SUGARBEET.CERCOSPORA.2017.MCGRATH

Evaluation and rating plots were planted at the Saginaw Valley Research & Extension Center (SVREC) in Frankenmuth, MI in 2017 that focused on Cercospora leaf spot (CLS) disease performance of a wide range of Beta vulgaris materials. CLS trials were conducted in conjunction with the Beet Sugar Development Foundation (BSDF) and CLS trials included USDA-ARS cooperator germplasm as well as germplasm screening for the National Plant Germplasm System. All trials were planted following normal fall and spring tillage operations with a USDA-ARS modified John Deere / Almaco research plot planter. The BSDF CLS nursery was planted on May 11, 2017. All plots were 15 ft long planted on 20 in rows. For non-commercial entries, as in previous years, weeds were controlled by a pre-plant application of ethofumesate, followed by intervals of post-plant mixtures of phenmedipham, desmedipham, triflusulfuron methyl, and clopyralid (4 times), and finally with S-metolachlor. Hand weeding was done as needed to control larger weeds. The BSDF trials were thinned by hand with the generous help of Michigan Sugar Cooperative.

Bolting beets were removed throughout the season. Quadris 2.08SC (azoxystrobin) was applied at 0.0091 kg/100 m row in a 14 cm band in-furrow at planting to help manage Rhizoctonia damping-off. Cercospora / Agronomic Nurseries: The nursery was inoculated on July 5 with a liquid spore suspension (approximately 1 x 103 spores/ml) of Cercospora beticola. Inoculum was produced from a mixture of leaves collected from the 2016 inoculated leaf spot nursery at the SVREC and on the Michigan State University campus farms in East Lansing, MI. Visual evaluations of the plot were conducted with a disease index (DI) on a scale from 0-10 where 0=no symptoms, 1=a few scattered spots, 2=spots coalescing or in large numbers on lower leaves only, 3= some dieback on lower leaves, but leaves not entirely dead, 4-8 are increasing amounts of dead and diseased tissue, 9= mostly dead with few remaining living leaves with large dead patches, and 10=all leaves dead. Disease severity peaked by late August, after which regrowth started to outpace new disease development. In addition to commercial entries, 30 Plant Introductions and 100 USDA-ARS breeding lines and checks from two USDA cooperators (Ft. Collins, CO, East Lansing, MI) were evaluated in randomized replicated trials and rated for disease reaction on two dates. Fort Collins' entry ratings (65 entries) ranged from 2.3 to 6.6, excluding the checks EL50/2 (score 3.2) and F1042 (score 5.7) (overall mean 4.6, LSD 0.05 = 1.4) at the last rating.