Loopers out in force in soybeans

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High soy­bean loop­er (Thysanoplu­sia orichal­cea) pop­u­la­tions (20–40/m2) have been report­ed in many regions in flow­er­ing and pod­ding soy­beans. While soy­beans can tol­er­ate 33% defo­li­a­tion with no yield loss dur­ing the veg­e­ta­tive stages, their defo­li­a­tion tol­er­ance slips to 16% dur­ing podset/early pod­fill. Con­se­quent­ly, con­sid­er tak­ing action if high loop­er pop­u­la­tions are threat­en­ing your crop.

Large soy­bean loop­er (38 mm). Note the tapered body (towards the head) and 2 pairs of ven­tral pro­legs.

The pre­ferred IPM option, where loop­ers are the sole cater­pil­lar in the crop, is a Bt-based biopes­ti­cide such as Dipel (1–1.5L/ha) or BioCrys­tal (0.5–0.75L/ha), both with an amino feed adju­vant at 1L/ha.

Biopes­ti­cides such as Bt are best applied in the ear­ly morn­ing or evening to min­imise their break­down due to ULV. If you are expe­ri­enc­ing very heavy ear­ly morn­ing dew, then evening spray­ing is prefer­able. Note that for inges­tion prod­ucts such as Dipel, good spray cov­er­age is crit­i­cal. This also applies to heli­cov­er­pa virus prod­ucts such as Vivus and Gem­star (which have zero impact on loop­ers), and indox­acarb (which is very effec­tive against loop­ers).

Small loop­er lar­va (10 mm) and typ­i­cal ear­ly dam­age leaf win­dow­ing symp­to­matic of ear­ly dam­age

Using a selec­tive option such as Bt pre­serves preda­to­ry insects in the crop and reduces the risk of flar­ing heli­cov­er­pa. In flow­er­ing crops in par­tic­u­lar, the use of Bt against loop­ers gives grow­ers the option of keep­ing the mod­er­ate­ly-selec­tive indox­acarb (Stew­ard®) option in reserve, should above-thresh­old pop­u­la­tions of the more-dif­fi­cult-to con­trol heli­cov­er­pa make an appear­ance.

Arti­cle by Hugh Brier