Pepper diseases in protected soil: control measures and prevention

Protective measures. Steam or chemical disinfection of the soil. Thorough removal of plant residues. Preventive spraying of plants with strobilurin-group preparations (Quadris and Strobi) effectively suppresses disease development for 2-3 weeks. It is recommended to use these preparations together or in combination with contact ones, for example, with Thiovit or Kumulus, and no more than two times per season. 2.4.3.8. Anthracnose of bell pepper Pathogen — Co//e/o/r/c/u/n c/p/c/ (Sy4) Vi//er et ///s/ Harmfulness. This disease is most dangerous during the fruit formation period. Affected fruits lose their marketability. Symptoms. At first, small, water-soaked brown spots appear on the fruits, which gradually deepen and usually take on a rounded shape with numerous black acervuli in the center. Soon, the spots dry out and crack. Pathogen biology. There are numerous dark brown setae in the black acervuli. Conidia are colorless, cylindrical, unicellular, straight, measuring 18.6-25x3.2-5.3 μm. O/H/ t % Fig. 147. SWEET PEPPER FRUIT AFFECTED BY 9 _

Disease development is favored by temperatures above 28°C and air humidity over 90%. Sources of infection are plant residues and seeds. Protective measures. Pepper plant lesions caused by various etiologies of spotting occur frequently in greenhouses, but they are usually of low harmfulness when cultivation technology is followed. When affected leaves or fruits appear, one most often has to be content with removing the damaged parts, as there are still no regulations for the application of most pesticides on this crop, except for sulfur- and copper-based preparations.

In personal subsidiary plots, it is recommended to spray damaged plants with Bordeaux mixture at two-week intervals. In commercial farms, plants are usually sprayed with a 0.4% working solution of Oxyhom or copper oxychloride.

Meloidogynosis Pathogens — M/e/o/d/g/n/ /e/c/o/n/c/ (K/f/ e/ /./e/) C/i/o/c/ (southern), M. /a/a/c/ (T/e/b/) C/i/o/4 (Javanese) and M. /e/a/a/ (M/e/a/) C/i/o/4 (peanut).

Harmfulness. A harmful disease in ground-based greenhouses.

Symptoms of primary infection are practically non-existent. Large galls do not usually form on the roots; more often, numerous small galls are formed. Microscopic examination of the roots reveals female root-knot nematodes.

Biology and protective measures are described in Chapters 1 and 3.

om 2.4.5. Non-infectious diseases 2.4.5.1. Sulfur compound poisoning

It has been noted that pepper is highly sensitive to sulfur dioxide and has medium resistance to hydrogen sulfide. Symptoms of damage by sulfur oxides can manifest as acute poisoning and necrosis of interveinal tissues or leaf margins. Chronic damage is characterized by the appearance of reddish-brown and chlorotic zones. Damage is rare on young leaves, but mature leaves are very sensitive to injury by sulfur oxides. 2.4.5.2. Blossom-end rot

Symptoms: This disorder first manifests as water-soaked areas on the fruits. Tissues near the blossom end of the fruit turn brown. Unlike the tomato, blossom-end rot of pepper does not actually appear only at the fruit tips.

The spots lengthen and become brown or black, dry, and leathery. The discolored tissue shrivels until the affected zone flattens or becomes concave. Spots can be from 0.5 to 8 cm long (fig.

149). Fruits affected by blossom-end rot usually ripen prematurely.

Causes. Blossom-end rot appears when the plant cannot provide the fruits with the necessary amount of calcium. This phenomenon is caused by sharp fluctuations in soil moisture (drought or waterlogging), large amounts of nitrogen fertilizers, or root damage during tillage. Wilting and increased transpiration exacerbate the problem. Fungi living on the surface or inside the affected fruits also aggravate the pathology. Disease development is facilitated by an increased level of K and Na ions (their total content should not be higher than the Ca level). Fruits are very sensitive to all these factors at 20-30 days of age. A combination of high temperature (>25°) and low humidity (<50%) is undesirable. Therefore, blossom-end rot most often causes significant damage in the spring, when sharp temperature fluctuations are possible, affecting the young plant. fig 118 BLOSSOM-END ROT ON A PEPPER FRUIT. 58 { | | г `. `\ $ у Fig. 149. YOUNG PLANT WITH FRUITS AFFECTED BY NON-INFECTIOUS BLOSSOM-END ROT. й ь? д ААА Г. — к у }. Я / | Protective measures. Regulation of temperature and air humidity reduces the risk of the disease. Uniform moisture supply to the soil, which provides the necessary amount of available water for transpiration, prevents rot development. To this end, the irrigation rate is increased and the EC is reduced to 1.5 mS during daylight hours. It is also necessary to control the ratios of Ca to Mg and K to Na. Foliar top dressing of plants with calcium nitrate accelerates recovery and prevents the development of the disease. 2.4.5.3. Edema Symptoms. The disorder manifests as the appearance of a multitude of small bumps on the underside of leaves, and sometimes on the petioles. The cause is apparently linked to excessive substrate waterlogging or high air humidity. Protective measures consist of reducing substrate moisture and lowering air humidity. 3 дв, Fig. 150. EDEMA ON A PEPPER LEAF в \ —ыц <; 4.5.4. Mutational changes

Symptoms manifest as variegation and fruit deformation, and may be mistakenly attributed to herbicide damage or viral infections. The disease is linked to genetic disorders in the chloroplasts.

Protection measures are unknown. However, they are not necessary, as this is a very rare phenomenon affecting a negligible number of plants. 2.4.5.5. Sunscald

Cause. Sunscald is caused by excessive exposure of fruits to light. For example, after removing a portion of the upper leaves, the bush becomes exposed, and direct sunlight hits fruits that were previously in the shade. Small-fruited cultivars with upright shoots are not as sensitive to sunscald as large-fruited cultivars. Green fruits are more sensitive than mature red fruits.

Symptoms manifest as necrotic or bleached zones on the sun-exposed side of the fruits. Fungi such as Alternaria spp. often appear on the affected fruit tissues.

Control measures. Using screens to shade plants from excessive sunlight. When tending to plants, one should not remove too many leaves, as the remaining ones do not sufficiently protect the fruits from sunscald E. y? Fig. 151. COLOR CHANGE ON PEPPER LEAVES / 5 AS A RESULT OF MUTATION < Z and Ro I *. 4: * a 2.5. Cabbage

In greenhouses, Chinese cabbage is grown as a salad crop, along with seedlings of other cabbage types for subsequent field cultivation. The areas under seedbeds are decreasing annually due to the development of direct sowing technology for mid-season and mid-late cultivars and hybrids. However, to obtain an early harvest of early-maturing and late cultivars and hybrids, raising seedlings is required.

In most cases, the same pathogens affect all types of cabbage, so protection measures against them are identical. Bacterial and fungal diseases affecting the plant vascular system are the most harmful. For salad cultivars and hybrids, leaf pathogens are of greater importance.

Three viroses have been recorded on this crop. Here we will examine the main one. 2.5.1.1. Cauliflower mosaic cauliflower

Pathogen — Cauliflower mosaic virus — mosaic virus of cauliflower.

Harmfulness. The most common virosis. If young plants are infected, the cauliflower head does not form. Symptoms. The first symptom is lightening and veinal chlorosis of young leaves, and necrotic spotting of the laminae. Later, the main vein deforms, and the leaves become boat-shaped or crinkled. Signs of the disease may vary, but they become invisible when temperatures exceed 22°C. Fig. 152. VIRAL MOSAIC ON CABBAGE LEAF 9 — PU STY b t A G =», - 65. > 4 RR. < y, | Zy j * 2 r \ / r u: l zh' U d DR r of /x

Pathogen biology. A DNA-containing thermolabile virus belonging to the Caulimovirus group. Virions are isometric, about 50 nm in size. The pathogen is transmitted persistently and non-persistently by aphids, mainly Brevicoryne brassicae. Sources of infection are cruciferous weeds and cultivated plants. The virus is not seed-transmitted. Transmission via sap inoculation is possible but rare.

Protection measures. In addition to standard agrotechnical practices used for virosis protection, special attention should be paid to controlling cruciferous weeds in the greenhouse area and aphids, which act as vectors for the pathogen.

Bacterioses 2.5.2.1. Black rot

Pathogen — Xanthomonas campestris pv. campestris (Pammel) Dowson.

Harmfulness. Cabbage infection by this disease is observed at all stages of cultivation: at emergence, on seedlings, and on adult plants. The harm of black rot lies in the reduction of head yield and the deterioration of their nutritional value. Affected heads contain 1.5 times less sugar and 11-17% less ascorbic acid than healthy ones.

The pathogen is almost ubiquitous. Bacteria are spread by rain droplets and cabbage pests. In 1905, this disease was first discovered in the Smolensk and Kharkov provinces. Later, it spread to all regions where cabbage, radish, and other plants from the Brassicaceae family were cultivated.

Symptoms. On cotyledons, the first signs of the disease appear as a lightening of their edges. Plants may die, or their growth may be stunted and they may become distorted.

On adult plants, infection also begins from the edge of the leaf blade as yellowing; the affected zone takes on a V-shaped outline, with the base of the V facing the center of the leaf. Within the yellowed tissue, the leaf veins become black, forming a black network, which gave this disease its name — black rot. A cross-section of the petiole of an affected leaf reveals browning or blackening of the vessels. Later, the affected zones turn dark brown and die off.

In the late stages of the disease, the black coloration from the affected leaf can spread to the main stem, where the darkened vascular system can be clearly seen extending up or down the stem. One way to identify the disease is to inspect the leaf scar on the stem after removing severely damaged leaves. A plant affected by black rot (vascular bacteriosis) displays characteristic black rings of vascular bundles on the scar. As the disease progresses, the symptoms manifesting as darkening of the vascular system can spread to the upper leaves, where chlorotic lesions resulting from systemic infection can appear in any part of the leaf. Affected plants show stunted growth. Lower leaves may drop off, and heads remain small.

Black rot of cabbage is a dangerous disease that continues to develop even during storage, rendering the heads completely unusable. Often, it is followed by soft rot, which turns the stems and leaves of the affected plant into a watery mass with an unpleasant odor. In cool weather, diagnosis is complicated: for example, when growing cauliflower in winter, the symptoms of bacteriosis are easily confused with bacterial leaf spot or yellow leaf spot.

Pathogen characteristics and pathways of infection

The pathogen of the disease is a rod-shaped, Gram-negative, non-spore-forming, obligate aerobic bacterium. On meat-peptone agar (MPA), the pathogen forms smooth, convex, yellowish colonies with even edges and crystals in the center. The bacterium is extremely resilient: it withstands both drying and deep freezing very well.

• Bacterial cell size — 0.4-0.5 x 0.7-3.0 µm
• Temperature for rapid development — 27-30 °C
• Period of symptom appearance — 10-12 days

Cabbage infection can occur at any stage of crop development. The pathogen enters plant tissue through natural openings and wounds. After that, the bacteria move along the main vein and leaf petiole, eventually penetrating deep into the stump.

• through hydathodes;
• through stomata (during heavy rains or excessive irrigation);
• through natural damage to the root system.

Massive disease development is triggered by a combination of heat and high humidity during the growing season, especially when the soil is fully saturated with moisture. Pests that damage plant tissues become an additional factor in the spread of infection. The speed at which the first signs of bacteriosis appear directly depends on the temperature regime in the field or greenhouse.