Description and Benefits of Invasive Grass/Weed Control

Weed control involves the containment, reduction, and/or elimination of certain plant species that are invasive and problematic in a rangeland system.  Weed control methods include mechanical removal, chemical applications, cultural practices, grazing, prescribed burning, biological control, revegetation with native species, and integrating various combinations of these methods.  Weed control can lead to increases in native plant species, forage quality for wildlife and livestock, wildlife populations, plant diversity, and soil water availability.  It can also decrease allergens, restore normal fire regimes into an area, and help prevent degradation of rivers and streams.  Due to the variability among control methods and their effectiveness on different weed species, any weed control program requires consultation with the County Agricultural Commissioner, University of California Cooperative Extension Specialist, and/or local Pest Control Advisor.

Conditions Where Invasive Grass/Weed Control Applies

Although not all weed control techniques are practical at all locations, most methods can be applied in rangeland systems.

•     Hand-pulling (and hand cutting), grubbing, and hoeing can be applied anywhere a person can access and are good options for controlling new (incipient), small infestations, or previously controlled weed infestations where plant density is low.

•     Grazing (if the weed is palatable) can be done just about anywhere.  

•     Mowing is effective in areas accessible by mowing machinery, typically flat or gently sloping areas, and where soil erosion (i.e. stream banks) and desirable plant species vulnerable to soil compaction/large equipment are NOT a concern. 

•     Chemical herbicides can be applied anywhere authorized by the specific herbicide label and is one of the most efficient weed control methods.  Many herbicides are registered for rangelands, and even some for use near water.  Herbicides are a good tool to utilize on large weed infestations, such as yellow starthistle and/or with the particularly problematic species perennial pepperweed.  Once a weed infestation is reduced, other methods can be integrated without significant loss of efficiency.

•      Prescribed burning can be done in most situations depending on the slope of the terrain and experience of the burn crew.

Materials Needed

Hand pulling, grubbing, and hoeing: leather gloves, grubbing hoe, mattock (head with both axe and hoe), shovel, bags (to collect plants if containing seed).

Mowers:  different types include the sickle-bar mower, rotary mower, flail and reel mower. 

Hand cutting tools:  hand sickles, scythes, machetes, brush/weed cutter.

Chemical:

•     Chemical: herbicide, adjuvant (surfactant or spreader), water, dye, soap, paper towels, absorptive material for spills (kitty litter), graduated cylinder or measuring cup, eye protection, tyvex jumpsuit, rubber gloves and shoes, long sleeve shirt and long pants, permits from Ag Commissioner’s office if necessary, herbicide label, location of nearest hospital, notepad to record amount of herbicide used and rate for county records.

•     Application Equipment: back pack sprayer (for spot applications), boom (for wider spray coverage); ATV, spray tank, and boom (for large area application); airplane/helicopter with tank and boom (extremely large scale applications), label containing name of chemical being used and applicator contact information.

 Implementation

Developing a Weed Management Plan
Frequently there are multiple ways to control a particular weed species. Often integrating several different control methods is more effective than just using one tool repeatedly. This makes careful planning of your weed control activities very important. In general the following 8 items should be addressed in strategizing a weed control plan:

1.   What is the goal of the site?

2.   What weeds are present?

3.   Prioritize your weeds.

4.   What control methods are available for each priority weed species?

5.   Develop a control plan or timeline for implementation of control methods.

6.   Implement control plan and monitor results.

7.   Did you achieve your goal?  If not, why?

8.   Make changes to the control plan and try again modifying goals if necessary.

Below there are several tips on how to organize your weed control activities.   Much of the information provided has been adapted from the Nature Conservancy’s Wildland Invasive Species program website: http://tncweeds.ucdavis.edu/index.html .  The Nature Conservancy’s Adaptive Management Tools are a great source of planning documents to use for large weed control activities and can be found at: http://tncweeds.ucdavis.edu/products.html

Weed Identification (What Weeds Are Present?)
Use a reference text like Weeds of the West by the Western Society of Weed Science or The Grower’s Weed Identification Handbook by UC Cooperative Extension to identify your weed species.  Take a sample to the County Agricultural Commissioner’s office.  They can tell you the best way to control the species and how problematic it is in the State.  The California Department of Food and Agriculture has a useful website for identifying noxious weeds in the state: http://www.cdfa.ca.gov/phpps/ipc/encycloweedia/encycloweedia_hp.htm

How to prioritize weed species to control
Prevention is the key to good weed control. If a weed is on your neighbor’s property and is a known problem – keep it off of yours. If a weed is just starting to invade your property, and is a known problem- control it first. This will save you time and money later. Focus weed control techniques initially on the perimeter of source populations and progress toward the heart or center of the weed population.  This will contain the spread of the weed while control measures are being taken. The more impact a weed can have on the overall ecological functioning of an area the more important it is to remove it early. Thus, species that are know to alter water flow, sedimentation, and other processes are high priorities. Do not waste time on species that you don’t have the tools to control; especially if there are other problem species you could focus your control efforts on more successfully. 

What Weed Control Methods Are Available?
There are many ways to research the best available control methods for a particular weed species.  Investigate control methods by talking to the County Agricultural Commissioner’s office.  You can also look up useful control techniques for many weeds on the web at http://tncweeds.ucdavis.edu/esadocs.html .  Call your local Farm Advisor or UC Cooperative Extension (UCCE) Weed Specialist.  They may be researching the most effective weed control methods.

•     Joseph DiTomaso, UCCE Non-Crop Weed Ecologist, (530) 754-8715

•     Morgan Doran, UCCE Farm Advisor, (707) 435-2459

•     Tom Lanini, UCCE Weed Ecologist, (530) 752-4476

•     Rachael Long, UCCE Farm Advisor, (530) 666-8734

Mechanical control: 
Plants that resprout from underground roots and structures, like perennial pepperweed will not be controlled using this method unless the entire root system can also be removed. Shallow rooted species, like barbed goatgrass and medusahead can be controlled by hand pulling. Yellow starthistle can also be controlled this way as long as the root crown can be removed and the soil is moist. Plants should be able to be pulled out with part of the root attached to be effectively controlled. This should be done after flowering but prior to seed maturation and dispersal for maximum efficacy. Plants can be bagged (recommended if seed has been produced) and removed from the site, piled for decomposition or burning, or left in place. Certain species resprout readily if the soil is moist and should be repositioned or removed from the site.   

Mowing or grazing: 
Mowing and/or grazing can help reduce seed production, but timing and growth stage of the plant are critical. Repeated mowing or grazing when the plant is just about to flower can be very effective at reducing seed production in annual plants and depleting underground storage carbohydrates of perennial plants. Mow or graze the weed below the lowest growing branch (2-4inches). If plants resprout, mow or graze again post flowering but before seed maturation or dispersal. Repeat to avoid seed production. May result in low branching pattern. This is very effective if competitive grasses are mixed in with the weeds forcing the weeds to branch higher and resulting in a more effective kill using mowing or grazing.  Thatch can be hayed, burned, removed from the site, or left on site to act as a mulch.  If thatch contains seeds or propagules of the weed, leave on site to avoid spreading the weed to non-invaded areas.

Chemical control:
Contact your local County Agricultural Commissioner for details on spraying herbicides: Yolo County Agricultural Commissioner, 70 Cottonwood St., Woodland, CA 95696, (530) 666-8140.

Weed Control Examples
The following weed control information should not be used as a recommendation for use on your site.  It is a discussion of successful treatments used for addressing these weeds. A licensed Pest Control Advisor (PCA) should be consulted to determine the best control methods to use at your site. 

Yellow Starthistle
Yellow starthistle is a broadleaf, summer annual from Southern Europe. It has invaded millions of acres in California. It is often found along roadsides and in pastures. Yellow Starthistle is extremely competitive for soil moisture and an abundant seed producer (large plants can produce over 100,000 seeds) some of which lay dormant in the soil for up to 3-5 years. Although this plant presents a problem in rangeland systems where its propensity for spread and competitive ability creates large scale problems, it can effectively be managed using integrated weed control methods. Transline® (clopyralid) herbicide can be applied in late winter-early spring (January – April) to control Yellow Starthistle seedlings and rosettes. It is considered the most effective herbicide for Yellow Starthistle control.  Transline® is a selective herbicide that does not injure grasses or many broadleaf species. Application rates are 4-10 oz product/acre (costing about $14-$35/acre).  If applied when Yellow Starthistle is in the seedling or rosette stage, no surfactant is needed. Mowing prior to this application may improve herbicide coverage. Roundup® (glyphosate) can be applied when Yellow Starthistle is bolting or early flowering at rates of 1.5-2.5 qt product/acre (costing about $20-$35/acre) in a broadcast spray or a 1% solution for spot treatments. This is a non-selective herbicide so care should be taken when applying around desirable plant species. Surfactants should be used with late season (bolting-flowering) treatments. Mowing can be used later in the season when Yellow Starthistle is in the bolting/early flowering stage.  It is best employed after initial control work has decreased the population (year 2 or 3, once control has begun). This treatment can be effective or very ineffective in that it is heavily timing and growth form dependent. Mowing must be done at the early flowering stage (late spring-summer when 2-5% of the spiny heads are flowering) and on plants that have a high branching pattern. If the blade doesn’t cut below the first branches, the plant will regrow with multiple branches and multiple seed heads! Mowing too early can stimulate this and mowing too late can spread viable seed. Integrated methods can be very effective at Yellow Starthistle control. Burning tends to stimulate seeds to germinate.  If a prescribed burn is performed, follow up treatments will be needed. One suggested reduction plan involves burning in year 1, and using Transline in year 2 and 3.  This exhausts the seed bank and reduces starthistle cover so further control can be done easily by mowing or hand pulling.

Perennial Pepperweed
Perennial Pepperweed is creeping broadleaf perennial plant from southeastern Europe and southwestern Asia. This is an extremely problematic weed in that it competes for light, is an abundant seed producer, and produces underground storage roots that make this species very difficult to control (40% of plant is underground). Prevention and maintaining high density stands of desirable vegetation are the best forms of control for this plant. Once established, no control option alone will be 100% effective. When using chemical control methods, getting thorough coverage and deposition on the lower leaves is important. Telar® (chlorsulfuron) applied to Perennial Pepperweed with a surfactant offers good control at the flower bud to early flowering stage. Use rates include 1.5 - 2oz product/acre (costing about $45-$60/acre) with 25% nonionic surfactant. Follow-up treatments will be needed in subsequent years. Telar® cannot be used near water and soil residual activity may inhibit other species recovering. It is selective and will not injure many native grass species if used at lower rates. Roundup® (glyphosate) applied at 4 qts product/acre (costing about $55/acre) provides good control of top growth only. Mechanical methods including hand pulling, burning, and mowing alone are not effective at controlling Perennia Pepperweed. Integrated methods include a combination of mowing and herbicide treatments.  Mowing at the bolting - flower bud stage followed by treatment with Roundup® on the regrowth can be effective at controlling Perennial Pepperweed. This is a good technique if the infestation is located near an aquatic area.  This method also leads to the most recovery of other species in the area.  The Bufferlands located near the Sacramento Regional County Sanitation District (SRCSD) has had good success using Garlon® (tryclopyr) at a rate of 1.5 qts/acre (if Garlon® 4 = about $46/acre) after repeated mowing (3x) at the bolting stage.

Johnsongrass
Johnsongrass is a perennial grass from the Mediterranean region.  It was introduced as a forage crop and rapidly develops colonies and that smother other species.  It can be found commonly along moist roadside ditches and is considered one of the ten most noxious weeds in the world.  Johnsongrass reproduces by seed and underground stems (rhizomes). It is best to treat seedlings if possible or mature plants in the flowering stage. Grass selective herbicides can be used to control Johnsongrass but may injure desirable grass species.  They may be used successfully to control grass weeds and preserve native forb species. One thing that can be used is a selective method of applying a non-selective herbicide: wicking or careful spot spraying.  Roundup® (glyphosate) is very effective at controlling Johnsongrass if applied broadcast at 1.5-2.5 qt product/acre (costing about $20-$35/acre) or a 1% solution for spot treatments. This should be applied while Johnsongrass is flowering but prior to seed set. Mechanical methods can be used to grub out small infestations while the soil is moist.

Annual Ryegrass
Annual Ryegrass also called Italian Ryegrass is a winter annual grass brought in for forage and lawn mixtures from Europe.  It is very competitive, reseeds readily, and creates large monocultures. Annual Ryegrass is difficult to remove from a native grass planting. Annual Ryegrass germinates in the fall following the first rains, sends up flowering stalks in the late winter/early spring, and goes to seed in the early summer. Control methods focus on preventing seed production and protecting desirable species.  A 1% solution of  Roundup® (glyphosate) can be used to spot treat Annual Ryegrass with good success. Preemergent herbicides may be used to control seedlings once desirable species are established.  Karmex® (diuron) applied as a preemergent at 2-6 lbs/acre (about $10-$35/acre) controls Annual Ryegrass and does not injure established species. Mechanical methods such as mowing can be used when plants are flowering and prior to seed maturation for good control (may need to mow more than one time).

Further References

One objective of this webpage is to provide information on particular weeds the RCD considers the most invasive in our county. These "weed summary sheets" are available in our Resource Library, on the Weeds Index Page.  Each sheet will show you how to identify weeds you don’t want, how they grow and prosper, and what are the best control methods. We provide additional information through links connecting you to other helpful weed learning centers.