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New Zealand Plant Protection 63 (2010): 274

Survival of weed seeds in cocopeat bricks for hydroponics

T.K. James, A. Rahman and M. Dickson

ABSTRACT

In 2007 seeds of 31 species previously unknown in New Zealand were identified in cocopeat imported from Sri Lanka. Cocopeat is used as a growing medium for hydroponic vegetable production. The aim of this study was to evaluate the viability of weed seeds present in cocopeat over a 12 month growing season. Twenty or forty seeds of five representative species were counted into fine mesh bags and inserted into the cocopeat bricks. Tomatoes (Lycopersicon esculentum) and capsicums (Capsicum annuum) were grown in the cocopeat with nutrients supplied via a constant trickle of hydroponic nutrient solution. After 3 (n=4), 6 (n=4) and 12 (n=8) months seed packets were removed for germination testing, which was firstly carried out over 28 days on KNO3-soaked blotters, after which ungerminated seed was pricked and left for a further 28 days. After 12 months 37% and 45% of the grass species Panicum miliaceum and Digitaria sanguinalis respectively germinated while that for the broadleaf species Cleome rutidosperma, Mollugo nudicaulis and Amaranthus viridis was 20%, 48% and 38% respectively. Results from the 3 and 6 month samplings were intermediate and show that long term exposure to hydroponic solution did little to reduce the viability of weed seeds found in imported cocopeat.

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