The effect of longer spray intervals, reduced rates, or mixtures of three fungicides on fruit rots in strawberry

W.S. WashingtonA, S. EngleitnerB and N. ShanmuganathanC

A Department of Natural Resources and Environment, Agriculture Victoria, Institute for Horticultural Development, Knoxfield, Private Bag 15, South Eastern Mail Centre, Victoria 3176, Australia.

B Present address: State Chemistry Laboratory, Sneydes Road, Werribee, Victoria 3030, Australia.

C Retired.


Summary

Three field experiments tested the effect of thiram, iprodione and dichlofluanid for the control of fruit rots in strawberry crops in Victoria, Australia. Each fungicide was applied at full label rate at 7 day or 14 day intervals, or at half label rate at 7 day intervals. In addition, half label rate mixtures of thiram and iprodione or dichlofluanid and iprodione were tested at 7 day intervals. Grey mould, caused by Botrytis cinerea, was the most common fruit rot in two of the three experiments (31.7 and 22.5% of fruit rotted in unsprayed plots) while anthracnose, caused by Colletotrichum acutatum, was the most common rot in one experiment (28.3% of fruit rotted in unsprayed plots).

The most consistent control when all rots were combined was achieved by half rate mixtures of either dichlofluanid with iprodione (reducing all rots from 39.1 to 4.9% in one trial) or thiram with iprodione (reducing all rots from 39.1 to 7.4% in the same trial), each applied at 7 day intervals. Half rates and 14 day spray intervals of most other treatments gave significant control of rots in most cases with the exception of iprodione in two of the experiments. Iprodione when sprayed alone at these sites failed to significantly reduce grey mould or total fruit rots, providing further evidence of the presence of dicarboximide resistant strains of B. cinerea in Victorian strawberry crops. Residue testing of fruit from one trial showed that residues of iprodione and dichlofluanid, but not thiram, were within the current approved maximum residue limits.

 

Plant Protection Quarterly (1999) 14 (3) 88-91.