Biological control has primarily focused on insects that attack the flower heads. Only two insects have proven somewhat effective, including the hairy weevil and the false peacock fly , having been reported to reduce seed production . Revegetation with native or introduced grasses, legumes, or other forbs is an important component of long-term yellow starthistle management.Methods for controlling medusahead have been studied and implemented since the 1950s with the goal of reducing thatch buildup and reducing flowering and seed production. Control approaches have often targeted windows for burning when medusahead is still growing but when most associated species are mature and dry . Grazing management approaches have successfully reduced flowering on a small scale by targeting a narrow period just before the flower emerges in April or May . On a large scale, grazing has been less successful because of management challenges, including availability and distribution of water and availability of sufficient cattle numbers for targeted grazing in later spring and early summer . Glyphosate can be an effective control method when applied in early spring to young medusahead plants. However, it is non-selective and can damage desirable broadleaf or grass vegetation, including native perennial grasses at moderate to high rates. In the correct ecosystem, vertical farm equipment proper timing and low rates of glyphosate can control medusahead without damaging desirable perennial plants . Fall applications of aminopyralid at high rates have been shown to prevent medusahead germination throughout the season .
Barb goatgrass was first identified in California in the early 1900s, but it has spread rapidly in recent years. Barb goatgrass grows in dense stands supported by deep and rapidly establishing root systems that make it extremely competitive in annual rangelands. Davy et al. reviewed the biology and ecology of barb goatgrass, as well as control methods. Fire can be an effective method of control if repeated for 2 consecutive years . While no grass-selective herbicides are registered for rangelands in California, glyphosate is a practical and effective method for controlling selected patches. Mowing and grazing can be effective if heavy defoliation is applied just prior to seed head emergence. Invasive plants cause serious ecological damage to California’s wildlands, and successfully addressing this widespread problem requires an integrated approach. Effective control will require long-term management using combinations of biological, mechanical, cultural, and chemical methods . Integrated management may incorporate specific sequences of practices and approaches, including targeted grazing and permanent changes in grazing practices. Successful control will also require cooperation of private landowners and public agencies working within organized weed control areas.Klamath weed is not considered a large rangeland weed problem because its control in the 1940s was so successful. The importation in 1944 of Chrysolina quadrigemina and its close relative, C. hyperici, was the first North American attempt at controlling weeds with insects. The insects are natural enemies of Klamath weed, also known as St. John’s wort. This native European plant is a pest on rangelands throughout the temperate regions of the world because it displaces forage plants and is toxic to cattle and sheep. In 1943 it was estimated that 400,000 acres of California rangelands were infested with Klamath weed.
The beetles Chrysolina hyperici and C. quadrigemina were first released in 1945 and 1946, respectively. Both species became established, but C. quadrigemina proved especially effective for Klamath weed control. Populations of the beetles quickly grew and spread. After 5 years, millions were collected from original release sites for redistribution throughout the Pacific Northwest. Ten years after the first releases, Klamath weed populations in California were reduced to less than 1 percent of their original size , and the weed no longer threatens the livestock industry. From 1953 to 1959 alone, California saved an estimated $3,500,000 per year due to this biological control program .Seeding of improved forage species has been the primary means of improving productivity of annual grasslands and cleared or thinned oak woodlands and chaparral. Introduction of annual legumes and perennial grasses from the Mediterranean region, often by way of Australian forage improvement programs, has been an integral part of range improvement programs. Subterranean clover was introduced from Australia in the 1930s. Rose clover was introduced in the 1940s by Professor R. Merton Love of the Agronomy and Range Science Department . Smilograss , an Asian native grass, was introduced from New Zealand by Drs. E. W. Hilgard and E. J. Wickson in 1878. Hardinggrass was introduced from Australia by Dr. P. B. Kennedy shortly after his arrival at UC Berkeley in 1912. Later, summer-dormant orchard grasses and summer-dormant tall fescue were introduced for rangeland seeding. Bur clover is an annual medic that was introduced during European colonization of California. In the 1950s and 60s, it was joined by other annual medics from Australian breeding programs. Lana vetch was introduced for rangeland seeding in the 1950s by USDA Soil Conservation Service .Seeding of rose clover and subterranean clover to improve productivity on Mediterranean-type rangelands began in the 1950s. The primary effect of annual legumes on annual rangeland productivity is to increase winter and spring forage production and to improve the nutritional quality of the available forage. Table 1 compares protein and crude fiber content of legumes, grasses, and other forbs.
Gains of 150 to 300 pounds of beef per acre can be consistently produced on annual legume– improved ranges. In “good clover years,” this type of production is possible on clover alone. However, since good clover years do not occur every year, the introduction of annual legumes, including subterranean clover, rose clover, and annual medics is recommended. Maximum profit per acre results from paying careful attention to adequate soil fertility, seeding adapted varieties, ensuring proper inoculation at planting, and providing good grazing management.Subterranean clover, rose clover, lana vetch, and the annual medics are adapted to annual rangelands where elevations are below 3,000 feet and rainfall exceeds 15 inches. Rose and subterranean clover are most commonly used and grow well together on neutral to acid soils. The annual medics tend to be best adapted to neutral to basic soils. Several varieties of annual clovers and annual medics mature over a wide range of dates from very early to very late spring . Some subclovers are adapted to wet or poorly drained soils. Most fields to be seeded contain a variety of soils, so the seeding mixture should contain several varieties and types of clover. It should include both earlyand late-maturing varieties that are adapted to a variety of sites to ensure good forage growth during very dry winters or springs, as well as under “normal” conditions.Murphy et al. published guidelines for planting and managing annual legume seedings. Most lands planted to annual legumes are deficient in either sulfur or phosphorus, or both, so that adequate amounts are required to produce a good initial stand and to maintain maximum forage and seed production. While there may be a carryover effect the year after fertilization, commercial indoor growing systems especially from phosphorus applications, maintenance fertilization is necessary to maintain clover stands and productivity. Clovers need to grow in association with certain soil bacteria to provide the nitrogen they need for growth . In most areas these required strains of bacteria are not present in the soil and must be furnished by inoculating the seed with the right bacteria at seeding time. Well-inoculated clovers supply extra nitrogen to make the associated grasses more productive. The pellet method of inoculation is recommended. Some seedbed preparation is often necessary to reduce competition, ensure the survival of rhizobium bacteria, and provide for seed coverage; however, direct seeding in low residue has been successful in many locations. Seed can be broadcast or drilled, but it should be covered by about 0.5 inch of soil. Seeds may not emerge if they are placed deeper. Seeding rates are often around 10 to 20 pounds/acre. A broadcast seeding should be lightly covered by ring rolling or harrowing. Broadcast seedings that are not covered are highly susceptible to failure in marginal rainfall areas. Range drills are sometimes available from area seed companies. Seeding should be done as close to the first fall rain as possible and before cold weather. Fall seedings in October and early November are much more successful than December seedings. If germinating rains do not come before cold weather, delay seeding until the following year.Legumes stimulate the early growth of grasses and filaree.
In the winter and early spring, seeded ranges should be grazed to use the grass and prevent nonlegumes from crowding the clovers. Reducing grazing while clover is blooming will allow an adequate seed set. Stands should be heavily grazed during the summer and fall to make use of the dry feed and to trample the seed into the ground. More stands of clovers have been lost by grazing too light than by heavy grazing.Annual ryegrass is the main improved annual forage grass used on annual rangelands. With proper fertilization it can provide high-quality forage during the growing season, and it remains an important species for improving forage quantity and quality. Annual ryegrass germinates rapidly and is able to quickly stabilize soils following burns and other disturbances. Unfortunately, this characteristic also makes annual ryegrass a strong competitor to native species. Consequently, it has been listed as an invasive non-native plant that threatens wildlands by the California Invasive Species Council. If your goal is to maintain and increase native grasses and forbs, excluding annual ryegrass is a legitimate management practice. However, if you need to stabilize soil quickly or you are seeking improved forage, seeding annual ryegrass remains an important agricultural practice. Like annual legumes, annual grasses should be seeded just prior to the fall rains. Annual grass seeds are small and should not be buried too deep when seeding. Seed can be broadcast or drilled, but it should be covered by about 0.5 inch of soil. Seeds may not emerge if they are placed deeper. It has generally been recommended that seed be drilled with a grassland or rangeland drill into existing but closely grazed stubble from the previous growing season. If a drill is not available, the soil should be lightly disked or harrowed to loosen the top 1 inch of soil and seed broadcast on the soil surface. Broadcasting should be followed by light rolling or dragging to cover the seed. Annual grass seeding rates are frequently about 5 to 10 pounds/acre. Blando brome and Zorro fescue are also available for seeding for erosion control. Soft chess brome is a desirable forage species that is naturalized and widespread on annual rangelands. Both of these grasses were selected from wild populations and developed into commercial varieties by the USDA NRCS Plant Materials Center.Seeding native or introduced perennial grasses into annual rangelands has always been challenging, with failure being more frequent than success. Competition from annual grasses and forbs during seedling establishment is a major source of failure, but improper grazing of successful seedings has also been a source of stand loss. The primary reasons that ranchers have seeded perennial grasses on annual rangelands is to provide a higher amount of winter feed and green feed several weeks later in the season than the naturalized annual grasses and forbs. Hardinggrass and some other perennial grasses have the ability to break summer dormancy and begin growth before the first fall rains and remain green until after seed has matured in early summer. This can add several weeks to the green forage season. However, when seedings are successful, establishment sometimes takes 3 to 5 years before perennial grasses are able to compete with annual grasses. Consequently, perennial grass seedings have not been widespread on annual rangelands, with most success being along the high-rainfall north coast. From 1937 to 1951, the University of California Extension Service and Agricultural Experiment Station planted thousands of test plots to determine what grasses were adapted to seeding following brush burns and other woody plant control. Planting methods and seeding recommendations were developed for the annual rangelands and intermountain areas where rainfall exceeded 10 inches . Hardinggrass was seeded in many counties, and remnants of those plantings can still be found. However, McKell et al. found that grazing during active growth reduced yields and increased mortality. Likewise, ranch managers have reported low persistence of grazed stands in all but the very best soils.