Determination of damage threshold levels of strawberries (Fragaria x ananassa)

Damage thresholds of strawberry plants (Fragaria x ananassa) were investigated by using two different methods. The first method was mechanical damage by punching holes in leaves such that a predetermined leaf area was removed from each leaf. The second method was terbacil application. Mechanical damage was applied such that 10%, 20% and 30% of the leaf area of a fully expanded single leaf was removed. Terbacil was applied to field-grown plants during 2001 and 2002. In 2001, terbacil was applied at concentrations of 12.5, 25, 50, 100, 200 and 400 ppm. In 2002, a previously untreated group of two year old strawberry plants were sprayed with terbacil at concentrations of 50, 100 and 200 ppm at two growth stages (during fruit set and after harvest stages).; Strawberry leaves that were mechanically damaged did not recover their photosynthetic capacity following the damage. Chlorophyll fluorescence (F _v/F_m) values were not affected by the mechanical damage. Increasing damage levels decreased the ability of the strawberry leaf to use light and carbon dioxide in photosynthesis. Difference in stomatal conductance and transpiration rates were insignificant. Internal CO₂ (C _i) levels were higher in damaged plants compared to the control plants.; Strawberry plants that were treated with terbacil (12.5, 25, 50, 100 and 200 ppm) were able to recover at certain levels, except 400 ppm level during the first year experiment. Recovery occurred between 4 and 10 days after the terbacil treatment. Average fruit weight was adversely affected during the year following the 400 ppm terbacil treatment. Other concentrations of terbacil did not have any affect on fruit yield. Stage of development did not alter the response of the plants to terbacil. Difference in stomatal conductance and transpiration rates were insignificant. Internal CO₂ (C _i) levels were higher in plants that were treated with high terbacil concentrations. Chlorophyll a and total chlorophyll content decreased following the terbacil treatment. However, chlorophyll a and total chlorophyll increased 8 days after terbacil treatment. Plant dry matter and chl b values were not affected by the terbacil treatments.