Effects of optical brighteners included in biopesticide formulations on the growth of crops

Stilbene-derived optical brighteners are compounds that absorb ultraviolet (UV) radiation and emit visible blue wavelengths. When mixed with baculoviruses they can enhance the infectivity, rendering the viruses more efficient as control agents of insect pests. Formulations of baculoviruses with optical brighteners are being tested for control of crop and forest lepidopterous insects in North America. A possible consequence of field applications of optical brighteners on the growth of crops was examined. Application of the optical brightener Tinopal CBS increased reflectance of leaf surfaces, particularly in the region 420-470 nm. In glasshouse trials, foliar applications of 5% solutions reduced growth of maize by about 25%, while 1% solutions reduced growth of barley by about 30-40%. Foliar applications appeared to have no effect on growth of three dicotyledonous crops. Possible explanations for these differences between crops are discussed. Field trials are needed to ascertain whether the increased efficacy of biopesticides gained by including optical brighteners in formulations is sufficient to offset the reductions in growth that can be expected in some crops.