Evaluating threecornered alfalfa hopper (Spissistilus festinus) as a pest in Mississippi soybeans

The threecornered alfalfa hopper is a pest of soybeans during the vegetative and reproductive stages of soybeans.  Primary damage from this pest is stem girdling.  During the vegetative stage they feed on the main stem and during the reproductive stage they move to the upper part of the plant to feed.  Early season feeding can be economic, but many fields are planted with treated seeds, which provide some protection.  Most foliar applications targeting threecornered alfalfa hoppers occur during later reproductive growth stages.  Previous research has shown that the former treatment threshold of 1 TCAH/sweep was too low.  In 2012 the threshold was raised to 2 TCAH/sweep.  No yield losses in recent research have been reported from TCAH feeding during reproductive stages, so this threshold may still be conservative.  Experiments were conducted during 2012 and 2013 in Starkville and DREC to test higher densities of TCAH and to estimate sweep net sampling efficiency for threecornered alfalfa hopper adults in soybeans.  For the sweep net efficiency, field cages (20’ x 20’) were erected in field once soybeans reached R3 growth stage.  Cages were infested with 0-6 TCAH adults/row ft. (0-900/cage). One sample was taken each day from each cage for four consecutive days, with 20 sweeps per cage.  For the threshold research, smaller field cages (6’ x 6’) were infested with 60 TCAH adults/row ft or left uninfested during R3-R4 stages.  Cages were maintained for 2 weeks and then removed and fields were sprayed.  Yield was measured at harvest.