Efficacy of Foliar Fungicides in Controlling Fire on Daffodils

Fire, caused by the fungus Botryotinia polyblastis (Botrytis polyblastis), can completely kill the foliage in a field of daffodils (Narcissus pseudonarcissus) within a few weeks under warm, moist conditions in the spring. The premature death of foliage reduces bulb yields and subsequent flower production. In the Pacific Northwest, research has shown that one or two applications of a dicarboximide fungicide when the disease first appears can provide very effective control of this disease. Because a number of newer Botrytis fungicides are now on the market, a trial was established to determine their effectiveness in controlling the development of fire on ‘Gigantic Star’ daffodils in a commercial field with a history of problems with this disease. Two plots were established. Each was a randomized complete block design with five blocks containing 1.2 m of row per treatment. Treatments were applied on 20 April and 3 May, 2006. All treatments were applied in the equivalent of 935.3 L of water per ha. Disease was rated on a scale of 0 to 10, where 0 = none, 1 = 1-10%, 2 = 11-20%, … and 10 = 91-100% of foliage still green. By late May, virtually all of the foliage had been killed in the checks. The most effective treatments in both plots were applications of 26 GT (iprodione). Applications of Switch (cyprodinil plus fludioxonil), Daconil Ultrex (chlorothalonil), Daconil Weather Stik (chlorothalonil), Medallion (fludioxonil), Vangard (cyprodinil), Insignia (pyraclostrobin), and Dithane Rainshield (mancozeb) reduced disease development, but were not as effective as 26 GT. By early June, the plants treated with the high rate of 26 GT were the only plants that retained a significant amount of green foliage. Of the 10 fungicides included in these trials, the dicarboximide fungicide (26 GT) was the most effective material in controlling fire on daffodils.