DODDER IN NEW-ZEALAND-GROWN CLOVERS.

New Zealand Journal of Agriculture, Volume XXVII, Issue 1, 20 July 1923, Page 19

DODDER IN NEW-ZEALAND-GROWN CLOVERS.

PRECAUTIONS TO BE OBSERVED.

NELSON R. FOY,

Biological Laboratory, Wellington

According to reports received from Great Britain and the United States, considerable trouble has been experienced through the occurrence of dodder-seed (Cuscuta spp.) in New Zealand white clover and cowgrass exported during 1922-23. < ■■

Previous to last year little had been heard of dodder in our clovers, and it was popularly supposed that the white clover and cow-grass rarely if ever contained this impurity. Whether it is that there is more of the. dodder-plant growing in the clover crops, or that the bringing into operation of the new British Seed Act has made it more difficult for affected seed to gain entry unnoticed, is not easy to say. The writer is inclined to think that the sudden prominence gained by the dodder question is due in part to both of the suggestions put forward. The most unfortunate feature is that .in many cases discovery of

the dodder does not take place until the seed reaches its destination, and then naturally the overseas buyers are not anxious to take delivery, as under the British Seed Act it is unlawful to sell clover containing dodder. Arbitration follows, and in many cases the seed has been returned to the shippers in New Zealand.

It is only fair to state that the New Zealand merchant does not knowingly ship such seed, but does so under the impression that it is “ dodder free,” such impression being gained from the analyses issued from the seed-testing branch of this Laboratory. Further, it is also fair to state that these analyses-reports issued are a true and correct statement of the purity of the sample forwarded.. From this it might appear that the trouble is beyond remedy, but such is not the case. present, dodder is always in small quantitiesfrom one seed in an ounce to one in a pound. Further, in New Zealand dodder grows only in small isolated patches, and it follows, therefore, that the seed will not be distributed evenly throughout the line. For example, the first two sacks examined may not contain it, and the third will. It will thus be seen that it is very possible to draw a sampleor, indeed, several samples—free from dodder, and then draw- a further one which does contain dodder. In an actual instance three samples were drawn from a line of white clover first prior to shipment, and the other two (from bulk sample retained in New Zealand) after the line had been held up in Great Britain on account of dodder content. The first and second samples were dodder-free, but the third contained two seeds of dodder to the ounce. 'Each sample was approximately I oz. in weight. Such occurrences mean bad business for the merchant, and are tending , to cause English seed firms to avoid New Zealand clovers —- in both cases a decidedly unsatisfactory state of affairs.

The remedy —or at least nine-tenths of it—-is in the hands of the New Zealand merchant and the grower; the other tenth must be left to chance. Particularly thorough sampling of export lines is absolutely essential. To obtain a thoroughly well-mixed sample one should be drawn from top, middle, and bottom of each sack of the line. This is especially necessary in the case of dodder, for, as already mentioned, the weed may occur only in quite small patches in the field, and only quite a few of the sacks may contain the impurity. The drawn seed should then be mixed, and as large a composite sample as is convenient drawn from it.

The foregoing may seem a somewhat laborious process, but it is the only way in which a thoroughly representative sample may be obtained, and a representative sample is essential if the analysis is to show the true state of the line as regards purity. Farmers themselves can also materially assist in maintaining the reputation of New Zealand clover by carefully examining their fields before harvesting, in order to ascertain whether any dodder is present.

Agricultural Exports. —The value of the agricultural products exported from New Zealand during the year ended 31st March, 1923, was £42,248,751, or 93 per cent, of the total exports in that period.