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Safj Single Treatment Of Azoxystrobin Inhibits Sporulation
December 2021 / January 2022

Green mould on citrus

SA Fruit Journal: December 2021 / January 2022

A sword hanging over the continued use of imazalil to control green mould on export citrus fruit, has led to the discovery of alternatives that might get the job done even better. By Dr Cheryl Lennox (Stellenbosch University)

Penicillium digitatum, the cause of citrus green mould, was first described and classified by PA Saccardo in 1881. Some 140 years later, the pathogen remains an unrelenting headache for citrus growers and exporters.

Citrus green mould is one of the most problematic and destructive postharvest diseases in citrus fruit, particularly oranges. It is responsible for 90% of fruit deterioration during storage, resulting in serious economic losses.

As much as 3 – 4% of citrus fruit is lost due to green mould in the postharvest supply chain. Based on the value of SA’s citrus export market, the economic impact of the disease is estimated to be between R798 million and R1.064 billion per year.

Citrus producers worldwide have long since counted on synthetic fungicides to control green mould. The South African industry is particularly dependent on chemical assistance, given the vast distances export fruit has to cover from the orchards where they are grown to the export markets where they are consumed.

Imazalil, the active ingredient, is a recognised stalwart in the battle against green mould. However, as fungicides develop resistance against chemical treatments and consumers’ demand for low, or no, residues on fruit grows louder, imazalil is under threat. A current review of the active ingredient and its residue levels could result in it being banned.

The risk of losing imazalil as a postharvest fungicide, and the implications for the local industry’s export viability, has triggered a search for alternatives. To this end, a study was led by Dr Cheryl Lennox, senior lecturer at the Department of Plant Pathology at Stellenbosch University, and Professor Paul Fourie of Citrus Research International, over the past two years. Charles Stevens, who holds a master’s degree in sour rot in citrus, conducted all the trials and analysed the data.

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