Although TSWV is vectored by thrips, the use of insecticides to control thrips in general has been ineffective for suppressing spotted wilt. While providing good control of thrips damage to plants, insecticide applications have been ineffective in preventing plant feeding and inoculation by viruliferous thrips that have migrated from areas outside the field. Despite the overall disappointing results with insecticides, phorate has provided consistent, low-level suppression of TSWV.

The mechanism of disease suppression has no direct link with thrips control, since phorate typically offers no better control than other insecticides. Phorate is phytotoxic, and often causes marginal chlorosis and necrosis on peanut leaves (shown above). This effect on young plants may induce a host defense response, or serve in some other way to inhibit virus replication or movement. The effect of this systemic insecticide may be worthy of investigation in the future as being a potential inducer of systemic acquired resistance. Regardless of the mode of action, in-furrow application of phorate at planting provides control of thrips and a low to moderate level of suppression of spotted wilt in peanut.

For more information on any of these or related topics, feel free to contact Albert Culbreath by phone (229) 386-3370, fax (229) 386-7285 or email (spotwilt@tifton.cpes.peachnet.edu).