A 79% active ingredient formulation of monocarbamide-dihydrogen sulphate (MCDS or sulfcarbamide), which is marketed in the USA as ‘Wilthin’, has shown promise in USA trials as an apple thinner (Williams, 1994).
- Trials using the product in high volume sprays at 1000‑4000 ppm on Queen Cox and Royal Gala at East Malling proved less successful (Webster and Spencer 1999; Webster and Spencer, 2000).
- Only at the highest dose rate tested, 4000 ppm, (which was above that recommended on the product label) was effective thinning achieved.
- Also, some phytotoxicity on spur leaves was noted. Phytotoxicity and variable responses have also been observed in USA trials with this product (Andrews and Collier, 1995).
- Although effective in USA trials on apples, ‘Wilthin’ gave disappointing results as a thinner in UK trials.
- ‘Wilthin’ is not approved currently for use as a flower thinner in UK orchard.