Now that most tobacco trays have been seeded, some reminders on minimizing disease as seedlings size up for transplanting.
Pythium Root Rot
The most common disease occurring in float bed plants, Pythium root rot is managed with a combination of sanitation and fungicides. Starting with new plastic, new or thoroughly cleaned trays, and preventing any introduction of natural soil will prevent or delay the onset of root rot. When roughly half of the cells have water roots, a well-circulated, preventative rate of Terramaster (0.7 – 1.0 oz / 1000 gal) will suppress low-level root rots. Using this low rate early in the transplant season allows many growers to avoid significant root loss after treatment of already-symptomatic plants. Oxidate is labeled for Pythium management in organic tobacco floatbeds, but relatively little is known about its curative activity.
As in 2015 and 2016, blue mold has already been reported in tobacco greenhouses in Georgia this year. While disease in the field did not materialize in 2015 or 2016, the threat of blue mold is one reason why tobacco transplants should be on a preventative foliar fungicide program in the greenhouse. Manzate ProStick can be applied to plants as small as dime size, at a rate of 0.5 lb / 100 gal. Since Manzate is a protectant, its efficacy is reliant on good coverage of foliar tissue, and applications should occur on a weekly basis for best results. Note, the Manzate ProStick label was renewed at the end of 2016, so a new supplemental label should be printed and included in production records. Link to 24(c) here.
Target spot is the most common foliar disease of tobacco transplants. To reduce pressure from the target spot pathogen, weeds should be managed in and around the greenhouse. A 5- to 10-foot plant free perimeter around the greenhouse is ideal, as pathogen spores may be blown into the transplant greenhouse from weedy areas. Manzate ProStick will suppress target spot, and Quadris is labeled for a single use in the tobacco greenhouse. Quadris (4 mL / 1000 sq ft) should be applied after the first or second clipping, and would be expected to remain effective for 2-3 weeks. However, Manzate applications should be resumed on a weekly basis to protect new plant tissue, since Quadris would not be expected to move to young leaves.
By Emily Pfeufer, Extension Plant Pathologist