The final report from Dr. Carol Lovatt, UC Riverside, for Uniconazole-P commercial field tests in California on Hass avocado trees resulted in negative effects on yield, fruit size and fruit quality. Uniconazole-P is a new formulation that was developed for use in California to increase fruit set and yield by inhibiting vegetative shoot growth at the apex of indeterminate floral shoots. Based on the negative results of the yearlong trials, at the October Commission Board meeting it was decided to no longer pursue a Uniconazole-P registration.
To determine its effectiveness at stopping the growth of vegetative shoots at different stages of development, Uniconazole-P was applied at the suggested rate for Sunny® in spring, summer, fall and winter in avocado groves located in San Jan Capistrano and Camarillo. Highlights of the findings are as follows:
- Following a spring application, there were no significant differences in the number of fruit set by the spring bloom or in the size of the fruit at either location.
- The summer application increased leaf burn and caused leaf curling and cupping in both orchards.
- Fruit quality at both orchards also was affected. The summer, fall and winter applications at San Juan Capistrano significantly reduced fruit length and width, and the summer application reduced the width of the edible portion of the fruit (the mesocarp). At Camarillo the summer application reduced mesocarp width, fruit width and fruit length, while the fall application reduced seed diameter and fruit width.
- At San Juan Capistrano, total fruit yield was reduced by the summer and winter applications. There was also a significant decrease in commercially valuable size fruit yields in summer and winter due to decreases in fruit of packing carton sizes 48 and 40.
- In comparison, at Camarillo, applications only slightly reduced the total yield. While the summer application slightly reduced fruit of packing carton sizes 48 and 40, there were significant increases in the yield of fruit sizes 84, 70 and 60.
Overall, the researchers note that due to the “negative effects on yield, fruit size and fruit quality” at both sites, it is “not possible to increase the concentration of Uniconazole-P in an attempt to achieve a greater reduction in shoot growth.”
The Production Research Report, “Studies on the efficacy of a new formulation of Uniconazole-P” can be viewed online.