Diseases

Symptoms

• On leaves — at first, velvety olive‑green spots appear on the lower side, then darken to black‑brown. In severe infection, leaves curl and fall (Agustí, 2010; Buckingham, 2010).
• On fruits — dark, almost black spots with clear margins, often cracking. Young fruits may become deformed and drop. The affected skin becomes hard, corky, making the fruit unmarketable (Ferree et al., 2003).
• On shoots and flowers — less frequently, dark spots and deformation may occur.

Development Conditions

The fungus overwinters on fallen leaves as pseudothecia (fruiting bodies). In spring, after wetting by rain, ascospores are released and infect young leaves. Infection requires continuous leaf wetness for 9–25 hours — the warmer it is, the shorter the required period (Ferree et al., 2003; Jackson, 2003). Spores are spread by wind and raindrops. Secondary infection (by conidia) occurs throughout the summer in wet weather.

Practical tip: Use the Mills table (Mills period) — if after rain the leaves dry faster than the critical time at that temperature, infection will not occur. This will help avoid unnecessary treatments (Agustí, 2010).

Control

Prevention:

• Collect and remove fallen leaves in autumn (incorporate into soil, compost, or burn).
• Autumn application of urea (5%) on leaves to accelerate decomposition of leaf litter (Ferree et al., 2003).
• Plant resistant varieties (e.g., ‘Liberty’, ‘Enterprise’, ‘GoldRush’, ‘Redfree’). They do not require frequent treatments (Rieger, 2006; Phillips, 2005).
• Ensure good canopy aeration through thinning pruning.

Chemical protection:

• First spray — from bud break to the “green tip” stage (beginning of leaf growth).
• During active leaf growth and until the end of flowering — treatments at 7–14 day intervals, especially in rainy weather.
• Use contact (captan, dithianon) or systemic fungicides (tebuconazole, difenoconazole). Alternate products from different groups to avoid resistance (Agustí, 2010).
• In organic gardening, sulphur (finely ground sulphur) is effective, but its action is limited and requires frequent repetition. Copper‑based products (Bordeaux mixture) are also used — but only before bud break to avoid burns (Phillips, 2005).

Biological control: Recently, the use of antagonistic fungi and compost tea has been studied, but in practice they do not yet provide reliable protection in epidemic years (Phillips, 2005).

Symptoms

• Shoots and leaves — white powdery coating on the lower leaf surface, then on the upper. Affected leaves become narrow, curled, brittle, and often drop. Heavily infected shoots have shortened internodes (“witches’ brooms”) (Buckingham, 2010).
• Flowers and fruits — flowers become deformed, fail to set fruit; fruits develop a russet network, reducing market quality (Ferree et al., 2003).

Development Conditions

The fungus overwinters as mycelium inside infected buds. In spring, “flag” shoots emerge from them, completely covered with powdery coating — they serve as the primary source of infection. The optimal temperature for spore germination is 20–22 °C, but infection occurs already at 10 °C. Leaf wetness is not required — relative humidity >90% is sufficient (Ferree et al., 2003).

Control

Prevention:

• Prune and destroy all shoots showing signs of powdery mildew during dormancy.
• Use resistant varieties (e.g., ‘Liberty’, ‘Florina’, ‘Enterprise’ have good resistance).
• Avoid excessive nitrogen fertilisation — it stimulates soft growth that is most susceptible to infection (Phillips, 2005).

Chemical protection:

• Treatments begin at the “pink bud” stage and continue until shoot growth ceases (approximately until July).
• Sulphur (especially in dry weather) and systemic fungicides (myclobutanil, penconazole) are effective. It is important to alternate products because the fungus quickly develops resistance (Ferree et al., 2003).
• In organic gardening, sulphur and potassium bicarbonate (baking soda) with a sticker are used.

Important: Do not apply sulphur at temperatures above 27 °C — it causes leaf burn.

Main types and symptoms

Brown rot (moniliosis) — caused by Monilinia fructigena (in Europe) or M. fructicola (in North America). Brown spots appear on fruits, spreading rapidly; yellowish‑white sporodochia form on the surface in concentric rings. Affected fruits often mummify and remain hanging on the tree (Buckingham, 2010; Ferree et al., 2003).

Bitter rot (anthracnose rot) — Colletotrichum gloeosporioides and C. acutatum. Characterised by sunken, circular, brown spots, often with a red border. The flesh under the spot shows a V‑shaped or cone‑shaped lesion profile. Common in warm humid regions (southeastern US, Brazil) (Ferree et al., 2003).

White rot (Botryosphaeria rot) — Botryosphaeria dothidea and B. obtusa. Affected fruits become light brown, soft, watery, and decay rapidly. Often attacks trees weakened by other diseases or injuries (Ferree et al., 2003).

Grey mould — Botrytis cinerea — affects fruits during storage, especially under high humidity. Appears as a grey fluffy coating (Buckingham, 2010).

Infection Pathways

Pathogens enter through wounds on fruits (insect damage, hail, birds, drought cracks). Spores survive on mummified fruits, in bark cracks, and in fallen leaves. In warm wet weather, infection spreads very quickly (Agustí, 2010).

Control

Prevention:

• Thoroughly collect and destroy all mummified and fallen fruits.
• Remove dead branches and bark areas showing signs of rot.
• Control insects that damage fruit skin (codling moth, fruitworms).
• Timely harvest and careful handling to avoid mechanical injury.

Chemical protection:

• Preventive sprays from flowering to harvest (especially during rainy periods), using captan, thiram, or systemic fungicides (benomyl, tebuconazole). Observe pre‑harvest intervals strictly (Ferree et al., 2003).
• For organic gardening — copper (Bordeaux mixture) only before flowering, after that sulphur, but sulphur is less effective against rots.

Biological control — experimentally, some strains of antagonistic bacteria and yeasts (e.g., Pseudomonas, Bacillus) can suppress rot development on fruits, but in practice they are still rarely used (Phillips, 2005).

Symptoms

• On leaves — in late spring, yellow‑orange spots appear, enlarge, become orange with a dark border. On the underside of the leaf, tubular outgrowths (aecia) develop, releasing orange spores (Buckingham, 2010; Phillips, 2005).
• On fruits — round, sunken spots; fruits may become deformed.
• On shoots — swellings may form, but less often.

Life Cycle

In spring, gelatinous orange masses (spores — basidiospores) appear on junipers (red cedar, etc.) and are carried by wind to apple trees, infecting young leaves during bud break. Warm wet weather favours infection. On apple, aecia develop, which then release aeciospores that infect juniper (completing the cycle in the second year). The apple tree itself does not get secondary infection from its own aecia — reinfection is only possible from juniper in the following year (Ferree et al., 2003).

Control

Prevention:

• Remove junipers within a radius of 1–1.5 km from the orchard (or at least prune branches with galls).
• Choose resistant varieties (e.g., ‘Enterprise’, ‘Liberty’, ‘William’s Pride’, ‘McIntosh’ have good resistance).
• Use spatial isolation — do not plant apples near junipers.

Chemical protection:

• Treatments from the “pink bud” stage to the end of flowering, then 2–3 times at 7–10 day intervals.
• Sulphur products are effective but only as protectants — they prevent spore germination, but do not cure already developed spots. Alternatively, systemic fungicides (myclobutanil) (Ferree et al., 2003).

Important: In regions where rust is not prevalent (northern Europe, dry areas), this disease is not a problem.

Symptoms

• Elongated, sunken areas with a reddish‑brown tint appear on the bark, gradually drying and cracking.
• Under the bark, many small black pycnidia (fruiting bodies) form — they look like dark dots.
• Affected branches die, bark peels off.
• In severe infection, the whole branch or even the tree may die.

Development Conditions

The fungus enters through wounds, frost cracks, and bark damage. Especially active under stress conditions (drought, temperature fluctuations, potassium deficiency). Overwinters in bark and dead branches (Westwood, 1993).

Control

• Timely pruning and burning of diseased branches.
• Treat wounds with grafting wax or sealing compound.
• Improve overall tree health through watering and balanced nutrition (especially potassium fertilisers).
• In severe infection — spray with copper‑based products during dormancy (Agustí, 2010).

Symptoms — How to Recognise

Fire blight manifests in several forms, which often occur together:

Blossom blight — the first and most characteristic sign. During flowering, individual flowers or whole clusters suddenly wilt, turn brown and black, but do not fall. In wet weather, droplets of sticky yellowish‑white or amber fluid (exudate) appear on infected flowers — this is “bacterial slime” (Ferree et al., 2003). Bees and other insects spread this slime to healthy flowers, causing an epidemic.

Shoot blight — young shoots and leaves turn black, dry up, but remain on the tree. The shoot tip bends into a hook, forming a characteristic “shepherd’s crook” — one of the most recognisable symptoms (Jackson, 2003; Phillips, 2005). Leaves on the affected shoot turn black along the veins and curl. The disease spreads rapidly from the tip to the base of the shoot, then to branches.

Canker blight (wound blight) — sunken, dark areas (cankers) appear on the bark of the trunk or main branches, from which bacterial slime oozes in wet weather. Cankers enlarge, girdle the branch and cause its death. Callus tissue often forms around the canker, but bacteria continue to develop inside (Ferree et al., 2003).

Root blight — if bacteria enter the root collar or roots (through wounds), the tree may die from girdling. Dwarf rootstocks (M.9, M.26) are especially vulnerable (Jackson, 2003).

Fruit blight — fruits become dark brown, shrivel and mummify, but often remain hanging on the tree through winter (Agustí, 2010).

Important to distinguish fire blight from other diseases: unlike fungal infections, leaves and flowers with blight do not fall off, but remain on the plant, and affected tissues have a characteristic scorched appearance. It differs from Cytospora canker by the presence of bacterial exudate and rapid spread through the vessels.

Life Cycle and Spread Conditions

Overwintering — the bacterium survives winter in living tissues at the boundary between healthy and diseased bark (in the marginal zones of cankers). With the onset of warm weather (spring), bacteria become active and are exuded onto the bark surface as slime (exudate) (Ferree et al., 2003).

Primary infection — droplets of exudate are dispersed by rain, wind, and insects (including bees) and land on open flowers. Bacteria colonise the stigma surface, multiply there, and, in the presence of moisture, enter the flower tissues through nectaries (Jackson, 2003).

Spread rate — at temperatures above 18 °C and high humidity, bacteria multiply exponentially. In tissues, they move through intercellular spaces and vessels at a speed of up to 25–50 mm per day, which explains the lightning‑fast wilting of shoots (Ferree et al., 2003).

Critical conditions for an epidemic:

• Warm weather (21–30 °C) during flowering
• Rain, dew, or high air humidity
• Activity of pollinating insects
• Presence of open wounds (hail damage, improper pruning, wind damage)

Control Measures

Choice of resistant varieties and rootstocks — the most reliable way. Apple varieties differ greatly in susceptibility:

• Relatively resistant: ‘Delicious’ and its clones, ‘McIntosh’, ‘Empire’
• Susceptible: ‘Gala’, ‘Fuji’, ‘Granny Smith’, ‘Cox’, ‘Idared’, ‘Jonagold’ (Ferree et al., 2003; Jackson, 2003)
• Among rootstocks, resistant: G.16, G.30, G.65 (Geneva selection), and some seedling rootstocks. Dwarf M.9 and M.26 are extremely susceptible to root blight (Ferree et al., 2003).

Proper nutrition — avoid excess nitrogen fertilisation, as it stimulates succulent, soft shoot growth, more susceptible to bacteria. Balanced nutrition with potassium and phosphorus strengthens tissues (Jackson, 2003; Phillips, 2005).

Irrigation management — do not use overhead sprinkling during flowering if there is a risk of fire blight. Drip irrigation is preferred because it does not wet leaves and flowers (Phillips, 2005).

Autumn and winter pruning — remove and burn all affected branches and cankers. Cut at least 20–30 cm below the visible margin of infection, as bacteria may already be inside healthy‑looking tissue (Ferree et al., 2003).

Summer sanitary pruning — immediately after detecting blight (within June), remove affected shoots, making a cut 20–30 cm below the last sign of disease. Use the “ugly stub” technique — leave a stub 8–10 cm long, so that later, in winter, you can make a final clean cut to healthy wood (Phillips, 2005).

Disinfect tools — after each cut, sterilise pruners with 70% alcohol, 10% bleach solution (dilute 1:9 with water), or specialised agents. This prevents bacteria transfer from diseased to healthy trees (Phillips, 2005; Buckingham, 2010).

Destroy diseased plants — if a tree is severely affected (canker on trunk or root collar), it is better to uproot and burn it to prevent spread of infection.

Copper‑based products — applied during dormancy (autumn after leaf fall or early spring before bud break). They create a protective film on buds and bark, reducing the risk of bacterial penetration. Bordeaux mixture, copper oxychloride, C‑O‑C‑S (copper oxychloride) are effective but may cause leaf burn if used during the growing season (Agustí, 2010; Phillips, 2005).

Antibiotics — streptomycin and others (where permitted) are applied during flowering to protect against blossom blight. Spraying is done during critical periods when temperature and humidity favour infection. However, frequent use of streptomycin leads to resistant bacterial strains, so it is used only on forecast, not prophylactically (Ferree et al., 2003; Jackson, 2003). In many countries, antibiotic use in orchards is restricted or prohibited.

Important: streptomycin is effective only against blossom blight, but does not act on already developed shoot or trunk blight.

Antagonistic bacteria — recently, products based on Pseudomonas fluorescens and other bacteria that compete with Erwinia amylovora on the flower surface are being actively developed. They are applied during flowering and reduce infection risk by preventing the pathogen from establishing. Products like “Blight Ban” and similar biological agents are available in some countries (Jackson, 2003; Phillips, 2005).

Bee delivery — a technique has been developed where bees pass through a powder containing antagonistic bacteria when exiting the hive, and then they carry beneficial bacteria to flowers along with pollen. This shows efficacy up to 90% (Phillips, 2005).

Use forecasting models (e.g., Maryblyt, Cougarblight, BIS) — they take weather conditions into account and allow you to determine periods of greatest risk. This helps carry out protective treatments only when truly necessary, saving resources (Jackson, 2003; Ferree et al., 2003).

Bacterial Leaf Spot (Pseudomonas syringae pv. syringae and pv. papulans)

• Causes small, dark, water‑soaked spots on leaves, which may later drop out, creating a “shot‑hole” appearance. Shoots and fruits may also be affected.
• More common in regions with wet and cool spring weather.
• Control measures: avoid susceptible varieties, spray with copper‑based products during dormancy, sanitary pruning (Agustí, 2010; Ferree et al., 2003).

Bacterial Canker (bacterial bark necrosis)

• Caused by various species of Pseudomonas and Xanthomonas.
• Dark, sunken areas appear on the bark, often with gum exudation (especially on stone fruits, but occasionally on apple as well).
• Control similar — remove affected branches, disinfect tools, copper products during dormancy (Westwood, 1993).

Bacterial Wilt (rare on apple)

• Caused by Xylella fastidiosa or other bacteria blocking vessels. Manifests as gradual wilting of individual branches.
• No treatment, only removal of diseased plants.

Blister Spot — Pseudomonas syringae pv. papulans

• Mainly affects the variety ‘Mutsu’ (‘Crispin’), causing brownish‑black blisters on fruits.
• The variety ‘Shizuka’ is resistant. Control — choose resistant varieties and copper products (Agustí, 2010; Ferree et al., 2003).

Leaf Mosaic

• Leaves show patches of different colour — light green, yellow, or white, alternating with normal green tissue (Ferree et al., 2003).
• For apple mosaic virus (ApMV), symptoms are especially noticeable in spring and early summer, then may disappear in hot weather. On highly susceptible varieties, mosaic can cover the whole tree, reducing photosynthesis and yield by up to 40% (Jackson, 2003).
• For chlorotic leaf spot virus (ACLSV), leaves show yellow spots or ring patterns, sometimes with necrosis. This virus is widespread and often asymptomatic on apple, but on pear and some indicator varieties it is very pronounced (Ferree et al., 2003).

Leaf and Shoot Deformation

• Curling, crinkling, reduction in leaf size.
• Shortened internodes, “dwarfing” of shoots.
• Formation of rosettes of leaves instead of normal growth (some viruses cause rosetting).

Fruit Colour Changes

• Spots, stripes, rings appear on fruits (e.g., with dapple apple caused by a viroid). In some viruses, fruits become deformed, with bumps or pits (Ferree et al., 2003).
• Fruits may ripen unevenly or drop prematurely.

Stem Pitting and Grooving

• Apple stem pitting — longitudinal pits and depressions appear on the wood, especially noticeable after bark removal. This disease is caused by ASPV and often leads to tree weakening, especially on sensitive rootstocks (e.g., ‘Virginia Crab’) (Ferree et al., 2003; Jackson, 2003).
• Apple stem grooving — deep grooves form on the bark and wood, often at the graft union. May cause scion dieback on sensitive rootstocks, leading to incompatibility (Jackson, 2003).

Union Necrosis

• A disease caused by tomato ringspot virus (TmRSV), transmitted by nematodes. A dark necrotic line appears at the graft union, bark becomes loose, tree weakens and may die. Often found in eastern North America (Ferree et al., 2003).

Reduced Growth and Yield — the most common but non‑specific sign

• Even without visible symptoms, viruses can reduce shoot growth by 10–30%, yield by 20–40%, and impair fruit quality (Jackson, 2003; Ferree et al., 2003).

Apple Proliferation

• Widespread in Central and Southern Europe. Caused by the phytoplasma Candidatus Phytoplasma mali.
• Symptoms: formation of numerous upright shoots (“witches’ brooms”) at branch tips, enlarged stipules, reduction in fruit size (by 30–70%), elongated pedicels. Yield is greatly reduced, fruits lose marketable appearance (Jackson, 2003; Ferree et al., 2003).
• Vectors: leafhoppers (e.g., Fieberiella florii). Also transmitted by grafting.
• Control: quarantine, use of healthy rootstocks, control of leafhoppers. In regions where the disease is absent (North America), strict restrictions on planting material import apply (Ferree et al., 2003).

Dwarfing (“Chat Fruit”)

• Named for the characteristic symptom — fruits become very small, deformed, often without seeds. Leaves and shoots may look normal, but tree productivity declines.
• Caused by a phytoplasma, but the exact agent is not always identified. Diagnosis is difficult, performed on indicator varieties (‘Lord Lambourne’) (Jackson, 2003; Ferree et al., 2003).

Pear Decline — although mainly affecting pear, it may also affect apple in mixed plantings

• On apple it is rarer, but in regions where pear is grown, the pear decline phytoplasma can be transmitted to apple by some psyllid species.

1. Through planting material (grafting, budding) — the most common route

• Viruses and phytoplasmas are transmitted through infected scions, buds, and rootstocks. This is the main reason for their widespread distribution in commercial orchards. Even if the donor plant has no symptoms, it may be a carrier (Ferree et al., 2003; Jackson, 2003).
• Therefore, using certified virus‑free planting material is the only reliable way to avoid infection.

2. Insect vectors

• Aphids, leafhoppers, nematodes, psyllids can transmit viruses and phytoplasmas from diseased to healthy plants when feeding on sap. For example, apple proliferation phytoplasma is transmitted by leafhoppers, and some viruses (e.g., tomato ringspot virus TmRSV) by nematodes (Ferree et al., 2003).
• Controlling vectors (insecticides, cultural practices) reduces spread risk, but does not guarantee complete protection.

3. Through infected seeds (rare)

• Some viruses can be transmitted through seeds, but for apple this is not a major route because apples are propagated vegetatively (Jackson, 2003).

4. Contact (tools)

• Viruses can be transmitted through plant sap during pruning, grafting, especially if tools are not disinfected. This route is particularly important for viruses that have no other vectors (Ferree et al., 2003).

1. Buy only healthy planting material

• Purchase saplings and cuttings from certified nurseries that have virus sanitation programmes. In developed countries, certification systems exist (e.g., EMLA programmes in Europe, certified virus‑free rootstocks and varieties) (Ferree et al., 2003; Jackson, 2003).
• When establishing an orchard, use only such trees. Saving on planting material can result in years of yield losses.

2. Maintain sanitary order

• Remove and burn all trees with obvious symptoms of viral diseases (mosaic, dwarfing, fruit deformation).
• Do not use cuttings from diseased trees for grafting.
• Regularly disinfect pruners and other tools (alcohol, chlorine solutions) when moving from one tree to another.

3. Control vectors

• Timely treatments against aphids, leafhoppers, nematodes reduce the spread of viruses and phytoplasmas. This is especially important in regions where active vectors are known (Ferree et al., 2003).
• Support natural enemies of vectors (ladybirds, lacewings) by avoiding broad‑spectrum insecticides.

4. Use resistant varieties and rootstocks

• Although absolute resistance to viruses does not exist, some varieties and rootstocks have tolerance — they do not show symptoms and suffer less from infection. For example, many commercial varieties are tolerant to chlorotic leaf spot virus, while indicator varieties (e.g., ‘R12740‑7A’) are very sensitive (Ferree et al., 2003).
• When choosing rootstocks, consider that some (e.g., ‘Virginia Crab’) are very sensitive to certain viruses (stem pitting) and their use may lead to tree death if the scion carries a latent infection (Jackson, 2003).

5. Consider regional features

• In regions where apple proliferation is widespread (Central Europe), regular leafhopper control is mandatory. In areas free from phytoplasmas, quarantine measures are very strict — import of plants from infected zones is prohibited (Ferree et al., 2003).

Site Selection and Soil Preparation

Choosing the right location for the orchard is the first step towards disease prevention.

• Drained soils — apple does not tolerate waterlogging. In waterlogged conditions, roots suffocate, the tree weakens and becomes easy prey for root rots (Phytophthora spp.) and other pathogens (Agustí, 2010; Westwood, 1993). If the site is wet, plant trees on raised beds or artificial mounds 30–40 cm high.
• Ventilation — avoid enclosed hollows where cold air stagnates and dew persists. Good air circulation speeds up leaf drying after rain, reducing the risk of scab and other fungi (Phillips, 2005).
• Fertility and pH — optimal soil pH for apple is 6.0–7.0. On acidic soils (pH < 6), calcium and magnesium uptake is impaired, increasing the risk of physiological disorders (bitter pit, spotting) (Rieger, 2006; Westwood, 1993). If necessary, apply lime 1–2 years before planting.

Soil preparation before planting:

• Remove perennial weeds, especially those that may be reservoirs of disease (e.g., hawthorn — a source of rust).
• Apply organic fertilisers (well‑rotted manure, compost) at a rate of 30–60 t/ha (or 3–6 kg/m²) to improve fertility and soil structure (Agustí, 2010).
• Deep tillage (ploughing or digging to 40–60 cm) improves aeration and deep root penetration.

Balanced Nutrition

Tree nutrition directly affects its resistance to diseases. Excess or deficiency of elements weakens immunity.

Nitrogen (N) — needed for growth, but its excess causes the formation of succulent, loose tissues, particularly susceptible to fungi and bacteria. Excess nitrogen fertilisation in combination with wet weather is especially dangerous — it provokes outbreaks of scab, powdery mildew and fire blight (Jackson, 2003; Phillips, 2005). Apply nitrogen fractionally, mainly in spring, and avoid high doses in the second half of summer.

Gardener’s rule: “Nitrogen for leaves, potassium and phosphorus for fruits and immunity.” Excess nitrogen makes the tree “fat” and sick.

Potassium (K) — increases cell wall strength, drought and frost resistance, and reduces susceptibility to fungal diseases. Potassium fertilisers (potassium sulphate, kalimagnesia) are applied in autumn or early spring (Agustí, 2010).

Phosphorus (P) — strengthens the root system and promotes flower bud initiation. Applied as superphosphate at planting or in autumn (Rieger, 2006).

Calcium (Ca) — critically important for cell wall strength and fruit disease resistance (bitter pit, rots). Calcium deficiency often occurs not because of its absence in the soil, but due to poor uptake (drought, acidic soil, excess potassium or magnesium) (Buckingham, 2010; Ferree et al., 2003). Apply calcium as dolomite flour or gypsum, and also carry out foliar feeding with calcium chloride (0.5%) during fruit growth.

Silicon (Si) — although not considered an essential element, silicon strengthens the cuticle of leaves and fruits, creating a mechanical barrier to pathogens. Biodynamic gardeners use horsetail infusion (rich in silicon) for spraying (Phillips, 2005). In conventional agriculture, silicon is rarely considered, but research shows its benefits.

Micronutrients — deficiency of boron, zinc, copper, manganese reduces immunity. Regularly conduct foliar feeding with complex micronutrient fertilisers (Agustí, 2010).

Watering and Moisture

Irrigation regime greatly influences disease spread.

• Drip irrigation is preferred over overhead sprinkling because it does not wet foliage and does not create conditions for fungal spore germination (Phillips, 2005).
• If using sprinkling, do it in the morning so that leaves dry by evening. This reduces the risk of night‑time infection by scab and other fungi (Ferree et al., 2003).
• Avoid prolonged waterlogging — it provokes root rots. In arid regions, on the contrary, lack of moisture weakens trees and makes them vulnerable to Cytospora canker and fire blight (Westwood, 1993).

Mulching of tree trunks with organic materials (compost, mown grass, straw) helps retain moisture and improve soil structure, but do not allow mulch to touch the root collar — this may cause collar rot (Phillips, 2005).

Pruning and Canopy Formation

Correct pruning is a powerful preventive measure.

• Thinning the canopy improves light and ventilation. Leaves and fruits dry faster after rain, hindering the development of scab, powdery mildew and fruit rots (Agustí, 2010).
• Removal of diseased and dry branches — sanitary pruning, which we will discuss separately.
• Rejuvenation pruning of old trees stimulates healthy shoot growth, but should be done gradually to avoid weakening the tree.
• Summer pruning (pinching, tipping) can reduce susceptibility to fire blight by removing soft growing tips during unfavourable periods (Phillips, 2005).

Important: always disinfect tools when pruning diseased branches. This is not only a sanitary measure but also an agronomic practice that prevents infection transmission (Buckingham, 2010).

Weed and Ground Cover Management

Weeds can be reservoirs of diseases and pests, and also create excessive moisture near the trunk.

• Trunk strips should be kept free of weeds — this improves root collar aeration and reduces the risk of root rots.
• Between rows can be sown with green manures or kept as permanent sod. However, tall grass promotes moisture accumulation and provides shelter for field mice, which damage bark. Regular mowing reduces these risks (Phillips, 2005).
• In arid regions, mulching tree trunks helps retain moisture and suppresses weeds.

Removal of Fallen Leaves

Leaves are the main overwintering site for scab pathogen (Venturia inaequalis) and some other fungi. In spring, spores are released from overwintered leaves, infecting young leaves and fruits (Ferree et al., 2003).

What to do:

• In autumn after leaf fall, collect and remove fallen leaves from the orchard (burn, compost separately, or incorporate into soil to a depth of 10–15 cm).
• Shredding leaves with a lawnmower or special machines accelerates decomposition and reduces the number of surviving spores (Phillips, 2005).
• Spraying leaves with urea (5% solution) in late autumn or early spring stimulates decomposition of leaf litter and destroys some spores (Ferree et al., 2003). In organic gardening, nettle infusions, compost tea, or EM‑preparations are used.
• In regions with severe scab development, removing leaves is recommended — it gives an effect comparable to 1–2 fungicide treatments (Jackson, 2003).

Removal of Mummified Fruits

Affected fruits that remain hanging on the tree (mummies) are a source of overwintering infection for fruit rots (moniliosis, anthracnose) (Agustí, 2010; Buckingham, 2010).

• In autumn and winter, remove and burn all mummified fruits.
• Also collect and destroy fallen fruit throughout the season.

Sanitary Pruning of Diseased Branches

Diseased branches with cankers, wounds, signs of fire blight, Cytospora canker and other trunk diseases should be removed with a margin of healthy tissue:

• For fire blight — cut 20–30 cm below the visible edge of infection (Ferree et al., 2003).
• For Cytospora canker and Nectria canker — at least 10–15 cm below the affected area.
• All cut diseased branches must be burned immediately; do not leave them in the orchard or put them in ordinary compost (Agustí, 2010).
• After pruning diseased trees, disinfect tools — wipe secateurs, saws, loppers with alcohol (70%) or a bleach solution (1:9 with water) (Buckingham, 2010; Phillips, 2005).

Cleaning Bark from Dead Areas

Under peeling bark, pests and fungal spores overwinter.

• Cleaning trunks of old dead bark (scraping with a wire brush or scraper) in dry autumn weather removes pathogen overwintering sites.
• Wounds and exposed wood should be covered with grafting wax or a special sealing compound to protect against infection entry (Westwood, 1993).

Control of Disease Vectors

Insects (aphids, leafhoppers, bees, flies, nematodes) often serve as vectors of viruses, bacteria and fungal spores.

• Regular monitoring and timely treatments against sucking insects reduce the spread of viruses and fire blight (Ferree et al., 2003).
• During flowering, use biological control methods (attracting entomophages, using bacterial antagonists) so as not to harm bees.
• Remove wild Rosaceae near the orchard (hawthorn, wild apples, mountain ash) — they are reservoirs of fire blight and rust (Jackson, 2003).

Spatial Isolation

• Do not plant apples near junipers (source of rust). If junipers are present, remove them or at least prune branches with galls (Ferree et al., 2003).
• Do not place new plantings near abandoned old orchards where there is a lot of infection.
• Maintain spacing between rows for good ventilation.

Resistance to Apple Scab

Scab is the main enemy of apple in humid climates. The Vf gene (from Malus floribunda 821) confers resistance to most scab strains. Based on it, well‑known varieties have been bred:

• ‘Liberty’ — highly resistant to scab and powdery mildew, moderately resistant to fire blight (Rieger, 2006; Phillips, 2005).
• ‘Enterprise’ — resistant to scab and rust, moderately resistant to fire blight.
• ‘GoldRush’ — resistant to scab and rust, but susceptible to powdery mildew (Phillips, 2005).
• ‘Redfree’ — very resistant to scab, early maturing.
• ‘Florina’ (Querina) — resistant to scab, powdery mildew, relatively resistant to fire blight.
• ‘Jonafree’, ‘Macfree’, ‘Priscilla’, ‘Trent’ — also have scab resistance (Rieger, 2006).
• ‘Dayton’, ‘Pristine’ — modern resistant varieties with good flavour (Phillips, 2005).

Important: resistance to scab does not mean absolute protection against other diseases (powdery mildew, rots, fire blight). Choose varieties with complex resistance.

Resistance to Powdery Mildew

• Varieties with the Pl gene (from Malus zumi and M. robusta) show resistance to powdery mildew (Jackson, 2003).
• Well‑proven: ‘Liberty’, ‘Florina’, ‘Enterprise’, ‘Prima’, ‘Priscilla’ (Phillips, 2005).
• Varieties ‘Jonafree’, ‘Redfree’ also have tolerance.

Resistance to Rust

Rust is a problem where junipers exist. Resistant varieties:

• ‘Enterprise’ and ‘Liberty’ — best for rust resistance (Phillips, 2005).
• ‘William’s Pride’ — has good resistance.
• ‘McIntosh’, ‘Cortland’, ‘Empire’ — moderately resistant, but in years of high pressure may be affected (Phillips, 2005).
• Avoid susceptible varieties: ‘Jonathan’, ‘Rome’, ‘Gala’ (they are heavily affected by rust) (Ferree et al., 2003).

Resistance to Fire Blight

Complete resistance does not exist, but varieties differ greatly in susceptibility (Ferree et al., 2003; Jackson, 2003):

• Relatively resistant: ‘Delicious’ (and its clones), ‘McIntosh’, ‘Empire’, ‘Liberty’, ‘Enterprise’, ‘Florina’, ‘Jonafree’.
• Moderately susceptible: ‘Golden Delicious’, ‘Gala’, ‘Fuji’, ‘Braeburn’, ‘Jonagold’.
• Highly susceptible: ‘Cox’, ‘Idared’, ‘Rome’, ‘Granny Smith’.

Rootstocks also play a role. Resistant rootstocks to fire blight: G.16, G.30, G.65, Bud.9. Very susceptible are M.9, M.26, MM.106 (Jackson, 2003; Ferree et al., 2003). If there is a risk of fire blight in your region, prefer resistant rootstocks, even if they are less dwarfing.

Rootstocks Resistant to Diseases

• Root rots (Phytophthora) resistant: M.9, G.16, G.30, seedlings. Susceptible: MM.106, M.26 (Rieger, 2006; Westwood, 1993).
• Woolly aphid (Eriosoma lanigerum) resistant: rootstocks of the MM (Malling‑Merton) series with an admixture of ‘Northern Spy’, e.g., MM.106, MM.111 (though MM.106 is susceptible to Phytophthora) (Agustí, 2010; Jackson, 2003).
• Viruses — most commercial rootstocks are tolerant, but some sensitive rootstocks (e.g., ‘Virginia Crab’) should not be used with infected scions (Ferree et al., 2003).

How to Choose a Variety for Your Region

1. Find out which diseases are most common in your area (consult local agronomists or nurserymen).

2. Choose varieties with complex resistance to 2–3 major diseases.

3. For commercial orcharding, consider market demand, but for home gardens it is better to sacrifice some popularity for the sake of health.

4. Purchase saplings only from certified nurseries that guarantee the health of the planting material.

Antagonistic Microorganisms

Some bacteria and fungi suppress pathogen development by competing for space and nutrients or by producing antibiotic substances.

Antagonistic bacteria:

• Against fire blight (Erwinia amylovora) products based on Pseudomonas fluorescens and Bacillus subtilis have been developed. They are applied to flowers during bloom and prevent the pathogen from establishing on the stigma. Studies show that the effectiveness of such products can reach 90% under favourable conditions (Phillips, 2005; Jackson, 2003). Products are available under trade names (Blight Ban, Serenade, etc.) in some countries.
• Against fruit rots (moniliosis, anthracnose), strains of Bacillus subtilis and yeast‑like fungi are being studied, but in practice their use is still limited (Phillips, 2005).

Antagonistic fungi:

• Some species of Trichoderma and Gliocladium suppress root rots (Phytophthora, Armillaria) and other soil‑borne pathogens. They can be applied to soil before planting or around tree trunks. Effectiveness depends on soil type and organic matter content (Jackson, 2003).
• For scab control, research is underway on fungi that decompose leaf litter and reduce the number of overwintering pseudothecia (Ferree et al., 2003).

Compost tea and microbial preparations:

• Aerated compost tea, containing a rich community of beneficial bacteria and fungi, is sprayed on leaves to create a protective microbial layer. When properly prepared, tea can cover the leaf surface by 60–70%, reducing the likelihood of fungal infection (Phillips, 2005).
• The effectiveness of compost tea varies depending on compost quality, preparation method and weather conditions. It works as a preventive measure, but does not cure already developed infection.

Application of Parasitic Nematodes

Although nematodes are more often used against insect pests, there is evidence of their effectiveness against some soil‑borne pathogens. For example, nematodes of the genus Steinernema can penetrate the larvae of insects that are vectors of diseases, thereby reducing the spread of infection (Agustí, 2010; Westwood, 1993). Nematodes are not used directly against fungi.

Stimulation of Plant Own Immunity

Some substances (inducers) activate the plant’s own defence responses — so‑called systemic acquired resistance (SAR).

• Salicylic acid and its derivatives are natural inducers, but are rarely used in horticulture.
• Chitosan (from crustacean shells) — stimulates the production of phytoalexins and strengthens cell walls. Used in some biological products.
• Plant extracts — horsetail infusion (rich in silicon), nettle or tansy can increase resistance to fungi by strengthening the cuticle and creating an unfavourable environment for pathogens (Phillips, 2005).

Limitations of Biological Methods

• Slow action — biological products do not give an instant effect like chemical fungicides.
• Dependence on conditions — effectiveness strongly depends on temperature, humidity and time of day.
• Short period of activity — many antagonists live on leaves for a short time and require frequent reapplication.
• Not suitable for emergency situations — during disease outbreaks, biological methods often fail to contain spread in time.

Classification of Fungicides

Contact (protective) fungicides — act on the plant surface, killing fungal spores on contact. Do not penetrate tissues. Require thorough and uniform coverage of all plant parts. Washed off by rain and need repeated applications (every 7–14 days depending on rainfall).

• Sulphur — a classic contact fungicide against powdery mildew and scab. Effective at 15–27 °C; at higher temperatures it causes leaf burn. Permitted in organic gardening but requires frequent application (Phillips, 2005).
• Copper‑based products (Bordeaux mixture, copper oxychloride, C‑O‑C‑S) — effective against scab, powdery mildew, fire blight (during dormancy) and Cytospora canker. However, copper accumulates in soil, is toxic to earthworms and beneficial microorganisms, so its use should be moderate (Agustí, 2010; Phillips, 2005).
• Captan, thiram, dithianon — synthetic contact fungicides with a broad spectrum, used against scab, fruit rots and other fungi. Relatively safe for beneficial insects (Ferree et al., 2003).
• Dithiocarbamates (maneb, mancozeb, zineb) — effective against scab, but have application restrictions (Agustí, 2010).

Systemic (penetrating) fungicides — absorbed by the plant and distributed through the vascular system. They act not only on the surface but also inside tissues, suppressing fungal development after penetration. They have curative (eradicative) effects: can stop infection within 24–96 hours after infection (Ferree et al., 2003).

• Triazoles (tebuconazole, penconazole, difenoconazole) — widely used against scab, powdery mildew and rust. Long duration of action (10–14 days). However, fungi can develop resistance, so rotation is required (Jackson, 2003).
• Benzimidazoles (benomyl, thiophanate‑methyl) — previously widely used, but due to resistance development in scab and rot pathogens, they are now used less frequently or in mixtures (Ferree et al., 2003).
• Strobilurins (azoxystrobin, trifloxystrobin) — modern fungicides with a broad spectrum and long action. Effective against scab, powdery mildew, fruit rots. Require rotation with products from other groups to prevent resistance (Agustí, 2010).
• Acylalanines (metalaxyl) — systemic fungicides active against Phytophthora fungi (Phytophthora), used against root rots (Agustí, 2010).

Principles of Selection and Application

1. Disease identification — make sure you have correctly identified the pathogen. Not all fungicides work on all fungi. For example, sulphur is effective against powdery mildew, less so against rust.

2. Timing of treatments — for fungal diseases, spraying before or immediately after the infectious period (rain) is critical. For scab, treatments begin at the “green tip” stage and continue until the end of flowering, then as needed (Ferree et al., 2003). For powdery mildew — from “pink bud” until shoot growth ceases. For fire blight — during flowering under favourable weather conditions (Jackson, 2003).

3. Alternation of products — to avoid resistance, do not use the same systemic fungicide more than 2–3 times per season. Change chemical classes: triazoles → strobilurins → dithiocarbamates → captan, etc. (Ferree et al., 2003; Agustí, 2010).

4. Pre‑harvest intervals — each product has a minimum interval between the last treatment and harvest. Strictly observe it for consumer safety.

5. Quality of spraying — thorough coverage of all parts of the tree (especially the underside of leaves, the inner part of the canopy) is critical. Use sufficient water volume (at least 1000–1500 L/ha for mature trees; in the home garden — until leaves are completely wetted) (Westwood, 1993).

6. Weather conditions — do not spray in strong wind, rain, or hot midday. Optimal time — early morning or evening, when temperature is below 25 °C and there is no direct sun.

Safety Measures

• Use personal protective equipment: gloves, goggles, respirator, protective clothing.
• Prepare solutions outdoors, away from children and animals.
• Do not exceed recommended dosages.
• Do not pour leftover solution into water bodies or soil in large quantities.
• Dispose of empty packaging according to local regulations.

When Chemical Treatments Are Necessary

• Under high infectious pressure (history of diseases in previous years).
• In years with prolonged rains and cool spring weather (risk of scab and fire blight).
• For susceptible varieties lacking genetic resistance.
• In commercial orchards where requirements for fruit appearance are high.

Important: chemical treatments are a tool, not a panacea. Even when using them, preventive and sanitary measures must be maintained.

Principles of Integrated Protection

1. Monitoring — regular inspection of the orchard to detect early signs of diseases and pests. Use:

• Visual inspections of leaves, shoots and fruits (at least once a week during the growing season).
• Pheromone and coloured traps for insect vectors (Phillips, 2005).
• Weather stations or weather data to calculate infectious periods (e.g., using the Mills table for scab) (Ferree et al., 2003).
• Indicator varieties that show symptoms earlier than main ones (Jackson, 2003).

2. Forecasting — use models to determine optimal timing for protection measures:

• For scab — heat accumulation models (degree‑days) to predict ascospore maturation and infection periods (Ferree et al., 2003).
• For fire blight — forecasting systems (Maryblyt, Cougarblight) that take into account temperature, humidity and flowering stage (Jackson, 2003).
• For powdery mildew — the Podem model, which calculates favourable conditions for infection spread (Ferree et al., 2003).

3. Economic thresholds — decisions on chemical applications are made only when expected damage exceeds treatment costs. For hobby gardeners, this principle means: do not treat “just in case”, assess the real threat (Agustí, 2010).

4. Priority of non‑chemical methods — first apply preventive (agronomic, sanitary) and biological measures. Chemical treatments are a last resort when other methods are insufficient.

5. Choice of products with minimal impact — prefer selective, low‑toxicity products for beneficial organisms. Use biologicals where possible.

6. Alternation and rotation — to prevent resistance, alternate fungicides of different groups, and also combine them with biological agents.

Example of an Integrated Strategy for Apple (by season)

Autumn — winter:

• Collect and destroy fallen leaves and mummified fruits.
• Sanitary pruning and removal of diseased branches.
• Clean bark on trunks.
• If necessary — liming soil and application of potassium‑phosphorus fertilisers.
• Treatment with copper‑based products on bare branches (if there were severe outbreaks of fire blight or Cytospora canker) — 1 application (Agustí, 2010).

Spring (before flowering):

• From “green tip” to “pink bud” — first treatment against scab (in wet weather) — contact or systemic fungicide (Ferree et al., 2003).
• If high risk of fire blight — apply biological products (antagonists) or (in extreme cases) antibiotics during flowering according to forecast (Jackson, 2003).
• Set up pheromone traps for pest monitoring.

Flowering — end of flowering:

• Scab treatments at 7–14 day intervals (depending on rainfall). Alternate contact and systemic products.
• Protection against powdery mildew — sulphur or triazoles.
• If necessary — treatment against fire blight (biologicals or antibiotics if forecast is critical).
• Do not apply insecticides during flowering to avoid harming bees.

Summer:

• Continue scab treatments (until shoot growth ceases) and powdery mildew (as needed).
• In warm wet weather — protect against fruit rots (captan, systemic products) 3–4 weeks before harvest.
• Regular inspections for signs of fire blight, timely pruning of affected branches.
• Maintain watering and nutrition to strengthen immunity.

Harvest and after:

• Careful fruit picking to avoid damage that promotes storage rots.
• Treat fruits with biological or chemical agents (if permitted) to extend storage life (Agustí, 2010).
• Autumn sanitation measures.

Advantages of Integrated Protection

• Savings — reduction in chemical treatments due to accurate forecasting.
• Environmental friendliness — preservation of beneficial insects, soil microflora and biodiversity.
• Sustainability — reduced risk of resistance development in pathogens and pests.
• Quality of harvest — fruits contain fewer pesticide residues and have better flavour (Phillips, 2005).