Tobacco
Target Spot
Rhizoctonia solani
Fungus
In a Nutshell
- Lesions initiate as small, transparent spots with little to no yellowing (chlorosis).
- The lesions can expand to softball sized or larger and are characterized by a concentric ring pattern.
Can also be found in
Tobacco
Symptoms
Small 2-3mm white or tan colored primary lesions appear on the surface of the foliage that is closest to the soil. The disease spread outwards as it progresses. Necrotic rings are created around the primary lesions. In the field, target spot occurs on the lowest, oldest leaves first, then progresses to upper leaves over time.
Recommendations
Organic Control
The efficacy of biological antagonism has been demonstrated in R. solani using Trichoderma sp.. Isolates of T. harzianum can reduce the growth of R. solani and enhance disease control in tobacco plants
Chemical Control
Always consider an integrated approach with preventive measures together with biological treatments if available. Foliar applications of mancozeb and azoxystrobin can be applied for the management of fungal leaf spots.
What caused it?
Damage is caused by the soil borne pathogen R. solani. The fungus exists primarily as hyphae or sclerotia within the soil. The disease can be transmitted with symptomatic greenhouse transplants or can be infected by target spot fungus that is naturally present in and around fields. The disease is favored by moderate temperatures, high humidity and prolonged period of leaf wetness. The disease has the ability to severely reduce yield when it is not adequately managed.
Preventive Measures
- The disease can be managed prevented with a combination of crop rotation and fungicide application.
- The incidence of target spot can be reduced by rotating fields away from tobacco for at least two seasons and avoiding soybean in rotations.
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