Bed mulch treatment affects strawberry fruit bronzing and yield performance

Strawberry plants ('Commander') were grown with different polyethylene bed mulches in the 1999-2000 and 2000-2001 production seasons to determine the effect of mulch on plant growth, yield performance and incidence of Type III strawberry fruit bronzing (T3B), a fruit disorder of unknown origin. In 1999-2000, T3B incidence ranged from 1.8% to 3.7% of total yield, and use of clear, full-bed (CFB) mulch resulted in significantly less T3B incidence than either clear center-strip mulch (CS), or yellow-on-black full-bed mulch. Plant canopy vegetative growth and shoot to root dry mass ratios were greatest for CFB compared to other mulch treatments, but there was no effect of mulch treatment on yield or fruit size. Winter temperatures in 2000-2001 were colder than in 1999-2000, with reduced vegetative growth and increased T3B incidence in spring for all mulch treatments. Use of CFB mulch resulted in greater vegetative growth, greater yield, increased fruit size and reduced T3B incidence compared to CS or green full-bed mulch, but there was no difference among mulch treatments for number of T3B fruit per plot for any single fruit harvest interval. In 2000-2001, the onset of severe T3B symptoms on 7 May was preceded by a brief period of ambient temperatures >31 degreesC. For all treatments, peak T3B incidence occurred from late May to mid-June, a period characterized by high ambient, temperatures and high irradiance conditions. Results indicate that temperature and radiation are significant factors in the development of T3B, and that increased plant vegetative growth in winter results in greater yields and a lower percentage of T3B-affected fruit, particularly in years with cold winters. Managing strawberry plantations to optimize plant growth and development in winter appears to be an effective strategy for reducing the severity of this disorder.