Effects of Calcium and Nitrogen Fertilizers, Fungicides, and Tillage Practices on Incidence of Sclerotium rolfsii on Processing Carrots. Z. K. Punja, Research Scientist and Manager, Campbell Institute for Research and Technology, Route 1, Box 1314, Davis, CA 95616. J. D. Carter, Research Assistant, Campbell Soup Company, Route 2, Box 98, Maxton, NC 28365; and G. M. Campbell, Research Scientist, and E. L. Rossell, Research Specialist, Campbell Institute for Research and Technology, P.O. Box 508, Cairo, GA 31728. Plant Dis. 70:819-824. Accepted for publication 22 March 1986. Copyright 1986 The American Phytopathological Society. DOI: 10.1094/PD-70-819.

Incidence of root rot caused by Sclerotium rolfsii on processing carrots in North Carolina and Georgia was reduced in 1983 and 1984 by deep plowing infested fields before planting compared with disking. Reduction in disease incidence after plowing was attributed to burial of sclerotia at depths where germination and infection were prevented. Three applications to deep-plowed plots of calcium nitrate or urea at 112 kg of calcium or nitrogen per hectare, respectively, ammonium bicarbonate (NH₄HCO₃) at 84 kg of nitrogen per hectare, or PCNB at 56 kg/ha reduced the percentage of dead plants at the end of the growing season to less than 5%; on untreated plots, disease incidence was 16.8%. On disked plots, only PCNB provided a similar level of control. Calcium levels in carrots receiving calcium nitrate or calcium sulfate were significantly (P ≤ 0.05) higher than in carrots from unfertilized plots. Application of ammonium bicarbonate, urea, or PCNB to soil reduced germination of sclerotia and the extent to which mycelia grew to infect carrot tissue. Viability of sclerotia buried in field plots was significantly reduced by one application of ammonium bicarbonate compared with sclerotia in untreated plots. Combining deep plowing and applications of a calcium fertilizer and ammonium bicarbonate provides effective and economical control of S. rolfsii on processing carrots.

Keyword(s): cultural control, southern blight.