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 that produces sexual spores is referred to as Mycosphaerella berkeleyi, whereas the asexual spore is referred to as Cercosporidium personatum (Helen & Grahame, 2015 ). Late leaf spot can be difficult to diagnose, and is even more challenging to control. This ascomycete infects the majority of peanuts worldwide and other hosts belonging to the genus Arachis (Tsatsia & Grahame, 2015). There are very small but distinguishable differences between early leaf spot of peanut and late leaf spot of peanut. However, each pathogen is treated quite differently.
Symptoms
Late leaf spot of peanut has become more common recently and has been the most significant leaf spot disease the past few growing seasons. 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 most places where peanuts are grown. Infection causes early death of the leaves and yield loss (Tsatsia & Grahame, 2015). Yield loss is dramatic, estimated to range from 10% to 80%. (McDonald et al. 1985; Miller et al. 1990). Losses in yield due to late leaf spot of peanut vary from place to place and between seasons. In the southern USA, where fungicide is a typical control method, yield losses are less than in 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 environmental conditions that favor the disease spread and development are valuable in facilitating detection of pathogen presence. This will benefit in differentiating between the two leaf spots as well as the implementation of management strategies and practices.
Management
Crop rotation is essential in preventing the occurrence and spread of late leaf spot of peanut (Shew et al., 2010). Also, 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). Make sure to inspect growth once a week, and spray chemical controls as soon as leaf spots appear (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 RW, Smith DH (1985) Early and late leaf spots of groundnut. Information Bulletin no. 21. International Crops Research Institute for the Semi-Arid Tropics, Patancheru, p 24
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