Sweet Woodruff Problems: What's Wrong and How to Fix It
If your sweet woodruff is turning brown, developing spots, or just looking off, you're in the right place. This page covers the most common sweet woodruff problems - from natural summer aging to fungal disease and slug damage, so you can quickly figure out what's wrong and what to do about it. Sweet woodruff is a tough ground cover, but like any plant, it runs into issues. The fixes are usually simple once you know what you're dealing with.
Sweet Woodruff Turning Brown or Collapsing (Natural Aging)
As the summer progresses sweet woodruff plants tend to grow leggy and rangy. They naturally collapse of their own weight, their foliage withering and browning except at the tips of the stems. Among the common sweet woodruff problems, this natural aging process is frequently observed. Plants that lack moisture and/or are in sunny locations tend to do this earlier in the season.
Locate sweet woodruff in the shade and keep the soil moist. Try cutting back plants that are showing signs of withering to encourage new growth. This is one of the most common reasons sweet woodruff appears to be dying mid-season - it usually isn't. A hard cutback in midsummer often brings a fresh flush of growth by fall.
Ragged Holes in Sweet Woodruff Leaves? Slugs Are the Culprit
Slugs are essentially snails without protective shells. They are typically 1 to 2 inches long and either white, gray, yellow, or brownish black. Slugs are attracted to moist, well-mulched gardens and acidic soil. They are active at night, rasping holes with their file-like tongues in leaf and stem surfaces. They often leave a telltale trail of silvery mucous behind as they travel.
They hide under boards or leaf litter during the day. Control them with a trap made from a shallow plate baited with beer set in the garden bed. The slugs are attracted to the yeast in the beer, climb in, and drown. Begin trapping the pests 3 to 4 weeks after the last frost. Iron phosphate-based slug baits are also effective and safe around pets and wildlife. Scatter lightly around the base of plants after rain when slug activity is highest.
For more information see file on Dealing with Slugs and Snails.
Pale Patches on Leaves: Downy Mildew in Sweet Woodruff
Downy mildews are caused by fungi that grow and spread on moist leaf and stem surfaces. These fungi form pale areas on upper leaf surfaces and gray or white or purplish "downy" patches on undersides. They are especially active in periods of cool wet nights and warm humid days, causing leaves to wilt and die. Plant sweet woodruff on well-drained, fertile soil; water in the morning.
Avoid crowding your plants. Try to keep their foliage dry by watering just the soil. Dig up out heavily infected plants together with any adjacent soil and discard them in the trash. Spray lightly infected plants with flowable sulfur or dust them with lime sulfur or Bordeaux mixture when downy mold first appears on leaf undersides. Several applications may be needed to achieve control. While mildew will probably not kill the plants, it will make them unsightly, defeating their value as attractive ground cover. Sweet woodruff used as ground cover in heavily shaded, humid spots is particularly prone to downy mildew. Thinning dense patches improves airflow and usually reduces recurrence significantly.
For more information see file on Dealing with Fungal Disease.
Sweet Woodruff Leaf Spots and Blotches (Fungal Disease)
Many kinds of leaf spots are caused by fungi that thrive on moist leaf surfaces and cause transparent to brown or black spots that disfigure the leaves. Some fungal spots are surrounded by flecks or black dots, their spore-bearing fruiting bodies. Often spots come together to form larger patches of dead tissue.
Pick off and discard any infected leaves on sweet woodruff. Remove any dead plant debris promptly from the yard to reduce overwintering spore populations. Dig out and discard seriously infected plants together with the soil round the roots. Mulching helps prevent splash-borne infection in outdoor plantings. Spray at weekly to 10 day intervals with wettable sulfur or Bordeaux mixture, particularly in wet weather. (Watch for leaf discoloration with the latter.)
For more information see file on Dealing with Fungal Disease.
Orangish Powdery Spots on Sweet Woodruff Leaves: Rust
Rust diseases caused by various fungi produce pale yellow areas on upper leaf surfaces and orangish powdery spots of fruiting bodies on undersides directly beneath. Infected sweet woodruff stems and flowers may be seriously deformed. Remove any infected leaves as soon as possible. Remove and destroy all garden debris before plants start to grow in the spring. Control weeds in and around the garden. Control insect pests which help spread rust with insectidical soap. Prevent rusts with periodic sprays of wettable sulfur on vulnerable plants, starting several weeks before the disease normally appears. Space plants widely apart for good ventilation, and avoid wetting the foliage when watering.
Is Sweet Woodruff Invasive? (And What to Do If It Spreads Too Much)
Sweet woodruff can spread aggressively, especially in ideal shady, moist conditions, and in some regions like Ontario, it's considered invasive. If your sweet woodruff is spreading beyond where you want it, pull back runners in early spring before they establish. A physical edging barrier helps contain the spread long-term. In Ontario and parts of British Columbia, check local invasive species guidelines before planting or expanding existing patches.
Sweet Woodruff Problems: Frequently Asked Questions
Why is my sweet woodruff turning brown?
The most common reason is too much sun or drought stress. Sweet woodruff often turns crispy and shifts into dormancy during hot, dry summers — and full sun will cause this to happen even faster. The good news is it usually recovers: even when the plant goes completely dormant due to drought or excessive sun, it will return when the weather cools in autumn.
If browning is happening in shade with adequate moisture, it could be fungal - Rhizoctonia web blight, caused by the fungus Rhizoctonia solani, can cause rapid die-off in hot, humid weather and is a documented disease of sweet woodruff.
Is sweet woodruff invasive?
It depends on your location and conditions. Sweet woodruff can be invasive by rhizome in optimum growing conditions, and although it is not yet on official invasive species lists, it is showing some invasive tendencies in southern Ontario.
In the US, it has sometimes escaped from cultivation, though only very locally. For most garden settings with average shade and moisture, it spreads gradually and stays manageable, but in ideal conditions (moist, shaded soil) it can take over.
Why is my sweet woodruff dying?
Most likely summer dormancy, not actual death. Sweet woodruff does not tolerate dry conditions well - during hot, dry summers the plant often turns crispy, goes dormant, and dies back to the ground, but it will return when the weather cools in autumn.
If die-off is sudden and patchy rather than gradual, it could be Rhizoctonia web blight, which develops in hot humid weather and spreads quickly, the University of Maryland Extension notes the blight usually doesn't kill the roots, so removing dead debris and thinning plants for airflow is the recommended response.
In Conclusion
Sweet woodruff problems are rarely fatal, this is a resilient plant that usually bounces back with a little attention. Whether you're dealing with browning leaves, slug damage, mildew, or unwanted spread, the solutions are manageable. Identify the symptom, match it to the cause above, and treat early for best results. If your sweet woodruff is struggling and you're not sure why, start with the most common culprit: too much sun or not enough moisture. Shade and consistent watering solve more sweet woodruff problems than anything else.
