Crop Profile for Wheat (Winter) in Wyoming

• Acres in Wyoming: 185,000
• Percent U.S. Acreage: 0.4%
• Per Acre Value: $76.34

Value of Production in Wyoming: $14,122,000.00

(1999 Data)

Cropping system:
Winter wheat is planted between September 1 and October 15. If the crop is planted too early, there is a higher risk for hessian fly and viral infestations. However, if wheat is planted too late, the plants may be underdeveloped when overwintering occurs (4 - 5 leaf stage is the optimal stage for overwintering). The wheat plants will vernalize during overwintering if they are properly developed. Vernalization entails a shift from vegetative growth to reproductive growth. Preferred soil texture is well-drained, with a soil temperature of 60 F or lower. Seeds should be planted at a depth of 1 - 3". Rows are generally 7 - 12" wide. Six inch row spacings are primarily used for irrigated systems. Optimal planting density is 500,000 - 750,000 plants per acre, depending upon whether it is a dryland or irrigated system (in dryland systems, there are fewer plants per acre). This is equivalent to 30 - 50 lbs. of seed per acre in dryland systems and 75 lbs. of seed per acre for irrigated systems.

Most wheat grown in Wyoming is dryland, with fewer center pivot and furrow irrigation systems.

The following are acceptable crop rotations: wheat-corn-fallow; wheat-sorghum-fallow; wheat-proso millet-fallow; wheat-corn-proso millet-fallow. Sunflowers may also be added into the rotation. However, the dominant rotation is still wheat-fallow. It is recommended to plant winter wheat following fallow; if this is not possible, plant a short season annual forage in the spring and harvest it prior to August 1.

No tillage is necessary when planting wheat; plant directly into forage stubble. However, most growers following a wheat-fallow rotation will clean till the seed bed before planting.

Winter wheat is usually harvested in July. The crop can be directly combined unless it is weedy.

Critical Pest Issues:
Volunteer wheat sometimes acts as a carrier or transitional host for some pests, including the wheat curl mite and certain viruses. Therefore, it is imperative to destroy volunteer wheat and allow a 2-3 week fallow period before planting winter wheat. The planting of varieties that are well adapted to local growing conditions reduces insect, disease and weed problems. Minimum or no-till increases the incidence of diseases like cephalosporium stripe, take-all and tan spot.

Jointed goatgrass is a common weed problem in wheat cropping systems, and is very difficult to control.

Sulfonylurea herbicides are not registered for use in the San Luis Valley.

Cultural Controls:
A good stand without skips in planting will control the germination of early spring weeds. Reduced tillage increases stored soil moisture which leads to healthier, pest resistant plants.

Wise management decisions lead to a better cropping system with fewer pest problems. Plant later to avoid wheat curl mite, hessian fly, and other aphid infestations. Planting varieties resistant to Russian wheat aphid, leaf rust and stem rust will reduce pesticide use in fields with a history of these problems. Killing volunteer wheat in adjacent fields three weeks prior to planting will help control wheat curl mites. Proper crop rotation that leaves the field out of wheat for 2 - 3 years will help to avoid take-all.

Wireworms can be controlled with seed treatment, and the remaining insect pests can be controlled with threshold-based insecticides.
 
 

Euxoa auxiliaris is one of several species of caterpillars that attack wheat in Wyoming. Army cutworms have a wide host range and feed on most crops grown in Wyoming, but are mainly pests of winter grains. Adult moths are brown with light brown or black markings on the forewings and have a wingspan of about 2". The larvae vary in color from dull green to brown with faint stripes on the back and a brown head. The army cutworm has one generation per year. Eggs hatch in the fall following sufficient moisture. The army cutworm larvae spend the winter as partially grown caterpillars. They feed on warmer days throughout the winter and feed more frequently in the spring as they mature. Army cutworm caterpillars are climbing cutworms that always feed above ground during the night and/or on cloudy days. They are found under soil clods and other debris during the day. After development is complete, they build a small pupation chamber several inches below the soil surface. Moths emerge in May and June and migrate to higher elevations in the Rocky Mountains to escape high summertime temperatures. In late summer and early fall, the moths return to the plains to lay their eggs in wheat fields and other cultivated areas. With adequate moisture, eggs hatch and larvae of the next generation start feeding as weather conditions permit. Army cutworm caterpillars feed on plant foliage. Their feeding has the most effect on yield when there is relatively little foliage for them to feed on, which increases the likelihood of damage to the crown.
 
 

The brown wheat mite, Petrobia latens, and the Banks grass mite, Oligonychus pratensis, are two important mite pests of small grains in Wyoming. Mites are tiny arthropods that feed on the sap of host plants. They have eight legs (six in the first stage). The brown wheat mite is about 0.025" long, oval shaped and dark red or brown in color. Banks grass mite is extremely small, 0.001", and yellow to cream colored. Banks grass mites overwinter as orange-yellow females. They may lay some eggs during prolonged warm spells. The Banks grass mite life stages include: pearly white, spherical egg; 6-legged light to dark green larva; 8-legged pale-bright green protonymph; 8-legged deutonymph with robust females and slender males; adult male with a deep green, pointed abdomen; and a large 0.018", active female. Immatures stop moving prior to molting. Generation times depend on temperature and are typically 10 - 20 days. Leaves injured by brown wheat mite first appear silvery and later take on a scorched appearance. Banks grass mites turn leaves silvery and the tips and margins later turn brown. Webbing is an additional sign that injury is caused by the Banks grass mite.
 
 

Grasshoppers follow a roughly 22-year cycle in Wyoming, with the last major outbreak occurring in the late 1970s and early 1980s. Grasshoppers vary considerably depending on the species. Grasshopper nymphs have a similar appearance to adults but are smaller in size. Grasshopper eggs are laid in undisturbed areas, usually in late summer and early fall. Small nymphs or "hoppers" hatch the following spring. Winged adults will appear 5 - 6 weeks after a hatch. Some of these species are important on rangeland, but none are considered a threat to field crops. The usual pattern of grasshopper damage in field crops is for early development to occur in weedy areas of roadsides, fence rows, irrigation ditches, and other noncrop areas. As these food plants are eaten or dry down, the grasshoppers leave in search of other food, often on irrigated crops or newly-emerged winter wheat. Here they will first feed in the field margins and then, conditions permitting, spread throughout the field. Most field crop damage is caused by the differential, redlegged, two-striped, and migratory grasshoppers.
 
 

Diuraphis noxia is one of the most destructive species in Wyoming. The Russian wheat aphid (RWA) damages small grains be injecting saliva into and sucking sap from plants. Yield losses of 50% or more to this pest can be expected if economic infestations are left untreated. RWA are yellow-green or gray-green in color and are often covered with wax. RWA are small, less than 0.897" in length, and are convex and elongate. Two forms of RWA are found in Wyoming during the year: a wingless female and a winged female. In Wyoming, most severe spring infestations of winter grains are caused by wingless aphids that overwintered in the crop. Winged aphids begin to appear in Wyoming in April and May and flights peak during July in most wheat-producing areas of the state. At this time winged aphids include both local aphids and immigrants from the south. Winged aphids infest late maturing winter wheat and spring grains as well as a number of cool-season grasses, particularly wheat grasses. These grasses serve as alternate hosts for RWA during the period between grain harvest and the appearance of new wheat in the fall. Volunteer wheat and barley are important sources of RWA for the new fall crop as soon as it emerges. Weather conditions that favor cool season grasses and volunteers will increase the number of aphids infesting the new wheat crop in the fall. RWA can be found in winter wheat, usually on the younger leaves, from emergence in the fall to grain ripening. Aphid feeding prevents young leaves from unrolling. RWA colonies are found within the tubes formed by these tightly curled leaves. This not only makes it difficult to achieve good insecticide coverage, but also interferes with the ability of predaceous and parasitic insects to reach and attack aphids. Leaves infested by RWA have long white, purple or yellowish streaks. Under some conditions, infested wheat tillers have a purplish color. Heavily infested plants are stunted and some may appear prostrate or flattened.
 
 

Aceria tosichella is a microscopic eriophyid mite of great economic significance in Wyoming. It vectors the causal agents of Wheat Streak Mosaic Virus and High Plains Disease. Wheat curl mites are microscopic long and slender mites that are visible with the aid of a hand lens (at least 10X). Eggs, immature stages, and adult wheat curl mites are found in the winter on wheat and other nearby perennial grasses. As temperatures rise in the spring, mite populations develop under leaf sheaths, inside newly emerged leaves, and eventually on green tissues in the head. Eggs are placed along leaf veins. An average complete generation requires eight to ten days. Most mites are found on the upper surface of the youngest fully expanded leaf, adjacent to the ligule. They seem to prefer the most tender leaf tissue and therefore move to each new leaf as it emerges. As the wheat plant dries down, the wheat curl mites congregate on green tissue in the upper parts of the plants where they are picked up by wind currents and carried to their oversummering grass hosts. As summer hosts start to dry down, the reverse process occurs and mites are carried by winds to newly emerged winter wheat. They are often found in the spaces between leaf veins. Damage leaves have tightly rolled leaves. Damaged plants have symptoms of Wheat Streak Mosaic Virus, which include chlorotic speckles or streaks and stunting.
 
 

Bird cherry oat aphids are olive-green in color with a reddish-orange area on their rear end. They are medium sized, 0.05 - 0.10", aphids with long antennae, long dark tube-shaped cornicles, and dark colored legs. The aphids feed on barley by sucking plant juices. Bird cherry oat aphids vector barley yellow dwarf virus.
 
 

Corn leaf aphids are small, 0.585- 0.975", bluish-green insects with a purplish patch around the base of the cornicles. They are usually wingless with short antennae and prominent cornicles. The aphids feed in groups, first appearing in the whorl. Adult females give birth to live young, but they do not lay eggs, with about two nymphs being produced per day. These aphids suck plant juices but damage is usually minor. However, they are vectors of barley yellow dwarf virus. Heavily infested leaves may wilt and have yellow or dead areas. Also, honeydew secreted by the aphid may accumulate on the plant facilitating mold growth and giving leaves a purplish-black appearance.
 
 

The English grain aphid is a yellow green to reddish brown, medium sized aphid with antennae greater than half the body length. The cornicles, also referred to as "tailpipes" are medium sized and black. Antennae and leg joints are dark colored. This aphid overwinters mainly in the mature and nymph stages, but a few individuals may overwinter in the egg stage. Only females overwinter, and with warm spring temperatures they begin giving birth to live young. Males appear during the fall and mate with true females. English grain aphid colonies often develop on leaves and then move to heads in the boot stage. Aphids may cluster about the bracts of wheat heads or other grains. The wheat kernals may shrivel as a result of aphid feeding. This aphid is a vector of barley yellow dwarf virus.
 
 

Hessian fly larvae are small, 0.1875", greenish-white, legless, headless maggots found underneath lower leaf sheaths. The pupal stage appears as a small 0.1875", brown seedlike cases containing a maggot, often referred to as a "flaxseed." Adult flies have a red-brown to dusky-black body and dusky wings. They resemble mosquitoes in form and are about 0.166" long. Hessian flies overwinter in volunteer of fall-sown wheat. After adults emerge in the spring they mate, lay eggs, and die after 1 - 2 days. Females lay eggs on the upper leaf surfaces that hatch in about 3 -10 days. Newly hatched maggots crawl down the leaf and enter the plant at the junction of the sheath and stem. There may be one or more generations in the spring and in the fall. Maggots feed by rasping plant tissue and sucking plant juices which ooze from the irritated surface of the stems of wheat and barley. Plant tissues near feeding sites are stunted and abnormal. Leaves may appear thickened, erect, and bluish-green in color. The central stem is often missing. Infested stems usually break over at the time of head formation.
 
 

Agrotis orthogonia is one of several species of caterpillars that attack wheat. In Wyoming, the pale western cutworm is a major pest of small grains. Adult moths emerge from the soil in late summer and fall. Eggs are deposited in loose soil and usually hatch in late winter. Under some conditions, eggs hatch in the fall and the insect overwinters as a partially grown caterpillar. Hatch may be delayed for up to several months if moisture and temperature conditions are unfavorable. Larvae prefer loose, sandy or dusty soil and are found most easily in the driest parts of the field, such as hilltops. After feeding is complete, pale western cutworm larvae move to pupal chambers constructed several inches below the soil surface. Adults start to emerge in August, but most egg laying occurs in September. Pale western cutworm is a subterranean cutworm, feeding on stems at the crown. Feeding results in severed stems. Entire fields may be lost in a matter of days. Outbreaks are associated with dry conditions in the previous spring.
 
 

The adult wheat stem sawfly is a wasp-like insect about 0.75" long. It has smoky colored wings and shiny black body with three yellow bands across the abdomen. When present in the field the adults are often seen resting upside down on the wheat stem. The sawflies will be active in the field when temperatures are above 50F and conditions are calm. They are not strong flies and usually only fly until they find the nearest wheat field. This often results in more serious problems occurring at the margins of the field. The sawfly larvae feed within the stem after hatching and gradually move down the stem, feeding as they move for about 30 days. The most dramatic impact of the wheat stem sawfly is the lodging of damaged stems and the subsequent losses from not being able to completely harvest these stems. In addition to losses from lodging, sawfly larvae cause physiological damage of 10 - 15% to the infested stems.
 
 

Insecticide Matrix:
 

	chlorpyrifos	carbaryl	carbofuron	disulfoton	lambda-cyhalothrin	dimethicote	phorate
Aphids	X			X
Army Cutworm	X				X
Banks Grass Mite	X
Brown Wheat Mite	X			X		X
Cutworm	X				X
Grasshopper	X	X	X			X
Harvester Ant							X
Russian Wheat Aphid	X			X		X
Spider mites						X

Data from pesticide use survey, 1997
 
 

Management:

Insecticides:

• chlorpyrifos (Lorsban 5G; Lorsban 4E)
• dimethoate (Dimethoate)
• disulfoton (Di-Syston 8; Di-Syston 15G)
• lambda-cyhalothein (Warrior)
• carbaryl (Sevin XLR Plus)
• carbofuran (Furadan 4F; Carbofuran 4F)
• imidacloprid (Gaucho)
• methyl parathion (Penncap-M)
• phorate (Thimet; Thimet 15G; Thimet 20G; Phorate 20G)

Barley yellow dwarf virus is a luteovirus that infects wheat. The vector is a number of aphids, including greenbug, oat bird cherry, corn leaf and English grain aphids. Plants are stunted and have a stiff, squashed appearance. Tillering is reduced and heads fail to fill. Individual leaves turn yellow from the tips in a chevron pattern that leaves the midvein green. The virus survives in aphids, grassy weeds and volunteers and in fall-planted cereals. Infected plants are located at random in a field where the winged adult landed. These plants develop into foci of disease. Disease is favored by cool, wet weather in the spring and early summer. Management of BYDV depends on late planting of winter cereals to reduce aphid populations or early planting of spring cereals to avoid infection at early growth stages. Use of insecticides is seldom economical.
 
 

Rots of roots and other plant parts are the most common and economically damaging diseases of field crops in Wyoming. Soilborne fungi such as Pythium, Phytophthora, Fusarium, Rhizoctonia solani, and Rhizopus cause rots of various plant parts. There are also soft rots caused by bacteria, primarily Erwinia. Symptoms of root and crown rots are seen first in the above ground parts of the plant as chlorosis, wilting, stunting, necrosis, collapse, reduced yield, and plant death. The affected roots, crown or stem will have darkened lesions and cankers.
 
 

Wheat streak mosaic virus is a viral disease transmitted up to 1.5 miles by the wheat curl mite and from plant to plant by leaf contact. The virus is worst in early-seeded, and autumn infected fields. Light green to faint yellow blotches, dashes and streaks parallel to the veins develop in the wheat leaves. Wheat streak mosaic virus can cause severe losses. Hail during harvest and a wet summer favors volunteer wheat, which harbors the virus. Yellow areas appear on the field edges adjacent to volunteer wheat during spring. Symptoms consist of leaves with a mosaic of long yellow streaks that are concentrated at the leaf tips and plants become stunted with prostrate tillers.
 
 

High Plains Disease is a new disease that is thought to be caused by a virus. Although this disease and wheat streak mosaic are frequently found together, it seems to be less common and less important than wheat streak mosaic. Symptoms of doubly-infected plants are severe chlorosis, strong mosaic, severe stunting, and rapid plant death. Occasionally, singly-infected plants have been found. Symptoms of pure high plains disease infection are quite variable. Some leaves have green and yellow stripes at the leaf tips similar to wheat streak mosaic. Others have yellow spots. Still others have green islands on a light green background and look similar to soilborne mosaic. All of these types of leaves can occur on the same plant. Hail at harvest and wet summer favor the growth of volunteer wheat. Early planting of wheat or planting near volunteer wheat increases this disease. Also, warm fall temperatures favor the wheat curl mite vector. Yellow areas in field appear in the spring especially near the edges adjacent to volunteer wheat.
 
 

Puccinia recondita appears as small, round-to-oval, orange-yellow dusty pustules on the leaves and sheaths, sometimes the stems, and occasionally the glumes and awns. On a resistant wheat only small yellow flecks or spots without uredia develop. As wheat matures, glossy, dark gray to black-covered telia are produced. The rust fungus overwinters in the urediospores spread northward as the season progresses.
 
 

Take-all is caused by the fungus, Gaeumannomyces graminis var. tritici. It is most serious in sandy, alkaline, infertile soil where wheat is grown intensively. Winter wheat is more seriously damaged than is spring wheat. Affected plants are stunted to severely dwarfed in localized areas. Such plants have a reduced number of tillers, somewhat yellowed leaves, ripen early, may lodge in all directions, and develop white heads that are sterile of poorly filled and later darkened by sooty molds. Roots, crowns and stem bases develop a brittle, dry, brown to-black rot. A superficial, coal-black mycelial mat forms under the lower leaf sheaths. The fungus over seasons in soil as well as on cereal and grass debris.
 
 

Pseudomonas glycinea occurs in poorly drained wet areas. The bacterium is easily spread in the field by tillage equipment, surface water, and animal life in the soil. Bacterial leaf blight usually only occurs on the upper leaves. Small water soaked lesions form that eventually coalesce to larger lesions that may cover entire leaf. These spots can advance rapidly and cause blight and generally are found associated with sprinkler irrigation in cool wet weather. The bacteria overwinter on and in seed and in debris. Management practices for bacterial diseases include use of pathogen-free or treated seed, crop rotation, field sanitation and use of copper-based bacteriacides.
 
 

Black chaff is caused by a bacterium, Xanthomonas translucens pv.translucens, which may be seedborne. Severe epidemics occur periodically in irrigated wheat. Symptoms generally appear after boot stage. Leaves develop small water-soaked spots which develop into tan to dark brown necrotic spots or streaks surrounded by lime-green chlorotic tissue that merges out to the healthy tissue. Initial symptoms frequently are on upper leaves in the middle of the blade. Entire leaves may die prematurely; if before the soft dough stage, yield reductions and shriveled grain of low test weight may result. Symptoms in heads consist of dark brown or black streaks and blotches, frequently concentrated on the glumes' upper portions. Diseased heads mature late and may be sterile if infected before flowering.
 
 

Xanthomonas campestris has symptoms of brown to black interveinal streaks and blotches on glumes and leaves.
 
 

Cephalosporium gramineum is usually found in low spots or drainage ways in fields of winter wheat. It is rarely seed-borne in wheat. To date no chemical has been found, either a seed treatment or foliar spray, that controls Cephalosporium stripe. When first studied, Cephalosporium stripe was found primarily around the periphery of the wheat region at higher elevations. It is now more widespread. Early seeding increases the disease. Infested straw on the soil surface favors disease more than buried straw, so minimum tillage tends to increase inoculum levels.
 
 

Common bunt is caused by two closely related fungi, Tilletia caries and T. foetida. Symptoms of common bunt usually are not apparent until heading time. On emergence from the boot, smutted wheat heads are slender and maintain their green color longer. The glumes of some or all of the spikelets are spread apart because they contain smutted kernels, or smut balls, in place of normal kernels. These smut balls resemble normal kernels but are shorter and thicker and a dull gray-brown. Each smut ball contains a mass of sooty, black powder, the individual particles of which are the spores, or "seeds" of the fungus. Seed contaminated with smut has a distinctive fishy odor. When the wheat is harvested, the mature smut balls break, releasing the spores that contaminate soil and healthy seed. Soil-borne spores of common bunt remain infective in areas where the soil remains dry from time of threshing until after seeding. Following seeding, as the young wheat sprout grows from the seed to the surface of the soil, spores on the seed or in the soil germinate in response to moisture and form slender infection threads (mycelium) that enter the seedling. As the plant grows the smut fungus grows inside it, finally replacing the kernel with fungus spores.
 
 

Tillers infected with Tilletia controversa are severely stunted, anywhere from half to a quarter normal height. Small smut balls are formed that are very black and have a "fishy" odor especially when moist.
 
 

Claviceps purpurea is a fungus that attacks wheat. The hard black sclerotia of the fungus germinate stroma, which form ascospores carried by wind or insects to the flowering cereal. A conidial stage, or honeydew, forms on the infected head; insects can transmit it to uninfected flowers. Sclerotia formed on the heads drop to the ground or are mixed with seed for the next year. Infections frequently spread from wild grasses into cultivated cereals. If livestock eat grain containing the sclerotia, severe losses can occur. The most conspicuous symptom is hard, pointed, black to deep purple sclerotia that replace one or more kernels within the head. Sclerotia are several times longer than the kernels and are easily observed on the head or mixed with grain.
 
 

Ustilago tritici destroys the grain and all glume structures of the spike leaving only the central rachis which head early. Infected plants, produce smut spores that are wind-borne to healthy plants at flowering time. Spores germinate and germ tubes penetrate the young wheat ovaries where the fungus remain dormant until those seeds germinate. Use of seed treatment fungicides and disease-free seed will prevent this disease.
 
 

Powdery mildew affects small grains when humidity is high. The white web-like covering on the top and bottom of leaves identifies powdery mildew. It can occur under wet or dry conditions and does not require a film of water on the leaf surface for infection to take place. Spores are produced continuously day and night throughout the summer. Fungi overwinter as mycelium on buds, twigs and fallen debris. They also produce a sexual structure, a cleistothecium, which produces ascospores in the spring. Management of powdery mildew is primarily through use of resistant cultivars. Cultural practices that increase airflow and enhance leaf drying are useful management tools. Protectant and systemic fungicides can be used when necessary.

Scab is caused by several Fusarium spp., fungi that live in soil and on old stubble and straw. They may also cause disease of the root and crown of wheat. The pathogens have simple nutritional requirements and are omnipresent as saprophytes. Lack of moisture during the flowering period usually is the limiting factor for parasitism. Infected kernels may contain a mycotoxin that can induce muscle spasms and vomiting in people and certain other nonruminant animals. On emerged immature heads, one or more spikelets or the entire head appears prematurely bleached. Salmon-pink sporulation on raches or glumes is diagnostic. Bleached spikelets usually are sterile or contain only partially filled seed.
 
 

The fungi Septoria tritici (leaf blotch) and S. nodorum (glume blotch) survives between crops on infected wheat stubble, volunteer wheat, and secondary weedy hosts. S. nodorum may be seedborne, but the importance of this in the disease cycle is unknown. The fungi spread by wind and rain. Leaf blotch appears first on lower leaves as light green or yellow spots between leaf veins. Spots spread rapidly to form brown, irregular blotches that tend to follow the leaf veins. Tiny dark dots (pycnidia), the fungal spore-producing chambers, form later in the brown lesions. Glume blotch has leaf symptoms similar to leaf blotch. Lesions are lighter brown and often lens-shaped with a darker brown center. Pycnidia of this fungus are difficult to detect without magnification. Lesions are dark brown and have a raised, crusty appearance. Seed from infected heads is shrunken and wrinkled. Although both diseases can occur on the heads, glume blotch is more severe than leaf blotch.
 
 

Symptoms of soil-borne mosaic appear early in the spring, usually when weather is cool and damp, but are rarely seen in fall or winter. Fields observed from a distance have irregular patches of light green or yellow plants. Symptoms on plant leaves range from mild green to yellow mottling and striping, giving the mosaic appearance. Stunting varies from moderate to severe. Symptom expression favors temperatures below 68 F. Symptoms gradually disappear before harvest time if normal temperature persists. A soil-borne fungus, Polymyxa graminis, which is a parasite of roots of many grass plants, is the vector of this disease. Virus particles are either inside spores of the fungus or are attached to the spores. The fungus invades the roots in the fall, when soils are cool and wet, carrying the virus particles with it. There is no practical way to rid the soil of the soil borne mosaic virus. Rotation out of wheat to other crops will reduce losses.
 
 

On wheat, yellow-red or black spots or stripes (pustules or spores) are observed to erupt through plant tissue. Generally high levels of control are obtained through use of resistant cultivars. They are characterized by orange to red pustules that occur on leaves, stems. Many but not all rust pathogens require alternate hosts. One or both of these may be of economic importance. Rusts overwinter in debris, volunteers and alternate hosts or are blown up from the south each year.

Pyrenophora trichostom can occur on top and bottom leaf surfaces. Initial symptoms will be tan-brown flecks and the spots will enlarge into lens-shaped lesions. The fungus grows as a saprophyte on crop residue. Because of this, it has been observed to be more severe in no-till wheat. Cultural practices such as deep burial of straw and rotation will help reduce tan spot. Fungicides may be economical if the crop has a potential yield of 40 bushels or more per acre.
 
 

Fungicide Matrix:
 

	propiconazole	triadimefon
Leaf Blotch	X
Rhizoctonia Root Rot		X
Rust	X
Septoria Leaf Blotch	X
Spot Blotch	X

Data from pesticide use survey, 1997
 
 

Management:

Fungicides:

• captan (Captan 30DD; Captan 400; Captan 75)
• carboxin (Vitavax 34; Vitavax 200)
• chloroneb (Chloroneb)
• difenconzole (Dividend 31FS; Dividend 15FS)
• mancozeb (Dithane DF; Dithane F45; Penncozeb 75 DF; Penncozeb 80W; Manzate 200)
• PCNB (Terraclor 75)
• propiconazole (Tilt 3.6E)
• RTU-carboxin-thiram (RTU-Vitavax-Thiram) RTU-PCNB (RTU-PCNB)
• thiram (Thiram 42S; Arasan 70S)
• triademefon (Bayleton 50)
• triadimenol (Baytan 30 FL)

Secale cereale is also called common or volunteer rye. The first blade is tall, narrow, and vertical. Blades are covered with short hair and have prominent veins above and a midrib below. Sheaths are covered with short hairs. The spikes are 4 - 6" long, slender, and long-bearded. Annual rye can be found throughout eastern Wyoming in wheat fields. Volunteer rye typically costs the Wyoming farmer 8 - 10 bushels of wheat yield per acre.
 
 

Cirsium arvense is a member of the Aster or Sunflower family. Canada thistle was introduced from Europe. It is a creeping perennial which reproduces by seeds and fleshy, horizontal roots. The erect stem is hollow, smooth and slightly hairy, 1 - 5' tall, simple, and branched at the top. The leaves are set close on the stem, slightly clasping, and dark green. Leaf shape varies widely from oblong to lance-shaped. Sharp spines are numerous on the outer edges of the leaves and on the branches and main stem of the plant. The flowers are small and compact, about 0.75" or less in diameter, and light pink to rose-purple in color, occasionally white. The seeds are oblong, flattened, dark brown, and approximately 0.125" long. Canada thistle emerges in April or May in most parts of Wyoming. It is one of the most widespread and economically damaging noxious weeds in Wyoming. Because of its seeding habits, vigorous growth, and extensive underground root system, control or eradication is difficult. It is distributed across Wyoming from 4,000 - 9,500'.
 
 

Helianthus annuus is a native weed. It is an annual, 1 - 10' tall. Stems are erect, simple to branched and rough. Leaves are alternate, simple, rough, and hairy. The flowers are yellow to orange-yellow ray petals with brown disk. The flowering season is from July to September. Seeds are the only source of reproduction.
 
 

Bromus tectorum, a member of the Grass family, is an annual or winter annual introduced from Europe. It usually germinates in the fall, lies dormant, and produces seed early in the spring. It has smooth, slender, erect stems. The plant grows 6" - 2' high from a much-branched base. The sheathes and leaves are covered with fine, soft hair. The leaves are 0.125 - 0.25" wide and flat. The head is branched and somewhat drooping. Seeds are long and flat with an awn about as long as the seed. It matures and sets seed in early spring, before most other grass species or crops. Downy brome is a strong invader and creates a serious fire hazard when the mature plant dries. Mature plants turn purple or brown. It is widely distributed in Wyoming from 4,000 - 9,000' and is a serious small grain problem.
 
 

Convolvulus arvensis is a member of the Morning Glory family. This creeping perennial was introduced from Europe. It reproduces by seeds and horizontal roots. The stems are smooth, slender, slightly angled, 1 - 4' long, and spread thickly over the ground or wind around erect plants or other objects. The leaves are alternate, 1 - 2" long, with great variation in shape. They are somewhat arrow-shaped with spreading, pointed, or blunt lobes at the base. The flowers are bell or trumpet-shaped, white, pink, or variegated, and about 0.75 - 1" broad. Field bindweed is a problem throughout Wyoming. It is one of the most competitive perennial weeds. A two or three-year food supply is stored in the extensive underground root system. This makes it hard to kill by cultivation because roots will live as long as their food reserve lasts. Seeds can also stay viable in the soil for up to 40 years. It is widespread in Wyoming from 4,000 - 8,000'.
 
 

Descurainlia sophin, a member of the Mustard family, is very similar and often confused with tansy mustard, Descurainia pinnata. It is an introduced annual or winter annual which reproduces by seeds. The stem is erect, branched, and 4 - 30" high. The leaves are alternate, 2 - 4" long, dissected to give a lacy appearance. The stem and leaves are covered with fine hairs. The flowers are small, pale yellow, and occur in small clusters at the tips of elongated racemes. The seed pods are 0.25 - 0.75" long and on a stalk. Tansy mustard seed pods are shorter and fatter. It is scattered across Wyoming up to 8,000'.
 
 

Aegilops cylindrica is native to southern Europe and western Asia. It is closely related to wheat and both species can interbreed. It is difficult to distinguish from wheat until spikes appear. It spreads exclusively by seed. Jointed goatgrass is a winter annual, but about 5% of a population may be spring annuals. Leaves grow up to a 0.5" wide, and have evenly spaced fine hairs along the leaf edges and down the sheath openings. The ligule is short and membranous; auricles are short and hairy. Stems can grow up to 4' tall and are tipped with slender, cylindrical spikes that appear to be a series of joints stacked on top of each other. Reddish to straw-colored spikes emerge in May and June, and upper most joints are tipped by straight awns. Up to three seeds are enclosed in each joint.
 
 

Kochia scoparia, a member of the Goosefoot family, was introduced from Europe and is an annual, reproducing by seed. The stems are erect, round, slender, pale green, branched, and 1 - 6' high. Leaves are narrow, bright green, hairy, numerous and are attached directly to the stem. The upper leaves are narrow. The flowers are inconspicuous in the axils of upper leaves. Seeds are about 0.0625" long, wedge shaped, dull brown, and slightly ribbed. Kochia can be found throughout the state up to 8,500'. In autumn the plants may become red and later turn brown, breaking away from the root, and tumbling over the ground scattering large amounts of seed.
 
 

Thlaspi arvense is also called fanweed because of its flat, broadly winged seed capsule. It is a white flowered mustard.
 
 

Descurania pinnata is a native annual which reproduces by seeds. The plant is covered with fine hairs. The stem is erect, branched and 4 - 30" high. The leaves are alternate, 2 - 4" long, pinnatified to give a lacy appearance. The flowers are small, pale yellow, and occur in small clusters at the tips of elongating racemes. It is scattered over Wyoming up to 8,000'. Tansy mustard spreads by seed from early to late summer.
 
 

Chorispora tenella is a winter annual weed, with seed germinating in late summer and fall. The plant overwinters as a rosette. The flower stalk usually elongates in March. With mild February weather the flower stalk may elongate in early March. Cold weather in February results in late March elongation. The flowers are bluish-purple to purple and appear in early April. Viable seed can be produced approximately 10 days after bloom. Blue mustard is a problem in winter annual crops, such as winter wheat.
 
 

Setaria viridis is generally shorter in height with roughened leaf sheaths, without hairs, and has much smaller seeds than other foxtails. These plants are native to Eurasia, but common throughout most of North America. These plants are responsible for reductions in yields, increased cleaning costs, and expensive control measures. Flowering and seed production occurs July to September.
 
 

Portulacca oleracea is a fleshy, prostate annual with smooth reddish or flesh colored stems. Branches radiating from a central rooting point reach lengths in excess of 12" and form dense vegetative mats. Smooth, shiny, succulent leaves are somewhat teardrop-shaped, wider at the tip than at the base. Five petalled yellowed flowers are borne singly in leaf axils, and open only in sunshine. It produces numerous seeds. Production of seed throughout the growing season and the ability to root again after cultivation make this plant especially difficult to control.
 
 

Amaranthus retroflexus is a member of the Amaranth family. It is a non-native plant introduced from Europe or tropical America and is an annual reproducing by seed. The stem is light green, erect, stout, tough, rough-hairy, branched and 1 - 6' tall with a long, somewhat fleshy, red taproot. The leaves are alternate with the lower ones ovate, about 3 - 6" long, pointed at the tip, dull green, rough-hairy, with prominent ribs and veins. The upper leaves are smaller, narrower, and more lance-shaped. Flowers are small, green, and densely crowded in large, bristly, simple, or branched, terminal or axillary clusters. Redroot pigweed grows in Wyoming up to 8,500'.
 
 

Salsola iberica is a member of the Goosefoot family. It was introduced from Russia and is an annual which reproduces by seed. It is a round, bushy, much-branched plant growing 1 - 3.5' high. The branches are slender, succulent when young, and woody when mature. The leaves are alternate with the first ones being dark green, soft, slender, and 1 - 2.5" long. These drop off and later leaves are short, stiff, spiny, and not over 0.5" long, with two sharp-pointed bracts at the base. The flowers are small, inconspicuous, green-white or pink, and are usually solitary in the leaf axils. Seeds are about 0.0625" in diameter and conical. At maturity, the plant breaks off at the base and because of its round shape becomes an excellent tumbleweed, scattering seeds for long distances. It is widespread over Wyoming up to 8,500'.
 
 

Polygonum convolvulus is an annual weed with arrowhead shaped leaves. It has trailing stems, often mistaken for field bindweed, with leaves that are more pointed. Stems can be 8 - 40" long. Clusters of inconspicuous, green flowers form in leaf axils or at the end of stems. Cotyledons are long and broad with a granular bloom and rounded tips. First true leaves are arrowhead-shaped with a rough stalk that forms a tight sheath around the stem at the base.
 
 

Avena fatua is an annual weed, 1 - 4' tall with erect hollow stems. Leaf blades are 0.125 - 0.625" wide, sheaths open, with membranous ligules. The seeding leaves twist counterclockwise. The inflorescence is an open panicle, 4 - 18" long, drooping, spikelets contain 2 - 3 florets which disarticulate above the glumes. Seeds are yellow to black, narrowly oval, 0.25 - 0.5" long. This species is distinguished from domestic oats by the twisted awn which bends at right angles and a horseshoe-shaped scar at its seed base.
 
 

Herbicide Matrices:
 

triasulfon

tribenuron-methyl

tribenuron-methyl + trifensulfur-methyl

metsulfuron-methyl

paraquat

picloram

glyphosate

glyphosate + 2,4-D

MCPA

bromoxynil

clopyralid

clopyralid + 2,4-D

dicamba

dicamba + glyphosate

dicamba + DGA

Bindweed

X

X

X

X

X

X

X

X

X

Blue Mustard

X

X

X

X

X

X

X

X

X

Canada Thistle

X

X

X

X

X

X

X

X

Diffuse Knapweed

X

Downy Brome

X

X

Foxtails

X

X

X

Johnsongrass

X

Kochia

X

X

X

X

X

X

X

X

X

X

X

X

X

X

Lambsquarters

X

X

X

X

X

X

X

X

Musk Thistle

X

X

Nightshade

X

X

Quackgrass

X

Pennycress

X

X

X

X

Pigweed

X

X

X

X

X

X

X

X

X

X

Russian Thistle

X

X

X

X

X

X

X

X

X

Wild Buckwheat

X

X

X

X

Sandbur

X

Sunflower

X

X

X

X

X

X

Tansy Mustard

X

X

X

X

X

X

X

X

Velvetleaf

X

X

Toad flax weed

X

Yellow Mustard

X

X

All vegetation and foliage

X

X

Purple top

X

X

X

Data from pesticide use survey, 1997
 
 
 

	chlorsulfuron + metsufuron	tribenuron,methsulfuron	trifluralin	atrazine	2,4-D	prosulfuron	chlorsulfuron\metsufuron
Bindweed					X
Blue Mustard	X	X			X		X
Canada Thistle					X	X
Downy Brome			X	X
Foxtails				X
Kochia				X	X	X
Lambsquarters					X
Musk Thistle					X
Nightshade					X
Pennycress					X
Pigweed				X	X
Russian Thistle	X			X	X		X
Sago pond weed					X
Tansy Mustard	X				X	X	X

Data from pesticide use survey, 1997
 
 

Management:

Herbicides (crop use):

• metsulfuron (Ally)
• 2,4-D (Hi-Dep; Savage; Salvo)
• bromoxynil (Buctril; Broclean)
• bromoxynil + MCPA (Bronate)
• cyanazine (Bladex 4L)
• imazamethabenz (Assert; Assert SG)
• thifensulfron + tribenuron (Harmony Extra)
• trisulfuron (Amber)

• dicamba (Clarity)
• triallate (Far-Go)
• 2,4-D (Weedar 64)
• 2,4-D + 2,4-DB (Weedone LVE)
• 2,4-D + glyphosate (Landmaster BW)
• chlorsulfuron + metsulfuron (Finesse)
• clomazone + atrazine (Command + Atrazine)
• clopyralid + 2,4-D (Curtail)
• dicamba + glyphosate (Fallowmaster)
• glyphosate (Roundup Ultra; Roundup Ultra RT)
• metribuzin (Sencor; Sencor 75 DF)
• paraquat (Cyclone; Gramoxone Extra)
• picloram + 2,4-D (Tordon 22K + 2,4-D)