Lychee and Longan Diseases
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Bitter rot and anthracnose, Colletotrichum gloeosporioides (Penz.) Penz. & Sacc.
  Fig. 1
Bitter rot and anthracnose, Colletotrichum gloeosporioides (Penz.) Penz. & Sacc.

Algal spot lesion
Fig. 2
Algal spot lesion

Green-orange algal spots or "green scruf" on leaf surface. The grayish-white and darker "crusts" are lichens of the genus Strigula resulting from fungal colonization of the alga.
Fig. 5
Green-orange algal spots or "green scruf" on leaf surface. The grayish-white and darker "crusts" are lichens of the genus Strigula resulting from fungal colonization of the alga.


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The principal diseases affecting lychee production in Florida include fungi and algae. Anthracnose (Colletotrichum gloeosporioides) is by far the most damaging disease for lychee trees. Stem canker (Botryosphaeria sp.) and pink limb blight (Erythricium salmonicolor) are other fungal diseases that affect lychee trees. Algal spot (Cephaleuros virescens) may become apparent on lychee trees in summer.
Fungal diseases of lychee that are non-manageable (removal and destruction) include the following: mushroom root rot (Armillaria tabescens), Fusarium root rot, Pythium root rot, and Rhizoctonia stem rot.
Longan appears to be little affected by fungi. Only algal spot and parasitic lichen (Strigula sp.) have been reported as pathogens of longan. 1



Anthracnose (Fig.1)
Colletotrichum gloeosporioides

Anthracnose attacks both leaves and fruit of the lychee tree. However, fruit of the lychee variety 'Mauritius' is more susceptible to anthracnose than is the fruit of the 'Brewster' variety. The lychee fruit is susceptible to anthracnose infection from blossom until the fruit is half-grown. Most of the decay on mature lychee fruit is from latent infection when the fruit is small. The small spots coalesce into large brown spots as the fruit ripens. A white mycelial mat grows over the fruit during storage. 2

Update on Anthracnose Disease Control from the University of Florida ext. link



Stem Canker
Caused by Botryosphaeria sp.

This fungus is normally found attacking the terminal branches of the lychee tree. Signs of infection include sunken, shrinking, oval to irregular lesions, which may crack and expose wood. The fungus is managed by pruning out infected branches and limbs. 2



Pink Limb Blight
Caused by Erythricium salmonicolor

This pathogen attacks the limbs and trunk of the lychee tree. The fungus grows above and below the bark. The outer layer appears light pink to white. The fungus encircles the plant part and girdles the vascular tissue, causing foliage wilt and death. This fungus is also managed by pruning exposed wood. 2



Algal Spot
Caused by Cephaleuros virescens

Algal spot has a wide host range among tropical trees, including both lychee and longan trees. Lesions on leaves are roughly circular, raised, and greenish-gray in color. The alga will eventually produce rust-colored, microscopic 'spores' on the surface of the leaf spots, giving the spots a reddish appearance. The alga may also spread to branches. If branch splitting occurs, the branches may become girdled and die. Algal spot seems to flourish in groves that are treated with organic fungicides, rather than with copper-based compounds. 2
 
Algal spot Algal spot
Fig. 3 Fig. 4

Reading Material
Cephaleuros Species, the Plant-Parasitic Green Algae from the University of Hawaii Extension CTAHR pdf 6 pages



Parasitic Lichen
(Fig.5)
Strigula sp.

Parasitic lichen may parasitize leaves on the longan. Symptoms include white star-shaped spots on leaf surfaces. This lichen colonizes leaves reducing their ability to photosynthesize. Please contact your local County Cooperative Extension Service for current control recommendations.



Reading Material

Crop Pest Management Profile on Lychee and Longan (Archived) from the University of Florida pdf 7 pages


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Bibliography

1 Crane, Jonathan H., Balerdi, Carlos F. and Maguire, Ian. "Lychee Growing in the Florida Home Landscape." edis.ifas.ufl.edu. This document is Fact Sheet HS-6, one of a series of the Horticultural Sciences Department, UF/IFAS Extension. First printed Oct. 1968. Revisions Oct. 2008, Oct. 2013 and Nov. 2016. Web. 22 Jan. 2017.
2 Mossler, Mark. "Florida Crop/Pest Management Profile: Lychee and Longan." edis.ifas.ufl.edu. This document is CIR1400, one of a series of the Horticultural Sciences Department, Florida Cooperative Extension Service, Institute of Food and Agricultural Sciences, University of Florida. Publication date Mar. 2002. Revised in June of 2009. Reviewed June 2012. (Archived). Web. 23 Mar. 2015.

Photographs

Fig. 1 Shen, Yuan-Min. Bitter rot and anthracnose, Colletotrichum gloeosporioides (Penz.) Penz. & Sacc. 2009. Taichung District Agricultural Research and Extension Station. bugwood.org. Under (CC BY-NC 3.0 US). Web. 26 Mar. 2015.
Fig. 2,3 Green alga (Cephaleuros virescens ) SymptomsGreen Alga Cephaleuros virescens Kunze on Southern Magnolia. 2008. Florida Division of Plant Industry Archive, Florida Department of Agriculture and Consumer Services. bugwood.org. Under (CC BY-NC 3.0 US). Web. 26 Mar. 2015.
Fig. 4 Barnard, Edward L. Lichen Strigula on Southern Magnolia. 2001. Florida Department of Agriculture and Consumer Services. bugwood.org. Under (CC BY 3.0 US).  Updated 2009. Web. 26 Mar. 2015.

Published 26 Mar. 2015 LR. Last update 22 Feb. 2017 LR
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