Golf course superintendents often differ on which pests are hardest to control – insects, weeds, diseases, birds and four-legged critters.
Within each group, there are often disagreements over which present the greatest problems. Likewise, there are some that are hardly ever mentioned but are still considered pests in one way or another. In the weed category, dandelions, lambsquarters and shepherd’s purse are typical members. The harder to control ones – goosegrass, nutsedge, knotweed, spurge and clover – require multiple strategies for control.
Yes, these five weeds are tough to control, but they’d be tougher if IPM (Integrated Pest Management) wasn’t practiced day in and day out. The tried-and-true tactic still rings true today: The best defense against weed invasion is to cultivate a thick, dense turf that naturally outcompetes them. This approach succinctly describes the IPM strategy, one that was introduced to control cotton boll weevils in the South.
Boiling it down further, the key word seems to be “integrated,” in that it implies there are many components to the methodology, and that they work together to produce the desirable outcome, which is certainly the case. The elements below produce an overlapping or almost synergistic result.
Fertilization: Balanced between en-couraging lush, vegetative top growth and lean, thin turf stands, applied nutrients go a long way toward keeping weeds out.
Cultivation: Facilitating drainage and optimal root zone moisture levels, aerification and other cultivation techniques promote a healthy root system.
Irrigation: Keeping the root zone moist, not soggy or dry is critical to the goal of producing robust turf plants.
Grass species/cultivar selection: Grass plants that grow vigorously are tolerant of temperature extremes and are naturally resistant to pathogens and insects give turf plants a leg up on weeds.
Circulation improvement: Turf stands that are cloistered by buildings, shrubs and other features often create unsuitable growing conditions.
Shading reduction/Right plant, right place: Sure, we all love shade on the golf course when waiting to tee off, but it can be a limiting factor in terms of photosynthesis rate and facilitate diseases such as powdery mildew.
Mowing height: Generally, the lower turf is mowed within its adapted range, the more stress is placed on its capacity to produce sufficient roots to withstand disease pressure, desiccation and other pests.
Insect and disease control: Turf plants that are infested with insects or infected with pathogens usually create thin stands that are conducive to weed invasion.
Weed control: Applied on a timely basis, in accordance with product label directions, pre-emergence and postemergence herbicides fit well into an overall weed control effort.
- It has dark green leaves that grow on stems that become white toward the base.
- The leaf blades are folded in the bud; about 0.25-inches wide and taper to a point.
- The ligule is membranous, toothed and divided at the mid-rib.
- Generally, it’s devoid of auricles.
- The sheath is light green on the upper parts and becomes white at the base. The sheath is also flattened, with a few long white hairs near the collar.
- The root system is shallow and fibrous.
- The seed head is divided into finger-like segments, but thicker and more robust than crabgrass.
- The segments are often described as “zipper-like.”
- If unmowed, seed heads grow 4 to 8 inches long.
- It germinates in late spring when soils have warmed and the soil temperature is consistently in the 60- to 65-degree Fahrenheit range. Germination may continue all season until temperatures cool in the fall – this characteristic can come in handy when developing a plan for control.
- The stems are thick and grow low to the ground. These prostrate stems have several basal tillers that radiate from a common growing point.
- This low-growing habit allows it to persist and thrive under low heights of cut, as the majority of the leaf tissue remains after mowing.
- One of the most effective control methods of weed control is mowing, which works quite well for some weeds such as shepherd’s purse that have an upright growing habit, but not so well for goosegrass and prostrate knotweed.
- As opposed to the inference of the name, that it’s not a weed, unfortunately it is.
- A low-growing annual, prostrate it’s especially well-adapted to compacted soils.
- Small, slender, dark green leaves are born on thin, wiry stems that radiate from a central growing point.
- The leaves rise from the nodes, which are surrounded by a thin, papery sheath. Depending on the growing season, they’re dull to moderately shiny green, alternate, oblong and pointed at the tip.
- Though hardly ever seen, the flowers are small, inconspicuous and born in clusters in the leaf axils.
- Prostrate knotweed germinates in cool soils in early spring and tolerates close mowing.
- While relatively easy to control when young, it’s very difficult to control when aggressively growing later in the season.
- It’s a significant problem on lower maintenance courses with excessive traffic and resource limitations relative to appropriate aerification equipment.
- Both species – purple and yellow – are slender, offering less surface area as a target than most other weeds.
- The leaves are moderately waxy, which tends to repel applied herbicides.
- When viewed in cross-section, instead of being round, they’re triangular in shape – if you remember your geometry, the shape is an equilateral triangle, as opposed to an isosceles, scalene or right triangle.
- Compared with the turfgrass stand that has been invaded, they grow at roughly twice the rate as desirable turf species. This can be problematic on various levels; severe infestations create a much different playing surface than turfs, and, because its leaves stand above the mowing surface, it has more visibility than most weeds and therefore tends to attract the attention of important golf stakeholders.
- All above-ground growth on nutsedge plants occurs from a central growing point and extends in an umbrella fashion. Many other weeds contain growth that either branches from the main stem (foxtail, crabgrass) or grows very low to the ground (prostrate spurge, ground ivy, prostrate knotweed).
- If unmown, they produce thin, brightly colored flowers, subtended by short leaves.
- Purple nutsedge produces reddish purple flowers, while yellow nutsedge has flowers that are – you guessed it – yellow.
- The biggest difference of all is that they have an extensive root system including rhizomes and tubers, making them among the most difficult weeds to control.
- The size of the tubers and the length of the rhizomes vary, but most tubers are in the fingernail range, while rhizome length can grow several yards long.
- Some references refer to nutsedges as “one of the world’s worst weeds.”
4. Spotted and prostrate spurge
- These summer annuals are very similar in appearance.
- The stems radiate from a taproot, forming a dense mat.
- Spotted spurge has smooth stems, while prostrate spurge has hairy stems.
- Leaves are dark green and oblong and may have a reddish splash in the center.
- The leaves of spotted spurge are somewhat toothed, while prostrate spurge has smooth leaves with some hairs on the underside.
- All plant parts contain a white milky sap.
- Compacted, thin turf is an open invitation for spurge invasion.
- Small, inconspicuous flowers are produced in the axils of the upper leaves.
- As warm-season annuals, spurge begins to germinate in late spring as soils begin to warm to the high 50s or low 60s. However, they germinate best when temperatures reach 75 to 85 degrees. They can actually continue to germinate with temps nearing 100 degrees, making them very competitive when cool-season grasses are struggling with heat-stressed conditions.
- They don’t necessarily thrive when competing with other plant cover but depend on their prolific seed production for survival.
- One plant can produce thousands of tiny seeds, with them germinating immediately if produced in the summer.
- Seeds produced at other times of the year can remain dormant until favorable soil conditions allow them to germinate later.
5. White clover
- A member of the legume family, it’s a cool-season perennial with 1- to 1.5-inch, dark green tri-foliate leaflets.
- The leaves have prominent, parallel veins and sometimes a white crescent-shaped mark.
- It has a strong spreading nature, due to the capacity to root at each node.
- White ball-shaped flowers are held above the leaves when mature.
- It’s often indicative of a soil low in nitrogen and may be suppressed by increasing nitrogen fertility.
- In a field, it may create a slippery surface and, if allowed to flower, is very attractive to bees – increasing the potential for bee stings, especially for youth activities where the participants often spend as much time rolling around on the turf as they do standing up.