Fertilising Concurbits

Press, Volume CVIII, Issue 31771, 30 August 1968, Page 6

Fertilising Concurbits

Cucurbits, which include pumpkins, cucumbers, squash and marrow, are widely grown, and often annoy the grower by failing to produce an adequate crop of fruit, in spite of all the care and attention lavished on them. One of the reasons for this is the weather during the season, particularly when the flowers appear. As is well known, male and female flowers are borne separately by these plants, and although the male organ appears first, nearest to the stem of the plant, the sequence is greatly influenced by temperature and length of day. It has been found that low temperatures and short days result in a proportionally higher number of female flowers, while hig(i temperatures and long days induce a preponderance of males to develop. In this respect there also exists a genetical difference in sex expression between varieties and Japanese and Fl hybrids may suffer from this effect. Experiments have also

shown that high availability of nitrogen in the soil tends to produce a proportionally higher number of female flowers and this aspect could be considered of great use during the growth of the plant to alter the sex proportions. Fruit set can be upset by cold nights followed by slowwarming early mornings, because at lower temperatures, particularly in the mornings up to 10 or 11 aun. when fertilisation is effected, dehiscence of pollen is very low or even nil. A minimum temperature of about 62 degrees is required for that with an optimum of 65 degrees to 70 degrees, a feature which, from various research, seems to be associated with internal plant functions, auxins or enzyme action. Thus no proper pollen would be available under such conditions and in consequence no pollination could take place below the minimum temperature mentioned.

Insects, particularly bees, are instrumental in the transference of pollen of cucurbits from male to female flowers and are less active in dull weather. The, presence of a few hives near large planting is always beneficial. In the-home garden, as in the glasshouse, pollination can be affected by hand, either by brushing the male flower against the female or better still by transferring the pollen from the anthers of the stamens to the stigma of the pistil by means of a fine haired paint brush. Fruit collapse is often found, sometimes when they have got quite large. This is most likely due to improperly achieved fertilisation.

The use of cloches to provide warmth, careful manuring, the presence of bees, hand pollination and even storage of pollen from a previous crop for use in the following season can assist in this problem.