Is Palmer Amaranth an Alternative Host for Soybean Looper?

Glyphosate resistant Palmer amaranth, Amaranthus palmeri (S. Wats.) has become a serious problem for southern soybean producers.  A consultant’s survey published in 2013 concluded that Palmer amaranth is the top weed problem in the MidSouth.  In addition to decreasing yields, weeds can affect soybean pest populations by providing alternate hosts.  Chrysodeixis includens (Walker), the soybean looper (SBL), is also an important pest of southern soybean production.  Previous studies have reported SBL on Palmer amaranth but have not elucidated its impact on SBL population dynamics.  The objective of this study was to confirm that Palmer amaranth is an alternative host for SBL and to conduct a life table study in comparison to soybean.  Preliminary data indicates that SBL fed Palmer amaranth took longer to pupate and had higher mortality than on soybean.  SBL fed Palmer amaranth consumed less tissue, produced 40% less eggs, and eggs were less viable, with only 70% hatching.  This study proves that SBL can utilize Palmer amaranth as a host but that population growth rates will be less than on soybean.  Palmer amaranth is not only a weedy pest of soybean but also an alternative host for SBL.