Silicon supplementation can reduce infestation by azalea lace bug

Authors: GRAHAM, KATERINA - Texas A&M University; Janasov, Eric; PAUL, RYAN - Oregon State University; Scagel, Carolyn; Lee, Jana

Submitted to: Journal of Economic Entomology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/16/2024
Publication Date: N/A
Citation: N/A

Interpretive Summary: The azalea lace bug damages the leaves of azaleas and rhododendrons and is often controlled with systemic insecticides. We tested supplementing rhododendrons with silicon for lace bug control since silicon has reduced herbivory in other plant-pest systems. Supplementation did not cause rhododendron leaves to accumulate extra silicon, but did reduce lace bug feeding and reproduction when lace bugs could move between treated and untreated plants or leaves. Moreover, silicon supplementation reduced the colonization of rhododendron aphids onto plants when unplanned outbreaks occurred.

Technical Abstract: The azalea lace bug (ALB), Stephanitis pyrioides (Scott) (Hemiptera: Tingidae) is a pest of azaleas and rhododendrons. Systemic insecticides control S. pyrioides, but landscape managers prefer alternative controls. Applying elemental silicon (Si) to plants increases tissue Si accumulation in other plants and enhances defense to other plant pests and diseases. We evaluated whether Si applications increase Si accumulation and improve resistance to ALB in rhododendron leaves. Potted plants were treated with 4 or 8 weekly applications with calcium silicate and calcium carbonate (calcium control, Ca) via foliar or soil application. Rhododendrons did not accumulate extra Si or Ca in leaves compared to controls. In three 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. In two no-choice studies, there was no differences between treatments in one test but oviposition was greater on foliar/soil Si-treated plants than controls in another test. Since rhododendron aphids (Illinoia lambersi) appeared in the greenhouse during or after studies, we also compared their natural 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 two studies. In general, silicon or calcium application protected rhododendrons from lacebug ovipoisiton and aphid colonization in free-choice conditions, and may be part of an IPM program to lower pest pressure and insecticide use.