Apple scab is a common and one of the most serious diseases of apple trees, causing a significant reduction in yield and deterioration of its quality. Symptoms of apple scab are most often visible on leaves and fruits, but the fungus also infects petioles, parts of the flower, and sometimes buds and shoots. Apple scab symptoms on leaves are brown-olive spots darkening with time, which mainly occurs on the upper side of the leaf blade. Strong pathogen pression can even cause leaf deformation in the place of spots.
Heavily infected leaves often fall off the tree too early, especially during drought. The presence of even a few spots on apple leaves has a negative effect on growth and fruiting due to disturbing the water relations in the tree and limiting the production of assimilates. The symptoms of apple scab on fruits are characteristic, dark, round spots within which the skin becomes necrotic. Early infection of fruit primordia leads to their deformation or cracking and the intensification of symptoms may cause premature fall of fruit primordia. In addition, infecting of fruits just before harvest leads to the development of pinpoint scab (storage scab).
Apple scab is caused by fungus Venturia inaequalis, which overwinters in fallen leaves infected during the growing season. Sometimes infected twigs or bud scales can also be a source of conidia infecting young apple tissues in the spring. The fungus overgrows tissues of fallen leaves, remaining on the ground. During this time occurs ascogamy - the sexual reproduction process and fruiting bodies are formed as a result of oogonium fertilization. Temperature in the range of 4oC – 10oC and high soil moisture are the most favourable conditions for forming fruiting bodies, which can be visible on fallen leaves as tiny, black spots. Fruiting bodies mature successively in the spring. Asci with ascospores are formed in the maturing fruiting bodies. Initially the ascospores are colorless and with the time they turn into olive green color, what indicates their maturity and ability to be released.
The protection of apple tree against apple scab consist in selecting cultivars that are less sensitive or resistant to apple scab, but first and foremost in application of appropriate plant protection products and limiting potential ascospore dose (PDA). Potential ascospore dose (PDA) is one of the most important factor affecting intensity of infection in orchard. PDA is the number of ascospores formed per 1 m2 of orchard, which is directly proportional to last year's leaf infection in the orchard (observed in the autumn of the previous year). PDA results from the level of leaf infection and can be modified by many factors, such as date of leaf falling, temperature and humidity of air and soil after leaf falling, apple tree cultivar as well as content of nutrients in soil, especially nitrogen and, related to the nitrogen level, presence of microorganisms inhibiting the formation of Venturia inaequalis ascospores and decomposing apple leaves fallen from trees. For many years urea has been used as standard formulation intended for decomposition of fallen leaves and thus limiting PDA. Applying urea became part of the apple tree protection program. However, due to the environmental protection and contamination of water with nitrates, there is a need to look for a different solution. In addition, in EU countries, due to regulatory changes, from the 2021 season, urea is available only in the combination with urease inhibitors or in the form of polymer-coated granules. Such forms of urea have not yet been tested in experiments aimed at accelerating decomposition of apple leaves in orchards. In such a situation, BACTIM® LEAVES becomes a perfect alternative in terms of limiting the source of infection caused by apple scab.
BACTIM® LEAVES is a fertilizer intended for accelerating decomposition of apple leaves, indirectly limiting the source of infection of fungus Venturia inaequalis, causing apple scab. The fertilizer is enriched with FORMULA FAST - consortium of Bacillus spp. bacteria. Bacteria contained in BACTIM® LEAVES have a high ability to decompose cellulose and pectin, which are integral part of apple leaves. Quick decomposition of pectin and cellulose causes the destruction of internal cells of fallen apple leaves. The destruction of leaf structure leads to the decomposition of leaf blades, which limits the possibility of forming Venturia inaequalis fruiting bodies causing apple scab. It results in the reduction of fruiting body number and limits the possibility of fruiting body maturation in spring. Limiting number of fruiting bodies formed on fallen leaves contributes to the lower number of Venturia inaequalis ascospores ready to be released in spring. Lower number of ascospores limits probability of young apple tissue infection and therefore increases the effectiveness of applied fungicides. BACTIM® LEAVES should be applied on trees just before the leaf falling. The product may also be used for spraying fallen leaves remaining on the ground, immediately after their falling.
Unique combination of FAST FORMULA and starting dose of nitrogen – effective decomposition of apple leaves
The results of studies showed that application of BACTIM® LEAVES , via spraying apple trees in the fall just before leaf falling, similarly to urea leads to a quick and effective decomposition of apple leaves (Figure 1 and Figure 2).
Faster decomposition of apple leaves contributes to the reduction in the number of fruiting bodies of Venturia inaequalis (Figure 3). Reduction of fruiting body number, formed on fallen leaves, leads to the lower number of Venturia inaequalis ascospores released in the spring. Lower number of ascospores limits probability of the young tissue infection.
The benefits of using BACTIM® LEAVES include accelerating decomposition of fallen apple leaves, which limits the source of infection of the fungus Venturia inaequalis, causing apple scab. Limiting the possibility of fruiting body ripening reduces the infectious potential of orchard, thus increasing the effectiveness of fungicide protection. Less utilization of fungicides, due to pressure from the pathogen, results in decreasing level of fungicide residues in fruits, reduces cost of fungicide protection in orchard and lowers probability of developing resistance of fungus Venturia inaequalis to fungicides. In addition, limiting use of urea for decomposition of leaves reduces the contamination of the environment with nitrogen fertilizers.