Marin IJ Articles

Two pests and a tree

• Anne-Marie Walker

• 

  An adult and a nymph (bottom) marmorated stink bug on a leaf of tree-of-heaven. Photo: Steve Ausmus, USDA/ARS

  This is not a riddle about which comes first, the chicken or the egg. Rather, it’s a tale about collecting trees, bringing them to non-native habitats, and a very interconnected world in which hitchhiker bugs invade and seriously threaten native landscapes and agricultural crops. The tree is tree-of-heaven (Ailanthus altissima), and the bugs are the spotted lanternfly (Lycorma delicatula) and the brown marmorated stink bug (Halyomorpha halys), all three of which co-evolved in Asia. The stink bug was first detected in California in 2006. It damages primarily fruits and vegetables. As of 2024, the spotted lanternfly is in 20 states, and the California Department of Food and Agriculture wants us all to be vigilant and stop the spotted lanternfly from arriving in California. Crops threatened include apples, cherries, stone fruits, walnuts, hops, and grapes. Scientists don’t know yet if the spotted lanternfly will threaten almonds and pistachios because these two crops are grown mostly in California. Trees threatened include maple, willow, birch, and poplar. The list is likely to grow as the pests spread to other regions. So, if you enjoy apple pie from your garden’s apple tree, a cold glass of West Marin pale ale, or sipping a California wine, read on and see how you can help stop the spread of two pests and an invasive tree.

  

  A tree-of-heaven resembles native sumac and hickory trees and is on the UC List of Noxious Weeds. Photo: Alice Cason

  Tree-of-heaven was brought to the northeastern United States in the late 18th century and to California during the gold rush as a unique and fast-growing deciduous shade tree. Today, tree-of-heaven is on our noxious weed list, having escaped gardens, established in the wild, and spread vigorously by seed and creeping roots that extend as far as fifty feet. Part of its success is attributed to chemical compounds produced by the tree to reduce competition from nearby plants, a phenomenon called allelopathy by which the tree’s chemicals spread into the surrounding soil, making unfavorable conditions for other plants.

  Tree-of-heaven has now been identified as the preferred host plant of both the spotted lanternfly and the brown marmorated stink bug. Host plants are those plants on which and off which insects live and reproduce. Both the spotted lanternfly and the brown marmorated stink bug are plant-hopping sap suckers that co-evolved with tree-of-heaven in A sia. With piercing-sucking mouthparts, they feed on the tree of heaven, ingesting alkaloids produced by the tree and becoming distastefully bitter to preying birds and insects. You have seen the headlines in Pennsylvania, New York, and other eastern states where the invasion of spotted lanternflies has overwhelmed gardens, parks, orchards, forests, and open spaces. The spotted lanternfly was detected in Pennsylvania in 2012 on a stone shipment from Asia; the insects can hitchhike on most hard surf ces. When it arrived in New York, officials asked the public to report sightings and to stomp on the insects. The bugs don’t harm, bite, or sting humans but inflict severe damage to plants and crops, including otherwise indestructible grapevines.

  

  An adult spotted lanternfly with red and white nymph stage spotted lanternflies. Credit: USDA/ARS

  UC Master Gardeners are on the lookout for tree-of-heaven, mapping locations for planned removal by the California Department of Food and Agriculture. While homeowners are encouraged to remove tree-of-heaven on their property, removal is a challenge. Don't cut the tree down, as roots will generate the sprouting of many more trees. Removal instructions are given at https://ucanr.edu/blogs/blogcore/postdetail.cfm?postnum=60006. Scientists are studying other pest control methods but ask that if you see a spotted lanternfly, report it to your local county Agricultural Commissioner’s office right away. Use your phone to document the exact location, collect the insect in a container, or take a photo to submit. This is your proactive step to keep the spotted lanternfly out of California. Repo t tree-of-heaven by phone or email to Marin Master Gardener at www.marinmg.org. With vigilance, each of us can contribute to mitigating the threat posed by these two pests and a tree.