Diagnostics of nitrogen deficiency in cucumber and disinfection of greenhouse structures

Symptoms and elimination of nitrogen deficiency in cucumber

When growing cucumber, the uptake of nutrients is directly linked to the increase in dry matter. Immediately after transplanting seedlings, the daily growth and nutrient uptake are minimal, but they increase sharply during the fruiting period. In greenhouse conditions, due to high humidity and reduced light, cucumbers absorb more potassium than nitrogen. A shortage of any element disrupts biochemical processes, which affects the color, size, and shape of leaves, as well as growth points, flowers, and fruit set.

Nitrogen deficiency can manifest at any stage of plant development — from emergence to ripening. Since nitrogen moves from older tissues to younger ones and to growth points, signs of starvation first appear on the lower leaves. The green color fades and gradually turns greenish-yellow, sometimes with yellowish spots between the veins. At the same time, new leaves grow slowly, stems become thin and harden, and the developing cucumbers grow small and deformed.

If nitrogen deficiency is confirmed, top dressing is carried out. The choice of products depends on the type of farm:

• In greenhouse complexes, soluble chlorine-free fertilizers are used: potassium or calcium nitrate, urea, and the complex fertilizer Kemira Hydro.
• In private subsidiary farms, ammonium nitrate, poultry manure, or manure/herbal infusions are used.

Greenhouse disinfection and soil sterilization

If annual replacement of greenhouse soil is impossible, pathogens and pests accumulate in it. Disinfection of cultivation facilities and soil after each growing season is an essential element of plant protection. To sanitize soils, agrotechnical, thermal, and chemical methods are used.

• Working solution consumption for wet disinfection — up to 10000 l per 1 ha
• Concentration of chlorinated lime for treatment in private farms — 4%
• Concentration of formalin for greenhouse complexes — 2-5%
• Formalin consumption for hot aerosols — up to 200 l/ha
• Lime dosage for biological soil sterilization — 4 kg per 1 m³

Wet disinfection is carried out after harvesting and removal of plant residues. The soil, structures, glazing, and foundation slabs are sprayed generously with the disinfectant solution.

1. Perform the first wet disinfection of the greenhouse surfaces.
2. Burn the trellis with a blowtorch or a gas burner.
3. Wash the roof from the inside with hot water using fire hoses, and from the outside with acid solutions, including oxalic acid.
4. Perform repeated wet disinfection.
5. Allow a break of at least two weeks between spraying surfaces and planting the new crop.

For gas disinfection of greenhouses, sulfur candles are placed on trays. Fumigation with sulfur dioxide is carried out with strict adherence to the temperature regime and exposure time:

The agrotechnical method of soil sterilization allows it to be returned to production after several years. Spent soil is removed from greenhouses and placed in piles 1.5-2 m high and up to 3 m wide, mixed with fresh manure or slurry, and added with lime. In this state, the soil undergoes biological sterilization for 2-3 years. During this period, it is turned over 2-3 times, and weeds are constantly eliminated.

Pre-sowing seed treatment and cucumber protection during the growing season

Pathogenic microorganisms can persist on the surface of seeds, in their outer tissues, or in the embryo. As a result, the young plant is already infected at the moment of germination. Most specialized parasites do not suppress the crop during early stages of development. For example, Fusarium mycelium grows inside the stem latently and activates only during the transition to fruiting, causing wilting, necrosis, and rot.

To combat surface infection, it is sufficient to treat seeds with TMTD or other fungicides, and in private farming conditions, soak them in a strong solution of potassium permanganate. Internal infection (virosis, Ascochyta blight, Fusarium) is destroyed via thermal treatment. To protect against white mold, seed pelleting with a chlamydospore-based preparation using the fungus Trichoderma lignorum (Trichodermin) is effective.

1. Warm the seed at 60 °C for 24 hours.
2. Calibrate the seed material in a table salt solution.
3. Keep the seed in a 1% potassium permanganate solution for 30 minutes, then rinse thoroughly with water and dry.
4. Soak the seed before germination for 18–24 hours in a micronutrient solution: 0.2% boric acid, 0.5% zinc sulfate, 0.1% ammonium molybdate, and 0.05% copper sulfate.

During the growing season, it is important to maintain a stable temperature regime in accordance with the level of solar radiation and avoid sharp diurnal fluctuations. For disease prevention, biological agents, chemical immunization, and treatment with growth regulators are used. Upon the appearance of the first disease symptoms, the plantings are sprayed with fungicides from the approved list. For white rot and Ascochyta blight, it is also effective to use proper plant rejuvenation.

• Reduction in white rot incidence with seed pelleting — more than 1.5 times
• Reduction in disease incidence with chemical immunization of seedlings — by 25–27 %
• Application rate of working solution for seedlings per 1000 m² — up to 100 L
• Application rate of working solution for mature plants per 1000 m² — 200–250 L

Specifics of tomato cultivation in protected ground

Tomato ranks second in production volume in protected ground. The crop is grown in glass and plastic greenhouses on soil or mineral substrates. Tomato is more plastic than cucumber and less damaged by pests and diseases, although it is inferior to it in terms of early maturity and overall yield.

In most farms, tomatoes are grown in a prolonged crop rotation from January to October, using domestic and foreign indeterminate and semi-determinate hybrids. Autumn rotation is practiced significantly less often due to the short daylight hours and more modest harvests.

In plastic greenhouses in southern regions, tomatoes are grown with minimal costs in the winter and early spring periods. For such conditions, agronomists choose semi-determinate and, less frequently, indeterminate hybrids. The main selection criteria here are fruit transportability and plant resistance to pathogens. In protected ground, the tomato is often affected by a whole complex of viruses: Potato virus Y (PVY), Tomato aspermy virus (TAV), Tomato black ring virus (TBRV), and Tomato ringspot virus (ToRSV). Mixed infections are also common, including Potato virus M, Potato virus S, Potato leafroll virus (PLRV), and Tobacco rattle virus (TRV).

Symptoms of tomato mosaic and streak development

Tobacco mosaic virus (TMV), known also as Tobacco mosaic, is one of the most common diseases of the crop. With early infection of plants, yield drops by half due to the appearance of defective fruits and general suppression of the plantings. The infection easily penetrates through micro-injuries of the epidermis and damaged leaf hairs during plant care.

• Yield loss with early infection — up to 50 %
• Thermal inactivation point of the virus — 95 °C
• Maximum size of enations on leaves — up to 1 cm
• Temperature for fruit necrosis activation — 30–35 °C

The first symptoms of mosaic appear as leaf mottling, which develops into a dark and light green mosaic. Leaves become deformed and wrinkled, acquiring a thread-like or fern-like shape. On the underside of such leaves, enation mosaic often develops with the formation of specific outgrowths — cup-shaped or ear-shaped enations. Enations serve as an unmistakable marker of viral infection, as this pathology has no non-viral analogues. As the temperature rises in the spring-summer period to 30–35 °C, the proportion of plants with fruit necrosis increases.

In the case of mixed infection of TMV with Potato virus X (PVX), Cucumber mosaic virus (CMV), or Tomato aspermy virus, a complex streak develops on the plants. It manifests as necrotic streaks and stripes on stems, petioles, and fruits. In cases of severe damage, the fruit skin ruptures, and the seeds become exposed. Single streak causes the same symptoms, but its causative agent is exclusively TMV.

The pathogen is extremely stable in the external environment, withstands desiccation, and persists on tools or in tobacco products. Introducing hybrids with resistance genes helps protect plantings. Three genes are responsible for this: Tm-1 (a tolerance gene on the 5th chromosome, derived from Lycopersicon hirsutum), as well as hypersensitivity alleles Tm-2 and Tm-22 (localized on the 9th chromosome of L. peruvianum). However, cucumber mosaic virus and potato virus X in mixed infections are capable of suppressing this protection, causing a complex streak.