Agricultural workers know firsthand how difficult it is to protect cereal crops from various diseases. From rust alone, the annual shortage of wheat is 5%, and from smut damage - over 1%. Significantly reduce yield and pests. How to recognize the signs of wheat damage, and what can be done to protect the cereal beds, read on.
Fungal diseases
With increased moisture, a pathogenic microflora develops on the host plant, which leads to the development of fungal diseases in it. The most common of them will be considered further.
Rust
One of the varieties of rust, which is provoked by various fungi of the Basidiomycetes department, can affect wheat:
- Sheet (brown). Its causative agent is the fungus Puccinia recondita. The primary infection is often introduced by airborne spores and slowly develops without causing serious consequences. In favorable conditions - with strong moisture and a temperature of about 20 ° C - the infection progresses very quickly. It has the following characteristics:
- manifests itself in the form of roundish or oval pustules on the surface of the leaf plate (less often they can be seen on the internodes of the stem);
- pustules do not merge with each other and contain orange or orange-brown uredospores that are generated every 10-14 days;
- at the stage of wax ripeness of grains in adverse weather conditions, a lot of black teliospores form on the tops.
- Stem (black, linear). Called by Puccinia graminis. Their intermediate hosts are barberries and mahonia. The conditions for the spread of infection are the same as in the case of leaf rust.
This disease is manifested by dark brown pustules with a ureospore mass content. They are formed not only on the stems, but also on the spikelets and on both sides of the leaves. With severe infection, pustules combine with each other and tear the epidermis of the plant.
The infection is indicated by small tears and roughness on the surface of the affected tissue.
- Yellow (striped). It is provoked by Puccinia striiformis fungi. In 2010, it was discovered in the USA that barberries were their intermediate owners. Pathology with pustules with lemon-yellow or orange-yellow uredospores is manifested. In large numbers, they appear on the leaves in the form of strokes and stripes. Less commonly, pustules are visible on the tops of the tops, the internodes of the stems, and the scales of the spikelets. If the temperature exceeds 25 ° C, then the formation of uredospores ceases and the development of black teliospores often begins.
With the early development of rust of any type, crop losses can be significant due to the reduction in the number of grains in the ear and the deterioration of their qualities.
Smut
The second group of diseases that is provoked by fungi of the Bazidiomycetes department. Such smut varieties can affect wheat:
- Common and Dwarf (smelly). The first bunt is caused by the fungi Tilletia tritici Wint and T. laevis Kühn, and the second - T. controversa Kühn. Both types of pathology are widespread and actively develop in temperate climates, although pygmy smut can also be found in areas with long snow cover.
Spores germinate in the soil and on the surface of the seed, infecting wheat seedlings. The defeat often occurs at low temperatures in the phase of seed germination.
Smut develops systemically and manifests itself after wheat heading. The types of pathology caused by these fungi have similar symptoms and are more pronounced in the phase of milk-wax ripeness of grains:
- the structure of the ears remains the same, but instead of grains, smut sacs (coma) with a black mass formed by mushroom teliospores appear;
- with ordinary or wet pathology, lumps resemble grains in shape, and with dwarf paths they are spherical formations;
- when smut smuts are destroyed, an unpleasant herring smell is emitted;
- the affected ears become bluish-green or lead-gray in color, and their scales are slightly apart;
- with common smut, plants are slightly inferior in height to healthy specimens, and with dwarf smut, they noticeably lag behind in growth and shrubs.
- Indian (Carnival). Its causative agent is the Tilletia indica Mitra mushrooms. It is characteristic of the Indian subcontinent, but is now also found in Mexico and the United States. Teliospores that form sporidia sprout on the surface of the soil. Subsequently, they are transferred by the winds to the surface of the flower and give a sprout tube, which falls under the spikelet scales of the forming grain. Further, the mycelium develops inside the cell - between the epidermis and the seminal membrane.
The disease is difficult to determine before the harvest, as it affects individual grains in the ear. After threshing wheat, diseased grains can be detected by visual inspection according to the following signs:
- a large number of black teliospores that affect the epidermis of wheat;
- unpleasant herring odor, which is "heard" when crushing sick seeds.
- Dusty. During the period of wheat germination, the teliospores of Ustilago tritici Rostr can fall on the stigmas of a flower. They germinate and infect the seed germ. The pest mycelium begins to develop in parallel with the growing part of the plant and penetrates all its organs, forming many dusty spores of black color. As a result, all parts of the inflorescence, except the spike stem, turn into a mass of smut spores. Pathology is found in all areas where it is customary to cultivate this grain crop.
- Stem. Smut, caused by the fungi Urocystis agropyri, is especially dangerous for common wheat. They are stored in soil and on seeds, and then they infect sprouted grains or very young seedlings with spores. The development of the disease occurs systemically, therefore, during the period of wheat heading under the epidermis of the leaves, narrow stripes of black teliospores can be seen on the vagina and internodes of the stem.
Affected plants do not grow well, do not cleave and noticeably bush. In the worst case, the leaves curl, which resembles the tops of capitate onions. Over time, their epidermis breaks, and teliospores are released outward. The smut is characteristic of the areas of cultivation of winter wheat or spring during autumn sowing.
Among the listed diseases, the most harmful is the smut. Crop losses depend on the number of affected ears and usually do not exceed 1%, but sometimes reach 30%.
Powdery mildew
It is provoked by the fungus Blumeria (Erysiphe) graminis from the Ascomycetes department. Favorable conditions for the development of the disease:
- moderate temperature (+ 15 ... + 22 ° C);
- cloudy weather;
- high humidity (75-100%).
In this regard, powdery mildew is widespread in areas of cereal cultivation, where there is a semi-arid climate and moderate humidity.
Symptoms of the pathology appear gradually as it develops:
- The upper surface of the leaves and their vagina (especially the lower tops), and sometimes the ears, are covered with a coating of white to light gray, which consists of colonies of mycelium and conidia of the fungus.
- With the development of the mycelium acquires a yellowish-gray hue, and its surface layer is easily removed by contact.
- Affected plant tissues undergo necrosis and die over several days.
- At the end of the vegetation period of plants, noticeable black spherical fruit bodies appear on the mycelium.
Powdery mildew can cause significant crop shortages if it affects wheat in the early phase of its development against the backdrop of favorable conditions and a high infectious background.
Leaf spotting
Depending on what fungi the infection provokes, leaf spotting can be of the following types:
- Septoria. The disease can be caused by three types of fungi - Septoria Tritici, Stagonospora nodorum and Stagonospora avenae. It is actively developing in areas of wheat cultivation, where cool temperature (+ 10 ... + 15 ° C) and humid weather prevail. This disease has the following characteristics:
- at first spotting is observed on the lower leaves, but under favorable conditions it actively develops, infecting the upper leaves and ears;
- oval or oval-elongated spots initially appear on the leaves, which gradually expand, and in the center are covered with grayish or straw areas with numerous small black pycnids;
- with a weak lesion, single scattered spots appear on the plant, and with a strong one, formations merging together, which ultimately cause premature death of the leaves, ears and even the whole plant.
In the field, it is almost impossible to accurately determine the type of septoria, so it is necessary to conduct a microscopic examination.
- on the lower leaves appear elongated oval spots of a dark brown color;
- spots gradually increase in size and acquire a dark brown or tan with dark brown rings;
- as the spots expand, they merge and cause leaf death;
- with a strong infection, lesions appear on the leaf sheaths.
- yellow or brown spots appear on the lower leaves, which gradually increase in size and acquire an irregular rounded shape;
- rims of a light brown or yellow hue are formed on the edges of the spots, and their center acquires a dark brown or black hue;
- spots merge with each other, forming large long stripes;
- the infection progresses, spreading to the upper leaves and spikelet scales, which is fraught with the death of the plant.
When the ear is infected during the grain filling period, the fungus remains in the form of conidia on the surface of the seeds or mycelium inside them. It can also spread through air currents, causing secondary infection of the leaves and other organs of the plant. This spotting is manifested as follows:
- small spots of oval or elliptical shape form on the lower leaves;
- spots gradually grow and take on an irregular shape;
- the rims of the spots turn dark brown;
- signs of damage are observed in all parts of the plant.
- in the phase of tubing and the formation of nodes on the bends of the leaves, a grayish-green mottled oval-elliptical shape appears;
- specks gradually grow, whiten and acquire a light gray center;
- splits or tears form on the leaves, which begin from the center of the lesions;
- seedlings fade, root rot and white-stalk develop, and in winter cereals - pink snow mold.
A strong defeat of wheat by leaf spot leads to the death of the tops and a significant reduction in the harvest due to the formation of punctured grains and a decrease in their natural mass.
Fusarium spike
Excited by Fusarium spp. It infects the ears and grains of cereals, as well as the ovary during the flowering period. Favorable conditions for its activity are a wide temperature range from +10 to + 28 ° C. After the initial infection, fusarium spreads along with the growing mycelium of the fungus to the ears.
Pathology is manifested by such signs:
- the flowers darken, especially on the outer surface of the spikelet scales, and become oily;
- in sporodochia conidia are formed, which color the ear in a pink tint;
- the affected grains are penetrated by the white mycelium of the fungus.
With severe infection with Fusarium, crop losses can exceed 50%. If wheat contains 5% of affected grains, then it is unsuitable for eating due to the excessive content of toxins.
Ergot
The ergot fungus is Claviceps purpurea. The primary infection of the plant comes from ascospores, which leave a sweet exudate on the flowers, attracting insects that transfer conidia to healthy flowers of the same ear or to neighboring ears. They activate these processes - rain and high humidity.
Ergot bodies remain on the infected ovaries, which persist and survive in the soil until the next season. In dry weather, they do not lose viability for several years, but sprout at low temperatures.
Ergot is manifested by the following symptoms:
- the selection of affected flowers of a sweet and sticky exudate of a yellowish color, which consists of conidia of the fungus;
- turning the infected ovary into brown or purple sclerotia up to 20 cm long.
The disease does not lead to large crop losses, but significantly reduces the quality of the grains.
Rot
A large group of pathogens of fungal origin can provoke rot in wheat. It comes in many forms:
- Common root rot (cervical, rot of nodal roots). In conditions of excessively dry or waterlogged soil, ordinary rot can cause fungi Cochliobolus sativus, Fusarium spp. and Pythium spp. Pathology is manifested by the following symptoms:
- darkening of the base of the stem, nodal roots and roots (acquire a brown tint);
- lodging of individual plants;
- development of white-headedness;
- the death of seedlings and aging (observed with early infection of a grain crop).
- Ophiobole Root Rot. In temperate regions, this pathology is provoked by the fungus Gaeumannomyces graminis. At low soil temperature (+ 12 ... + 18 ° C), its alkaline reaction or lack of nutrients, it causes rot of the root system and lower stem internodes. This is especially promoted by nitrates. The following signs testify to infection:
- the lower part of the stem and vagina of the leaves acquire a glossy black surface;
- using a magnifier on the lower internodes, under the dead leaf sheaths, you can see the dark mycelium of the fungus;
- in conditions of severe damage, the whiteness and whiteness of wheat develops;
- with damage in the early phase of plant development, bushiness and sterility of the ear decreases.
- Root of the cervix (eye spotting or brittle stems). In regions with a cooler climate, where wheat is often sown before winter, two types of fungi can cause pathology - Oculimacula acuformis and O. yallundae. Their conidia or mycelia are preserved on plant debris and in the soil, and upon contact with coleoptile and the lower part of the young stem, they are infected with its initial infection. The following symptoms indicate it:
- elliptical eye spots with a straw-yellow center and a dark brown or dark green border (often appear under the leaf sheaths on the lower internodes);
- distinct eye spots of coal-black color;
- lodging of the stem with a strong development of pathology (can occur without manifestation of symptoms of root rot).
- Rhizoctonia root rot ("sharp-eyed" spotting). In the soil and on plant debris, the fungus Rhizoctonia cerealis is often parasitic, which provokes this rot in conditions of dry sandy soil, low temperatures and high humidity. In contrast to eye spotting, with this pathology, dark brown spots with a straw-yellow center cover not only the roots, but also the rosettes of the leaves. Affected plants are stunted, and their bushiness is reduced as a result of the death of diseased roots.
Rot infections often develop in autumn and early spring, causing a decrease in the productivity of bushiness, a decrease in the mass and number of grains in the ear.
Bacterial diseases
Unicellular bacilli from 1 to 3 mm long can cause bacterial diseases in wheat. They are distributed in various ways:
- insects
- rain spray;
- air currents.
In humid climates, through mechanical damage, these pathogens, together with life-giving moisture, penetrate the plant tissue, are transported through their vascular system and multiply in intracellular spaces. At the same time, they secrete toxins and various enzymes, which cause tissue necrosis. Although these processes do not cause noticeable crop losses, they worsen the marketability of wheat. Common pathologies will be considered separately.
Striped bacteriosis (chaffiness)
The bacterium Xanthomonas campestris causes blackness on the spikelet scales, and striation on the leaves and their vaginas. As it develops, the disease manifests itself with the following symptoms:
- narrow watery (weeping) spots or stripes;
- droplets of convex, yellow, and sticky exudates (formed during periods of prolonged rain or growth);
- translucent films on the surface of the affected tissue, which remain after the exudate, can collapse and acquire a scaly structure;
- damage to the ear, which becomes sterile (occurs when infected in the early phase of plant development);
- the death of leaves and ears (observed with severe infection).
Basal bacteriosis
The disease is provoked by the bacterium Pseudomonas syringae. It covers all parts of wheat - leaves, stems, spikelets and even grains. This bacteriosis develops gradually:
- Small dark green or watery (weeping) spots form at the base of the spikelet scales.
- Formations spread over the entire surface of the scales and become dark brown, almost black.
- Sick scales become translucent, but later acquire a dark brown or almost black color.
- The rods of ears are exposed to defeat, on which dark spots appear. The same thing happens with the grain.
- In humid weather, whitish-gray bacterial mucus also appears on diseased tissues. Affected stems acquire a dark color, and small watery spots appear on the leaves.
Bacteriosis yellow (mucous)
Pathogens are Rathayibacter tritici and Clavibacter iranicus. Their distribution is often promoted by the nematode A. tritici. The disease is more characteristic of the Asian subcontinent. She is characterized by such a development:
- On the spikelets, yellow exudate forms, which leaves behind bacterial burns.
- Gradually, the exudate dries, acquiring a white tint.
- An ear from the sinuses of the upper leaves often comes out curved and filled with a sticky mass.
- The upper leaves are deformed or curled.
Striped mosaic of wheat
A viral disease transmitted by a curling tick. In addition, the virus can be transmitted through the seeds from which infected plants grow.
Symptoms of striped mosaics depend on the variety of wheat, the strain of the virus, the time of infection, and environmental conditions. They may not appear when sown in autumn or early spring, but always become noticeable when the temperature rises to 10 ° C and above.
Pathology is manifested by the following symptoms:
- the plant is stunted;
- leaves become variegated green;
- yellow stripes appear on the surface of the leaves, which run parallel, but are often interrupted;
- the plants infected in the tillering phase do not produce seeds, and in the bumping phase they form too small seeds;
- severely affected specimens acquire sterile ears or die.
Striped mosaic causes the death of sprouts, but with late infection leads only to a slight death of crops.
Wheat Disease Control Methods
To protect cereal crops from the above diseases, it is necessary to strictly observe preventive measures and take steps to combat them. Here are the effective interventions:
- to cultivate modern highly productive varieties that are more resistant to fungal spores, bacteria and viruses;
- to prevent the spread of pathologies, use elite seeds with varietal purity of at least 99.7%;
- before sowing, subject the seeds to thermal disinfection or dressing with systemic fungicides (Cruiser, Maxim, Celest);
- comply with crop rotation rules, avoiding close distribution of winter and spring wheat crops, as well as other representatives of grain crops, otherwise favorable conditions will be created for the rapid spread of pathogens of dangerous diseases;
- maintain the spatial isolation of the sown areas (place them at a distance of at least 1 km from the commodity crops);
- use only disinfected implements and agricultural machinery;
- comply with the optimal sowing dates established for each zone;
- timely apply organic and mineral fertilizers;
- regularly inspect crops for lesions;
- timely destroy weeds, affected plant debris and seedlings, to prevent the spread of diseases.
Wheat pests and protection against them
The danger to the cereal crop is not only various diseases, but also pests. Their main representatives can be found below.
Wheat thrips
Small insects (1 mm long) brown or black with a tapering segmented belly. They often settle on the lower parts of flag leaves and eat the stem.
Thrips lay eggs inside or on the surface of tissues. They are characterized by a short generation period, so they can give up to 10 generations per year. Larvae are really dangerous, because they first suck out juices from spikelet scales, and then eat the contents of grains, because of which they lose their seed qualities and become feeble.
With a large invasion of pests and larvae of the tissue, the plants become deformed and acquire a silver color. As a result, leaves, stems and young ears are damaged.
In the fight against thrips, systemic insecticides or combined preparations containing substances of contact and systemic action (Enzhio 247 SC) should be used.
Aphids
Aphids are practically translucent soft-bodied sucking insects, which are considered one of the most dangerous pests for wheat, especially two of their species - large cereal (Sitobion avenae F.) and ordinary cereal (Schizaphis graminum Rond).
These insects feed on wheat from the time of emergence to the waxy ripeness of the grains. Their number is gradually growing and reaches a maximum in the grain filling phase. Aphid gives 10-12 generations per season.
The following signs indicate the defeat by this pest:
- ants “run down” to the garden, as the aphid emits “honey dew” attractive to them in the form of drops of sweet liquid;
- the leaves become covered with stripes, prematurely turn yellow and die;
- parts of plants are deformed or curled and covered with necrotic spots;
- white long leaves appear on the leaves, after which they curl;
- the grains become squishy and light.
Aphids can not only cause significant damage to plants, but also become a carrier of viruses, so modern systemic drugs must be used immediately against them.
Gray grain scoop
Adult insects (butterflies) do not harm the plant, but only feed on flowering vegetation, but caterpillars can cause significant damage to it.
Females lay eggs on ears of wheat with clutches of 10-25 pieces. Their embryonic period lasts 1-2 weeks. After this, caterpillars appear that have 8 ages. At each stage, they are dangerous in their own way:
- From the 1st to the 3rd age, spawning caterpillars, singly or in groups, are inside the spike and eat the grain from the inside.
- From 3 to 4 years of age, the caterpillars go outside at night and feed on openly ripened grains. In the afternoon, they hide in the axils of the leaves or in the upper layer of soil.
- From 5 to 8 years of age, the caterpillars feed on crumbled grains, absorbing them whole. They need such food for wintering and withstanding steady colds within a month. They can tolerate a drop in temperature to -10˚C.
Caterpillar harmfulness increases gradually:
Age | The amount of grain eaten |
1 to 4 | less than 50 mg |
5 | 50 mg |
6 | 100 mg |
7 | 300 mg |
8 | 1330 mg |
Over the entire period of development, one caterpillar is able to destroy 2 g of grain, which is equivalent to 2 ears. To prevent such consequences, you need to fight the scoop in phase 3 age, using combined insecticides for processing wheat.
Bed bug bug
The insect is able to infect the plant throughout the entire growing season. Adult bugs and their larvae are harmful to the culture. Females lay 14 eggs in 1-2 weeks of active nutrition. This process lasts from 10 to 20 days. Larvae appear on average on day 9-16 and also begin to feed on the plant.
The pest causes significant harm to wheat:
- In the early stages of development, the plant inflicts injections at the base of the stem, which affects the point of growth and the germ of the ear. At the injection site, partial or full whiteness appears, and the stem itself is deformed. Against this background, the leaves turn yellow prematurely, but the spike does not form. For this reason, productivity decreases from 0.3 to 3 kg / ha.
- In the phase of filling the grains, the ears attack, sucking all the contents from the grains. In the phase of milk ripeness, they shrink and shrink, and starting from the phase of milk-wax ripeness, they become loose and crumble easily. For this reason, the quality of flour from such grains is significantly deteriorating, but moreover, it becomes unsuitable for consumption in the presence of 3-15% of damaged grains in the ear.
In the fight against bedbugs, wheat should be treated with insecticides twice: the first treatment is against overwintered insects, and the second is against larvae. In the case of winter wheat, treatments are best carried out against the wintering bug in the tillering phase.
Sawflies
These are insects that look like small fly-like wasps. Two of their representatives are dangerous for wheat - ordinary bread (Cephus pygmaeus L.) and black (Trachelus tabidus F.).
If the first sawfly is found in any areas of wheat cultivation, the second - mainly in the central regions. In any case, they cause the same grain crops, affecting as follows:
- Females give one generation a year, laying about 50 small white eggs on the upper internodes under an ear.
- Larvae spend the winter season in stubble and pupate in spring.
- Spawning caterpillars suck out all the contents from the stem and gradually descend to its base. After feeding, they file around the circumference of the processes from the inside at ground level. At later stages of plant development, this becomes the cause of the lodging of the stem.
- Larvae close up the passage of the straw with a cork, equip the cocoon and winter in it. Grain yield for this reason is reduced by about 1 kg / ha.
In some years, sawflies can cause significant damage to crops, so it is better to cultivate the most resistant varieties to their attacks. These are wheat species with dense or semi-dense stems.
White grubs
May or June beetles lay eggs in the soil, and the white larvae hatching from them with three pairs of legs on their belly infect wheat.
These pests partially or completely cut through the roots of plants, which leads to the following consequences:
- the formation of sowing bald patches on the crops;
- growth retardation of plants, because of which they may not have to gouge.
Symptoms of the lesion resemble the appearance of root rot, but a detailed examination of the area with dying plants in the soil can reveal white larvae. As they mature, they reach a length of 2-3 cm and almost 1 cm in thickness.
To prevent pest attacks, it is important to subject the site to proper pre-treatment.
Wireworms
In spring, nutcracker beetles lay eggs in the soil, from which larvae with three pairs of legs hatch, called wireworms. In length, they reach 2-3 cm, and their color varies from milky cream to brown.
Wireworms eat grain endosperm, causing withering or death of seedlings in a row or in a small bed. The seedlings of damaged seedlings, on which larvae can be found, are eaten right above the seeds.
So that wireworms do not ruin the wheat crop, the crop cannot be sown on the same site for several seasons in a row or after perennial grasses.
Hessian fly
It is considered one of the most dangerous pests for grain. This is a small insect (up to 3-4 mm in length) of a dark gray or brown color with a pink or tan belly. It is widely distributed in different regions of the world, but is found annually in the United States and North Africa.
Such a fly lays eggs, from which larvae dangerous for wheat hatch. They suck vital juices from plant tissues, penetrate into the vagina of leaves and eat the stem. All this is accompanied by such signs:
- the stalk is deformed, twisted or cracked;
- the spike is empty or with a small amount of small seeds;
- sprouts quickly weaken and immediately turn yellow in the spring, so they dry quickly;
- the plant remains in growth and over time believes.
The intensive propagation of the Hessian fly is facilitated by carrion after the last harvest, so it needs to be smelled as soon as possible. This will help the rapid death of the larvae and stop their mass reproduction.
In case of severe damage to the Hessian fly, wheat can be chemically treated using special preparations (Hexachloran, Chlorophos, Metaphos, Phosphamide).
Wheat can be affected by various diseases and be attacked by dangerous pests. Knowing the reasons for their appearance, you can take all the necessary measures in a timely manner to protect your crop from such misfortunes. If the plant shows signs of damage, then you need to establish their cause in a timely manner and begin to improve your site.