Gardening in the Black Hills can be challenging due to unpredictable weather, but we are often blessed with lower pest pressure than more humid parts of the country. This guide helps you identify common local pests and diseases and explains when you might expect to see them.
Remember: Healthy plants are the best defense. We only stock resilient plants built for the local environment.
Common Black Hills Pests & Management
We usually deal with insects, not diseases (which prefer more humidity).
| Pest | When to Watch | Where They Are Worse | Management Strategy (Organic) |
|---|---|---|---|
| Grasshoppers | Mid-Summer (July/Aug) | Drier, open areas (Belle Fourche, Edgemont, Nisland) | Hand-pick if numbers are low. Use Nosema locustae (a natural biological control). |
| Aphids | Late Spring/Early Summer | All areas, especially on new, tender growth (Lilacs, Maples) | Strong spray of water to knock them off. Use insecticidal soap or Neem oil if persistent. |
| Spider Mites | Mid-to-Late Summer | Dry, hot periods in all areas, especially foothills (Rapid City, Hermosa) | Strong spray of water on the underside of leaves. Neem oil or insecticidal soap. |
| Leaf Miners | Late Spring/Early Summer | All areas; often visible on Aspen leaves | Generally cosmetic damage; tolerate or prune affected leaves. |
| Boring Insects | Year-Round | All areas; target stressed/weakened trees | Prevention is key: Keep trees healthy and watered. No effective home treatment once inside the wood. |
| Tent Caterpillars | Late Spring (May/June) | More common in the central/southern hills | Prune out the nests when they are small. Use Bt (Bacillus thuringiensis) spray. |
Regional Pest Variations
Pest pressure isn’t uniform across the Black Hills:
- Drier, Lower Elevations (Belle Fourche, Edgemont, Nisland): These areas often have higher populations of grasshoppers and struggle more with spider mites during hot, dry spells.
- Higher Elevations (Lead, Deadwood, Custer): These areas are wetter and cooler, which naturally suppresses spider mites and grasshoppers. However, you might see slightly more occasional fungal issues if airflow is poor.
- Rapid City Corridor (Rapid City, Hermosa, Sturgis): We have a balanced mix of everything. Aphids and spider mites are our most common seasonal nuisances.
Your Seasonal Alert System
We keep an eye on pests in our nursery and will post timely updates here on this page or our blog:
- MAY ALERT: Aphids are starting to appear on new lilac growth. Use a jet of water to spray them off!
- JULY ALERT: Spider mites are active during the hot weather. Check the undersides of your leaves and use a water spray in the mornings.
- AUGUST ALERT: Grasshopper damage is at its peak in open areas. Keep an eye on new shrubs.
Bookmark this page for the latest updates and plant health information tailored to our unique climate!
Identifying Garden Pests in the Black Hills
There have been several times when I found damage on my plants, but didn’t see the culprit. Knowing what to look for is the first step in protecting your garden. Here is a guide to identifying the damage caused by common local pests.
| Pest | What the Damage Looks Like | When/Where to Look |
|---|---|---|
| Grasshoppers | Large, irregular holes chewed out of leaves, stems eaten down to the ground on small plants. Damage can appear overnight and is widespread. | Mid-Summer (July-Aug). Active in hot, dry, open areas (prairie edges). |
| Aphids | Curled, yellowing leaves; sticky residue (honeydew) on leaves below the infestation. Tiny insects cluster densely on the underside of new growth tips. | Late Spring/Early Summer. Found everywhere, especially on lilacs and maples. |
| Spider Mites | Stippling (tiny yellow/white dots) on leaves. Leaves turn bronze or dusty gray and may drop early. Fine webbing may be visible on the underside of leaves or branch tips. | Mid-to-Late Summer during hot, dry spells. They thrive in heat. |
| Leaf Miners | “Scribbles” or meandering, pale/white tunnels visible inside the leaves. The insect lives between the top and bottom layers of the leaf. | Late Spring/Early Summer. Common on aspen and birch. |
| Boring Insects | Small, perfectly round holes in the trunk or branches. Sawdust-like material (frass) may be found near the holes. Wilting branches in summer (the part above the damage dies). | Year-round activity, but damage is noticed in summer when branches die back. |
| Tent Caterpillars | Silken, web-like “tents” in the forks of branches. Leaves around the tent are completely stripped bare. Caterpillars leave the tent to feed during the day. | Late Spring (May/June). Visible in the hills on chokecherry and apple trees. |
Are Slugs and Snails a Problem Here?
The Black Hills region is generally too dry for significant slug and snail problems.
The climate is a major deterrent. Slugs and snails require consistently damp, humid environments to survive, as they lose moisture rapidly through their skin.
- In general garden areas: They are not common enough to be listed as a primary pest concern for most gardeners in Rapid City, Hermosa, or the foothills.
- Exceptions: You might find them in highly specific, overly wet microclimates:
- In a poorly drained vegetable garden with constant overhead irrigation.
- Under very thick, perpetually wet mulch next to a leaking spigot.
- In the very wettest, shadiest spots of Lead or Deadwood.
For the vast majority of us, we won’t need to worry about providing slug and snail deterrents. The dry air of South Dakota is a natural defense!
Keep in mind that some pests are cyclical. If we’ve had a few dry springs in a row, be prepared for heavier grasshopper pressure in mid-summer. Monitoring these weather patterns helps you prepare ahead of the curve.
The Grasshopper Cycle: Highly Cyclical
The idea of a 3-year cycle for grasshoppers is a commonly observed pattern. Their population dynamics in the Black Hills area are heavily influenced by drought conditions:
- Drought Years = Boom Years: Grasshopper eggs hatch best in dry, warm soil. A few consecutive dry springs often lead to massive spikes in the grasshopper population (an “outbreak” year).
- Wet Years = Bust Years: A wet, cool spring increases the rate of fungal diseases that kill young grasshoppers and also harms the eggs in the soil.
- The Pattern: You often see low numbers for 1-2 years, followed by a significant increase in the third year, which crashes again after a natural die-off or bad weather cycle.
Other Cyclical Pests
Other pests are cyclical based more on immediate weather conditions than multi-year patterns:
- Spider Mites: These pests are highly cyclical within a single summer. They “boom” rapidly during periods of prolonged heat and drought (mid-July/August) and disappear almost entirely during rainy or cool periods. A very hot, dry summer usually means a heavy mite year.
- Tent Caterpillars: While they appear annually, severe widespread outbreaks tend to happen every 5 to 10 years. During these outbreak years, they can almost totally defoliate entire hillsides of chokecherry and aspen. The population usually collapses again due to disease or parasites after a few peak years.
- Aphids: Their population spikes are purely seasonal. They appear with the new, succulent spring growth and usually decline once natural predators (ladybugs, lacewings) catch up or the weather gets too hot and dry in mid-summer.
The Tents (webs)
Tent caterpillars in trees and shrubs can be identified by their tough, silken tents found in branch forks [0]. Physical removal using a stick or pruning is recommended, ideally done in late May or early June when tents are small [0]. Alternatively, an organic spray containing Bacillus thuringiensis (Bt) can be applied to nearby leaves in the evening if tents are out of reach [0]. Following removal, maintaining tree health through adequate watering is important [0]. More information is available on the Ask Extension website.
What happens if a person does not notice the tent until much later?
If a person doesn’t notice the tent caterpillar web until much later in the season (late June, July, or August), the management approach changes, and the news is both good and bad.
The good news is that the immediate damage to the tree is likely over, and the tree is usually fine. The bad news is that it is often too late to effectively stop the current generation of caterpillars, and physical removal might be pointless or cause more harm than good.
Here is what happens and what a person can do:
What Happens When You Find a Late-Season Tent
By mid-to-late summer, the situation has changed significantly:
- Feeding is Finished: Tent caterpillars typically finish their 4-to-6 week feeding cycle by late June. They grow to their full size and wander away from the tree to find a place to spin a cocoon.
- Tree Recovery Begins: Most healthy, deciduous trees (which is what tent caterpillars prefer, like cherries, aspens, and maples) are highly resilient. They can regrow a second set of leaves within a few weeks of being defoliated, minimizing long-term damage.
- The Tent is a Ghost Town: If you find a large, old tent in July or August, the caterpillars are likely gone, pupating elsewhere or having already emerged as moths. The unsightly web will just persist until winter, when it eventually breaks down on its own.
What to Do If You Find the Web Late
In the late season, control measures are often unnecessary and can be less effective:
- Do Nothing is a Valid Option: Since the damage is primarily cosmetic and the caterpillars are gone or almost gone, often the best course of action is to simply ignore the web. The tree will recover.
- Physical Removal (If Desired): If the appearance bothers the homeowner, they can still physically remove the empty or nearly empty tent with a long stick or pole pruner. Tearing the tent open can also allow birds and beneficial insects access to any remaining caterpillars or pupae.
- Caution: Avoid excessive pruning of healthy branches just to remove an empty web, as this can stress the tree more than the caterpillars did.
- Insecticides Are Ineffective: Insecticides like Bt or chemical sprays are largely ineffective against full-grown caterpillars or those no longer feeding on the leaves. They work best on small, young caterpillars early in the season.
Prevention for Next Year
The most important step for a late-season discovery is to plan for prevention next winter:
- Winter Inspection: Inspect your trees during the winter months when the leaves are gone. Look for the shiny, dark brown egg masses that encircle small twigs.
- Scrape or Prune: Scrape off these egg masses or prune the small twig they are on and destroy them to prevent a new generation from hatching the following spring.
So, these ‘tents’ don’t actually kill the tree, they are just unsightly?
That is correct. For healthy, established deciduous trees in the Black Hills, tent caterpillar infestations are rarely fatal.
The damage they cause is primarily cosmetic (unsightly) and typically a temporary stressor for the tree.
The Real Impact of Tent Caterpillars
- Unsightly, But Resilient: The large, messy tents and the defoliation of leaves make the tree look bad for a time. However, healthy trees are surprisingly resilient. They are built to withstand occasional insect feeding or weather events.
- The Tree Fights Back: Most healthy trees will produce a second flush of leaves a few weeks after the caterpillars finish feeding, especially with a little extra water during the recovery period.
- The Only Real Risk: The only time a tree is at risk of dying from tent caterpillars is if it is a very young, newly planted sapling that is already severely stressed (e.g., struggling with drought, borers, or disease), and it is defoliated multiple years in a row.
For the established trees in most Black Hills yards, the main issue is simply tolerating the temporary inconvenience of the ugly tents and the sight of stripped branches.
Are the moths an issue in the garden?
The moths that emerge from the tent caterpillars are not a direct issue for the garden or your plants. They are completely harmless and generally go unnoticed by most gardeners.
Here is what you need to know about the adult tent caterpillar moths:
The Harmless Adult Moth Stage
- They Don’t Eat Leaves: Once the caterpillar pupates and emerges as a moth (typically in July), it stops eating plant material entirely. It has no mouthparts designed for chewing leaves.
- Their Only Job is Reproduction: The adult moths live for only a few days to a week. Their sole purpose during this short lifespan is to mate and lay eggs for the next spring’s generation.
- Appearance: They are usually plain, reddish-brown or tan moths that are attracted to lights at night. They aren’t colorful or invasive like other garden pests.
The Real “Issue” is the Eggs They Leave Behind
While the moth itself causes no damage, it is the act of laying eggs that poses a problem for the next year’s garden:
- A female moth finds a suitable twig (usually on a chokecherry, aspen, or apple tree).
- She lays an egg mass that looks like a shiny, dark brown or grayish band that wraps around the twig.
- She dies shortly after.
The issue for the gardener is preventing those eggs from hatching next spring.
What you should Do (me too):
“Don’t worry about the adult moths flying around in July; they won’t harm your plants. The best time to break the cycle is in the winter: look for the shiny, dark egg masses wrapped around the twigs of your fruit and aspen trees, and prune them off before spring!”
Grasshoppers
Question- For the grasshoppers, I have heard of a spray that you can put on the lawn that targets young grasshoppers and kills them before they grow to maturity. And if applied to the yard at certain times, it dries before pets are out on it.
That is a common request. You are thinking of specific insecticides for turf or granular baits that target the young grasshopper nymphs when they are small and most vulnerable.
Here is what you need to know regarding lawn sprays for grasshoppers and pet safety:
Using Sprays for Young Grasshoppers
The timing of application is crucial for success and safety. The best time to apply any treatment is early in the season (late May/early June), when grasshopper nymphs have just hatched and are still small and concentrated in grassy areas.
Option 1: Granular Insecticides (Lawn Application)
This is likely what you heard about. Granules are applied to the lawn with a spreader and then watered in to release the active ingredient into the soil/thatch layer where nymphs live.
- Active Ingredients: Look for products containing carbaryl (often sold as Sevin) or bifenthrin.
- Pet Safety: Pets must be kept off the treated area until the granules are completely dissolved and the lawn is fully dry. This typically takes a few hours (1-3 hours), but follow the product label’s specific instructions. Once dry, the risk is significantly lower.
- Benefit: These provide longer protection, often up to three months.
Option 2: Organic Baits
For a safer, more targeted approach, especially if you prefer organic methods or have pets that chew on grass, baits are excellent.
- Active Ingredient: Nosema locustae (Trade names: Nolo Bait or Semaspore).
- How It Works: This is a naturally occurring pathogen mixed with wheat bran that grasshoppers eat. It only affects grasshoppers and certain crickets; it is harmless to humans, pets, birds, and other beneficial insects.
- Pet Safety: Extremely low toxicity to mammals and birds.
- Benefit: Very selective and safe, but it is slow-acting and works best on young nymphs. It needs to be reapplied weekly and after rain.
Key Safety Takeaway
Regardless of the product used (spray or granules), the main safety rule for pets is consistent:
“Keep pets and people away from the treated area until the product has completely dried.”
Always read the specific product label directions, as drying times and re-entry instructions can vary.
Question- Do you know about a product called seven? For some sort of pest control?
Yes, Sevin is a well-known, broad-spectrum insecticide used to control a wide variety of pests in lawns, gardens, and on ornamental plants.
Key Information About “Sevin”
- Broad-Spectrum: It is designed to kill over 500 different types of insects by contact, including grasshoppers, aphids, Japanese beetles, cutworms, and tent caterpillars.
- Active Ingredients: The active ingredient can vary depending on the specific Sevin product you buy (liquid concentrate, ready-to-spray, or granules):
- Carbaryl: The original active ingredient in many Sevin products, which works by affecting the nervous system of the insect.
- Zeta-Cypermethrin or Bifenthrin: Many newer Sevin formulations have transitioned to these synthetic pyrethroid ingredients, which offer a fast knockdown and longer residual activity (up to 3 months).
- Forms: It comes in various forms, including liquid concentrates, ready-to-spray bottles that attach to a hose, and granules for lawn spreaders.
- Safety for Pets/People: Sevin products are generally considered safe for people and pets once the applied product has completely dried. It’s crucial to follow all label instructions and keep animals off the treated area until it is dry (usually a few hours).
- Environmental Impact: It is highly toxic to beneficial insects like honeybees and aquatic life. It’s recommended not to spray open blooms to protect pollinators and to avoid runoff into drains or waterways.
Question- If used on the open lawn, will it harm beneficial insects?
Yes, if Sevin (which contains active ingredients like carbaryl, zeta-cypermethrin, or bifenthrin) is used on an open lawn, it will very likely harm beneficial insects.
Here’s why, and what that impact entails:
Why Sevin Harms Beneficial Insects
Sevin is a broad-spectrum insecticide, which means it doesn’t differentiate between “bad” pests (like grasshoppers) and “good” pests (like ladybugs or pollinators).
- Contact & Residual Kill: Insects come into contact with the chemical residue on the grass blades and die.
- Affects Predators: Beneficial insects like ladybugs, lacewings, beneficial wasps, ground beetles, and spiders that hunt the target pests in your lawn will also be killed by the residual chemical.
- Harm to Pollinators: If there are any flowering weeds in the lawn, foraging bees and butterflies that land on the treated area will be poisoned.
The Impact on Your Garden Ecosystem
Using broad-spectrum pesticides has a knock-on effect on the entire garden:
- Pest Population Bounce-Back: The beneficial insects you killed were actually helping control the pest populations naturally. Without them, pest populations can often rebound faster and stronger than before (a “secondary pest outbreak”) because they have no natural predators left.
- Harm to the Food Chain: Birds and other small wildlife that eat insects from your lawn may be exposed to the chemical residue.
A Note on Broad-Spectrum Sprays: Products like Sevin are effective, but they kill all insects, including beneficial ones like ladybugs and bees that help keep pests in check. Use them only as a last resort. We recommend organic options like Nosema locustae baits for grasshoppers, which only target specific pests and leave beneficial insects and pollinators unharmed.