Silicon supplementation can reduce infestation by azalea lace bug-(Hemiptera: Tingidae)

The azalea lace bug (ALB), Stephanitis pyrioides (Scott) (Hemiptera: Tingidae), is a pest of azaleas and rhododendrons. The application of silicon (Si) to plants has been shown to accumulate in other plants and enhance defense to other plant pests. We evaluated whether Si applications decreased ALB infestation on rhododendron leaves and increased Si accumulation in leaves. Potted plants were treated with 4 or 8 weekly applications of calcium silicate and calcium carbonate (calcium control, Ca) via foliar or soil application. In 3 out of 4 choice studies, plants treated with calcium silicate or calcium carbonate had less frass deposition and oviposition by ALB compared to controls, but treated plants did not consistently have fewer ALB adults. Leaf damage was quantified in one study and leaves with more frass as an indicator of feeding had more visible damage. In no-choice studies, there were no differences between treatments in one study, but oviposition was greater on foliar/soil Si-treated plants than controls in another study. Since rhododendron aphids (Illinoia lambersi) appeared in the greenhouse during or after studies, we compared their colonization on previously treated rhododendrons. Infestation of new leaf rosettes or random leaves by I. lambersi was lower on plants sprayed with foliar silicon or calcium applied via soil in 2 studies. Treated rhododendrons did not accumulate extra Si or Ca in leaves compared to controls. In general, silicon or calcium application protected rhododendrons from ALB oviposition and aphid colonization in free-choice conditions, and may be part of an integrated pest management program.