Mycosphaerella berkeleyi
| Mycosphaerella berkeleyi | |
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| Species: | M. berkeleyi
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| Binomial name | |
| Mycosphaerella berkeleyi W.A. Jenkins, (1938)
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Cercospora personata (Berk. & M.A. Curtis) Ellis, (1885) | |
Mycosphaerella berkeleyi is a fungal plant pathogen. It is the causal agent of the peanut foliar disease Late Leaf Spot.
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Late Leaf Spot of Peanut
Late leaf spot of peanut has been the most important leaf spot disease the past few growing seasons (Shew et al., 2010). This foliar disease causes significant yield loss, and can be found wherever peanuts are grown. This includes areas such as Oklahoma, the southern USA, Fiji, Solomon Islands as well as Tonga (Tsatsia & Grahame, 2015). Alternate hosts that suffer from late leaf spot include groundnut species belonging to the genus Arachis hypogaea (Tsatsia & Grahame, 2015). Late leaf spot of peanut that produce sexual spores is referred to as Mycosphaerella berkeleyi, whereas the asexual spore is referred to as Cercosporidium personatum (Helen & Grahame, 2015 ).
Symptoms
Late leaf spot of peanut symptoms usually appear between 30–50 days following planting (Damicone, 1990). Symptoms include dark brown to black pin-point spots on the upper and under side of the leaf surface. This contrasts the fewer, lighter brown spots that early leaf spot of peanut present (Damicone, 1990). Late leaf spot of peanut produces symptoms later in the season. These spores can be seen without magnification and give the spot a velvety appearance as opposed to early leaf spot of peanut, which can be seen with higher magnification (Shew et al., 2010). Even though these differences are slight, it is what helps to distinguish between the two pathogens.
Importance
Late leaf spot of peanut is a serious disease that occurs in places where peanuts are grown worldwide. Infection causes early death of the leaves and dramatic yield loss (Tsatsia & Grahame, 2015). This is estimated to range from 10% to 80%, (McDonald et al. 1985; Miller et al. 1990), and varies according to the environment and availability of control methods. In the USA, where fungicide application is a typical control method, yield losses are less frequent as opposed to the semi-arid tropics, where fungicides are seldom used. It is estimated that Cercosporidium personatum reduce yields by 50% or more in Pacific island countries (Tsatsia & Grahame, 2015). Therefore, early detection is crucial, and successful management efforts must be implemented once the disease has been recognized. To help achieve this, early symptom recognition, as well as the timing of control practices are valuable.
Management
Cultural controls help to delay the onset and development of symptoms, and reduce the level of the primary inoculum present. This includes crop rotation, along with tillage of the soil (Damicone, 1990) . As opposed to irrigation methods, growers are encouraged to apply proper amounts of water in order to maintain a drier canopy (Damicone, 1990) . Spores are able to survive in the soil; so this practice is encouraged for a minimum of two years (Chapin, 2015). It is recommended that growers try to allow at least one year’s time between planting new crops so that the previous season’s harvests are able to decompose. When planting new crops, plant as far away as possible, since late leaf spot spores travel far distances through wind dispersal. Try to avoid planting crops downwind from one another due to spore’s ability to travel between neighboring crop fields (Tsatsia & Grahame, 2015).Different varieties of peanut differ in their reaction to the pathogen, but none have proven to be resistant, and are able to be used as a control method (Damicone, 1990) . Spanish varieties are most susceptible, Virginia varieties are intermediates, and runner varieties are partially resistant (Damicone, 1990) . In order to prevent yield loss, spray chemical controls as soon at the onset of symptom development (Tsatsia & Grahame, 2015). Very specific chemical controls are used to prevent spore dispersal, and are required in a very narrow, specific time period in order to be most effective. Fungicide application is recommended, on a 14-day set calendar schedule, or according to weather based leaf spot advisory (Shew et al., 2010). In fields that utilize crop rotation, fungicides should be sprayed during the early pod stage (R3), which typically occurs during July, but can vary according to environment (Shew et al., 2010). After the first spray, the grower should continue to apply fungicides every 14 days or according to the leaf spot advisory (Shew et al., 2010). Chlorothalonil (Bravo; various generic brands), are the most successful fungicides, and have reduced the risk of host resistance (Chapin, 2015). An alternative approach to calendar sprays are to spray crops based on weather patterns. However, this method has proven to be less effective than calendar treatment approaches (Chapin, 2015). Following a harvesting season, growers should collect, burn, or bury the remains of the crops to prevent the soil-borne pathogen from surviving and causing future disease outbreaks (Tsatsia & Grahame, 2015).
Works Cited
Chapin, J W. (2012) Peanut Disease Management. South Carolina Pest Management Handbook for Field Crops, Extension Peanut Specialist Emeritus.
Damicone, J (1990) Foliar Diseases of Peanut. Oklahoma Cooperative Extension Serivce. EPP-7655
McDonald, D., Subrahmanyam, P., Gibbons, R.W.,and Smith, D M . 1985. Early and late leafspots of groundnut. Information Bulletin no. 2 1 , Patancheru 502 324, Andhra Pradesh, India: International Crop Research Institute for the Semi-Arid Tropics. 24 pp.
Miller IL, Norden AJ, Knauft DA, Gorbet DW (1990) Influence of maturity and fruit yield on susceptibility of peanut to Cercosporidium persoratum. Peanut Sci 17:52–58
Shew P, Lassiter B, Wilkerson G., (2010). Early and Late Leaf Spot. Peanut Information for the Carolina’s and Virgina. Retrieved from http://www.peanut.ncsu.edu/Diseases/Early_and_Late_Leaf_Spot.aspx
Smith AF (1984) Management of peanut foliar diseases with fungicides. Plant Dis 64:356–361
Tsatsia H, Jackson G. (2015). Peanut leaf spots (036). Australian Centre for International Agricultural
Research under project . University of Queensland and the Secretariat for the Pacific Community. Retrieved from http://www.plantwise.org/KnowledgeBank/Uploads/PestNet/Peanut _leaf_spots_(036).htm