Heterodera glycines can reduce soybean yield even in the absence of obvious symptoms
Heterodera glycines (EPPO A2 list) is an economically important pest of soybean in the north-central region of USA where most soybean production occurs. In Illinois, Iowa and Missouri, the annual yield loss caused by H. glycines exceeds 300 million USD. In this part of USA, significant yield losses are observed without above-ground symptoms (i.e. stunting, yellowing). It is therefore difficult to convince growers to implement management practices before symptoms become obvious. From 1997 to 1999, field experiments were conducted in Illinois, Iowa and Missouri to investigate the effects of H. glycines on soybean growth, development and yield throughout the growing season. At each location studied, 2 locally adapted cultivars (one resistant, one susceptible) were grown according to a special plot design allowing for destructive sampling. Population densities of H. glycines were determined at each location, and a wide range of infestation levels was found. Four weeks after planting, soybean plants were sampled every two weeks. On resistant cultivars, it was observed that infection by H. glycines reduced plant height and leaf/stem/canopy weight in the first 12 weeks after planting, and delayed pod/seed development 12 to 14 weeks after planting. However, resistant cultivars consistently produced higher yields than susceptible cultivars (on the average, yield is double than that of susceptible). On susceptible cultivars, reduction of biomass accumulation started 10 weeks after planting and reduction in pod and seed development occurred throughout the reproductive stages. Above-ground symptoms were not observed during the experiment. These results demonstrate that on both types of cultivars, yield reduction occurs without visually detectable symptoms.
Wang, J.; Niblack, T.L.; Tremain, J.A.; Wiebold, W.J.; Tylka, G.L.; Marett, C.C.; Noel, G.R.; Myers, O.; Schmidt, M.E. (2003) Soybean cyst nematodes reduces soybean yield without causing obvious aboveground symptoms.
Plant Disease, 87(6), 623-628.