Leaf spots have been found during fall (September and October) on Long Island. Spots are tan and round unless bordered by a vein causing their shape to become angular. There were spots on the midrib of leaves as well as the leaf blade. Severe leaf spotting can lead to leaf death and defoliation which could result in the taproot being smaller than on a healthy plant.
Symptoms were most severe in the section of the planting in a low area where trees created shade and consequently conditions were likely more favorable for infection due to longer periods of leaf wetness.
Cercospora leaf spot was the dominant disease. Numerous spores and conidiophores of Cercospora were observed in the leaf spots. Some spots had Alternaria.
These fungal pathogens can be seed-borne and can survive in crop debris. Pathogen spores are moved by wind and rain, which also provides leaf wetness for infection.
Labeled fungicides that can be used in commercial production include Endura (FRAC 7) and a QoI fungicide (FRAC 11) such as Quadris or Cabrio.
Please Note: Fungicides mentioned are for use in commercial production, not gardens. The specific directions on pesticide labels must be adhered to — they supersede these recommendations if there is a conflict. Any reference to commercial products, trade or brand names, is for information only; no endorsement is intended. For up-to-date information on labeled conventional fungicides see Cornell Integrated Crop and Pest Management Guidelines for Commercial Vegetable Production and biopesticides see the Biopesticides website.
