from 5.5 to 6.5, so lime is usually not applied. The harvesting and cleaning process has not changed substantially over time. The delicate strawberries are still harvested by hand. Grading and packing often occurs in the field, rather than in a processing facility. In large operations, strawberries are cleaned by means of water streams and shaking conveyor belts. Pests Around 200 species of pests are known to attack strawberries both directly and indirectly. These pests include slugs, moths, fruit flies, chafers, strawberry root weevils, strawberry thrips, strawberry sap beetles, strawberry crown moth, mites, aphids, and others. The caterpillars of a number of species of Lepidoptera feed on strawberry plants. For example, the ghost moth is known to be a pest of the strawberry plant. The strawberry aphid, Chaetosiphon fragaefolii, is a bug species found in the United States (Arizona), Argentina and Chile. It is a vector of the strawberry mild yellow-edge virus. The amounts of pesticides required for industrial production of strawberries ( in California per acre) have led to the strawberry leading the list of EWG's "Dirty Dozen" of pesticide-contaminated produce. Diseases Strawberry plants can fall victim to a number of diseases, especially when subjected to stress. The leaves may be infected by powdery mildew, leaf spot (caused by the fungus Sphaerella fragariae), leaf blight (caused by the fungus Phomopsis obscurans), and by a variety of slime molds. The crown and roots may fall victim to red stele, verticillium wilt, black root rot, and nematodes. The fruits are subject to damage from gray mold (Botrytis cinerea), rhizopus rot, and leather rot. To prevent root-rotting, strawberries should be planted every four to five years in a new bed, at a different site. The , AtNPR1, confers A. thalianas broad-spectrum resistance when transexpressed in F. ananassa. This resistance includes resistance to anthracnose, powdery mildew, and angular leaf spot. A 1997 study assessed many and found all effective against gray mold (B. cinerea). Both Tribute and Chandler were tested and benefited from the treatments, although there are large differences between the substance x variety effects. Strawberry metabolizes these volatiles, and does so more rapidly than either blackberry or grape. The plants can also develop disease from temperature extremes during winter. Watering strawberry roots, and not the leaves, is preferred as moisture on leaves encourages fungal growth. Strawberries may also often appear conjoined together or deformed due to poor pollination. Domestic cultivation Strawberries