**8. Plant protection**

Alongside the expanding export to Europe during late 1990s, the approach to plant protection issues has drastically shifted from massive use in pesticides to biologically based integrated pest management. For this purpose, specific beneficial insects such as wasps and predator mites against strawberry pests make chemical use against pests almost unnecessary.

The mostly common pest in greenhouses-grown strawberry is the red spider mite (*Tetranychus urticae*) that feeds from chloroplasts in the leaves, leaving typical yellowish signs. At high infestation levels, leaves and whole plants are severely damaged and fruit production declines. Although red spider mite is the main pest throughout the growing season, its population substantially declines during cold periods. Therefore, the risk of red spider mite infestation of winter strawberries occurs mainly during crop establishment in October-November or during March-April, and is subject to weather fluctuations. To date, red spider mites are effectively treated using the predator mite *Phytoseiulus persimilis* (Bio-Bee, Israel). These predatory mites are applied at the beginning of the season, when it is still warm, and a balance is reached between the pest and the predator populations. As long as this balance is preserved, no pesticides are needed. However, once disrupted (e.g., in incidents of hot and dry weather), the balance must be re-established using a pesticide spray.

More recently, infestation by Castor thrips (*Scirtothrips dorsalis*) has been increasingly observed. This pest causes blackening of main leaf veins and petioles and to growth retardation. Such infestation may be acute mainly during autumn, when high temperatures and humidity stimulate pest population and, if not treated timely and appropriately using Abamectin or Spinosad, the damage to the young seedlings might be quite severe.

Strawberries are susceptible to a wide range of plant diseases. The hung growbags culture, which provides enhanced aeration and light interception for the canopy, reduces risks of canopy diseases related to high air humidity or long-lasting dew. Strawberry gray mold (*Botrytis*), a well-known disease under cold and moist conditions, hardly occurs on fruit hanging in the air. In a similar way, anthracnose (mainly *C. acutatum*), which often spread under warm and humid conditions when grown on plastic-covered soils, rarely strikes the hung strawberry culture. In contrast, powdery mildew (*S. macularis*), which harms greenhouse crops primarily in the fall, requires careful attention. Practically, susceptible cultivars, such as 'Tamir', are gradually withdrawn from the lists of cultivars recommended to farmers. Avoiding contaminated young plug plants is of primary importance. Under conditions of warm and dry days followed by cool and humid nights, powdery mildew can be efficiently prevented using sulfur vaporizers during the night. In case of disease outbreak, mild chemical sprays that are even permissible for use according to the organic standard are quite effective.

Soil-borne diseases are extremely rare in the hung growbag technology, particularly when propagation is carried out according the methods described above. Among soil diseases, *Macrophomina phaseolina* has recently become a threat endangering

increasing areas of various crop species, including soil-grown strawberries [47, 48]. This pathogen might be introduced to a hung strawberry greenhouse only through contaminated plug plants, which must be carefully avoided. So far, no chemicals were found adequately effective against *Macrophomina* and hence, in case it does occur, an early removal of the infected growbags should easily solve the problem.

Nevertheless, the main and long-term strategy is breeding for disease-resistant cultivars. Alongside the approach of minimum use of chemicals and no plant growth regulators, this crop protection strategy supports high yields of high quality offseason strawberries.
