If there’s a single thing on the golf course that catches a golfer’s attention, it’s a broadleaf weed in the playing surface.
Sure, they might notice browned-out turf because of anthracnose (they’ll never know why, just that it’s brown), but a weed is easy to see and object to.
It’s something that they can relate to; they may even have similar weeds in their own lawn and make the connection. Not that they would take the stick out of their own eye before they complain about it, but that’s another issue for another day.
Why are weeds such a pervasive, troublesome problem in the first place? There are many reasons, but the first and foremost is supply. The weed scientists tell us that there are between 10,000 and 40,000 weed seeds in the average cubic foot of soil. That’s simply a staggering amount, one that is tough to relate to – a never-ending supply.
Weeds are opportunists
In addition to the volume issue, weeds are very competitive. When turf becomes thin because of a malady or abiotic causal agent, weed seed in the upper soil layers is exposed to sunlight, allowing it to germinate and grow instead of being suppressed by the formerly robust turf stand. This also is the case when a divot is taken or a careless golfer cleans mud off his shoes in the teebox turf instead of using the bristles on the ball washer.
Because weeds take advantage of openings, it’s sound to prevent them by growing a thick, dense turf. The sound cultural practices of keeping turf shoots and roots moist instead of soggy or dry, fertilizing according to soil test results, preventing compaction through cultivation and controlling insects and disease can go a long way toward broadleaf weed prevention.
Weeds in new seedings
One common opportunity for weeds to become established is a newly developing stand of turf. Fortunately, several herbicides are labeled for their control. Specifically, carfentrazone, pyraflufen, isoxaben, mesotrione and glufosinate have been designed for this purpose.
A wide range of broadleaf weeds, including lamb’s quarters, plantain, purslane, dandelion, chickweed, pigweed, carpetweed and henbit, can be controlled with these products, so it’s wise to check with suppliers and university websites and to read the product labels for specific information on rates, precautions and restrictions.
Keep in mind that almost all broadleaf herbicides will damage young turfgrass, especially if hot, dry conditions are present at the time of the application. However, a small amount of phytotoxicity is usually preferable and acceptable in the short run compared with the dramatic reduction of broadleaf weed competitors during establishment.
Weeds are indicators
In addition to the potential for broadleaf weeds to become established in new seedings, other scenarios are conducive to them gaining a competitive advantage.
The following observations and notations regarding soils and weeds were made by Tom Voigt and L. Cella of the University of Illinois at Urbana-Champaign. It’s important to keep in mind that these are tendencies, not absolutes in terms of weed establishment.
Acid soils – prostrate knotweed, plantain and red sorrel.
Wet soils – curled dock, henbit, yellow wood sorrel and white clover.
Dry soils – black medic and red sorrel.
Infertile soils – yarrow, plantains, red sorrel and white clover.
Fertile soils – pigweeds, purslane, dandelion, lamb’s-quarters, henbit and yellow woodsorrel.
Shaded soils – common chickweed, ground ivy, mouse-ear chickweed and violets.
Low mowing height – white clover.
Compacted soils – dandelion, plantain, common chickweed, knotweed, mouse-ear chickweed and prostrate spurge.
Some weeds are harder to control than others, but all weeds are a concern in that they compete with desirable turf plants for space, light, water and nutrients. In addition, weeds detract from the appearance and function of the playing surface.
Several of the more difficult to control include:
Plantain – Blackseed and broadleaf plantain are different species of the genus Plantago, but similar in appearance. They are perennials, with a shallow, fibrous root system.
Above ground, the growth consists of a rosette of basal leaves. The leaves are large, oval to elliptic (oval for broadleaf plantain, elliptic for blackseed plantain) with very prominent veins and a long petiole attached to the crown. Blackseed plantain has purple coloration at the petiole base, while the petiole of broadleaf plantain is green and shorter.
For both species, long rat-tail-like flower stalks extend up to 10 inches above the base of the plant and produce many inconspicuous flowers. Mid-fall applications of combination products such as Speedzone, Q4 and Trimec offer some degree of control. Plantains tend to have a waxy leaf surface, which limits absorption of the herbicide into the plant. If the product doesn’t have an adjuvant component, consider adding one to improve efficacy.
Prostrate knotweed – Small, ovalish, dark-green leaves are produced on low, wiry stems. Well adapted to compacted soils, prostrate knotweed can grow quite well where desirable turf species will not.
Some pre-emergence control is available through many pre-emergence products with application timing critical. Prostrate knotweed is often the first annual to emerge in the spring; it’s not uncommon to see its fine, grass-like seedlings soon after snow melt in mid- to late March. Early-season applications of combination broadleaf products such as Speedzone, Trimec and Q4 are most effective in the seedling stage. Control drops dramatically as the weeds mature.
Additionally, Isoxaben-containing products (Isoxaben, Gallery or Snapshot) provide good residual control of knotweed within landscape beds or in turfgrass areas.
Wild violets – Often mistaken for ornamental, wild violets have dark green, roundish leaves that grow in a tight cluster. White, purple or light blue flowers are produced from the crown of healthy plants.
As these weeds prepare to go into winter, fall treatments of combination broadleaf products such as Speedzone, Trimec and Q4 offer some degree of control. Confront, with its combination of triclopyr and clopyralid, has demonstrated very good control of weeds like wild violets. Just be sure to read and follow the labels carefully.
Because of violets’ waxy cuticle, a spreader sticker is recommended for herbicide applications. Repeat applications usually are necessary.
Ground ivy – Somewhat similar in appearance to wild violets, ground ivy leaves are usually medium green and slightly scalloped on the edges. Ground ivy spreads through growth of stolons, which spread rapidly in the spring and fall. Control is as for wild violets.
Field bindweed – A rhizomatous species, bindweed is easily identified by noticing the medium-green, arrowhead-shaped leaves. Occasionally, bell-shaped, whitish flowers are produced. Because of its aggressive stoloniferous nature, avoid pulling or tilling. Excellent control has been reported with quinclorac (Drive, Q4). Methylated seed oil (MSO) is strongly recommended when using quinclorac, especially Drive, to treat field bindweed.
White clover – Identification is straightforward for white clover, as well. The dark green leaflets of three that alternate on the stems are unmistakable. The stems are low growing and able to root at each node, providing a strong advantage for itself.
Products containing mecoprop will provide excellent control of white clover. In taller grasses, such as rough and fairway transitions, combination products containing quinclorac, 2,4-D and dicamba can be effective.
Puncturevine – A warm-season annual, puncturevine is particularly tough to control because it can produce 200 to 5,000 seeds in a single growing season. Many of these seeds can carry over into the next year and contribute to that year’s weed population. Unchecked, puncturevine can create a thick mat and dangerous conditions for people and animals alike. Removing and reducing the number of seeds available for growth can achieve long-term control.
Pre-emergence herbicides like benefin can provide partial control of germinating weeds, and products containing 2, 4-D and dicamba can be used as a selective post-emergence herbicide. Glyphosate can be used for spot treatments or areas in need of renovation.
Speedwell – Often found with henbit, speedwell is a winter annual that germinates mid-fall, and its ability to compete can be reduced with a dense stand of turfgrass cover. Preventive measures must be taken in early fall and could also target other annuals like chickweed and possibly knotweed. Post-emergence control is most effective when speedwell is at the four-leaf to flowering stage. Most three-way herbicides are effective in controlling it, as well as many ester-based herbicides such as Speedzone or TZone SE.
The common thread to maximizing the effectiveness of controlling troublesome weeds is (1) solid agronomic maintenance of the existing turfgrass stand, (2) proper ID of the weed and (3) really matching the best product with the best time of year for application. That last one may require patience on your part but can lead to the best control and the most efficient use of your weed control budget dollars.