Sugarcane aphid spatial distribution in grain sorghum fields

Authors: Elliott, Norman - Norm; BREWER, MICHAEL - Texas A&M University; SEITER, NICHOLAS - University Of Arkansas; ROYER, THOMAS - Oklahoma State University; BOWLING, ROBERT - Texas A&M University; BACKOULOU, GEORGES - Oklahoma State University; GORDY, JOHN - Texas Agrilife; GILES, KRISTOPHER - Oklahoma State University; LINDENMAYER, JESSICA - Oklahoma State University; MCCORNACK, BRIAN - Kansas State University; KERNS, DAVID - Texas A&M University

Submitted to: Southwestern Entomologist
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/1/2016
Publication Date: 3/1/2017
Citation: Elliott, N.C., Brewer, M., Seiter, N., Royer, T., Bowling, R., Backoulou, G., Gordy, J., Giles, K., Lindenmayer, J., McCornack, B., Kerns, D. 2017. Sugarcane aphid spatial distribution in grain sorghum fields. Southwestern Entomologist. 42(1):27-35.

Interpretive Summary: Sorghum is an important summer grain crop in the United States. In 2014, the U.S. produced 432 million bushels of sorghum valued at $1.67 billion on more than 6 million acres. The sugarcane aphid, Melanaphis sacchari (SCA), was discovered in damaging numbers in grain sorghum in Texas and Louisiana in 2013. SCA can be very damaging to sorghum grown for grain and forage and is capable of explosive population growth. Sampling methods would be useful for determining when the aphid has reached damaging levels in a sorghum field. Developing effective and accurate sampling methods depends on knowledge of the distribution of the aphid in sorghum fields, which can be affected by a number of environmental factors such as weather and agronomic methods used to produce the crop. The objective of the research was to evaluate several aspects of SCA distribution within and among sorghum plants in commercial grain sorghum fields in relation to environmental factors. Environmental factors were found to affect SCA spatial distribution in sorghum fields indicating the importance of incorporating or otherwise accounting for such factors in developing operational sampling plans for the SCA.

Technical Abstract: Sorghum is an important summer grain crop in the United States. In 2014, the U.S. produced 432 million bushels of sorghum valued at $1.67 billion on more than 6 million acres. The sugarcane aphid, Melanaphis sacchari (Zehntner), was discovered in damaging numbers in grain sorghum, Sorghum bicolor (L.) Moench, in Texas and Louisiana in 2013. Melanaphis sacchari (SCA) can be very damaging to sorghum grown for grain and forage and is capable of explosive population growth. A sequential sampling plan would be useful for pest management decision making. The objective of the research described in this paper was to evaluate several aspects of SCA distribution within and among sorghum plants in commercial grain sorghum fields. We sampled 94 commercial grain sorghum fields in five southern states during two years to obtain data that were used to assess variation in SCA spatial distribution. There were frequently significant differences among upper and lower leaves for fields in each state. However, there were no consistent patterns in whether the upper or lower leaf had more SCA. Autocorrelation coefficients were calculated for consecutive plants and for plants separated by one and two intervening plants. Numbers of SCA on adjacent plants and plants separated by intervening plants were not autocorrelated, indicating that there is no correlation in SCA numbers among plants in close proximity to one another. Taylor’s power law parameters modeling the variance to mean relationship of SCA counts on sorghum plants differed significantly for fields sampled in different states, but not for fields in vegetative versus reproductive growth stages, fields with markedly different planting dates (early or late), or fields sampled in different years.