Some effects of shading and para-chlorophenoxyacetic acid on fruitfulness of tomatoes
Moore, E.L.; Thomas, W.O.
Proceedings American Society Hort Science 60: 289-294
This study concerns the effects of reducing the light intensity and applying para-chlorophenoxyacetic acid (PCA) upon flowering and fruiting of late summer tomatoes. Stokesdale tomato plants of uniform size were transplanted to the field July 31, 1951, at State College, Mississippi. They were grown in high, medium, and low light intensities. High light intensity was full sunlight (about 8000 foot candles), medium intensity was 50% and low was 25% of full sunlight. The air temps. ranged from 70 to 102[degree] F during the pollination period of the first 2 flower clusters. The inflorescences of half of the plants under each intensity were sprayed with 25 ppm. of PCA when the calyx and corolla were beginning to separate. The light intensities used had no effect on the date of appearance of the 1st or 2d flower clusters or date of 1st harvest. PCA reduced the time by 9 days from flowering to 1st harvest. Early yields were tripled by reducing the total light intensity 50% or by the PCA treatment. The combined effects of the reduced light intensity and PCA were even more pronounced. When compared with the check plot, the total yields were greater from the plants receiving PCA under medium light intensity. The main response occurred during the early harvests which contained fruits that were set under conditions of high temp. and high light intensity. Plant growth was greater and the fruit were larger under medium light intensity than under high light intensity. The data strongly indicate that high light intensity as well as high temp. is harmful to tomato fruit-set. Unfruitfulness due to these conditions can be overcome by shading out 50% of the light and/or by a cluster spray of 25 ppm. of PCA.