Grain sorghum hybrid resistance to insect and bird damage-2014

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

Submitted to: Agricultural Experiment Station Publication
Publication Type: Experiment Station
Publication Acceptance Date: 12/9/2014
Publication Date: 12/15/2014
Citation: Ni, X., Toews, M.D., Buntin, G., Knoll, J.E., Harris-Shultz, K.R. 2014. Grain sorghum hybrid resistance to insect and bird damage-2014. In: J.L. Day, A.E. Coy, and J.D. Gasset (eds.), Georgia 2014 Soybean, Sorghum Grain and Silage, and Summer Annual Forages Performance Trials - Annual Publication 103-6, December 2014.

Interpretive Summary: not required

Technical Abstract: Thirty seven grain sorghum hybrids were evaluated for resistance to insect and bird damage in 2014 in Tifton, and a total of 10 insect pests were observed. While sorghum midge and bird damage was relatively low, sorghum webworm and aphid damage was high. Those insects in order of importance are: sugarcane aphid, sorghum webworm, sorghum midge, leaf-footed bug, fall armyworm, corn earworm, corn leaf aphid, stink bugs (southern green and brown stink bugs), and chinch bug. Diseases were of minimal importance in the experimental plots. The hybrids were planted with four replications on May 29, 2014. The flowering date (or days to anthesis) occurred in July through early August. The flowering time (50% panicles are flowering) of the hybrids was between 43 and 61 days after planting. Fall armyworm and corn leaf aphid damage was assessed in May and June, but the data were not included because the foliar damage ratings were low. Similarly, corn earworm, leaf-footed bug, stink bug, and chinch bug populations were low after flowering, and thus those data are not included either. Sugarcane aphid, a new pest to Georgia, was first observed on the back surface of the leaves in late August. The infestations of the sugarcane aphid can be determined by the shiny honeydew deposition and sooty mold growth on the surface of lower leaves of the sorghum plants. Although the sugarcane aphid is a new sorghum pest in Georgia, it has been a serious problem in other sorghum growing areas in the southern states. Given the fact that the aphid has other perennial grass hosts for overwintering, its prevalence in Georgia in the coming years needs to be closely monitored. Sugarcane aphid, sorghum midge and bird damage were rated on September 7, 2014. Sugarcane aphid was rated using the following scale: Very Good (VG) =no aphid or few aphids colonizing the leaves; Good (G) = a lot of aphids without damage symptoms, but with their honeydew visible on the surface of lower leaves; Fair (F) = high aphid population with lower leaves covered with honeydew that had attracted many predators, bees and wasps. In addition, sooty mold and aphid exuviae (or whitish-caste skins) are abundant on the surface of lower leaves of a plant; and Poor (P) = dead plants caused by aphid feeding, which was also covered with sooty mold. Sorghum webworm and midge-caused grain loss was rated together according to the visual estimates of empty glumes (%) per panicle. Grain loss attributed to sorghum webworm was identified by the webworm feeding hole at the tip of an empty glume, whereas midge damage lacked a feeding hole, but had a whitish-caste skin hanging at the tip of a glume. Both sorghum webworm and midge damage was assessed in combination according to the following rating scale: Very Good (VG) = 0-15% empty glumes on any of the sorghum panicles in an experimental plot; Good (G) = a few empty glumes (16-30%) observed on a panicle; Fair (F) = 31-75% empty glumes on a sorghum panicle; and Poor (P) = majority of sorghum panicles with more than three quarters (> 75%) empty glumes. Finally, bird feeding damage on developing kernels was determined by the partial kernels, and the splattering of the kernel juice on the leaves. Bird damage was based on the following scale: Very Good (VG) = less than 10% grain loss; Good (G) = 11-25% loss; Fair (F) = 26-50% loss; and Poor (P) = greater than 50% loss of grains per panicle. In general, the bird damage could be reduced by timely harvest of the crop. The attached table showed that three hybrids (i.e., 83P17, SPX3550, and GX13231) had the least amount of aphid damage. Sorghum midge and webworm are cyclic insect pests in grain sorghum production in the southern Coastal Plain region. Damage caused by webworm are usually high on late flowering hybrids. The combined sorghum webworm and midge damage rating was high in 2014, which could be the resul