Maleic hydrazide - optimisation as a sprout suppressant
Historically, the primary use of maleic hydrazide (MH) was as an in-field spray for the control of volunteer potatoes. However, since the loss of CIPC sprout suppressant in 2020, MH has taken on an important role in potato storage by providing a base level in control of sprouting that has been supplemented with alternative products applied in storage. The use of MH provides a degree of residual control (ie control after the application event) which was a great asset of CIPC and remains important in markets where there is a need to preserve crop condition during shelf life.
A review on the use of MH as a sprout suppressant was published in 2019. It identified research gaps that were addressed in subsequent trials.
Assessment of the MH residue concentration required for control of sprout growth, and the variability in residue concentration that occurs as a result of plant-to-plant variation.
Samples with a range of residue levels were generated, and efficacy assessed after a period of storage at 9oC. Limited efficacy of sprout control was evident at low (1-2ppm) concentrations and increased with MH residue level, but the increase in efficacy with residue concentration was not linear. The lowest recorded residue level was approximately 60 to 70% of the mean value. This value is of greater importance to store managers, as it is the lesser efficacy of these samples that prompt in-store treatments.
Humidity and MH uptake
Field observations suggests that MH application in a larger volume of water and application early or late in the day will result in higher tuber residue values. However, it is not clear what the mechanism for this is. An experiment was conducted in which the humidity of the air around plants was maintained at an elevated level, in comparison with control plants, to determine the impact this had on subsequent tuber MH residue levels.
In a greenhouse trial, maintaining very high humidity levels for a 24 hour period after application resulted in a three-fold and highly significant increase in tuber MH residue concentration compared to plants kept in less humid conditions.