**4. Fungal disease on strawberry plants**

*Colletotrichum acutatum* and *Botrytis cinerea* are the most common pathogens in the strawberry field. Among the fungal pathogens, *B. cinerea* causes significant economic losses in the strawberry industry. In wet conditions, more than 80% of strawberry flowers and fruit can be lost if plants are not sprayed with fungicide [58, 59]. Strawberry quarantine agents include *Colletotrichum acutatum, Botrytis cinerea,* and *Phytophthora* spp. It is included in the EPPO A2 list, but as of 2015, only *Phytophthora fragariae, Verticillium dahliae, Verticillium albo-atrum,* and *Fusarium oxysporum* are included in the final A2 list [60].

Common Leaf spot (*Mycosphaerella fragariae* [Tul.] Lindau): The leaf spot pathogen, *Mycosphaerella fragariae, also* recognized as Mycosphaerella leaf spot, "rust or white spot. This disease starts on leaves as purplish spots that look like leaf scorch. Plant vigor, fruit quality, and yield are reduced by leaf spot disease [61]. Typical symptoms are on the leaves small and circular leaf spots. Leaf lesions start as small,

deep purple, irregular-shaped necrotic spots on the upper leaf surface. *M. fragariae* also causes spots on fruit, petioles and cause black seeds. Plants are mostly susceptible early in the growing season. Spores of the fungus form on the spots and are spread by rain, by farm implements, or on hands when plants are wet [61, 62]. The use of resistant varieties is the utmost practical and efficient method to control leaf spot disease. Timely applications of protective fungicides and non-infected nursery plants are suggested (**Figure 1**) [63].

Antracnose (*Cercospora fragariae*): Anthracnose leaf spot disease of strawberry which caused by *Colletotrichum acutatum, C. gloeosporioides,* and *C. fragariae* species. Lesions are circular, irregular purplish/reddish, with very light-colored centers seeming merely on the upper surface and small. The spots look like usual leaf spots (caused by *M. fragariae*) but are tinier with lighter centers and further uneven shapes [64]. Lesions are dark brown, almost black, and slightly sunken on petioles and fruit. Spore production appears on the leaf, in the white centers, which develop dotted with tiny dark stroma or knots of fungal cells. Infested buds and flowers may become dry and weakened. Spread of pathogen inoculums by rain and by irrigation as well as by movement of farmer beings and animals [65]. The control of leaf spots is very difficult; fungicides may not be very effective against anthracnose of strawberries. Anthracnose can be lessened using disease-free nursery plants and elimination of infected fruit and plants from fruiting fields followed by prompt fungicide applications subsequently each rain period. In addition, resistant cultivars should be used (**Figure 2**).

Powdery Mildew (*Sphaerotheca macularis f.sp. fragariae*): Powdery mildew, caused by the fungus *Sphaerotheca macularis f.sp. fragariae* results in purplish or reddish blotches on leaves and sometimes a powdery growth. This fungus is an obligate pathogen and survives only in the living tissues of its host. This pathogen affects all aboveground parts of (leaves, flowers, etc.) the strawberry plant. In susceptible cultivars, white Powderly mycelium mass develops on the lower leaf surface. Flowers and fruit in all stages of development are susceptible to attack. Infected mature fruit remains soft and pulpy. The major effect of this pathogen is that it weakens plants and reduces yields [61, 66, 67]. The application of protective fungicides is an effective method

#### **Figure 1.** *Symptoms of common leaf spot (*Mycosphaerella fragariae *[Tul.] Lindau) in strawberry leaves.*

*Pests, Diseases, Nematodes, and Weeds Management on Strawberries DOI: http://dx.doi.org/10.5772/intechopen.103925*

**Figure 2.** *Symptoms of Antracnose (*Cercospora fragariae*) in strawberry plants.*

of control. In addition to controlling powdery mildew, to use of resistant cultivars recommends. Farmers should prefer plantings with disease-free plants and mowing as suggested to remove infected plants (**Figure 3**) [68].

Gray Mold (*Botrytis cinerea*): Gray mold caused Botrytis cinerea by is a significant disease in strawberry production, which utterly affects the yield and quality of strawberries. *B. cineria* affects fruit in the field, storage, transport, and market. This pathogen is also known as 'Botrytis rot fruit' which causes huge losses in the field (more than 80% loss) during rainy and cloudy periods, just before or during harvest and storage [69]. *B. cinerea* can live in soils such as sclerotia or mycelium. Infection usually begins in fruits that come into contact with the soil. Gray mold affects flowers and green or mature fruit. Infection begins in the flower and may enter the calyx or stem, later causing fruit rot [61]. Control measures that can be taken to diminish losses due to Botrytis fruit rot contain preventing excessive vegetative growth by regulating plant density, removing diseased fruits from the field, timely fertilization, harvesting the fruit before it is fully ripe to prevent injuries, and rapid transfer of the harvested fruits to the cold storage. Protective fungicide application is recommended during the flowering period (**Figure 4**) [70].

Fungal disease also damages the roots of strawberries*. Rhizoctonia solani, Fusarium oxysporum, Pythium* sp. cause root rot disease in strawberries. In addition to the difference in the disease factor in a region, factors such as root rot formation, accumulation of soil water, oxygen deficiency in the soil, and temperature were also found to be efficient in the growth of the disease [71]. Roots die as a result of prolonged water accumulation in the soil. Instead of these roots, short thick new rootlets are formed [71]. Root rot disease agents (*Rhizoctonia solani, Fusarium oxysporum, Pythium sp*.)

#### **Figure 3.** *Symptoms of powdery mildew (*Sphaerotheca macularis f.sp. fragariae*) in strawberry plants.*

**Figure 4.** *Symptoms of Gray Mold (*Botrytis cinerea*) in strawberry fruits.*

cause stagnation in development, shrinkage of leaf surfaces, shortening of leaf stalks are in the form of drying of leaves and wilting of plants as the disease progresses. In the sub-soil part, due to the disease, the hairy roots quickly turn black and rot. Easily peeling of the bark is one of the most typical features of the disease [71]. When the roots are damaged, there is a pause in plant growth, shortening, and shrinking of the leaves. As the disease progresses, the main roots turn black and rot. With the intense death of the hairy roots, the plant loses its vitality and efficiency and dies suddenly [71]. Macrophomina crown rot (*Macrophomina phaseolina)* is also an important strawberry disease that causes plant stunting, drying of older leaves, wilting of leaves, and discoloration, which are some of the symptoms in strawberries plants [71].

Phytophthora Crown Rot of Strawberry (*Phytophthora cactorum*) causes the collapse of plants, and dark red discoloration of the crown is seen. Plants are stunted, or young leaves are wilted as initial symptoms, the disease progresses, widespread necrosis appears that is homogeneously brown in tissues [71].
