Are you noticing pests or diseases on your lavender plants? Find out what they could be, and how to prevent them!
Lavender is an extremely hardy plant. They fall victim to few pests, and very few diseases. But despite their hardiness, pests and diseases do still take hold of these plants. In this article, organic gardening expert Logan Hailey (who has worked at a large lavender farm) walks through the most common lavender pests and diseases, as well as how to preven them!
Lavender is one of the most resilient and beautiful perennial herbs to grow in your garden. Its dreamy, sweet fragrance is known for its calming properties. And the contrast of vibrant violet blossoms against silvery green foliage is enough to warrant a lavender plant in every herb garden.
However, in spite of its remarkable drought tolerance and problem-free attitude, not even lavender is perfect. Regardless of the lavender type, this Mediterranean herb is still subject to attack from a few pesky pathogens and insects. Thankfully, they are quite easy to deal with organically.
If you’re having trouble with your lavender plants or want to prevent future problems, here’s the most common pest and disease problems you should know about.
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Lavender is native to the Mediterranean basin, where it thrives in the hot, dry weather and rocky soils of high-elevation hillsides. While this hardy perennial can be cultivated in most of the United States growing zones 5-10, growers often encounter problems in excessively wet regions or make mistakes by using poorly drained soils.
If you over-water or live in an area with heavy rainfall, you may have problems with one or more of the following diseases. Here’s how to identify, prevent, and treat them:
Root rot is the number one most common problem with lavender. This aggressive rotting disease can be caused by a range of pathogens, namely Fusarium spp., Phytophthora, spp. Pythium spp. and Rhizoctonia spp. They are most common in the chilly, wet and waterlogged soils of the Northeast and Pacific Northwest.
Root rot first manifests itself as wilting and yellow or brown leaves. The entire plant may appear droopy, in spite of having plenty of water. You will also notice stunting or halted growth. If you remove soil from around the root zone, you may discover mushy, discolored roots that are blackened or smelly. As the roots succumb to the infection, the plant will be unable to properly absorb nutrients and water, ultimately resulting in death.
Root rot often infects lavender during rainy winters, especially in areas where the soil lacks drainage. This fungal-like pathogen attacks the herb specifically in cold, wet soils. The biggest major cause of root rot is overwatering, whether from excess rainfall or too much irrigation.
Nobody can control the weather, but you can ensure that your lavender is growing in soil that is as well-drained as possible. Before planting, generously amend the soil with sand, gravel or peat moss. Double dig or use a broadfork to loosen the soil. Avoid dense composts or heavy clay soils that may hold extra moisture.
Root rot can also travel through infected nursery starts. Be sure that you buy disease-free plants sourced from a reputable, quality supplier. They shouldn’t show any signs of sickness before you transplant them into your garden. If you’re installing a large lavender planting, you can also test them with a plant pathogen test from Agdia.
Cultural preventative controls are the most effective means of dealing with root rot. But if your plants have already succumbed to root rot, you can try to stop the disease from spreading by pruning away damaged tissues and treating the soil with an organic fungicide like baking soda, horsetail (Equisetum), or sulfur.
However, if the root rot is caused by Phytophtora or Pythium, fungicides won’t work because these are technically oomycetes, or water molds. If the infection has started to severely affect the plant, it’s best to remove the entire shrub to prevent spread to nearby plants. Avoid re-planting in the same area.
Similar to root rot, crown rot is caused by a species of that attacks the above-ground center of the plant. This “crown” is the woody base of lavender from which all the stems emerge. Phytophthora
This fungus-like organism typically takes hold of lavender during the wettest seasons. It starts at the bottom with browning or yellowing lower leaves and creeps up the plant. The bark of the woody part may look blackened or stained with a cinnamon brown color. There are often dead patches near the base of the plant. The plant begins to dramatically wilt and eventually will die.
The most critical thing to remember when irrigating is to avoid wetting the root crown. Keeping moisture away from the crown of the plant is the easiest, most effective way to prevent crown rot. Only irrigate around the edges of the plant’s root zone rather than wetting the crown. Drip irrigation lines spaced 4-6” from the base of the plant are best.
Allow lavender to dry out in between watering. If using mulch, avoid mulching too close to the base of the plant by leaving a small ring 1-2” around the crown.
There are no fungicides or known treatments for crown rot once it takes hold. The best thing you can do is remove heavily infected plants and practice preventative cultural controls for other lavender plantings.
Alfalfa Mosaic Virus (AMV) is a common virus with a wide range of host plants. You’ll see it on lavender and rosemary to potatoes, tomatoes, legumes, and many ornamentals. This virus is transmitted primarily through insect feeding, unsanitized garden tools, and physical contact between plants.
Lavender infected with Alfalfa Mosaic Virus may be stunted with patches of yellow leaves that look contorted and mutated. The disease is most often found on plants with aphids.
Aphids and human hands are the most common vectors of the mosaic virus. First, be sure that you are using the methods outlined below to prevent aphid infestations. Wear gloves to remove infected plants and destroy them so they don’t infect any other plants. It’s also important to keep weeds under control near lavender beds.
There are no approved sprays or treatments for AMV. Remove and destroy infected plants, then thoroughly sterilize your garden tools.
The bacteria Xylella fastidiosa causes the Xylella disease in hundreds of different trees and shrubs, including lavender. It is extremely destructive and most commonly spread by sap-sucking insects. It’s most common in the southeast and southwest of the U.S. near moist riparian areas.
Stunted growth and foliage that appears scorched or wilted are the main signs of Xylella.
Staying on top of pests and weeds are the main ways to prevent the spread of Xylella. Maintain healthy plants by properly preparing well-drained soil. You can also plant companion plants near lavender to attract parasitic wasps and dragonflies that may feed on the bacterium as well as the sap-sucking pests that spread it.
Once Xylella symptoms take hold, it can be difficult to control or eradicate the bacteria.
Phomopsis lavandulae is a fungus that attacks the stems and branches of lavender plants. But it often takes months or years to show symptoms, then suddenly all the shoots begin to wilt and die. It is spread by wind and most problematic in larger-scale plantings.
In the spring, young shoots that suddenly start wilting, turning brown, or developing black spots most likely have shab. As it spreads down toward the branches, they begin to brown and die. There may also be small black shapes on the bark where spores spread from.
Source only certified disease-free plants, remove sick plants, and avoid taking lavender cuttings from infected plants. Varieties like “Dwarf French” and any French Lavender (Lavandula dentanta) are immune to the fungus.
Carefully dig up and burn shab-infested plants. There are no effective sprays or fungicides for this disease, so prevention is key.
This ultra-common fungal disease affects a range of garden plants in areas with high humidity and low airflow. It often spreads from nearby grapevines or squash plants.
Graying of foliage begins near the base of the plant and spreads upward. As it spreads, Botrytis can look fuzzy and white and may lead to yellowing, wilted, or dead leaves.
Soggy, waterlogged conditions are the most detrimental to this Mediterranean herb. Ensure that lavender is planted in soil that is as well-drained as possible by amending with sand, gravel, peat moss, or bark.
Avoid overwatering. Avoid overhead irrigation (in fact, once established, lavender can typically go without irrigation in most climates). Be sure to maintain proper air flow and spacing (2-4 feet) between plants.
Remove infected leaves and stems, then throw them away or burn them to prevent spread of the fungus. If growing in a pot, replant in a better drained potting mix. Use a diluted neem solution spray or organic fungicide and avoid watering for a few weeks to ensure the fungus has been eliminated.
Like most of the pathogens above, Septoria lavandulae is another fungus that loves high humidity and water sitting on lavender leaves. This species only attacks lavender, but there are closely related pathogens that can attack tomatoes, cannabis, and many field crops.
The disease first appears as tiny gray spots with brown or purple margins on the lower, older leaves. The spots expand and form larger irregularly-shaped brown blotches that eventually overtake and kill the leaves. Over time, the plant can lose most of its foliage and become weakened and stunted, but it’s unlikely that it will fully die.
The easiest way to prevent Septoria is to keep leaves as dry as possible. Avoid overhead irrigation. Ensure plenty of air flow. In rainy climates, ensure proper drainage and mulch the soil to prevent splashing water. Remove infected leaves to stop the spread. Allow soil to dry out between waterings.
*Pro Tip: Wait until the top few inches of soil are dry to the touch before watering. This will help prevent most diseases.
Copper and neem oil are the most common fungicides used to deal with Septoria Leaf Spot. It also helps to remove infected leaves as soon as possible.
Thanks to its fragrant aroma, lavender is typically known for repelling pests rather than attracting them. It is often planted as a companion plant for different garden vegetables.
However, a few insects are willing to brave the perfumey herb. Here’s how you can find them and get rid of them:
Sometimes called frog hoppers, these white or black and orange (“two lined”) striped bugs are most well known for their spit-like encasing. Their foam is also found on rosemary, strawberries, and beans. While unattractive, they aren’t typically harmful to the overall plant health.
Look for a foamy white substance that looks like spit on the plants in the spring. Spittlebugs rarely harm lavender health, but heavily affected stems may die back.
If they get out of hand, a homemade garlic-pepper spray can help repel spittlebugs. Mix ½ cup of jalapeno peppers, 6-10 peeled garlic cloves, and 2 tbsp. cayenne pepper in a blender, then mix with a few tablespoons of dish soap and spray onto spittle foamy areas.
The easiest way to remove spittlebugs is by hand or with a hefty dose of water. However, this is only recommended in hot, dry climates, as water on leaf surfaces can lead to fungal disease issues in humid weather.
These sap-sucking insects have soft bodies and wings that closely resemble aphids. There are hundreds of species of whiteflies that attack tomatoes, peppers, eggplant, cabbage, sweet potatoes, and some herbs.
Whiteflies are tiny, white, triangular, and powdery. They hang out in clusters on the undersides of leaves. Larger populations can cause yellow or mottled foliage, sooty or brownish mold (on their honeydew secretions), or an overall lack of plant vigor. Infested leaves may shrivel and die from heavy whitefly feeding.
Reflective mulches or aluminum foil at the base of lavender plants can be quite effective at preventing both whiteflies and aphids. You can also grow companion plants like white alyssum, dill, or calendula to attract predators.
While there aren’t many pesticides for controlling whiteflies, there are lots of biological control options. The predatory ladybug Delphastus pusillus can be purchased and released into your garden to control whiteflies. You can also use a heavy spray of water or a neem oil solution to remove whiteflies from leaves.
Aphid feeding doesn’t cause nearly as much direct harm to lavender as it does to many of our brassica crops. However, the main issue arises when aphids feed on lavender and spread Alfalfa Mosaic Virus (discussed above).
Aphids are small, oval-shaped, and whitish or green. They hang out underneath lavender leaves or on the stems. You can easily spot their honey-like sticky secretions. If heavily infested, leaves may look yellow or deformed.
Aphids most commonly attack lavender that has a lot of nitrogen fertilizer, which isn’t great for lavender flower production anyhow. Avoid fertilizing and don’t amend with manure-based composts. Diatomaceous earth and neem oil can also be used topically to repel aphids. You can also introduce beneficial insects like ladybugs to keep aphid population under control.
Spray and wipe leaves with a neem oil solution or essential oil blend (4 to 5 drops of peppermint, clove, and rosemary with 1 cup of water seems to work well). You can also spray plants with a heavy blast of water.
This major pest causes mostly cosmetic damage. It is a sucking insect that eats new leaves and stems, often reducing bloom production. Thankfully, its lifespan is short, however, it often coincides with the initial flush of flowers and may result in reduced or damaged blooms.
Nymphs are black and red and move very quickly. Adults are greenish-yellow beetles with four black stripes that run down their back. The bugs are most active in late May and early July in many regions. They feed on lavender stems and cause elongated pale lesions where they bite. Sometimes secondary infection of Septoria Leaf Spot can enter through the feeding wounds.
Natural predators of FLPB include damsel bugs, pirate bugs, and jumping bugs, which can be attracted to your garden by companion planting alongside dill, chamomile, or purple prairie clover.
FLPB feeding is usually short, quick, and mostly aesthetic. You can use neem oil, horticultural oil, or insecticidal soap to kill the nymphs. Alternatively, pinch off damaged foliage in early July and be assured that the bugs won’t reappear until the following year.
Whether you grow it for culinary, herbal, or ornamental enjoyment, lavender is a garden staple that offers a range of benefits to other garden plants. It doesn’t require much care and is quite resilient to pest and disease issues. The secret to preventing lavender problems comes down to two simple measures:
By sticking to these basic maintenance recommendations, you’ll be sure to minimize the pests and diseases this plant may be susceptible to.