Prevention of Ambrosia Beetles (Coleoptera: Scolytinae) and Phytophthora Root Rot with Stress-mitigating Fungicides

Ambrosia beetles (Coleoptera: Curculionidae: Scolytinae) and Phytophthora are important insects and pathogens in nurseries that can kill trees. Fungicides were evaluated for efficacy against Phytophthora cinnamomi Rands in flood-stressed trees. Empress™ Intrinsic™ Brand Fungicide (Empress), Orkestra™ Intrinsic® Brand Fungicide (Orkestra), and Subdue MAXX® were the most effective preventively-applied fungicide treatments, while Empress, Orkestra, Tartan® Stressgard® (Tartan), and Aliette® 80 WDG were the most effective curatively-applied treatments against Phytophthora on flooded flowering dogwood (Cornus florida L.) seedlings. Fungicides also were evaluated for efficacy against Scolytinae. In 2017, Orkestra (container substrate drench) and Pageant ® Intrinsic® Brand Fungicide (Pageant) (trunk spray) reduced ambrosia beetle attacks on flooded flowering dogwoods, while the drench-applied Empress, Orkestra, and Pageant were effective on flooded tulip poplar (Liriodendron tulipifera L). In 2018, Pageant treatments (drench and spray) reduced ambrosia beetle attacks on redbuds ( Cercis canadensis L.), but results were inconsistent in 2017. Ambrosia beetle behavior was observed using webcams on trees treated with Pageant (drench) or Tartan (trunk spray). Both Pageant and Tartan fungicide treatments reduced ambrosia beetle attacks. With Pageant, beetle presence on trees was similar to the untreated control, suggesting the reduction in attacks were not caused by reduced landing rates, but rather a probable post-landing effect. In contrast, fewer beetles landed on Tartan-treated trees than the untreated control, indicating a probable pre-landing effect. A final study evaluated insecticide residual effects. Permethrin (Perm-Up 3.2EC) was sprayed onto tree trunk sections (bolts) at 0-, 8-, 17-, or 24-d before ethanol introduction to evaluate residual activity against ambrosia beetles. In another experiment, permethrin was sprayed onto bolts 8- or 22-d before ethanol introduction and half of the tree bolts were exposed to simulated rain. Bolts with permethrin residue ages ≤ 17 d provided protection against ambrosia beetles. Simulated rainfall did not affect permethrin efficacy relative to the non-irrigated treatment. Although fungicides and insecticides demonstrated value against ambrosia beetles, most treatments did not completely prevent beetle attacks or disease. More research will be needed to determine the most effective way to employ these products. The information obtained from these studies will improve management programs for these pathogens and beetles