Basil Diseases
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Basil Downy Mildew Sign © Sandra Jensen, Cornell University, Bugwood.org

Fig.1 Basil, Downy Mildew

Peronospora belbahrii
Sign

A closer view of a lesion with dense sporulation that looks like a grayish-purple mold on the leaf

Basil Downy Mildew Symptoms © Bruce Watt, University of Maine, Bugwood.org

Fig. 2 Basil, Downy Mildew
Peronospora belbahrii
Symptoms

Basil with Cercospora Leaf Spot Credit: Margaret Williamson Margaret Williamson, Plant Disease Diagnostician, Plant Problem Clinic, Clemson University

Fig. 3 Basil, Cercospora Leaf Spot

 

Bacterial Leaf Spot Sign © Florida Division of Plant Industry Archive

Fig. 4 Basil, Bacterial Leaf Spot Pseudomonas cichorii

Sign

Bacterial Leaf Spot Sign © Florida Division of Plant Industry Archive

Fig. 5 Basil, Bacterial Leaf Spot Pseudomonas cichorii

Sign

Basil with Fusarium Wilt Credit: Debbie Roos, NCSU Agricultural Extension Agent, Chatham County, NC

Fig. 6 Basil, Fusarium wilt

Fusarium oxysporum f. sp. basilicum

Note: the shepherd's crook bending the ends of the stems.

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Downy Mildew (Peronospora sp.) 1

Symptoms: Symptoms initially appear as yellowing of leaves and are typically concentrated around the middle vein. The discolored area may cover most of the leaf surface. On the underside of leaves, a gray fuzzy growth of the pathogen may be apparent by visual inspection. Under high humidity, the chlorotic areas turn to dark brown quickly. Sporangia, the reproductive structures of the pathogen, are easily detected under magnification.

Cultural Controls: Use disease-free seed as the pathogen is believed to be seed transmitted. Reducing the period of leaf wetness by avoiding overhead watering may also be helpful.


Further Reading
Downy Mildew of Basil in South Florida from the University of Florida pdf

Leaf Spot (Colleotrichum sp.)

Symptoms: Dark spots form on leaves and the dead tissue within leaf spots may drop out, causing a shot-hole symptom. The disease can cause defoliation, tip dieback, stem lesions, and sometimes loss of entire plants. Spores are water-splashed from diseased tissue.

Cultural Controls: Sow seed in sterile containers in sterilized soil or a soilless mix. Since wet conditions favor disease development, reduce periods of leaf wetness by reducing humidity and increase plant spacing to increase air movement. Avoid overhead irrigation. Remove diseased plants to reduce inoculum levels.


Bacterial Leaf Spot (Pseudomonas cichorii)

Symptoms: Spots on leaves are water-soaked and dark. They may be both angular and delineated by small veins in the leaves or irregular in shape. A wet stem rot may occur. Bacterium is reported to be seed-borne. The disease is favored by wet, humid conditions and is disseminated by splashing water or by handling infected tissue and then touching other plants.

Cultural Controls: Decrease moisture on plants with low humidity and sufficient plant spacing for adequate movement to reduce periods of leaf wetness. Use disease-free seed and transplants. Remove diseased leaves and plants to reduce inoculum levels. Avoid overhead irrigation. Use clean, sterile equipment and do not move between infected and healthy plants.


Fusarium Wilt (Fusarium oxysporum)

Symptoms: Initial disease symptoms are yellowing of the shoots, distorted young leaves, and internal vascular discoloration of stems. As the disease advances, plants wilt and die. The pathogen is seed-borne and survives in the soil for many years.


Cultural Controls: Use disease-free seed in sterilized soil or a soilless mix. Seed may be disinfested. Rotate fields to another crop besides basil. Use resistant cultivars as some resistant cultivars have been reported. 1

Fusarium wilt of basil is caused by a soil-borne fungus (Fusarium oxysporum f. sp. basilicum). The fungus attacks the water-conducting tissue (xylem) within the stem. Infected basil plants will grow normally until they are six to twelve inches tall, then become stunted and exhibit browning of terminal growth. Once water uptake is totally blocked, the basil plants will suddenly wilt. Promptly remove and dispose of any wilt-infected plants. 2

Control: The Fusarium wilt pathogen can survive for many years in the soil; therefore plant resistant basil varieties. Three Genovese-type cultivars of basil have been selected for resistance to Fusarium wilt. The first cultivar released was ‘Nufar’, which grows to 24 inches tall and has medium-sized leaves with mild flavor. More recently ‘Aroma 1’ and ‘Aroma 2’ have been released and have very good fragrance. These cultivars are readily available from mail-order seed companies. 2


Further Reading
'UH sweet Basil'. A New Basil Cultivar Tolerant of Fusarium Wilt from the University of Hawaii Cooperative Extension Service pdf

Bibliography

1 Zhang, Shouan. Roberts, Pamela D. "2009 Florida Plant Disease Management Guide: Sweet Basil". edis.ifas.ufl.edu. Plant Pathology Department, Florida Cooperative Extension, Institute of Food and Agricultural Sciences, University of Florida. Oct. 2003. Web. 20 Mar. 2014.

Williamson, Joey. "Basil". clemson.edu/extension. Clemson University Cooperative Extension, South Carolina. Dec. 2008. Web. Mar. 2014.

Photographs

Fig. 1 Jensen, Sandra. "5458092. Basil Downy Mildew Peronospora belbahrii Sign". 31 Jan. 2012. University of Maine. Bugwood.org. Web. 21 Mar. 2014.

Fig. 2 Watt, Bruce. "5458610. Basil Downy Mildew Peronospora belbahrii Symptoms". 2 Feb. 2012. University of Maine. Bugwood.org. Web. 21 Mar. 2014.

Fig. 3 Williamson, Margaret. "Basil with Cercospora leaf spot (Cercospora sp.)". N.d. Cooperative Extension, Clemson University. clemson.edu/extension. Web. 20 Mar. 2014.

Fig. 4, 5 " Bacterial Leaf Spot Pseudomonas cichorii Sign". 2008. Florida Division of Plant Industry Archive, Florida Department of Agriculture and Consumer Services. Bugwood.org. Web. 21 Mar. 2014

Fig. 6 Roos, Debbie. "Fusarium wilt of basil (Fusarium oxysporum f. sp. basilicum)". N.d. Cooperative Extension, Clemson University. clemson.edu/extension. Web. 20 Mar. 2014.

Published Mar. 2014 KJ. Last update 2 Nov. 2015 KJ
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