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Section 14: Noxious Weeds and Pests on the Right of Way

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Overview

A variety of plants are considered pests along the highway right of way. Pest plants are generally those species which pose safety, maintenance or public relations problems for the department.

The predominant pest species in Texas include Johnson grass, Giant Ragweed, Musk Thistle, Sunflower, Field Bindweed, Bermuda grass, Mesquite, Huisache, Retama, Georgia Cane, Kochia, Russian Thistle, Switchgrass, Turnip Weed, Morning Glory Vine, Western Bitterweed, African Rue, Cattails, Saltcedar, Wildoats, Jointed Goatgrass and Kudzu.

Some of these are native to Texas. Others are introduced species which have become naturalized, taking advantage of environmental disturbance to invade and become established in the right of way. Minimizing disturbance caused by construction or maintenance activities is the best way to reduce the spread of such species. However, once these species become established in an area of the right of way which must be maintained, properly selected and applied herbicides may be used to control the pest and to re-establish desirable vegetation.

This section addresses important characteristics of the major pest plants of concern to the department, and the recommended methods for their control.

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Johnson grass

Johnson grass (Sorghum halepense) is a perennial grass that can grow to approximately six feet tall. It spreads vigorously by rhizomes (i.e. underground runners) and by seed. It flowers throughout the growing season under favorable growing conditions. Most Johnson grass plants, however, mature and flower later in the growing season. Johnson grass is commonly found growing along roadsides, in ditches, open areas, fields and waste places.

 Johnson grass. (click in image to see full-size image) Anchor: #i1005829

Figure 3-34. Johnson grass.

Johnson grass is most effectively controlled in an overspray program either with Roundup Pro + Escort XP + Outrider (until July 31) or with Roundup Pro + Outrider alone later in the growing season (until October 15). Johnson grass around fixtures may be controlled by spraying the Roundup Pro + Escort XP + Outrider combination at any time during the growing season.

In areas where Johnson grass and Blood weed control is necessary, Outrider and Roundup Pro can be mixed with 10 ounces per acre of Vista. Blood weed must be actively growing with adequate soil moisture to achieve the best results.

Also see: Use of Roundup Pro for Johnson grass Control (Bermuda Release), Use of Roundup Pro + Outrider Combination for Johnson grass Control, Use of Roundup Pro + Escort XP + Outrider for Johnson grass Control, Application with the Fixture Boom on All Herbicide Units.

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Field Bindweed

Field Bindweed (Convovulus arvensis) is a long-lived perennial, which produces a dense ground cover. The twining stems vary from 1.5 to 6 feet or more in length. It produces white to pink flowers from April through September and seeds that may lie dormant in the soil for 30 to 40 years.

 Field Bindweed. (click in image to see full-size image) Anchor: #i1005837

Figure 3-35. Field Bindweed.

Field Bindweed occurs from the Panhandle to Central and West Texas along roadsides, railroads, fields, gardens and waste places and is a serious agricultural pest. Field Bindweed invades and becomes rapidly established in disturbed areas; minimizing disturbance in the right of way will reduce the spread of this pest plant.

The most effective herbicide to control Field Bindweed is Escort XP applied at a rate of one ounce per acre during the flowering period. Always add one quart of approved surfactant per 100 gallons of water.

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African Rue

African Rue (Peganum harmala) is a perennial plant with a rounded tuft of fleshy stems from a twisting, woody root. The flowers are white to pale yellow appearing from April through November. Each flower produces a small marble-sized capsule filled with seeds.

 African Rue. (click in image to see full-size image) Anchor: #i1005845

Figure 3-36. African Rue.

 African Rue. (click in image to see full-size image) Anchor: #i1005847

Figure 3-37. African Rue.

African Rue reportedly occurs in Edwards and Garza counties though it is most abundant in the Trans-Pecos region. This plant is reportedly poisonous to livestock.

African Rue is extremely aggressive and readily invades disturbed areas, but seems to be largely excluded from areas where native vegetation persists. Curtailing disturbances in the right of way will likely restrict the spread of this pest species.

Currently, the most effective means of controlling African Rue is an application of Escort XP at a rate of three ounces per acre while the plant is flowering. Always add one quart of approved surfactant per 100 gallons of water.

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Mesquite

Mesquite (Prosopis glandulosa) grows either as a shrub or a tree and is abundantly armed with stiff spines. The plants usually flower in the spring, but sometimes later. The flowers are very small and grouped together in conspicuous yellow bunches. Mesquite is widely distributed in west and south Texas, generally in deep soils. It increases in abundance in disturbed grasslands.

 Mesquite. (click in image to see full-size image) Anchor: #i1005855

Figure 3-38. Mesquite.

Where it occurs in areas of the right of way that must be maintained, mesquite may be mowed annually at the fall full-width mowing. Alternatively, where the plants are large enough and removal is necessary, Pathfinder II should be applied in a low volume application or with Transline at 21 ounces per acre plus 2 quarts surfactant per 100 gallons of water, applied in mid-summer to early fall.

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Huisache

Huisache (Acacia farnesiana) is a brushy species which occurs as both shrubs and trees, usually with several trunks. The branches are numerous and armed with many paired, pin-like pale spines. The fragrant yellow flowers are clustered in small spheres. The plants flower in the spring, but many produce flowers again after rain during periods of drought.

 Huisache. (click in image to see full-size image) Anchor: #i1005863

Figure 3-39. Huisache.

Huisache is primarily found in South Texas, extending north to Travis County and west to Brewster County.

For areas of right of way that must be maintained, Huisache may be mowed annually at the time of the fall full-width mowing. Where the plants are large enough that they need to be removed, it can be controlled with the herbicide Pathfinder II applied at a low volume application at any time of the year, or with Transline, at 21 ounces per acre plus 2 quarts surfactant per 100 gallons of water, applied in mid-summer to early fall.

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Retama

Retama (Parkinsonia aculeate) generally occurs as a small, widely branching tree with sharp, slightly curved spines on green barked branches. The flowers are yellow and are identifiable as distinct, individual flowers (unlike Mesquite and Huisache). The plant may flower spring through fall, depending on location and climate.

 Retama. (click in image to see full-size image) Anchor: #i1005871

Figure 3-40. Retama.

Retama is distributed throughout South Texas, extending northward to at least Williamson County and east to Brazos County.

For areas of right of way that must be maintained, Retama may be mowed annually at the time of the fall full-width mowing. Retama can be controlled with Pathfinder II applied at a low volume application at any time of the year. Control also can be achieved with Transline at 21 ounces per acre plus 2 quarts surfactant per 100 gallons of water, applied in mid-summer through early fall.

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Cattails

Cattails (Typha latifolia) are perennial aquatic plants which may grow to 10 feet tall from the creeping root to the tip of the flowering stem. The flowers are extremely small and are clustered together in a cylindrical brown tuft. Flowers usually develop from March through May.

Cattails. (click in image to see full-size image) Anchor: #i1005879

Figure 3-41. Cattails.

The plants are scattered throughout Texas in marshes, streams and other shallow water areas impeding drainage.

Cattails and other associated aquatic vegetation are controlled with an Approved Aquatic Herbicide at a two percent eight quarts per 100 gallons of water solution using a handgun. Always add two quarts of an approved surfactant to each 100 gallons of water.

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Bermuda grass

Bermuda grass (Cynodon dactylon) is a low-growing perennial grass which spreads mostly by underground and above ground runners, although common Bermuda grass produces viable seed. This plant grows primarily in loamy, seasonally moist soils; it is commonly found in rights of way. Although Bermuda grass is a valuable cover species and reduces erosion, it is a potential pest when it grows into the pavement. Bermuda grass often penetrates the pavement shoulder contributing to pavement breakdown.

Bermuda grass growing at the edge of pavement is generally best controlled by an early fall application of Roundup Pro (four quarts per acre) plus Landmark XP (three ounces per acre).

Bermuda grass. (click in image to see full-size image)

Figure 3-42. Bermuda grass.

Bermuda grass growing in riprap and on concrete fixtures is generally best controlled with an application of Roundup Pro at a rate of four quarts per acre. Landmark XP is left out of this solution due to the possible runoff onto desirable vegetation after rainfall.

Applications should be restricted to no more than six inches from the edge of the paved surface and 12 inches behind the guardrail. Applications wider than 12 inches may result in erosion and sediment loss.

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Wild oats and Jointed Goat grass

Wild oats (Avena fatua) and Jointed Goat grass (Triticum turgidum) are two annual cool season grasses which often occur on the right of way in North Texas. Both of these grasses are annuals that spread only by seed. The seeds germinate in the fall or winter. An early application of Roundup Pro (usually late March) at one quart per acre as an overspray is effective in controlling these plants.

Wild oats. (click in image to see full-size image)

Figure 3-43. Wild oats.

Jointed Goat grass. (click in image to see full-size image)

Figure 3-44. Jointed Goat grass.

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Musk Thistle

Musk Thistle (Carduus nutans) is a biennial plant which can grow up to eight feet tall. Musk Thistle takes two years to mature and die. The first year the plant is a rosette. The second year the plant grows tall and blooms. The leaves are dark green, deeply lobed, hairless and have a light green mid-rib. A silver gray leaf margin is characteristic of each spine tipped lobe. The leaf base extends down the stem to give the plant a winged appearance. The terminal flower is large (one to three inches in diameter), solitary and usually nodding or bent over slightly. The flowers are purple and "powder puff" shaped producing thousands of straw-colored seeds per plant. Seed dispersal begins seven to 10 days after blooming. The seeds are attached to parachute-like hairs (pappus) which allow for their dispersal by wind currents.

Musk thistle reproduces only by seed so it's very important to control this plant before it goes to seed. It grows from the Panhandle to Central Texas. It can become a serious agricultural pest as well as a safety problem.

Musk Thistle. (click in image to see full-size image)

Figure 3-45. Musk Thistle.

Musk Thistle can be controlled with an application of Transline at a rate of 10 ounces per acre applied early spring (March - April).

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Giant Ragweed (Blood weed)

Giant Ragweed (Ambrosia trifida), also known as Blood weed, is an annual broadleaf weed that can obtain heights of more than 10 feet. The plant germinates in the spring and flowers in the fall. The flowers are small and inconspicuous. The plant is blamed for hay fever problems while it is blooming.

It normally grows in the eastern two-thirds of the state. It generally prefers moist soil in and around ditch areas.

Giant Ragweed. (click in image to see full-size image)

Figure 3-46. Giant Ragweed.

Giant Ragweed can be controlled with an application of Vista at a rate of 10 ounces per acre applied late spring to early summer.

Note: Spraying mature plants will yield poor results.

In areas where Johnson grass and Giant Ragweed control is necessary, Outrider and Roundup Pro can be mixed with 10 oz per acre of Vista without surfactant. The Ragweed must be actively growing with adequate soil moisture to achieve the best results.

Also see Use of Roundup Pro + Escort XP + Outrider for Johnson grass Control and Application Procedures for Vista on Giant Ragweed (Bloodweed).

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Sunflower

Sunflowers (Helianthus annuus) are broadleaf weeds which may reach a height of eight to10 feet. Yellow daisy-like flowers with dark centers grow two inches across. Sunflowers Multi-stemmed plants grow irregularly and are common throughout the state, but usually occur in disturbed areas.

Sunflowers are a common weed problem that quickly emerges after construction projects are over, especially when new topsoil is added to the right of way from outside sources when stockpiled topsoil is depleted.

Sunflowers. (click in image to see full-size image)

Figure 3-47. Sunflowers.

Sunflowers may be controlled with an application of Transline at a rate of 10 ounces per acre or with Escort XP at the rate of one ounce per acre plus surfactant at the rate of one quart per 100 gallons of water. Plants should be sprayed when they are two to three feet tall.

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Kochia and Russian Thistle (Tumbleweed)

Kochia (Kochia scorparia), a member of the Goosefoot family, was introduced from Europe and is an annual, reproducing by seed, which can grow up to six feet tall. Leaves are narrow, bright green, hairy, numerous and are attached directly to the stem. Kochia can be found in cultivated fields, waste areas and roadsides.

 Kochia. (click in image to see full-size image) Anchor: #i1005915

Figure 3-48. Kochia.

 Russian Thistle. (click in image to see full-size image) Anchor: #i1005917

Figure 3-49. Russian Thistle.

Russian Thistle or Tumbleweed (Salsola iberica), also a member of the Goosefoot family, was introduced from Russia and is an annual which reproduces by seed. Mature plants are spherical bushes up to five feet tall. After they turn grayish brown in the fall, the plants break away from the roots at the soil line, becoming tumbleweeds that scatter their 250,000 seeds per plant in their path.

Kochia and Russian Thistle normally grow in the northern and western part of the state. In optimum conditions Kochia can be the dominate species when growing on the roadside. Russian Thistle generally grows into large, wide spherical bushes.

Kochia and Russian Thistle can be controlled with Vista at an application rate of 10 ounces per acre applied early spring or on actively growing plants.

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Georgia Cane or Giant Reed

Georgia Cane (Arundo donax), also known as Giant Reed and Wild Cane, is a tall perennial grass that can grow to more than 20 feet tall. Its fleshy, creeping rootstocks form compact masses from which tough, fibrous roots emerge that penetrate deeply into the soil. Leaves are elongate, one to two inches wide and a foot long. The flowers are borne in two-foot long, dense, plume-like panicles during August and September. Georgia Cane is found throughout the state along ditches, streams and rights of way.

Georgia Cane was probably first introduced into the United States from India at Los Angeles in the early 1800s. Since then, it has become widely dispersed into all of the subtropical and warm temperate areas of the world, mostly through intentional human introductions along ditches for erosion control.

Georgia Cane is controlled with an Approved Aquatic Herbicide at eight-quarts per 100 gallons of water solution using a handgun.

NOTE: Always add two quarts of an approved aquatic surfactant to each 100 gallons of water.

 Georgia Cane (click in image to see full-size image)

Figure 3-50. Georgia Cane

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Salt cedar

Salt cedar (Tamarix ramosissima), grows five to 20 feet tall. Smooth woody stems are reddish brown, turning gray and cracked as the tree ages. Leaves are small, scale-like, and give the slender stems a wispy green appearance. Flowers are pink to white, blooming from spring through late summer. They are very attractive and from a distance look like pink feathers at the end of the stems. Range is generally in the western part of the state along streams and rivers. Salt cedar was introduced from Eurasia.

Salt cedar is a small, shrubby tree and is often referred to as Tamarisk. It was introduced as an ornamental and was also used for stream bank erosion stabilization. Salt cedar has naturalized throughout the desert southwest, particularly along waterways and in wetlands. It is well adapted to salty, alkaline soils, to temperature extremes and to windy sites. Its aggressive root system uses excessive ground water (one plant draws and transpires 200 gallons of water per day from ground, stream or river), out-competing native species.

Salt cedar is controlled with Habitat at two quarts per acre overspray or two quarts per 100 gallons of water solution using a handgun.

NOTE: Always add 1 quart of an approved aquatic surfactant to each 100 gallons of water.

Contact the Vegetation Management Staff of the Maintenance Division for specific recommendations for controlling Salt cedar.

Salt cedar. (click in image to see full-size image)

Figure 3-51. Salt cedar.

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Kudzu

Kudzu (Pueraria lobata) is an aggressive perennial trailing or climbing vine of the legume family. A dense stand of identically colored plants growing on and around everything in its path is a familiar field mark.

Rarely flowering, kudzu stems and roots spread out in all directions from root crowns, with new plants beginning at stem nodes every one to two feet. This dense packing of Kudzu can result in tens of thousands of plants occupying a single acre of land. Kudzu leaves are hairy beneath, often tri-lobed, and in groups of three on the vine. The half to three-quarter inch elongated purple flowers with a fragrance reminiscent of grapes are pea-like in shape and are produced on plants exposed to direct sunlight. Kudzu fruits, present in October and November, are hairy, bean-like pods which produce only a few viable seeds in each pod cluster. It is thought that some seeds can remain dormant for several years before they germinate.

During peak growing season in early summer, this prolific vine can grow at a rate of a foot a day, easily covering and choking trees and understory vegetation.

Range consists of small pockets in the eastern part of Texas with one infestation being eradicated by the Colorado River in south Austin. Kudzu was introduced from Japan.

Kudzu is controlled with Transline at 21 ounces per 100 gallons of water solution using a handgun.

NOTE: Always add 2 quart of an approved aquatic surfactant to each 100 gallons of water.

 Kudzu. (click in image to see full-size image)

Figure 3-52. Kudzu.

Spraying Kudzu. (click in image to see full-size image)

Figure 3-53. Spraying Kudzu.

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Switchgrass

Switchgrass (Panicum virgatum) is a native, warm-season perennial tall bunchgrass that grows from two to seven feet tall. Leaf blades are four to 24 inches long and .two to .six inches wide. Switchgrass flowers from August through September. Switchgrass roots can sometimes reach down 10 to 11 feet deep. Switchgrass is very palatable to livestock.

Switchgrass is no longer seeded on the state's right of ways because of its large size and fast growing habits which can cause sight distance issues.

Switchgrass can be controlled by spot treating clumps using Roundup Pro in a two percent solution with water applied with a handgun or pump-up sprayer. Another method would be to use a Rotowiper® application system with a 33 percent Roundup Pro solution in water.

Switchgrass. (click in image to see full-size image)

Figure 3-54. Switchgrass.

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Turnip Weed

Turnip Weed or Bastard Cabbage (Rapistrum rugosum) is an annual, many-branched herbaceous plant that grows from one to five feet (or more) tall and has a taproot that can become quite large. Leaves are deep green, lobed and wrinkled, and sometimes have a reddish cast. The terminal lobe is larger than the lateral lobes, especially on the basal leaves. Younger leaves growing higher up on the plant are less lobed and more elongated. Turnip Weed typically flowers from early spring into summer, bearing clusters of small, showy yellow flowers at the tips of its branches, resembling those of broccoli and cabbage. Turnip Weed can be identified more easily and certainly by its unusually shaped fruit - a two-segmented seed capsule, called a silique. The seed capsule is stalked, with a long beak at the tip, and contains one to two seeds. The seeds are tiny, oval-shaped, dark brown and smooth.

Turnip Weed is one of the first plants to emerge in the spring and since it is faster growing than most spring wildflowers, it competes with them for moisture, nutrients and sunshine, causing problems where wildflowers are present.

Turnip Weed. (click in image to see full-size image)

Figure 3-55. Turnip Weed.

Turnip Weed can be controlled by applying Escort XP at a rate of one ounce per acre early in the spring. Always add one quart of surfactant per 100 gallons of water.

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Morning Glory Vine

Morning Glory Vine (Ipomoea purpurea), related to Field Bindweed (Convovulus arvensis) and Sweet Potato, forms twining vines with bell-shaped flowers, and its varieties have also become intertwined botanically under the name "morning glory." The name comes from the flowers, which last a single day. Flowers are white, blue, pink, purple, red, and multicolored.

The vines grow quickly to 10 feet or more only two months after seeds sprout. The leaves are heart-shaped, and the flowers are normally open from dawn to midmorning, then closing.

Morning Glory Vine has become a pest plant on the right of way twining up into signs, delineators, bridge structures, guard rails, barrier fences and landscaped shrubbery.

The most effective way to control Morning Glory Vine is with Escort XP applied at a rate of one ounce per acre during the flowering period. Always add one quart of surfactant per 100 gallons of water.

Morning Glory Vine. (click in image to see full-size image)

Figure 3-56. Morning Glory Vine.

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Western Bitterweed

Western Bitterweed (Hymenoxys odorata) is an erect, annual composite plant growing from three inches to two feet tall. Stems are purplish near the base. Leaves are alternate and usually woolly underneath. Bright yellow flowers bloom from April through June and occasionally in the fall. This plant has a bitter taste and a distinct odor. Bitterweed is toxic to sheep and is generally unpalatable.

Western Bitterweed is located throughout the western portion of the state in various counties and concentrated in the Trans-Pecos region.

Western Bitterweed readily invades disturbed areas, but seems to be largely excluded from areas where native vegetation persists. Curtailing disturbances in the right of way will likely restrict the spread of this pest species.

Western Bitterweed. (click in image to see full-size image)

Figure 3-57. Western Bitterweed.

Western Bitterweed can be controlled by using Escort XP at the one ounce per acre rate plus one quart of surfactant per 100 gallons of water. Control of Western Bitterweed can be accomplished by overspray application or by spot spraying small concentrations of the plant with the handgun sprayer.

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Itchgrass

Itchgrass (Rottboellia cochinchinensis), is an annual, erect, up to nine-foot-tall grass. Stems are supported by prop roots, nodes smooth, leaf sheaths are smooth or with sparse tubercular-based hairs. Leaf blades are straight to broadly straight, apex slender, smooth or with sparse tubercular-based hairs. Flowers one to six inches long, terminating with several reduced spikelets; directly attached spikelets and seed bearing spikelets. Native to the Philippines, Itchgrass was introduced into Florida as a potential pasture grass in the late 1920s. Later it spread into Texas through shipments of grass seed containing small amounts of this noxious weed. Itchgrass can be controlled by using a spot treatment of Roundup Pro in a two percent solution with water while actively growing. Another method is by overspray with the fixture boom or Flex-5 spray head the herbicides Roundup® Pro and Landmark XP® at a rate of 16 ounces plus two ounces per acre solution in water.

Itchgrass (click in image to see full-size image)

Figure 3-58. Itchgrass

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Other Right of Way Pests

Applications of all pesticides for the control of right of way pests including, but not limited to, burrowing rodents, fire ants, other destructive insects, etc. must be made in a manner consistent with all current and pertinent laws and regulations as established by the Texas Department of Agriculture and the Structural Pest Control Board. All label directions must be followed in detail.

Contact the Vegetation Management Staff of the Maintenance Division for specific recommendations.

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