Fumigation methods and phytosanitary plant protection for greenhouse soil

Soil disinfection: protection against pathogens and prevention of toxicoses

Effective phytosanitary preparation of greenhouse soils minimizes the risk of crop infection throughout the entire season. The use of methyl bromide helps to reliably clean the substrate of major pests and disease agents, including root-knot nematodes. However, when working with fumigants, it is important to strictly observe dosage rates and consider the consequences of sterilization for soil microflora.

• Dose for microorganism suppression — 50 µg/ml
• Application rate against root-knot nematode — 80 g/m²
• Interval between cucumber crop rotations — at least 3–4 weeks

For reliable plant protection against root rots in fumigated soils, an agronomist needs to perform two consecutive operations. These allow for closing the main pathways of infection spread and restoring the balance of the microflora.

1. Steaming or fumigation of the transplant medium as a potential source of infection.
2. Restoration of the biological diversity of soil microflora using manure or humus.

The application of methyl bromide at a rate of 80 g/m² effectively suppresses all soil-borne pathogens. However, after fumigation, saprotrophic bacteria remain in the soil and begin to multiply rapidly in the clean substrate. Their metabolic products cause soil toxicoses, which lead to the death of some of the root hairs in transplants and cause the plants themselves to lose resistance.

Protective measures are always planned taking the previous crop into account. For example, a winter-spring cucumber crop can be preceded by tomato, extended or autumn cucumber, leafy greens, eggplant, or pepper. The complex of harmful organisms accumulated on them persists in the greenhouse and affects new plantings. Autumn cucumber following a winter-spring crop suffers severely from mosaic, ascochyta blight, phoma root rot, root rots, and powdery mildew, which require a technological break for prevention.

Phytosanitary role of drip irrigation in a greenhouse

The method of water supply directly determines the humidity level of the air and the substrate in the greenhouse. Traditional irrigation systems often trigger infection outbreaks due to sharp fluctuations in the microclimate. Modern drip irrigation helps to automate the processes of plant nutrition and simultaneously improve the overall phytosanitary conditions.

In modern greenhouse farms, water or nutrient solutions are supplied in several ways:

• surface irrigation;
• hose irrigation;
• sprinkler irrigation using nozzles;
• drip irrigation.

With traditional overhead or hose irrigation, optimal humidity is created only periodically. Immediately after water application, the substrate becomes waterlogged, air does not reach the roots, which weakens their absorptive function and opens the way for pathogens. Intensive evaporation of moisture from the leaves sharply increases air humidity, provoking morning guttation and creating an ideal environment for spore germination.

Drip irrigation using "Supertif" or "Hydrogol" emitters delivers the solution directly to the substrate, keeping the above-ground part of the plants and the air dry. This prevents the development of fungal diseases such as gray mold on tomato, pepper, eggplant, and ascochyta blight on cucumber. If the technology requires increasing air humidity, an overhead misting system with "Rondo" micro-sprinklers is used, which creates a semi-fog in 5–7 seconds of operation.

Drip irrigation is most often used when growing plants in small-volume substrates: in containers, in pots, in heat-resistant Mapal trays on racks, on peat slabs, on Grodan, and on other mineral and organic substrates. The transition to small-volume substrates is driven not only by economic calculations but also supported by phytosanitary considerations. For example, the transition to this technology allows solving the problem of controlling a number of dangerous pathogens, such as root-knot nematodes, and certain root rot pathogens.

Drip irrigation is also used for the prophylactic application of systemic preparations, such as Previcur, Aktara, or Confidor, which allows protecting plants from both pests and diseases. The application of these preparations in the greenhouse can be carried out by one person, saving time and labor. Moreover, these preparations can be applied periodically, protecting plants throughout the growing season via the drip irrigation system with minimal labor requirements.

Mineral nutrition of vegetable crops

Soil preparation, maintaining an optimal microclimate, proper care, and plant nutrition contribute to increasing their resistance to pests and diseases. When developing rational crop nutrition plans, one should proceed from the main strategic line: plants should never starve; moreover, one should never apply less than the amount of fertilizer that a crop can assimilate. Increased quantities of Ca, B, Cu, Zn, Mn, and Mo by 10-15% are necessary, as this contributes to increasing plant disease resistance to root rots and certain other diseases. Consequently, the key to success is the use of high-quality fertilizers. Modern greenhouse vegetable production places increasingly higher demands on the economic side of farm performance. Stability and the production of high-quality, competitive produce come to the fore. A great deal depends on mineral nutrition, especially when enterprises switch to modern low-volume growing systems. In low-volume substrates, practically all nutrients are applied with the irrigation solution, while basal dressing is used only in soil-based greenhouses in combination with the application of dolomite flour as a source of cheap Ca and Mg nutrients.

Under current conditions, the prices of mineral fertilizers offered to Russian greenhouse enterprises by various manufacturers are at approximately the same level. Therefore, the quality of fertilizers becomes of particular importance: their composition balance, ease of use, reliability, and stability. They must contain all the nutrients necessary for the plant and strictly correspond to the stated composition. As an example, let us consider the assortment of fertilizers offered on the Russian market by ZAO Kemira Agro. It includes all necessary fertilizers, both for drip irrigation and for soil-based greenhouses, meeting high standards; therefore, most greenhouse complexes, by using them, obtain a high-quality harvest and, consequently, a noticeable economic effect.

Nutrition systems for vegetable and flower crops using the low-volume growing method are based on the application of one complete water-soluble fertilizer and several simple fertilizers as a base:

Kemira Kombi is a complete fertilizer for peat substrates with a high content of microelements in the form of chelated compounds. This is an acidic fertilizer, the application of which into peat as a basal dressing together with dolomite flour creates optimal soil acidity at the pH level (5.8-6.2) due to the fact that in an acidic environment, such nutrients as Ca and Mg contained in dolomite flour become more accessible to plants. As a result, the consumption of expensive soluble calcium and magnesium fertilizers and acids is noticeably reduced.

Kemira Hydro is a complete, soluble, chlorine-free fertilizer with a high content of microelements in the form of chelated compounds, designed for use on any substrate. On its basis, one can obtain a nutrient solution with various element ratios.

Calcium nitrate is a simple fertilizer containing water-soluble calcium, which makes it indispensable when growing plants using the low-volume hydroponics method.

Potassium sulfate is an impurity-free, chlorine-free, almost completely water-soluble (at least 99.8%) simple fertilizer, which makes it suitable for drip irrigation.

Potassium nitrate is ideal for greenhouse crops, both due to its high quality and thanks to its convenient packaging and resistance to caking during storage.

TABLE 13. FORMULATIONS OF NUTRIENT SOLUTIONS for CUCUMBER AND TOMATO CROPS WHEN GROWN ON PEAT HCO3- - 2.3mmol, Ec -0.2mS/cm Resulting working nutrient solution Ec 2.8, pH - 5.6-5.8 in mg/l, MK 1:1.4 N Ca Mg K [in mg/l] [284] [43] [391] [176] [64] [36] [18] [0.9] [0.14] [0.4] [0.2] [0.02] [0.01] Solution for cucumber crop on peat (For 1000l of 1:100 stock solution). For raw water containing Ca - 0.8mmol, Mg - 0.6mmol, HCO3- - 2.3mmol, Ec 0.2mS/cm Kemira Kombi Nitric acid 68% Conductivity Ec mS/cm Resulting working nutrient solution Ec - 2, pH - 5.6-5.8 in mg/l, MK 1:1.1. [in mg/l] 0.013 | 0.007

Magnesium nitrate, being a liquid fertilizer, contains water-soluble magnesium, which ensures ease of use. As an example, the formulation for preparing a nutrient solution for top dressing cucumbers and tomatoes in low-volume culture should be cited.

Fertilizers of the "Kemira Agro" line contain chromium, iodine, cobalt, and selenium. These microelements are not vital for the plants themselves, but they are actively assimilated by them. As a result, the grown vegetable produce is enriched with valuable substances, acquiring dietary properties.

For base application and top dressing of vegetables and flowers in open ground and greenhouses, granulated complexes "Kemira Universal" and "Kemira Universal-2" are effective. Nutrients reach the roots gradually throughout the entire growing season. This prevents nutrients from leaching out of the root zone, increases their utilization rate, saves resources, and reduces environmental impact.

"Kemira Super" complex fertilizer has been specifically developed for amending peat substrates. It contains microelements both in a rapidly available chelated form and as slowly soluble carbonates. To reduce plant stress during unfavorable weather, mineral top dressing is combined with growth regulators and hormones, which adjust hormonal balance and stimulate yield.

* Iron, zinc, copper, manganese, and cobalt are in the form of EDTA chelates.

Phytosanitary seed and planting material preparation

Seed lots completely free from latent infection are rare. Pathogens of fusarium wilt and bacterial diseases are easily transmitted via seeds, whereas grey mold does not spread this way. In tomatoes, the most dangerous pathogen is the causative agent of pith necrosis of the stem (Pseudomonas corrugata).

• Baktofit dosage for tomato seeds — 1.5–5 kg/t
• Phytolavin-300 working solution — 0.2%
• Soaking time in Phytolavin — 2 hours
• Phytolavin-300 application rate — 10 g/kg of seeds
• Cucumber seed infestation — 5–35%