Problem Weed of the Month: Common Mallow

Problem weed:

Common Mallow

Other names:

Malva neglecta, cheeses, cheese-weed, garden mallow, malice, round dock, button weed, round-leaved mallow (a misidentification)

Growth habit:

Annual, winter annual, biennial or short-lived perennial

Description:

• Low growing weed, with a deep fleshy tap root
  
• Leaves: rounded or kidney-shaped leaves with a deep heart-shaped base, young leaves may be crinkled, with toothed margins; alternate on stem
  
• Stems: flexible stems come from the central point, often lounging on the ground
  
• Flowers: 5-petaled white, pinkish or lilac flowers grow in the leaf axils;
  1-1.5 cm
  
• Fruit pod (shizocarp): 12-14 round sections in a ring, resembling cheese wheels
  
• Seeds: dark reddish brown to black, with a small notch

Common Mallow

Common Mallow: flowers

Common Mallow: tap root

Spreads by:

Seed only. Flowers from June to late autumn with seeds germinating through the summer. Broken stems can also root.

Reasons for concern:

A difficult-to-control weed in orchards, raspberries and nursery crops, where competition is not great. Seeds move in from grassy areas, roadsides and in straw. Harvesting juice apples is challenging in dense masses of mallow. Plants may stay green all winter.

May be confused with:

Round-leaved mallow that has smaller flowers, or with creeping Charlie with similar shaped but smaller leaves, and purple flowers.

Chemical control:

Soil applied residual herbicides (eg. simazine, Sinbar, Devrinol) should control new seedlings, but a 2nd (or even 3rd) application may be needed for late germinations. Postemergent herbicides (eg. glyphosate, Amitrol, Gramoxone, Ignite) are best applied to small plants. Repeat applications over several years are needed for established populations. Postharvest applications of 2,4-D or Lontrel may weaken established plants.

Cultural control:

• Prevent seed shed by weeds on field edges by frequent mowing
  
• Use only weed-free straw as mulch
  
• Scout for new infestations, and cut weed below the soil surface
  
• Frequently mow infestations in weakened sod
  
• Band applications of fertilizer on the edge of weed-free strips

Learn more:

• Ontario Weeds, OMAFRA Publication 505
  
• Common Mallow, Ontario Weed Gallery
• Ontario Weed Gallery online

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