Keep Target Spot of Tomato in Your Sights
February 1, 2012 Target spot is frequently misdiagnosed in its early stages as symptoms are difficult to recognize and can be confused with bacterial spot and early blight.
The name derives from the bull’s-eye appearance that is often displayed in lesions caused by the disease. Since concentric rings are not always visible and not all lesions with concentric rings are target spot, it is recommended a laboratory diagnosis be obtained to ensure that a correct diagnosis is made.
On tomato leaves and stems, foliar symptoms of target spot consist of brown-black lesions with subtle concentric rings giving them a target-like appearance. These can sometimes be confused with early blight. On tomato fruit, lesions are more distinct. Small, brown, slightly sunken flecks are seen initially and may resemble abiotic injury such as sandblasting. As fruits mature, the lesions become larger and coalesce, resulting in large pitted areas. Advanced symptoms include large deeply sunken lesions, often with visible dark-gray to black fungal growth in the center. A zone of wrinkled looking tissue may surround the margins of lesions on mature fruit.
Placing suspect fruit in a moist environment for 24 hours will often induce the growth of dark-gray mycelia providing telltale diagnostic evidence of target spot infection.
Survival And Spread
In addition to tomato, this fungus has a wide host range and may attack such diverse crops as papaya, passion-vine, pepper, cowpea, cantaloupe, squash, and snap beans, as well as a number of common ornamentals.
The pathogen has several means for survival and spread in the field. It may survive up to two years in crop debris. The wide host range of this fungus also may contribute to survival of the fungus in Florida. The primary means of spread in the field is by airborne conidia.
Optimum conditions for disease development include temperatures from 68°F to 82°F and long periods of free moisture.
In trials, wounding was essential for reproduction of the fruit symptoms.
Management Methods
Strategies for the management of this disease require an integrated approach for best results. Currently, target spot is controlled primarily by applications of protectant fungicides. It should be noted that tank-mix sprays of copper fungicides and maneb do not provide acceptable levels of target spot control. In recent trials at the University of Florida, fungicides were rated for efficacy as follows:
1) Switch (cyprodinil and fludioxonil), Inspire Super (difenoconazole and cyprodinil) both from Syngenta Crop Protection
2) Revus Top (mandipropamid and difenoconazole, Syngenta Crop Protection) and Scala (pyrimethanil, Bayer CropScience)
3) Tanos (famoxadone and cymoxanil, DuPont Crop Protection), Endura (boscalid, BASF), Quadris (azoxystrobin, Syngenta Crop Protection) and other strobilurins, and Reason (fenamidone, Bayer CropScience)
4) Bravo (chlorothalonil, Syngenta Crop Protection)
5) Mancozeb, Copper.
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