A new, high concentrate version of a reliable fungicide is good news for macadamia growers to add to their management programs for the potentially devastating husk spot disease. 

Husk spot is caused by the pathogen, Pseudocercospora macadamiae which is only found in Australia and costs the industry around $10 million a year. It infects the fibrous husk around the macadamia shell, causing nuts to drop-off prematurely, and spreads from old husks to new green ones.

Growers have previously had limited fungicide options against husk spot and they involved strong use of Group 1 chemistry and copper-based fungicides, however they can now add Custodia Forte from Adama Australia to some of the newer fungicides being used in their strategic management programs.

Jim O’Connor, Adama Australia’s market development manager in Southern Queensland, said compared with its predecessor fungicide, Custodia Forte contains almost twice the amount of the active ingredients, tebuconazole (Group 3) and azoxystrobin (Group 11).

“Compared with some of the latest fungicides for husk spot, Custodia Forte offers a more cost-effective and reliable option, as well as the convenience of reduced handling, packaging and, hence, waste.”

He said the higher concentrate, low odour formulation can be applied at about half of the recommended application rates of the former Custodia.

Custodia Forte, which has a harvest withholding period of 15 days, also is highly compatible for tank mixing.

“As part of preventative fungicide programs for husk spot, we recommend Custodia Forte be applied from the match head stage, with a maximum of two applications per season spaced 14 to 28 days apart and separated by another fungicide treatment with a different mode of action.”

Mr O’Connor said specific fungicide programs for husk spot in macadamias should be determined by the disease levels, prevailing conditions and orchard hygiene, which, in more recent times, has been enhanced by cultural methods including tree shaking.

“Mechanically shaking of trees and adoption of other cultural controls to improve orchard hygiene is increasingly playing a key role in conjunction with new fungicide tools to reduce the risk of husk spot infection in macadamias.

“The industry has continued to evolve and become more sophisticated, and this has resulted in greater understanding and fine-tuning around husk spot disease control in order to maximise yields and quality,’’ he said.