Maleic Hydrazide

Maleic Hydrazide (MH) is a popular plant growth regulator applied in the field and used to control growth of potatoes in store and those left behind in harvesting operations that might otherwise become volunteers

Use of Maleic Hydrazide 

Last updated Jan 2022

Maleic Hydrazide (MH) is used on onion and potato with EAMUs for several other food crops. It is generally applied as a foliar spray to crops in the field. There are approvals for different formulation types for application to potatoes; these vary in terms of application timing and application water volume, but all deliver 3kg active substance per hectare. Only a single application is permitted and product labels are for volunteer control as well as sprout control in storage. Usage of MH has increased since the non-renewal of CIPC.

Effective application of MH to potato requires plants to be actively growing. High temperature and plants suffering water stress must be avoided  as should rain for 24 hours after application. Ideally applications are carried out under humid conditions (as far as this is possible).  This extends the period of absorption by maintaining MH in solution on the leaf as long as possible. Applications late in the day or following irrigation may help with this.

Absorbed MH is translocated from leaves to tubers in the phloem. Residue (and efficacy) tends to be greatest in larger tubers, and smaller tubers  may be seen to start sprouting first in store. Although exceptions are reported, in AHDB work residue levels tended to be static during the period from harvest through long-term storage.

Residues of MH are systemic and provide long periods with reduced sprouting potential. MH is therefore particularly effective for long-term storage where an initial treatment is used to reduce the number or volume of post-harvest treatments. MH is also useful for control of internal sprouting, the risk of which may be increased by post-harvest treatments requiring frequent re-applications.

What to remember when using MH

• Applied in the field
• MH must be taken into the tuber - requires good growing conditions and timing
• Can be used in combination with other sprout suppressants

2019 Review of MH use in GB

An industry questionnaire was used to understand current practice

• 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.