| A survey of Wisconsin in 2000 led to the first molecular characterization of aster yellows phytoplasma in soybean [Glycine max (L.) Merrill]. Two plants of 121 soybean tested were positive for aster yellows phytoplasma, subgroup A (16SrI-A). One plant was dually infected with a new phytoplasma subgroup, 16SrI-O. A survey of carrots (Daucus carota L.) found phytoplasmas in the aster yellows phytoplasma group, subgroups 16SrI-A and 16SrI-B. Phylogenetic analysis indicates that the phytoplasmas found in soybeans and carrots are indistinguishable.; The arrival of the soybean aphid (Aphis glycines Matusmara) in Wisconsin in 2000 marked the arrival of the first colonizing aphid in North American soybeans. Aphis glycines is a vector of many viruses, including Soybean mosaic virus (SMV). Our goal was to determine if insecticide and the herbicides glyphosate and imazamox would alter the epidemiology of SMV. In both 2001 and 2002, A. glycines comprised the majority of aphids landing, and the peak A. glycines flight occurred from late July to early August. The incidence of SMV increased when the number of A. glycines alates increased. Insecticide application resulted in increased landing rate of A. glycines in 2001, and decreased landing rate in 2002. There was no difference in the SMV incidence due to insecticide in 2001, but there was a significant decrease in the amount of SMV in insecticide treated plots during 2002. There were no differences in landing rate due to herbicide in either year. Imazamox slowed the increase of SMV in both 2001 and 2002.; We also tested whether glyphosate and imazamox could directly alter the soybean-SMV interaction. Imazamox repeatedly slowed the infection of soybean plants with SMV in the field. Imazamox slowed the systemic infection of soybean plants challenged with SMV and Bean pod mottle virus under controlled conditions. Cultivars which varied in their sensitivity to herbicides (Roundup ReadyRTM and sulfonylurea tolerant soybeans) did not differ in their reaction to herbicide and SMV treatments. These results, and other field observations, suggest that imazamox may be useful to slow the increase SMV incidence in the field. The mechanism of this phenomenon is unknown. |
