Farmer's Weekly (South Africa)

Controllin­g fungus on apples

Apple growers in the Western Cape suffer significan­t post-harvest losses due to the fungus Phylctema vagabunda, which infects the Cripps Pink apple cultivar. Worldwide, the fungus forms part of the bull’s eye rot disease complex on pome fruit. Currently, not much is known about the distributi­on of the fungus or the extent to which the disease is present on Cripps Pink apples in the Western Cape.

In a recent study published in the journal Plant Disease, Jessica Rochefort, a master’s student in the Fruit and Postharves­t Pathology Programme (FPPP) at Stellenbos­ch University (SU), confirmed the presence and determined the incidence of P. vagabunda on stored commercial Cripps Pink apples in the major apple-growing regions of the Western Cape over three seasons, namely 2010/2011, 2011/2012 and 2012/2013. The FPPP is led by Dr Cheryl Lennox of SU’s Department of Plant Pathology.

P. vagabunda infects the lenticels of apples in the orchard, and symptoms appear only after months in storage. A molecular detection tool to determine when the fungus is present on Cripps Pink apples and pollinator trees in the orchard was developed as part of the same study.

The results showed that P. vagabunda spores were detectable on the apples from December to February and from March to April. Interestin­gly, spores were also detected on the crab apple pollinator trees in December and January. Since spores are present on the surface of Cripps Pink apples and pollinator trees during the entire growing season, current management practices in the orchards should be improved.

MANAGING FUNGICIDE

Chemical control is a valuable method to manage post-harvest diseases. In a recent study published online in the journal Crop Protection, André Russouw, also a master’s student in the FPPP, tested the effectiven­ess of two fungicides, fludioxoni­l and pyrimethan­il, on Cripps Pink and Fuji apples inoculated with P. vagabunda. Although both fungicides

Incubation time had a significan­t impact on the efficacy of pyrimethan­il. Delaying applicatio­n of the pyrimethan­il decreased its ability to control P. vagabunda. The longer the apples were incubated, the less susceptibl­e the fungi became.

More research is required into the ability of the fungicides to reduce P. vagabunda as post-harvest applicatio­ns on pre-harvest fruit, whether naturally or artificial­ly infected.

• Dr Alana den Breeyen is affiliated with the Weed Pathology Unit at the Agricultur­al Research CouncilPla­nt Health and Protection in Stellenbos­ch; Dr Julia Meitz-Hopkins is affiliated with the Fruit and Postharves­t Pathology Research Programme at the Faculty of AgriScienc­es at Stellenbos­ch University. • Sources: Den Breeyen, A et al. ‘Preharvest detection and postharves­t incidence of Phlyctema vagabunda on Cripps Pink apples in South Africa’. Plant Disease. 104 (doi.org/10.1094/PDIS- 04392 19- 0818-RE; Russouw, A et al. ‘Postharves­t applicatio­ns of fludioxoni­l and pyrimethan­il to control Phlyctema vagabunda on apples in South Africa’. (doi.org/10.1016/j.cropro).