Managing Weeds in Turf
Prevention
Site preparation
The healthy lawn starts with a properly prepared site before planting. All of the methods discussed in the landscape section apply to the establishment of a new turf area as well including amending the soil with organic matter or nutrients to improve seed plant establishment and improvement of drainage.
Selection of Grass Species
Turf grass species vary widely in their tolerance of sun, shade, drought and the amount of water needed to maintain them. The selection of the turf grass for site should be discussed with knowledgeable experts in the field; it is suggested that you contact ACWM or University of California Extension office for this input as we/they can provide advice regarding selection of an appropriate grass species.
Irrigation
Incorrect irrigation practices can weaken turf grass growth allowing weeds to invade. Proper irrigation is discussed in Section 13 but it can be reiterated here that one of the keys to maintaining a healthy lawn rests on a well-thought-out irrigation plan. The entire success or failure of your weed management plan may revolve around this fundamental basis.
Mowing
Proper mowing can help keep lawns from being susceptible to weed invasion by keeping them healthy and growing vigorously. The correct height depends on the actual grass species making up the turf. Consultation with ACWM or UC Extension can help determine the correct turf height.
Fertilizing
To maintain healthy turf, fertilization guidelines need to be followed carefully. In general, turf areas need to be fertilized approximately four times per year with no more than 1 pound of actual nitrogen per 1,000 square feet per application. Consultation with ACWM or UC Extension personnel can help you determine the requirements for your specific turf grass species.
Thatch Removal & Aeration
Regular thatch removal will help keep your turf grass healthy and competitive with weeds. Thatch is defined as the layer of organic matter that develops between the soil surface and the turf grass blades. A thin layer of thatch is beneficial; however, you should dethatch your turf when the thatch layer is more than ½ inch thick. Depending on the species of turf grass, this may need to be done yearly or every 5 years or not at all. Dethatching improves the circulation of air, water and nutrients into the soil. Dethatching can be done in small areas by use of a dethatching rake or over larger areas by a motorized or towed dethatcher.
Heavy traffic can compact soil over time. Soil compaction restricts the flow of oxygen, water and nutrients into the roots causing the turf grass to grow slowly and making it more susceptible to weed infestation. Depending on the soil type, soil aeration may need to be done several times per year as with the case with heavy clay soils or heavy foot or vehicular traffic areas to as little as once per year or less for areas with light activity. Aeration can be accomplished with a hand held device for small areas to large and machine driven aerifiers for larger turf areas.
Weed Identification and Monitoring
Just as with landscaped areas, turf areas need to be monitored for the invasion of weeds, and key to that process is being able to identify the weeds encountered so that they can be controlled before they get out of hand. The ability to differentiate between broadleaves, grasses, perennials and annuals will also help with decisions about the available control options.
Management Practices
Hand weeding
As with landscaped areas, sometimes in well maintained and regularly inspected turf areas, hand weeding can be an effective, and cost efficient weed management technique if done on a regular basis.
Herbicides
In general, if turf areas are well maintained, herbicides are not necessary. However, when they are needed they should be a part of your overall weed management plan that includes good cultural practices.
Managing Weeds in Non-landscaped Areas (Integrated Vegetation Management)
Managing weeds in large areas qualifies as Integrated Vegetation Management (IVM), which, as mentioned in a previous section, can be one of the most challenging missions facing any county department charged with maintaining those areas. Much of it involves a scale and complexity that are outside the scope of this general IPM Program requiring specialized IVM programs developed on a case-by-case basis. Notwithstanding the likely complexity of any IVM programs, they will all still follow the same five basic elements of successful IPM which are:
- Pest Prevention
- Pest and symptom identification
- Regular pest surveys
- Action thresholds and guidelines
- Sound management methods
Prevention
Much of the prevention element of IVM falls outside of the ability/authority of most County departments and includes things like:
- Plant Quarantine laws at the federal and state Level
- Local enforcement of restrictions on the sale or movement of certain plants, soil or other potentially infested carriers
- Requiring the use of Certified Weed Free Forage in recreational areas
Mulch is a prevention method that can be employed by County IVM programs including in relatively large areas. For it to work properly, the mulch will need to be applied thick enough initially (3 to 5 inches) and then monitored periodically to make sure it is not getting thin in spots or weeds will break through. It is not a good choice in areas where it will be washed away by rain or subject to frequent disturbance. Cleaning equipment before moving it into a new area can help prevent the introduction of seeds or other plant propagules. Once established, certain invasive weeds can be spread by weed abatement mowing or discing. In these situations, the source plants or seedlings may need to be controlled with herbicide spot treatments.
A mountain of mulch! Mulch is a very effective way to prevent weed growth, even in larges areas.
ALLIGATORWEED HOLD AREA ALERT! Areas in and around Puddingstone Lake, the San Gabriel River, Los Angeles River and other aquatic features in south east Los Angeles County are under a hold order. Before entering these areas, see Appendix L for restrictions.
Plant (Weed) Identification
The degree to which weeds/plants need to be accurately identified depends on the purpose of the control and the control method selected. For fire prevention using mechanical methods (discing, mowing, string trimmers), there is rarely a need to know the actual plant species except that it may help to time the control to prevent weeds from producing seeds. Also, careful timing can reduce the number of times control may be needed.
For vegetation management using herbicides, identification of the weeds is very important. The weed species dictate the herbicide product choice, application rate and seasonal timing. Some herbicides can harm desirable plants, including full-sized trees, by volatilization or when applied in the root zone. Knowing which plant species are susceptible to this kind of damage will help keep you out of trouble! CAUTION! Most open area herbicide applications fall into the category of non-production agricultural use of a pesticide and require a written Pest Control Recommendation. Section 15 has more information on this as well as other requirements for pesticide use in these areas.
Weed Surveys
For weed abatement intended for fire prevention using mechanical methods, weed surveys are not always critical although cutting the weeds right as they start to get brown at the approach of summer very often prevents them from growing back until the next season. When herbicides are used, surveys allow precise timing of the application at a growth stage of the weeds during which they are most susceptible. Applying herbicides when weeds are most susceptible also reduces the amount of herbicides required making surveys for this purpose a very important element to a successful and environmentally responsible IVM program.
Damage Thresholds
Damage or action thresholds for weeds are very difficult to establish in a document like this one. The amount of weeds that can simply be tolerated will range from 0 (none!) for certain highly invasive species all the way to somewhere at the other end of the spectrum. Each department will need to develop their own based on the purpose for controlling the weeds at all.
This is the invasive weed Marestail. The image in the center shows an only partially successful attempt at control, possibly because of the late growth stage. The plant is much more vulnerable in the rosette stage shown on the right. Much less herbicide is also required.
Management Practices
IVM practices include tractor mowing and discing, handwork with string trimmers and other tools, herbicides and goats. Small area control methods like flaming, steam, hot foam, etc., are generally impractical for larger IVM areas. Biological control is also a management method, but usually one only undertaken by Federal and State agencies.
Tractor Mowing
Mowing is a very cost effective method of weed management, especially for fire prevention, large open areas for aesthetics, roadside clearance, etc. It is the only method recommended for tumbleweed abatement projects of any size. Over the seasons, mowing tends to smooth out minor land imperfections resulting in a very pleasing park-like appearance. One of the most significant downsides to mowing is the very real potential for mower-sparked fires which must be carefully considered before deciding to mow. Compared to discing (see below), mowers are also relatively fragile so expect a few breakdowns during the course of a season. Mowing is probably not a good choice for rough, rocky areas, or properties with a significant amount of trash.
Tractor Discing
Discing is a management method most often used for fire prevention. It is very efficient, and ideal for large fire breaks, steep hills and rocky terrain. If a well-maintained tracked (crawler) tractor is used, the operation is very reliable and rarely ever has to be stopped for break downs. If necessary, discing can actually plough under a certain amount of trash/illegal dumping. Discing is without question the cheapest and most effective method for fire prevention, but it must be timed properly or dust can be become a problem. There are AQMD restrictions on discing in much of Los Angeles County.
Handwork
This method of weed control usually involves a crew using handheld equipment such as string trimmers, chainsaws and polesaws. Handwork is more expensive then mowing or discing, but a large enough and experienced crew can move through an area with reasonable speed and leave it looking very neat and well-trimmed. This is a viable method for fire prevention, roadside clearance or vegetation management in other large areas, especially where tractor access is limited. There are a fair number of safety requirements associated with handwork, including Cal-OSHA regulations related to Heat Illness Prevention, power equipment safety, hearing conservation and traffic safety (for roadsides).
Herbicides
Herbicides are a valuable tool for vegetation management. They are virtually the only method recommended for situations where practically no amount of weeds can be tolerated such as flood control levees and petroleum tank farms. They can be used with almost surgical precision to remove invasive plants intermixed with desirable vegetation such as the case with arundo* in fragile watershed areas. Properly chosen and carefully applied, selective herbicides are commonly used to reclaim/restore land that has been overrun by exotic invasive plants like yellow starthistle. Herbicides are a good choice for vegetation control along roadsides where speed and efficiency translate to worker and motorist safety.
The use of herbicides in the situations described above requires an excellent understanding of product chemistry, accurate plant identification, careful calibration of equipment, and a host of other requirements including virtually everything outlined in PART 2 (SAFE AND EFFECTIVE USE OF PESTICIDES AND FERTILIZERS).
Goats
Goats hard at work clearing weeds in the Thompson Creek Dam, Los Angeles County, October 2012. (Image courtesy Gemelee Cruz)
The use of goats to graze down vegetation is a method used occasionally in Los Angeles County. Goats are actually a good choice for very steep slopes where fuel reduction is the management goal, and goats will even eat poison oak! Goat clearance is very slow compared to the other vegetation management methods, and they also leave the area looking somewhat trampled over. Since it might take goats several days or longer to finish their “work”, an onsite staging area for the herder and his or her trailer as well as a place where the goats can be safely penned up at night, is a requirement. Hay or other forage used as supplemental food for goats while they are “working” can contribute to the spread of invasive weeds. Consider using certified weed-free forage and allowing the goats to purge for a few days before entering the new area to avoid any invasive weed seeds that may have been consumed from their last assignment.
Chicken Tractors
Chicken tractors can be a fun way to manage weeds in small situations, especially if the area is maintained for kids or educational opportunities.
*Arundo (Arundo donax) or Giant Reed, is probably Los Angeles County’s most hated invasive weed.
