot have primarily been reported in pivot-irrigated crops in Queensland, particularly in the Atherton Tablelands and surrounding areas. The development of this disease is favored by prolonged periods of leaf wetness, moderate temperatures (around 25-30°C), and high relative humidity.

"If said conditions are met, crop managers are encouraged to scout for disease symptoms from flowering onwards to determine the course of action," says Mr. Krekeler. "Preliminary trials have shown that fungicides can be very effective for managing Target Spot. However, the disease's impact on yield and optimal management are subjects of currentresearch."

Another disease that is being studied in Northern Australia is Ramularia, also known as Grey Mildew. The impact of Ramularia is expected to vary across different cropping regions in northern Australia due to climate differences. In the Northern Territory (NT), Ramularia infection in rainfed crops and surface-irrigated crops in Western Australia (WA) appears to be sporadic, occurring after crop cut-out and closer to defoliation. These scenarios leave limited opportunity for disease buildup and are unlikely to affect yield. However, pivot-irrigated crops in the NT may create more conducive conditions for an earlier and more persistent infection. Active monitoring is advised to determine course of action.

Leaf blights (caused by Alternaria sp., Cercospora sp., and Stemphylium sp.) have also been reported in Queensland, WA, and NT. In northern Australia, these tend to appear late in the cropping cycle. The exact behaviour of these fungal pathogens is currently being investigated in more detail, but field observations indicate that cooler temperatures might favour their occurrence. Disease development has been observed to be slow and mild, with no cases of defoliation reported in modern commercial varieties. Overseas literature suggests that the incidence of these leaf blights might be linked to low potassium levels in the soil during times of high demand by the plant (i.e., boll-filling). Potassium fertilization is currently being investigated as a potential strategy to mitigate these leaf blights.

There are now four minor use permits available for controlling foliar diseases in cotton, with the two new options for Target Spot and existing permits for the control of Ramularia. Follow the links below to access these permits from the APVMA website.