By Steve Okula CGCS, MG
SOWING AND MANAGING COOL SEASON TURFGRASS
In temperate climates such as in northern Europe and the British Isles, golf course roughs are typically sown with cool season turfgrass species, such as perennial ryegrass (Lolium perenne) or tall fescue (Festuca arundinacea). The seed may be a mixture of these and could sometimes include fine fescues (Festuca rubra) or meadow grass (Poa pratensis, P. trivialis).
Weeds are opportunistic and will take advantage of bare soils and sunlight where there is little competition from established plants. Newly seeded soil is exposed to infestations of both broadleafed (dicotyledenous or dicots) weeds and narrow leafed or grassy (monocotyledonous or monocots) weeds. Prevention of both types of weeds as well as perennials can begin before seeding by treating with a non-selective herbicide such as glyphosate to eliminate the existing growth.
Broadleaf weeds infesting newly planted turf.
If time allows before planting, after the initial treatment of herbicide mechanically cultivate the soil with a rototiller. If irrigation is available, water on a daily basis to encourage the germination of existing weed seeds. Two to three weeks after the weeds reappear, repeat the treatment with non-selective herbicide. Ideally, the process should be repeated to germinate and eradicate as much of the seed bank of undesirable growth as possible.
If the procedure above was initiated in April, for example, by mid-August when the ideal season to sow arrives the soil should be relatively free of weed seeds and allow for germination of the desired species with a minimum of competition from weeds, either dicots or monocots.
Seeding rates and methods will depend on the selected species, soils, and available resources. The goal is to have the turf seed germinate and establish as rapidly as possible so it will out-compete the weeds trying to establish themselves post sowing.
Management practices to maintain a dense, vigorous turf is the best and most lasting method for broadleaf weed control.
There are several aspects to management which will encourage a rapid germination and establishment:
- Sow by late summer while temperatures are still warm.
- Include balanced fertilizer at the sowing, with special care to ensure that there is an adequate supply of phosphorous on the soil surface where it will be in contact with the seed.
- The surface should be kept moist with daily irrigation until there is abundant germination and then gradually reduced appropriately to prevailing weather conditions.
Maintain high levels of nutrition for the first two months with regular applications of a balanced fertilizer to encourage the grass to cover as quickly as possible and deny open soil and sunlight to opportunistic weeds. When the grass reaches 80-100mm in height, normally a few weeks after planting, begin mowing with a rotary mower at 50mm height. It is important that the mower blades be as sharp as possible to cleanly cut the leaf blades and not bruise or uproot the plants. The mowing should be repeated on a weekly basis and it will eradicate many species of weeds that do not tolerate a low height of cut.
Veronica (aka speedwell) is one of the more difficult weeds to control.
After the third mowing, normally 6-8 weeks after sowing, there is still an unacceptable infestation of broadleafed weeds, it may be necessary to begin a programme of herbicide treatments.
Two or more different herbicides are frequently sold as pre-packaged mixtures. Most of the materials discussed are sold by several manufacturers, often under different trade names differing in formulation and concentration. Therefore, no rates are presented here. READ and FOLLOW carefully the label directions on the herbicide container. Applying rates too low may result in inadequate control, while applying rates too high may cause turfgrass injury.
The effectiveness of herbicide applications is normally enhanced by adding a non-ionic surfactant or adhesive agent to the spray tank to maximize contact with the leaf blade. A small amount of soluble nitrogen (such as 5kg/ha of ammonium sulphate) in the treatment will induce plant growth and accelerate the adsorption of the molecules into the leaf.
Depending on the region, the following herbicides may be available for the selective removal of broadleaf weeds from cool season turfgrasses.
2,4-D is the oldest and most widely used herbicide and provides broad spectrum weed control in turfgrass. This chemical is particularly effective for control of weeds with taproots such as dandelion, broadleaf plantain, mustards, and shepherd’s purse. Amine formulations are most commonly used. However, the low volatile ester form of 2,4-D is often recommended for control of wild garlic and wild onion. Some weeds not controlled well by 2,4-D are white clover, chickweed, purslane, and ground ivy.
MCPA is chemically-related to 2,4-D and may be used as a substitute for 2,4-D in pre-packaged mixtures. MCPA is not a broad spectrum herbicide as is 2,4-D and its use alone (i.e., not mixed with another herbicide) is not usually recommended.
MCPP is most effective in the control of several perennial or winter annual weeds such as chickweed and clovers.
Dicamba controls many different weeds, several of which are not easily controlled by 2,4-D or MCPP. Of particular importance are the summer annual weeds that have a prostrate growth habit, including knotweed, purslane, and spurge. Dicamba however, does not control plaintains.
Dichlorprop (2,4-DP) and Triclopyr are sold in prepackaged mixtures with 2,4-D and provide broad spectrum weed control.
Triclopyr + Clopyralid is a non-phenoxy, prepackaged mixture that provides broad spectrum control of many common broadleaf weeds including oxalis.
Quinclorac effectively controls a few broadleaf weed species including white clover and corn speedwell, but the primary use of quinclorac will be for postemergence crabgrass control.
Carfentrazone is a quick acting herbicide that will cause rapid desiccation of the foliage of many broadleaf weed species. It will normally be sold in combination with other herbicides such as 2,4-D, MCPP and dicamba.
The use of mixtures of the above-mentioned herbicides is very common, such as 2,4-D, MCPP, and dicamba. Combination products result in the control of a broader range of weeds than single herbicides. Some herbicide mixtures may effectively control certain weeds that cannot be easily controlled by the individual herbicides used alone. The best times of year to control most broadleaf weeds are fall (especially late September) or spring (especially May).
To use these herbicides effectively for broadleaf weed control in turf, remember several points:
- Respect national and regional regulations governing herbicide usage.
- READ and FOLLOW the label directions CAREFULLY.
- Spray when the temperature is above 20°C and the weeds are actively growing. Do not spray when the temperature is over 30°C because turfgrass injury may result.
- Treat only when soil is moist and plants are growing vigorously. Do not apply herbicides during drought periods or when soil is dry.
*Source: Stephen Hart, Rutgers University