Water Hyacinth Reproduces by Seed in New Zealand

New Zealand Journal of Agriculture, Volume 96, Issue 2, 15 February 1958, Page 191

Water Hyacinth Reproduces by Seed in New Zealand

By

J. G. MANSON and B. E. MANSON,

Department of Agriculture, Palmerston North

FROM 1948, when the potential danger of water hyacinth was recognised, until 1955 its eradication was largely unsuccessful. This may be attributed, partly to the fact that it was not realised that it can and does set viable seed in this country. The fact that it is setting seed has increased both the difficulty of its eradication and its potential danger, particularly in streams, where the seeding plants can be distributed by the running water.

SINCE late in 1955, when a concentrated plan of eradication was initiated, the areas where viable seed has been set have been clearly defined. Of the 45 areas in which water* hyacinth is known to be established, from Kaitaia in the north to Shannon in the south, seedling plants have been found in 19 and viable seed has been collected in several others.

Water hyacinth flowers from late December through to March in North Auckland and from January to March in areas south of Auckland. There is usually one flowering spike, but sometimes up to three spikes, with about 20 flowers on each plant. When the capsules burst the seeds from the bent spikes are discharged into the water and sink. As there are up to 300 seeds per capsule and as each spike may contain 20 capsules, each plant is capable of producing 5000 to 6000 seeds. The seed falls to the bottom of the pond and will not germinate until the water recedes and the seeds are dried.

At Tiniroto, between Wairoa and Gisborne, a water hyacinth infested lake was drained some 4 years ago. Each summer water hyacinth seedlings strike, but are easily killed by the dry weather that follows. In other areas water hyacinth seeds have germ-

mated on damp soil or on rafts of partly decomposed water hyacinth or damp projections above water level. At Onehunga, Auckland, where the water hyacinth is growing in water which is heated to 100 degrees F. by a hot-water overflow from a factory, five successive crops of seedlings struck in one season.

Water hyacinth seeds usually germinate from January to March, depending on the length of dry weather and the recession of the water level. . Up to 1000 seedlings per square foot have been recorded. At Tikitiki, north of Gisborne, in 2 months 15 seedlings multiplied to 140 plants by vegetative propagation and covered approximately 40 sq. ft. The period of seed viability is not known, but at Waima in Northland, successive crops of seeds have struck over the last 6 years. During this period all plants have been destroyed before setting viable seed. This shows that seed will remain viable for at least 5 years. '

Because water hyacinth is now known to be setting seed even more vigilance is required in the detection and destruction of infestations as soon as possible. Anyone knowing of areas of water hyacinth is requested to inform the nearest office of the Department of Agriculture so that they can be eradicated.