Fungal, bacterial, and viral pathogens and pests attack the plant throughout the growing season. They not only reduce the yield but also reduce its quality. Plants that are severely affected may not produce at all or may even die. Diseases affect different parts of the plant: stems, leaves, flowers, berries, and shoots. When introducing plants from natural habitats or from other countries, it is very important that the plants selected for propagation or the varieties introduced into production are resistant to the most common fungal diseases. Several diseases have been diagnosed in the country’s natural lingonberries and their causal agents identified.
Exobasidiosis (causal agent Exobasidium vaccinii (Fuck.) Woron., Figure 4)
The fungus damages the stems, leaves, flowers, and stamens of plants. The first signs of the disease appear in May-June. The plant tissues thicken in the affected areas. Initially, the lower half of the leaves are whitish and the upper half turns reddish. The fungus is spread by basidiospores. Affected parts of the plant break easily. Microtomic sectioning showed that the damaged cells do not die but grow faster (Figure 5). These cells are 2-4 times larger than normal cells. The shape of the damaged cells changes – they become elongated and abnormally long. If the stem or the peduncles with flowers are affected by the fungus, the plants are not suitable. Damage to the leaves results in lower yields and poorer quality plants. The disease agent is widespread in all the country’s natural lingonberries. It often affects 30% of plants. Disease intensity is 20-30%.
Leaf spot (causal agent Mycosphaerella stemmatea (Fr.) Schröt., Fig. 6)
The disease agent damages the leaves. Initially, the leaf lesions are reddish-black, then greyish-black, dry, irregular, oval-shaped spots of varying sizes (4-7 mm). Sometimes the spots merge. The affected leaf cells decompose and dry out. This can be seen by microtomic sectioning (Figure 7). On the upper half of the leaf, black dots are visible in the demesne. These are the fruiting organs of the pathogen. It often affects about 20 % of plants. Disease intensity is 5-10%.
Rust (causal agent Thekopsora myrtii (Schum.) Tranz
Small brown dots – calyxes – are visible on the underside of the leaves. This disease is relatively rare and its damage to beetroot is not significant.
Degradation (causal agent Gloeosporium myrtilli Allesch.)
Small, rounded, irregular, brown spots surrounded by a purple border on both sides of the leaves. This is a relatively rare disease of lingonberry and is of no major importance for the introduction of these plants.
Berry rot (causal agent of Sclerotinia vaccinië Woron.)
A white, cotton-wool-like mycelium forms on the surface of the berries. After a while, the mycelium begins to disappear as the sclerotia of the fungus form. Initially, they are white, but as they age the surface becomes black. The mycelium of the disease-causing agent may also develop inside the berries. The berries then decay without any outward signs. The pathogen spreads strongly where it is moist.
Protecting lingonberries against disease
The main and most important measure to protect against pathogens is the selection of healthy seedlings when introducing new plantations. Subsequently, the plantations must be maintained: weed control and fertilization with complex fertilizers. Nitrogen fertilizer should be used sparingly. Overwatering will also have a negative effect on the plants.
Without waiting for pathogens to damage the plants, at the beginning of the growing season and after harvesting, the plants should be sprayed with a 1% Bordeaux mixture prepared as follows: 10 g of copper sulfate dissolved in 0,5 l of water, 15 g of quicklime also dissolved in 0,5 l of water. The two solutions are mixed and the resulting solution is sprayed on the lingonberries. The recommended rate of the solution is 1,5 liters per 10 square meters of lingonberry plant. It is advisable to use chemical protection only in the first half of the growing season and after harvesting.
According to data published in the press and our experience, the most common pests affecting lingonberries are flea beetles, ring beetles, and aphids (Stephanitis oberti Kol., Exapate congenatella Cl., Rhopobota naevana (Hbn.). The pests must be eradicated as they not only feed on the plant but can also transmit mycoplasma and viral pathogens.
The lingonberry is an evergreen plant, so its leaves are eaten by a variety of wild herbivores in winter.