Resistance to insect, disease, and bird damage in grain, silage, and forage sorghum hybrids - 2020

Authors: Ni, Xinzhi; BUNTIN, G. DAVID - University Of Georgia; Harris-Shultz, Karen; Knoll, Joseph - Joe; TOEWS, MICHAEL - University Of Georgia; DUNN, DUSTIN - University Of Georgia

Submitted to: Agricultural Experiment Station Publication
Publication Type: Experiment Station
Publication Acceptance Date: 1/19/2021
Publication Date: N/A
Citation: N/A

Interpretive Summary: not required.

Technical Abstract: Basic field plot information: Commercial hybrids of grain, silage and forage sorghum were evaluated at both Griffin and Tifton locations to identify the best performing hybrids in Georgia. The experimental plots were four rows by 20 ft and entries were planted in a randomized complete block design, with three replications for silage and forage trials, and four replications for the grain trial. All grain, silage and forage sorghum trials were planted on June 22, 2020 at Griffin. The number of the sugarcane aphids (SCAs) were estimated on Aug 12 and Aug 26, 2020, while the SCA damage ratings were performed on Aug 26 and Sept 3, 2020 at Griffin. At Tifton, silage and forage sorghum trials were planted on May 5, 2020, while the grain trial was planted on June 22, 2020. The silage trial was evaluated at pre-harvest on July 21, 2020, while the forage trial was evaluated before two harvests on June 25, and August 18, 2020, respectively. The grain sorghum trial at Tifton was evaluated on September 25, 2020, prior to harvest. A total of seven groups of insect pests were observed throughout the field season of 2020: aphids (sugarcane aphid and corn leaf aphid), fall armyworm, chinch bug, stink bugs (southern green and brown stink bugs), sorghum headworm complex (corn earworm and sorghum webworm), sorghum midge, and leaf-footed bug. Although the infestations of some insect pests occurred, they were not included in this report because the infestations caused minimal damage. Headworm and bird damage was evaluated in the grain trial at Tifton. Evaluation of pest damage presented in this report includes good (viable) panicle percentage, number of SCAs per leaf, SCA damage, disease (anthracnose) severity, as well as the percentage of headworm and bird damage on panicle of the grain hybrids. Rating scales used for hybrid evaluations: At both Griffin and Tifton in 2020, the percentage of panicle with kernels was assessed. The number of SCAs was estimated by averaging the number of aphids on 6 mid-canopy leaves (or top and bottom green leaves of three randomly sampled plants) per plot. The number of SCAs per leaf was estimated using the following 0-6 scale; 0=no aphid, and then estimated as 1 =1-25 aphids, 2=26-50, 3=51-100, 4=101-500, 5=501-1000, and 6=over 1000 aphids. The SCA damage was rated using a 1-9 scale, where 1 = no damage, 2 = 1-20%, 3 = 21-30%, 4 = 31-40%, 5 = 41-50%, 6 = 51-60%, 7 = 61-70%, 8 = 71-80%, and 9 = greater than 81% of the leaves are dying, which also included aphid-killed plants. At Tifton, headworm and bird damage were assessed by proportion (converted to the percentage) of damaged kernels per panicle in the grain sorghum trial, while growth stage, lodging, and anthracnose severity (damage) were evaluated in the silage and forage trials. The growth stage was assessed using a scale of 0-9 from the publication S3 by the Kansas State Research and Extension Service. The lodging was assessed by the percentage of root- or stalk-lodged plants per plot. Anthracnose disease was rated using a 1-5 scale, where 1 = no symptoms, 2 = colored spots on leaves but no sporulation, 3 = some sporulation on lower leaves, 4 = moderate sporulation, 5 = heavy sporulation up to the flag leaf. Hybrid ranking criteria: Hybrid performance at Griffin was ranked as Resistant (R), Moderately Resistant/Moderately Susceptible (MR/MS), and Susceptible (S) to the SCA damage. At Tifton, the hybrid performance was ranked based on the biplot separation of the principal component analysis. All hybrid performance in the Tifton trial was designated as Very Good (VG), Good (G), Fair (F), and Poor (P), respectively. The overall hybrid ranking in 2020 was designated as VG, G, F, and P, was also based on the biplot separation of principal component analysis of the pooled Griffin and Tifton data. Results from grain, silage and forage trials: A