Determination of the cause of phylloid strawberry fruit in annual strawberry production in central Florida

During the 2003-04 strawberry (Fragaria x ananassa Duch.) season, an increased number of phylloid strawberry fruit were observed. In affected fruit, achenes became masses of vegetative tissue and fruit were typically elongated and had enlarged sepals. Symptoms of phylloid strawberries usually have been associated with phytoplasmal diseases. A quick diagnostic test by Polymerase Chain Reaction (PCR) was developed for detection of phytoplasma, but all petioles and fruit tested negative. Glyphosate (Roundup Ultramax) herbicide has also been reported to cause flower abnormalities and phylloid strawberries. The effect of three concentrations of glyphosate applied one day before or 4 weeks after transplant was tested on two cultivars, 'Strawberry Festival' and 'Camarosa'. At the highest rate (120 mg center dot L-1) applied after transplant, severe phytoxicity symptoms developed and no fruit was produced. At 12 mg center dot L-1 applied after transplant, plants developed moderate phytotoxicity symptoms including stunting and chlorosis. At this concentration, approximately 25% of 'Strawberry Festival' and 30% of 'Camarosa' fruit produced were phylloid. No other treatment had a significant percentage of phylloid fruit compared to the controls. Residues of the post-emergent herbicide glyphosate, usually applied to the row middles for control of weeds in strawberry production, can adversely influence flower differentiation and induce phylloid strawberry fruit.