Angular leaf spot

The disease is found in conditions if high humidity, especially in poor ventilated greenhouses or where the ventilation is not controlled properly. Optimum temperature for disease development is between 24-27°C (75.2 – 80.6°F)¹⁾Bradbury, J.F. 1967. Pseudomonas lachrymans. Description of Pathogenic Fungi and Bacteria, No 124. Commonwealth Mycological Institute, Kew, England.It is caused by Pseudomonas syringae pv. lachrymans ²⁾Newberry, Eric & Jardini, Teresa & Rubio, Isael & Roberts, P. & Babu, Binoy & Koike, Steven & Bouzar, Hacene & Goss, Erica & Jones, Jeff & Bull, Carolee & Paret, Mathews. (2016). Angular Leaf Spot of Cucurbits is Associated With Genetically Diverse Pseudomonas syringae Strains. Plant Disease. 100. on cucurbits and Xanthomonas fragariae on strawberries ³⁾Kwon, Jin-Hyeuk & Yoon, Hae-Suk & Kim, Jeong-Soon & Shim, Chang-Ki & Nam, Myeong-Hyeon. (2010). Angular Leaf Spot of Strawberry Caused by Xanthomonas fragariae. Research in Plant Disease. 16. . It infects all cucurbit family vegetable crops, but there are many cucumber resistant varieties on the market today.

FRANK et al., (1996)⁴⁾Franc, G.D. & Beaupré, C.M.-S & Gray, F.A. & Hall, R.D.. (1996). Nematode angular leaf spot of dry bean in Wyoming. Plant Disease. 80. 476-477. found a new angular spot strain Aphelenchoides ritzemabosi on dry beans. Although not significant enough, only causing 17% drop in yields, it survived for 27 months in plant debris which is a concern. Alfalfa was also affected in Wyoming, USA.

Although not a significant disease in greenhouses, angular leaf spot is a major problem in Kenya and  can cause yield losses as high as 80% on bean crops ⁵⁾Leitich, Robert & Omayio, Dennis & Mukoye, Benard & Mangeni, Bonphace & Wosula, D & Arinaitwe, Warren & Otsyula, R & Were, Hassan & Abang, Mathew. (2016). Pathogenic Variability of Angular Leaf Spot Disease of Common Bean in Western Kenya. International Journal of Applied Agricultural Sciences. 2. 92-98. .

Angular leaf spot is also referred to as Brown-spot blight⁶⁾Walker, J.C. 1952. Diseases of Vegetable Crops, McGraw-Hill, New York. p14..

Pseudomonas syringae is a gram negative organism with rod-shaped cells bearing single or multiple polar flagella.

Symptoms of Angular leaf spot

Initially the disease is found on leaves, fruit and stems as small water soaked lesions of 3 mm in diameter. They have a creamy tan colour on the upper surface but gummy and shiny on the lower surface. As the lesions grow they become angular in shape as they are delimited by the veins of the leaf. The necrotic spots soon fall out.

The fruit show a crusty bacterial excretion and brown lesions in the fleshy tissue beneath the skin of the fruit, develop. Secondart infestation is bacterial soft rot.

Controlling Angular leaf spot

• Do not plant infected seedlings.
• Obtain seed from a reputable supplier
• The disease can live in debris for up to two years. Make sure plant debris or compost heap is far away from production area, preferable covered.
• It is possible to control angular leaf spot on beans with Bacillus cereus and Pseudomonas putida ⁷⁾Garcia, Flávio & Romeiro, Reginaldo. (2011). Biocontrol of bean angular leaf spot by bacterial antagonists. Pesquisa Agropecuária Brasileira. 46. 1603-1608.
• Potassium silicate (KSi) reduced angular spot disease severity by 42%. Although disease severity levels were significantly higher compared to conventional chemicial control with tebuconazole ⁸⁾Rodrigues, Fabrício & Duarte, Henrique & Rezende, D. & Filho, J. & Korndörfer, G. & Zambolim, L.. (2010). Foliar spray of potassium silicate on the control of angular leaf spot on beans. Journal of Plant Nutrition. 33. 2082-2093..
• It was found that a rhizobacteria isolate, Pseudomonas putida, significantly reduced average disease severity of angular leaf spot by 34% in susceptible cultivars and 21% in the tolerant cucumber cultivars⁹⁾Akköprü, Ahmet & Ozaktan, Hatice. (2018). Identification of rhizobacteria that increase yield and plant tolerance to angular leaf spot disease in cucumber. Plant Protection Science. 54. 67-73.. It just shows that soil health plays an important part in plant health and that enough organic matter can reduce plant disease.
• Positive results were found with the application of fungicide (fentin hydroxide), Ascophyllum nodosum, Bacillus thuringiensis, Trichoderma asperellum, acibenzolar-S-methylic (ASM), manganese and potassium phosphate, copper phosphite, Hight Roots® and Wert Plus®¹⁰⁾Hennipman, Hagata & Dalla Pria, Maristella & Christmann, Polyana & Jacques, Filipe & Baptistão, Amanda. (2019). Biotic and Abiotic Products for Bean Angular Spot Control. International Journal of Advanced Engineering Research and Science. 6. 139-147..
• At the end, controlling  Pseudomonas Syringae depends on intimate knowledge of all forms of the pathogen and application of sprays and or pruning (for instance roses) to remove the infection at the right time before it can spread further.

NOTE: If someone has an image of Angular Leaf Spot that they want to share I would appreciate it. We will place a referrence back.