In a recent article for this publication, I encouraged the selection of native plants that shared qualities similar to plants we have enjoyed in other states and ecosystems. My reasoning included the idea that native plants are more pest-resistant than non-natives. While that tends to be true, it does not mean that all natives are resistant to all pests or vice versa. Indeed, some non-natives, including those considered invasive, do extremely well here in part because their natural predators have been left far behind. Indigenous plants have evolved for millennia alongside indigenous insects, which offer crucial benefits even as they do some damage.
How much damage are we willing to accept to any of our plants, native or not, before we feel the need to intervene? There are many points of view.
Some gardeners have a very low threshold for plants that look unhealthy to them. Holes in leaves or nibbled buds are deemed unsightly and seem to imply a lack of success as a gardener. The horticultural industry is at the ready, with broad-spectrum insecticides galore. These treatments will kill many garden pests successfully but often with unintended consequences. Such products raise health and environmental concerns and often also kill pollinators and insects that have great value in the landscape.
If you want to eliminate any and all damage to your plants, it’s a good idea to start with an integrated pest management (IPM) approach. Start with the least toxic alternatives; it’s often possible to solve a problem without using chemicals or, if that fails, with single-ingredient products that are targeted to your problem. For more information on IPM, take a look at New Mexico State University’s “Integrated Pest Management (IPM) for Home Gardeners” circular (https://aces.nmsu.edu/pubs/_circulars/CR655).
Other gardeners are more tolerant of noticeable damage to their plants. Those hoping to attract butterflies know that in order to have swallowtail, painted lady, or monarch butterflies, they must also allow the larvae to feed. Our native plants are hosts to pollinators and beneficial insects that we hope to preserve. Spring azure butterfly larvae feed on our native cliffbush (Jamesia americana); even with some nibbling at the leaves, I for one would enjoy having small blue butterflies grace my garden.
That said, when a pest defoliates whole plants, shrubs, or trees, most gardeners become alarmed. For farmers it can be catastrophic, and eradication is often necessary. For the home gardener, the choice is more personal. In an August column in NMSU’s Southwest Yard and Garden, guest columnist Alissa Freeman suggests that if you want a garden that is also a pollinator habitat, you should plant more than you need. If swallowtail caterpillars eat your dill or parsley, plant extra. Row covers can be used to cover most but not all of your cabbages or tomatoes.
From experience you will learn what plants are most vulnerable. Natives often fare better, but they are not exempt from attacks of aphids or boring insects. Some pests are harder to control than others. But what looks like pests are not always the bad guys. Some are predators of the offending insect or larvae; others may grow into powerful pollinators or beautiful butterflies.
It’s very important to know what pest you are dealing with. I recently suggested using native fernbush in place of white lilacs and pointed out that my white lilac looked unattractive by the end of summer, with leaves tattered and chewed by grasshoppers. It was easy for me to reach this conclusion because of what I saw: chewed leaves and grasshoppers. But I never actually saw grasshoppers on that shrub. I never saw any pests on it. It turns out that what is eating the leaves are lilac root weevils, which are only active at night. Had I spent the time and money to attempt to eradicate grasshoppers from my garden, I would be looking at tattered leaves again next year. I will need an entirely different program to deal with the root weevils.
To determine if the critter you are seeing might actually be a good guy, check out NMSU’s detailed guide to identifying beneficial insects in New Mexico: https://aces.nmsu.edu/pubs/_h/H172/welcome.html. As for those pests you don’t see, come spring when you notice damage but no visible culprits, grab a flashlight and have a backyard adventure.
Laurie McGrath has been a certified Master Gardener in Santa Fe County for 19 years and is a founding member of the Santa Fe Native Plant Project (SNaPP). She was a co-host of “The Garden Journal” on KSFR radio. Before moving to Santa Fe she helped design a Hummingbird Garden at the Jeanne and Charles Schultz campus of Canine Companions for Independence in Santa Rosa, California.