The Asian soybean aphid was first seen in North America in the state of Wisconsin in 2000. In 2001, it made its official appearance in Québec, following some severe infestations reported in Ontario.
Considered one of the major pests in soybean culture, it is now found in most of our fields in every season! But what are the consequences of its passage for growers? That is what this new article will explore.
The damage
Soybean aphids use their piercing-sucking mouthparts to extract plant sap. This causes several kinds of damage, including: leaf puckering, weakened plant growth, early senescence, and reduced pod and seed counts.
The insect is also a vector of numerous viruses, such as soybean and alfalfa mosaics. Viruses affect grain quality, which downgrades it at the time of sale, consequently causing serious financial losses for the grower.
That’s not all, the accumulation of sap (honeydew) secreted by the aphid also leads to the formation of a fungus called sooty mold. The affected leaves turn black, limiting photosynthesis, as well as the plant’s growth.
Yield loss
Research conducted in the U.S. at the University of Minnesota offers an estimate of the yield losses caused by the soybean aphid. The estimate is based on a new unit of measure used for calculating the aphid feeding rate, namely the aphid-day.
1 aphid-day = 1 aphid feeding for one day.
10 aphid-days = 1 aphid feeding for 10 days, or 10 aphids feeding for one day.
Formula for calculating your yield % :
(aphid-days x 0.0688/10,000)
To compute yield, consider that yield is reduced by 6.88% for every 10,000 aphid-days accumulated. Thus, 500 aphids per plant, feeding for 20 days, will lead to a yield loss in the order of 7%.
These studies have shown that yield loss is dependent on aphid populations, but also on their length of exposure on the plants. For instance, 5 days (200 × 5) = 1000 (aphid-days) is equivalent to a single day of 1000 aphids /plant.
Happy growing!
D. W. Ragsdale, B. P. McCornack, R. C. Venette, B. D. Potter, I. V. MacRae, E. W. Hodgson, M. E. O’Neal, K. D. Johnson, R. J. O’Neil, C. D. DiFonzo, T. E. Hunt, P. A. Glogoza, and E. M. Cullen Journal of Economic Entomology, 100(4):1258-1267. 2007. Published By: Entomological Society of America DOI: http://dx.doi.org/10.1603/0022-0493(2007)100[1258:ETFSAH]2.0.CO;2 URL: http://www.bioone.org/doi/ full/10.1603/0022-0493%282007%29100%5B1258%3AETFSAH%5D2.0.CO %3B2