Skip to main content
CORESTA Congress, Online, 2020, Agronomy/Phytopathology Groups, AP 08

Potential fungicides and biocontrol agents to manage target spot (Thanatephorus cucumeris) on flue-cured tobacco in Virginia

JOHNSON C.S.
Virginia Tech, Southern Piedmont Agricultural Research and Extension Center, Blackstone, VA, U.S.A.

Target spot (Thanatephorus cucumeris) remains a threat to flue-cured tobacco production in Virginia, and field experiments since 2001 have sought to identify effective fungicides for target spot control. Trials in 2017-2019 included fungicides from FRAC groups 4, 7, 11, and 44, and biocontrol agents from FRAC groups P01, P05 and P06. Plots were arranged in a randomized complete block design with 5-6 replications, and consisted of one border row on either side of a 40 ft test row on 4 ft row centers. Percent leaf area damage (%LAD) was subjectively rated using a 0-100 % scale. Tobacco leaves were harvested as they ripened and cured as recommended. Data were evaluated via analysis of variance and the Waller-Duncan test (k-ratio=100; P ≤ 0.05). Inpyrfluxam reduced %LAD in 2017 compared to the untreated control when other spray programs did not. Target spot damage in 2018 was also significantly lower where inpyrfluxam had been applied vs no treatment. Azoxystrobin alternated with Bacillus mycoides isolate J reduced %LAD on 23 July, but only on lower leaves. Azoxystrobin sprays at layby and topping reduced %LAD on lower leaves only on 6 August. Target spot damage just before harvest in 2019 was again significantly reduced by inpyrfluxam versus the untreated control, but not by any other fungicide or biocontrol treatments. Disease was significantly lower than the control on 7 August where inpyrfluxam, flutriafol, metconazole, azoxystrobin, azoxystrobin alternated with Bacillus mycoides isolate J, or mancozeb had been applied. Although fungicide treatments never increased total cured-leaf yield compared to the untreated control in these experiments, yields from plots receiving inpyrfluxam were often the highest in each trial, and were 282-342 lb/A higher than the untreated control in 2019.