What Kinds Of Diseases Affect Tree Mallow: Expert Tell You

Tree mallow, a popular plant, is susceptible to leaf spot, powdery mildew, and root rot. Learn how to identify, treat, and prevent these diseases.

Understanding the Basics of Tree Mallow

Tree mallow (Lavatera arborea) is a fast-growing shrub belonging to the mallow family.[^1] It thrives in full sun, requiring well-drained soil and regular watering. The tree mallow’s small pink flowers bloom from late spring through summer, attracting bees and hummingbirds to the garden.
The shrub can grow 6 to 10 feet tall, with an equal spread.Its leaves are alternate, simple, and palmate in shape with 5 to 7 lobes. The serrated margins and hairy texture help minimize water loss.
More comprehensive information and care guidelines can be read here.

tree mallow, powdery mildew, bouquet of green flowers
Photo by Serafima Lazarenko / Unsplash

Identifying and Treating Leaf Spot in Tree Mallow

Leaf spot is a common fungal disease that affects tree mallow leaves. The symptoms of leaf spot include:

  • Small, circular spots on leaves. The spots are yellow or brown and vary in size.
  • As spots increase, leaves yellow, wilt and drop prematurely.
  • Severe leaf spot infections can defoliate the entire tree mallow plant.

Causes: The disease is caused by several species of fungi that thrive in warm, wet conditions. Fungi penetrate leaves through natural openings or wounds, then feed on plant tissues.

Treatment and Prevention:

  • Improve air circulation and reduce leaf wetness through pruning and plant spacing.
  • Water early in the day so leaves can dry quickly.
  • Apply fungicides containing copper, sulfur or trifloxystrobin. Products labeled for roses work well on tree mallow.
  • Remove and destroy severely infected leaves.
  • For organic options, apply compost teas or neem oil which has some fungicidal properties.

As long as new leaf growth isn’t severely damaged, tree mallow plants can usually recover from leaf spot with early detection and treatment. Severe infections year after year can weaken plants and reduce flowering.

tree mallow, powdery mildew, red car scale model on red plastic toy
Photo by Elena Mozhvilo / Unsplash

Combatting Powdery Mildew in Tree Mallow

Powdery mildew is a common fungal disease that affects tree mallow plants. It shows up as a white or gray powdery growth on leaves and stems.


  • White to gray powdery growth on leaves, stems and flowers.
  • Leaves appear dusty and can become curled or twisted.
  • Yellowing or browning of leaves.
  • Defoliation in severe cases.

Causes: Powdery mildew is caused by various species of fungi that thrive in warm, humid conditions. They spread via airborne spores.

Treatment and Prevention:

  • Improve airflow by pruning branches, weeds and crowded growth.
  • Water plants in the morning to allow leaves to dry.
  • Apply fungicides containing sulfur, neem oil, potassium bicarbonate or pyrethrin.

Repeat applications every 7 – 10 days for 3-4 weeks.

Spray leaves, stems and soil until runoff.

  • As a last resort, prune severely infected branches back to healthy tissue and destroy them.

Regular preventative treatments are key to slowing the spread of powdery mildew. Even resistant tree mallows may still get some mildew under optimal fungal conditions.

tree mallow, powdery mildew, red car scale model on red plastic toy
Photo by Elena Mozhvilo / Unsplash

Preventing Root Rot in Tree Mallow

Root rot is a fungal disease caused by overwatering that affects the roots of tree mallow plants. It can severely damage or kill plants if left untreated.


  • Yellowing or wilting leaves
  • Stunted or slowed growth
  • Brown, mushy roots

Root rot symptoms appear above ground, while damage happens below ground level.

Causes: The fungi that cause root rot thrive in overly moist, poorly drained soil conditions. Signs often appear after periods of excessive rainfall or overwatering.

Treatment and Prevention:

The best method is to improve soil conditions to inhibit fungal growth:

  • Reduce watering frequency to allow soil to dry out between waterings. Water deeply and less often.
  • Improve drainage by adding organic matter, raised beds or permeable materials beneath the soil.
  • For severely infected plants, remove from the soil. Gently wash the roots and prune away rotten areas. Place the plant in fresh potting mix with vermiculite or perlite for improved aeration.

Once root rot sets in, treatment options are limited. Preventive measures and improving growing conditions offer tree mallow plants the best defense against this destructive disease. Regular monitoring of soil moisture levels and pruning wilted or dying growth can also help minimize damage from root rot.

tree mallow, tree mallow, photo of brown wood slab
Photo by Joel & Jasmin Førestbird / Unsplash

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