Maleic Hydrazide (MH) is a sprout suppressant that inhibits cell division.
The reduction in permitted treatments rate for CIPC have driven an increase in MH use in recent years. A total of 20,000 acres (15% of all crop) was treated in the UK in 2016.
Interim data from AHDB at Sutton Bridge has shown that in the absence of CIPC, MH can offer good sprout control and boost efficacy of alternative treatments when used in combination with them.
MH is applied to the growing crop as a foliar spray, not as an in-storage treatment. It is also able to provide control of volunteer/groundkeepers from potato crops.
- MH efficacy is dependent upon the weather at application as uniform uptake by the foliage is needed. Poor uptake through the leaf will results in a reduction in sprout control performance.
- The crop’s hydration at treatment is also vital factor as it affects uptake and impacts on the crops reaction to treatment (in 2018 – a very dry season – many UK crops were reported to have suffered markedly following MH application due to their drought-affected condition).
- Timing of application is a crucial component of MH use. Applying too early reduces yield, too late reduces the efficacy of uptake and sprout control is compromised.
- Application timing of around late July or early August (circa 5 weeks before defoliation) is favoured for best results. Crop should be actively growing.
- Temperature of storage will have an effect on efficacy. MH used in combination with storage temperatures of 7-10oC has provided short term sprout control (2-4 months) in processing or chipping stocks – usually without any further treatments, in the UK since its introduction to the market in the 1980’s.
- Control for up to 3 months if application of MH is made correctly
- A residue of 12ppm has been reported as necessary for maximum sprout control (more research into MH residue began in 2019)
- In recent trials investigating alternative sprout suppressants, combinations containing MH, used in conjunction with other actives substances, have performed better than the single products alone.
Current use of MH in the UK
Industry questionnaire demonstrating current practice: In a survey for this Review of MH use in GB (yielding 51 responses)
- 78% of users said they apply MH for sprout suppression compared with 66% for volunteer control.
- 95% of respondents applied MH with the foliage was more than 75% green and over half did so when the canopy was fully green.
- 13 of 18 respondents not currently using MH for sprout control felt they were likely to need to apply it as a sprout suppressant in future.
- The total volume of MH applied varied between respondents substantially from less than 300L/ha up to 500L/Ha.
Use of MH in Europe
In a visit to mainland Europe in spring 2019 by AHDB staff, all commercial processing stores visited were using combination treatment that included an application of MH. It was a ‘must-have’ component of control strategies in the European processing stores visited by AHDB staff.
Comparison: Sprout length in five varieties without MH (left) vs with MH (right)
Please note: different left hand axis
Effect on dormancy
MH also markedly extended the dormancy the five varieties tested. Some varieties were more affected than others, with dormancy extended between 20 and 45 days.
The performance of future sprout control options in potato storage will be much less predictable than CIPC. MH, whilst inconsistent in its own level of control, does provide an element of stability to a sprout suppression strategy. MH useful in nearly all situations. There is still some more work to optimise the timing of application.