If you’re growing milkweed for monarch butterflies, finding spider mites on milkweed can be a real frustration. These tiny pests can quickly overwhelm your plants, but don’t worry—there are many effective natural solutions.
The good news is you can manage spider mites without resorting to harsh chemicals that could harm the butterflies and other beneficial insects you’re trying to support. This guide will walk you through simple, proven methods to get the situation under control.
Spider Mites on Milkweed
Spider mites are not true insects; they are tiny arachnids related to spiders. They thrive in hot, dry conditions and suck the sap directly from plant leaves. On milkweed, you’ll often first notice a subtle stippling or pale dots on the leaves before webbing becomes visible.
Left unchecked, a severe infestation can cause significant leaf drop and weaken the plant. This is a problem not just for the milkweed, but for the monarch caterpillars that depend on it for food. Natural control focuses on disrupting their environment and using physical and biological methods.
Identifying the Problem Early
Catching spider mites early is key to easy control. Here are the main signs to look for:
* Fine Webbing: Look for delicate, dusty webs on the undersides of leaves or where leaves join the stem. This is often the most obvious sign.
* Leaf Stippling: Tiny yellow or white speckles on the leaf surface where the mites have fed.
* Bronze or Yellow Leaves: As feeding continues, leaves may turn a bronze color, then yellow, and eventually dry up and fall off.
* Visible Mites: Shake a leaf over a white piece of paper. If you see tiny, moving specks that look like dust, those are spider mites.
Why Natural Control is Essential for Milkweed
Milkweed is a host plant, meaning it’s essential for the lifecycle of monarch butterflies. Using broad-spectrum chemical pesticides can have devastating effects:
* They can directly poison monarch eggs and caterpillars.
* They kill beneficial insects that prey on spider mites, like ladybugs and lacewings.
* Pesticide residues can remain on the plant leaves for weeks.
Natural pest control protects the entire ecosystem you’re fostering in your garden. It’s safer for you, the pollinators, and the soil.
Immediate Action: Physical Removal
When you first spot an infestation, start with these physical methods. They can reduce numbers dramatically with no side effects.
1. The Hose Blast Method
This is remarkably effective. Every 2-3 days, use a strong jet of water from your hose to spray the undersides of the milkweed leaves. This knocks the mites off the plant. Since they are poor climbers and dislike moisture, many will not make it back. Be sure to support the plant stem with your hand to avoid damage.
2. Hand Wiping
For light infestations on a few plants, wipe the tops and bottoms of leaves with a damp cloth. You can dip the cloth in plain water or a mild soapy water solution (see next section) to kill mites on contact.
3. Pruning Heavily Infested Leaves
If certain leaves or stems are completely covered in webbing, it’s best to prune them off immediately. Place the cuttings directly into a sealed bag and throw them in the trash, not the compost, to prevent the mites from spreading.
Creating a Simple Soap Spray
Insecticidal soap works by breaking down the mites’ protective outer coating. You can buy a ready-to-use product or make your own.
DIY Insecticidal Soap Recipe:
* 1 tablespoon of pure liquid castile soap (avoid detergents or degreasers)
* 1 quart of lukewarm water
* Optional: 1 teaspoon of neem oil (adds fungicidal properties)
Mix in a spray bottle and shake well. Always test the spray on a small part of the plant first and wait 24 hours to check for damage. Milkweed leaves can be sensitive.
How to Apply:
1. Spray in the early morning or late evening to avoid sun-scorch on leaves.
2. Thoroughly coat the undersides of the leaves where the mites live.
3. Reapply every 4-7 days for at least two weeks to break the mite life cycle.
4. Avoid spraying when monarch caterpillars, eggs, or butterflies are present on the plant.
Introducing Natural Predators
This is a fantastic long-term strategy. You can attract or purchase beneficial insects that see spider mites as a food source.
* Ladybugs & Lacewings: Both adults and larvae consume large numbers of mites. You can buy them online, but first try planting pollen-rich flowers like dill, fennel, and yarrow to attract them naturally.
* Predatory Mites (Phytoseiulus persimilis): These are mites that eat spider mites. They are available from biological control suppliers and are highly effective in greenhouse settings or during warm, humid weather.
To keep these helpers in your garden, you must avoid using any pesticides, even organic ones like pyrethrin, that could harm them.
Using Horticultural Oils
Oils like neem oil or horticultural oil smother spider mites and their eggs. They are most effective when applied regularly.
* Neem Oil: Mix according to bottle instructions (usually 1-2 teaspoons per quart of water with a bit of soap as an emulsifier). It disrupts the mite’s hormonal systems.
* Horticultural Oil: Use a dormant or summer-weight oil. These provide excellent physical control.
Apply oils with the same care as soap sprays—test first, cover leaf undersides, and avoid application in peak heat or direct sun. Reapply weekly.
Cultural Practices to Prevent Future Outbreaks
Prevention is always easier than cure. Spider mites love stressed plants and dry, dusty conditions.
* Water Regularly: Keep your milkweed adequately watered. Occasional overhead watering can raise humidity and wash off dust that mites love.
* Avoid Over-Fertilizing: Excess nitrogen can promote the soft, succulent growth that spider mites prefer. Milkweed generally doesn’t need much fertilizer.
* Inspect New Plants: Always check new milkweed plants (or any plants) thoroughly before adding them to your garden. Quarantine them for a week if possible.
* Promote Biodiversity: Plant your milkweed among a variety of other plants. A diverse garden supports natural predators and makes it harder for any one pest to spread.
What About Companion Planting?
While some plants are said to repel pests, evidence for spider mite repellants is anecdotal. However, planting strong-scented herbs like garlic, chives, or mint nearby may offer some deterrence. The real benefit of companion planting is attracting beneficial insects. Consider adding:
* Marigolds
* Cosmos
* Alyssum
* Sunflowers
These plants provide nectar and pollen for the good bugs that will help patrol your milkweed.
Monitoring and Persistence
Natural control requires consistency. You won’t get rid of spider mites with one treatment. Implement a weekly routine of checking your milkweed leaves, especially during hot, dry spells. Alternate between physical blasts of water and applications of soap or oil sprays for 3-4 weeks to ensure you get all the emerging generations.
Remember, the goal is management, not necessarily complete eradication. A few mites might remain, but if your plants are healthy and you have predators present, they will keep the population in check without harming your monarchs.
FAQ: Natural Control for Spider Mites on Milkweed
Q: Will vinegar kill spider mites on my plants?
A: While vinegar can kill mites on contact, it is a harsh herbicide that can easily damage or kill your milkweed leaves. It’s not recommended for this purpose.
Q: Can I use rubbing alcohol on milkweed leaves?
A: A diluted solution (1 part alcohol to 3-4 parts water) can be dabbed directly on mites with a cotton swab for spot treatment. However, spraying it broadly can damage the plant, so test a small area first and use cautiously.
Q: How do I get rid of spider mites without hurting monarch caterpillars?
A: Timing is everything. If caterpillars are present, avoid any sprays (even soap) directly on them. Use the strong water blast method instead, or carefully move caterpillars to a clean leaf or plant before treating others.
Q: Are spider mites harmful to monarch caterpillars?
A: Not directly, but a severely weakened milkweed plant may not provide adequate food quality. The main harm comes from the methods we might use to control the mites.
Q: Why do my milkweed plants keep getting spider mites every year?
A: They likely overwinter in plant debris or nearby vegetation. Clean up fallen leaves around the plants in fall and ensure your plants are not chronically stressed by drought or poor soil, making them more susceptible.
By following these natural strategies, you can protect your vital milkweed patch and ensure it remains a safe, healthy haven for monarch butterflies throughout the season. The key is to act fast, be persistent, and always choose the method that is safest for the butterflies you aim to support.