Monday, April 28, 2014

Weed of the month for October 2013 is White Clover

White Clover  

Biology: White clover (Trifolium repens) is a perennial broadleaf weed that can be found throughout the United States. Seeds can germinate in moist-cool conditions in spring, early summer, or early fall. Because it tolerates close mowing, can grow in multiple soil types, and has the ability to fix its own nitrogen, it competes with the surrounding turf. As a result, white clover is a common occurrence in lawns and other high-maintenance turf throughout the state of Indiana.

Some view white clover as a weed - hence it's appearance in this weed of the month series - while others view white clover as an important component of the turf which provides beneficial nitrogen contributions to the soil. Current research efforts at Purdue led by Dr. Cale Bigelow and his graduate student Gabe Macke are focused on learning more about the potential benefits of grass-clover systems and the challenges in maintaining these mixed swards. More information about white clover management (both control and culture) will continue to be provided as we learn more.

Identification: White clover forms mat-like patches in lawns as it spreads via low-creeping stolons that can grow at a rate of 18 cm per year. Stems can be smooth or sparsely covered with hairs. Leaves are generally arranged in threes; however, occasionally the appearance of 4 leaves can give white clover a ‘shamrock’ or a ‘4-leaf clover’ appearance. Leaves are predominantly egg-shaped, grayish-green on the bottom, and bright-green on top with a distinctive gray-green splotch or watermark at the base. Flowers are white, often with pink tinge, and are arranged in aggregated, rounded heads that can hold up to 85 flowers. Seed coats are extremely hard, thus allowing for extended dormancy periods in the soil. Other trifoliolate (3 leaves) legumes, such as red clover, are similar but generally larger in size, have more pubescent stems, and more elongated leaflets than white clover.

White clover in cool-season turf.

Rounded flower clusters can hole up to 85 flowers.

Pink tinge at the base of white flower petals.

Trifoliate (3-leaf) arrangement with distinctive watermark.

Appearance of 4 leaves produce a 'shamrock' or '4-leaf clover' appearance.
White clover in closely mown turf.

Presence of white clover may be an indication of low nitrogen fertility.

Large patches of white clover in dormant bermudgrass turf.
Large patch of dense, mat-like growth.
Cultural control: The use of cultural practices, such as increased mowing height, adequate irrigation, and overseeding to enhance cool-season turf density and vigor may help the lawn to out compete white clover infestations. Since white clover is a legume capable of fixing its own nitrogen, adequate nitrogen fertilization will often help to reduce clover and further develop a more competitive turf.

Biological control: None known for specific use in white clover. There are some organic postemergence herbicides available for turf weed control. For example, pelargonic acid (Scythe) and acetic acid (5% or greater solutions) may be used to manage weeds. Other products such as Eugenol, which contain medium-length fatty acids and clove oil, have shown some promise as an effective weed control tool. However, these organic herbicides do not differentiate between the target weed and the desired turf (non-selective) and should only be applied as spot treatments in direct contact with the weed only. As a result, most of these organic herbicides have limited use in turf and are better suited for weed control in parking lots, along fence rows, and in other bare-ground areas.

Many new organic products contain essential micronutrients, such as iron HEDTA (FeHEDTA) as the active ingredient. Though multiple applications of these products are required, turf injury is generally decreased (can actually make the turf darker); however, their ability to provide long-term weed control is not well-documented.

Chemical control: Chemical management of white clover is generally focused on a postemergence strategy over a preemergence strategy because of the few preemergence herbicides available for broadleaf weeds in cool-season turf and because white clover may germinate at different times throughout the year. The best selective herbicide management strategy is repeat applications of two- or three-way mixtures of 2,4-D, dicamba, MCPP. Products that contain one or more of the following ingredients should also provide effective control in cool-season turf: clopyralid, dicamba, florasulam, MCPP, and quinclorac. 

For more information on weed control, search this blog and check out our Turfgrass Weed Control for Professionals Publication.

For archives of past weed of the month postings, visit our Weed of the Month Archive.

Aaron Patton, Turfgrass Extension Specialist
Leslie Beck, Postdoctoral Research Associate


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