Evaluation of fungicides applied at different times for control of sclerotial blight on sweetpotato, 2009.

摘要

Sclerotial blight was severe on some commercial farms in Louisiana in 2008 in seed beds of the new cultivar ‘Evangeline’ despite the use of standard applications of Botran to seed roots. This study was conducted to determine if augmenting Botran with other fungicides that have not previously been evaluated on sweetpotato might improve disease control without adversely affecting plant production or quality. The test was conducted in a field at the LSU AgCenter Burden Center in Baton Rouge. The studysite had been used for bedding sweetpotatoes for several years and had a history of low to moderate incidence of sclerotial blight. On 20 Mar 2009, roots of ‘Evangeline’ sweetpotato (not presprouted) were laid out in a randomized complete block designwith five replications each consisting of plots with 30 roots placed in open furrows approximately 4 ft in length. Three blocks were bedded with roots harvested 18 Aug 2008 and two blocks were bedded with roots harvested in 7 Oct 2008 following floodingassociated with Hurricane Gustav. The furrows were covered with hippers to a depth of 1-2 inches above the roots and black plastic mulch was installed using a mulch layer. Fungicides were applied in one of the following manners: 1) seed - a spray over the roots after they were placed in the beds, 2) bed - sprays applied to the surface of the soil after roots had been covered with soil but before plastic mulch was applied, 3) emergence - sprays to the plants and soil surface immediately after plastic mulch was removed, or 4) after cutting - sprays to the plant stubs and soil surface after the first cutting of plants. All sprays were applied using a hand-pump sprayer with a flat fan nozzle on a 1.5-foot-wide band delivering 14 gal water per 1000 ft2 ofbed. Seed and bed applications were applied on 20 Mar and holes for aeration were poked in the plastic mulch on 30 Mar. Plastic mulch was removed and emergence treatments were applied on 22 Apr. Plants were first cut and the after cutting treatments wereapplied on 20 May, and on 19 Jun a second cutting of plants was made and seed roots were dug and survival determined. Prior to cutting, the number of sclerotial blight infection foci was counted. At each cutting, the total weight of plants was measuredand the number of plants exceeding 10 inches in length was counted. Yield tests were conducted to evaluate whether any of the fungicide treatments might have affected the suitability of plants for transplanting or subsequent development. Plants from eachtreatment in the first cutting were transplanted in a randomized complete block design using five replications of 25-plant plots on 22 May. On 19 Jun, plants from the control and after cutting treatment were planted in a similar trial. Yield trials wereplanted in a silt loam soil at the Burden Center with 48-inch row spacing and plants on 12 inch centers. Routine production practices were followed including incorporation of 8-24-24 fertilizer (400 lb/A) prior to planting. Plots were harvested on 26 Aug (first planting) and 30 Sep (second planting) and roots were sorted into commercial grades and weighed.