Cold storage after combined packhouse treatments improved control of Citrus black spot

Citrus black spot (CBS) is caused by?Phyllosticta citricarpa, which is regarded as a quarantine pathogen in certain countries. Pest risk assessments disagree on the risk of fruit as a pathway for introduction of the pest to new areas. Some countries accordingly regulate the movement of fruit from production regions where CBS occurs. Preharvest?fungicide?sprays are very effective in controlling CBS, but cannot consistently achieve complete control. The effect of?postharvest?treatments on CBS infections and on the reproductive ability of?P. citricarpa?in lesions that formed after these treatments was studied. Trials were conducted using naturally infected ?Eureka? lemon and Valencia orange fruit. Asymptomatic fruit were treated using commonly used packhouse sanitation and fungicide treatments, and cold storage (individually and combined), as well as alternative stand-alone treatments. After treatment, fruit were stored for 5 weeks (in the dark) at ambient temperature (20?22??C) or ?0.5?7??C, whereafter they were incubated for a further 2?weeks?at conditions conducive to expression of symptoms and formation of?pycnidia. Individual treatments generally resulted in variable levels of control. The combination of packhouse treatments (including pre-packhouse drench with guazatine or?propiconazole?in combination with?pyrimethanil, thiabendazole and?2,4-D; chlorine wash; dip treatment in?imazalil; and brush application of a wax coating incorporated with imazalil, thiabendazole and 2,4-D) consistently showed moderate to high levels of control of CBS development from latent infections on lemons (32.4?43.4% for incidence and 61.6?68.3% for severity) and oranges (58.3?85.7% for incidence and 54.1%?88.8% for severity). However, cold storage subsequent to packhouse treatments (as is common shipping protocol) further improved the levels of control (44.0?58.3% for incidence and 78.1?82.5% for severity on lemons; 66.1?93.5% for incidence and 85.3?98.5% for severity on oranges). An average of 10% of new lesions on lemons and 15% on oranges formed pycnidia, indicating that?P. citricarpa?generally had a low reproductive capability in fruit lesions, which was in most cases further diminished by the combination of treatments followed by cold storage.? Sources Postharvest fungicide treatments and cold storage control citrus black spot infectionsWouter Schreuder (a),?Wilma du Plooy (b), Arno Erasmus (b), Catherine Savage (b), Elaine Basson (b), Cheryl Lennox (a), Paul H. Fourie (ab)(a)??? Department of Plant Pathology, Stellenbosch University, Private Bag X1, Matieland, 7602, South Africa(b)?? Citrus Research International, P.O. Box 28, Nelspruit, 1200, South AfricaCrop Protection Volume 112, October 2018, Pages 332-342 Picture by?Barmac