Wheat

Triticum spp.

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Description

Wheat, is the name given to several plants in the genus Triticum including Triticum aestivum, Triticum compactum, Triticum spelta and Triticum durum, which are annual or biennial grasses grown primarily for their grain. Wheat species possess an erect smooth stem with linear leaves that grow in two rows on either side of the stem with larger 'flag' leaves at the top of the stem. The stem terminates in a spike that is made up on individual spikelets, each possessing 3–9 florets. The wheat fruit develops within the spikelets, maturing to a seed (kernel). Wheat can reach 1.2 m (4 ft) in height and like other cereals, has been developed into different varieties that are adapted to planting at different times of the year. Spring wheat is planted for a late summer harvest, whereas Winter wheat is planted for harvesting in early to mid summer. Overwintering varieties are more commonly grown in regions with mild winters. Wheat may be referred to by variety and these include durum or macaroni wheat (Triticum durum), club wheat (Triticum compactum), spelt wheat (Triticum spelta) and bread wheat (Triticum aestivum). Wheat originated in the Fertile Crescent of the Middle East.

Uses

Wheat is one of the most important food plants in the world. It is used primarily to produce flour for bread. It is used widely in the production of many other baked goods. Wheat grain is also used in the manufacture of alcoholic beverages and alcohol. Wheat straw is used as an animal feed and in the manufacture of carpets, baskets, packing, bedding, and paper.

Propagation


Wheat varieties
One of the first things to consider before planting is which type of wheat you want to grow. There are several different varieties to choose from depending on the time of year and how you want to utilize your harvest. Wheat is broadly categorized into Winter wheat and Spring wheat. Winter wheat is high yielding and is planted in the Fall and harvested in the Spring or Summer of the following year (depending on location). Spring wheat is not as high yielding but tolerated drier conditions. It is planted in the Spring and harvested in the Fall. Both Spring and Winter wheat is then further categorized as soft wheat, hard wheat, spelt or durum.

General requirements
Wheat can be grown in a wide variety of climates but grows best in cool regions where the temperature is between 10 and 24°C (50–75°F). Wheat will not grow at temperatures above 35°C (95°F). Wheat will grow optimally in a deep, fertile, well draining and well aerated soil at a pH between 5.5 and 7.5.

Planting
Winter wheat varieties should be planted in the Fall approximately 6 to 8 weeks before the first frost date. Spring wheat varieties should be planted as soon as the soil can be worked in the Spring. Commercially grown wheat is usually mechanically drilled using a machine that creates a furrow and drops the seed in before covering it back up. Wheat seeds can be sown by hand broadcasting in smaller areas, or using a hand-cranked seeder. Seeds are usually sown to at depths ranging from 2 to 12 cm (0.8–4.7 in) depending on soil conditions (seed must be sown deeper in drier soil). Once the seeds have been scattered, the soil should be raked lightly to set the seeds at the desired depth.

Harvesting
Wheat is ready to harvest when the stalks and heads have turned from green to yellow and the seed heads are drooping towards the ground. Check the seeds for ripeness before harvest. The should be firm and crunchy and not doughy in texture. Commercially produced wheat is usually harvested using a combine. Smaller plots can be harvested by hand using a scythe or sickle. Small plots can be harvested by snipping off the heads with a pair of scissors.

Diseases

Aphids (Bird cherry-oat aphid, Russian wheat aphid, Corn leaf aphid, etc.) Insect Rhopalosuphum padi
Diuraphis noxia
Sitobion avenae

Symptoms

Yellow or white streaked leaves; flag leaves may be curled up; plants may be stunted and tillers may lie parallel to the ground; plants may turn a purple color in cold weather; insects are small and soft-bodied and may be yellow, green, black or pink in color depending on species; insects secrete a sugary substance called "honeydew" which promotes the growth of sooty mold on the plants

Comments

Fields should be checked for aphid populations periodically after emergence

Management

Sturdy plants can be sprayed with a strong jet of water to knock aphids from leaves; insecticides are generally only required to treat aphids if the infestation is very high - plants generally tolerate low and medium level infestation; insecticidal soaps or oils such as neem or canola oil are usually the best method of control; always check the labels of the products for specific usage guidelines prior to use; in commercial plantations aphid numbers are usually kept in check by predators and natural enemies; beneficial insect populations should be assessed before chemical control is considered; if no beneficial insect populations are present and aphids are damaging then apply appropriate insecticides

Armyworms (Armyworm, Western striped armyworm) Insect Mythimna unipunctata
Spodoptera praefica

Symptoms

Entire leaves consumed; notches eaten in leaves; egg clusters of 50-150 eggs may be present on the leaves; egg clusters are covered in a whitish scale which gives the cluster a cottony or fuzzy appearance; young larvae are pale green to yellow in color while older larvae are generally darker green with a dark and light line running along the side of their body and a pink or yellow underside

Comments

Insect can go through 3–5 generations a year

Management

Organic methods of controlling armyworms include biological control by natural enemies which parasitize the larvae and the application of Bacillus thuringiensis; there are chemicals available for commercial control but many that are available for the home garden do not provide adequate control of the larvae

Bacterial leaf streak and black chaff Bacterium Xanthomonas campestris

Symptoms

Sudden appearance of water-soaked, light brown, elongated lesions on upper leaves; lesions quickly dry out and turn into necrotic streaks on the leaves; black stripes occur on glumes and purple black lesions appear on rachis and peduncle if infection is in the head

Comments

Disease spread through infected seed and splashing water

Management

Avoid planting seed from infected fields; avoid overhead irrigation; plant less susceptible cultivars

Barley yellow dwarf Virus Barley yellow dwarf virus (BYDV)

Symptoms

Yellowing leaves, particularly the flag leaves; stunted plants due to shortened internodes; leaves may be red, purpple, orange, green or brown; leaves may be distorted

Comments

Transmitted by a few species of aphid; spread of disease is completely dependent on the movement of aphid vectors

Management

Control of aphid population can provide some control of disease but is dependent on knowing which aphids are active in the field; planting to avoid periods of peak aphid activity can provide a measure of control

Basal glume rot Bacterium Pseudomonas syringae

Symptoms

Dull brown to black discoloration of glumes which is more pronounced on the inner side; seeds may be shriveled; if infection is severe, entire glume may be discolored; small water-soaked lesions may form on leaves

Comments

Disease spreads primarily through infected seed

Management

Avoid planting seed from plants grown in fields where the disease is known to be present

Common bunt (Stinking smut) Fungus Tilletia tritici

Symptoms

Slender heads which take longer to turn color than healthy heads; glumes spread apart to reveal spori or "bunt balls" (balls containing fungal spores) which are a similar size to normal kernel but are gray-brown in color; bunt balls break open on harvest and give off a fishy odor

Comments

Disease is most commonly introduced through infected seed although spores are spread by wind

Management

Disease can be controlled by planting resistant wheat varieties, planting disease-free seed and using a seed treatment prior to planting; disease may also be avoided by planting wheat early in the Fall and by shallow seeding

Ergot disease Fungal Claviceps purpurea

Symptoms

Main symptoms of ergot is the grains in the head are replaced by dark purple to black sclerotia. This ergot bodies were made up of vegetative strands of fungus. The sclerotic interior is white or tennis white in color. The size of grain kernel and ergot are similar in size.
The initial symptom before sclerotia bodies is honey dew symptom occur during flowering stage. The fungus produce yellowish, sugary excretions and can see as droplets on flower parts.

Comments

Ergot is toxic to animals including birds.

Management

Follow crop rotation with non host crops for one year. Deep summer ploughing kills sclerotia bodies present in soil. Keep the field free from grasses and other weeds. Use disease free seeds.

Eyespot Fungus Oculimacula spp.

Symptoms

Elliptical lesions that first appear on leaf sheath and gradually spread to stem; lesions are yellow-brown to tan in color and occur length-ways down the stem; lesions can occur individually or groups of lesions can coalesce to form large areas of discoloration; lesions may eventually girdle the stem; a gray, thread-like fungal growth may occur on the stem beneath the lesion; mature stems may have a charred appearance; infected tillers mature early and develop white heads and poorly filled seed; tillers may fall if stems are severely infected

Comments

Primary route of infection is by splashing water; emergence of disease favored by high soil moisture content and a dense crop canopy

Management

Rotation of crop away from cereals for a period of 2-3 years will reduce levels of inoculum in the field; fungicides are commonly applied close to stem elongation to control the disease; plant resistant wheat varieties if available in your area

Fusarium head blight (Scab) Fungus Fusarium spp.

Symptoms

One or more spikelets on newly emerged head bleached; pink or orange fungal masses may be visible at the base of infected spikelet; infected spikelets do not produce seed or produce shriveled and/or discolored seed; severe infections can cause the kernels to have a chalky appearance and are frequently lost during harvest

Comments

Fungus survives between seasons on host plant debris - other host include corn and barley; fungus can survive on host debris for several years; warm, moist conditions promote the spread of the disease when present

Management

Control of the disease can be difficult; durum wheat appears to be more susceptible to the disease than common wheat; crop rotation to a non-host is recommended for at least one year; applications of appropriate fungicides if available can help to control the disease in conjunction with the other measures detailed here

Phythium root rot Fungal Phythium sp.

Symptoms

The infected plants become chlorotic and/ stunted. Often the symptom is confused with nitrogen deficiency. And the plants may produce shriveled grain. Even a mild infection reduce tillers, plant population and maturity. Since symptom appear through out the field make if difficult to diagnose the disease.

Comments

Fungus live for years in soil and on old root debris.

Management

Use good quality seeds. Provide supplemental phosphorous. Sowing when soil temperature is about 50 F increase germination and establishment. Seed treatment with suitable fungicides.

Powdery mildew Fungus Erysiphe graminis

Symptoms

Patches of cottony, white-gray growth on upper surface of leaves which turn gray-brown; chlorotic patches develop on leaves opposite fungal growth; fungal fruiting bodies usually become visible as black dots on the mildew

Comments

Disease emergence favors heavy nitrogen fertilization; high humidity and cool temperatures

Management

Planting resistant wheat varieties is one of the best ways to protect plants from powdery mildew; other control strategies include: application of appropriate foliar fungicides, if available; removal of crop debris from field after harvest to reduce the level of overwintering fungus; removal of volunteer wheat plants which can act as a reservoir for the disease

Rusts Fungus Stem rust (Puccinia graminis)
Leaf rust (P. triticina)
Stripe rust (P. striiformis)

Symptoms

Chlorotic flecks or brown necrotic spots on leaves or stems; yellow streaks or patches on foliage; brown necrotic streaks on foliage; raised orange pustules may be present on lesions

Comments

Disease emergence favors cool, wet conditions

Management

The most effective method of controlling rusts is to plant resistant varieties of wheat; other methods of control include: destroying alternate hosts; applications of appropriate protective fungicides; growing wheat varieties that mature early

Stinkbugs Insect Euschistus spp.

Symptoms

Damage to head during milk or soft dough stage; stink bugs often carry pathogens in their mouthparts which can cause secondary infections; adult insect is shield-shaped and brown or green in color; may have pink, red or yellow markings; eggs are drum shaped and laid in clusters on the leaves; larvae resemble the adults but are smaller

Comments

Adult insects overwinter under leaves, on legumes, blackberries or on certain weeds such as mustard or Russian thistle

Management

Remove weeds around crop which may act as overwintering sites for stink bugs and practice good weed management throughout the year; organically accepted control methods include the use of insecticidal soaps, kaolin clay and preservation of natural enemies

Tan spot Fungus Pyrenophora tritici-repentis

Symptoms

Oval or diamond shaped necrotic lesions with brown centers and yellow halos on leaves

Comments

Disease infection requires a wet period of between 6 and 48 days

Management

Disease can be significantly reduced by rotating crops with non-hosts and tilling crop debris into soil after harvest

Wireworms Insect Aeolus spp.
Anchastus spp.
Melanotus spp.
Limonius spp

Symptoms

Death of seedlings; reduced stand; girdled stems and white heads; wireworm larvae can be found in soil when dug round the stem; larvae are yellow-brown, thin worms with shiny skin

Comments

Larval stage can last between 1 and 5 years depending on species

Management

Chemical control impossible in a standing crop, must be applied at preplanting or as a seed treatment; if wireworms are known to be present in soil fallow field during summer and till frequently to reduce numbers; rotate to non-host crop where possible; avoid planting susceptible crops after a wireworm infestation on cereals without either fallowing of applying appropriate pesticide

References

Bockus, W., W., Bowden, R. L., Hunger, R. M., Morrill, W. L., Murray, T. D. & Smiley, R. W. (eds.) (2010). Compendium of wheat diseases. American Phytopathological Society Press. Available at: http://www.apsnet.org/apsstore/shopap.... Available for purchase from APS Press.

CABI Crop Protection Compendium. (2008). Triticum aestivum (wheat) datasheet. Available at: http://www.cabi.org/cpc/datasheet/55204. [Accessed 21 April 15]. Paid subscription required.

Duke, J. A. (1983). Triticum aestivum L.. Handbook of Energy crops, unpublished. Available at: http://www.hort.purdue.edu/newcrop/du.... [Accessed 21 April 15]. Free to access.