System to detect CBS in citrus groves

The Citrus Black Spot (CBS), caused by fungus Guignardia citricarpa, was detected in Florida, near Immokalee, in the spring of 2010. It is a disease that affects both quality and yield, so much so that it is considered the most destructive citrus fruit fungus in the world. 

The symptoms are the black spots and lesions on the skin, and that is why fruit affected cannot be sold on the fresh market.

In addition, the most serious infections could lead to drops, thus drastically reducing yields. Even the fruit that does not show symptoms when harvested can still develop the disease during transport or storage.

CBS lesions often appear during ripening, as early as two months before harvesting. In addition, warm temperatures and sunlight can increase the number of lesions.

The two main sources of inoculum are infected decomposing leaves left in the grove and lesions on branches, fruit and leaves. The disease can be transmitted to healthy plants through wind and water. 

In order to monitor the disease, infected trees should be identified, preferably during the first stages of the infection, so specific effective treatments can be employed. 



Image sensor (5-band cameras). (a): two mirrorless Canon M10 cameras on a bracket and shutter controller. (b): 5-band imaging system mounted on a robot for autonomous field inspections.

Researchers at the University of Florida introduced a detection system based on a multi-spectral NIR imaging system that can identify fruit with CBS lesions directly at the grove. In the lab, the system identified infected citrus fruit with a 100% precision using only information on colour. 

An image analysis algorithm was developed to distinguish potential spots and confirm whether they are CBS lesions. Morphological characteristics were taken from potential spots in all their colour components. The algorithm can determine whether a fruit is CBS negative or positive. This method can diagnose CBS directly in groves and it is not only effective but also economically accessible.

Source: Alireza Pourreza, Wonsuk Lee, Jun Lu, Pamela Roberts, 'Development of a multiband sensor for citrus black spot disease detection', Proceedings of the 13th International Conference on Precision Agriculture, July 31 – August 4, 2016. St. Louis, Missouri, USA.

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