Ashfall affects plants differently depending upon development stage.
Periods when a selection of crops are most at risk (from research in the temperate regions of New Zealand):
(Neild et al., 1998)
- Pea: from emergence until end of flowering.
- Squash: during the initial stages of growth and flowering.
- Tomatoes: during seed emergence and flowering stages.
- Sweetcorn: during the early stages of growth.
- Pipfruit has three danger periods:
- During blossom where severely acidic ash (pH less than 3) could burn plant tissue and result in poor pollination.
- 6 to 8 weeks after blossoming, when the skin of fruit is particularly sensitive.
- Later stages of development when fruit is prone to cosmetic blemishing.
- Stonefruit is also susceptible at the same times as pipfruit, except that the early fruit development period is 4-6 weeks after blossoming, when sensitive fruit skins could be damaged, and show russet or deformation in severe cases.
- Kiwifruit is also at risk at, and 6-8 weeks after, blossom. There would also be a problem at harvest time. As kiwi fruit cannot be washed prior to packing, the hairy nature of the fruit would make ash removal very difficult.
- Grapes have three main periods when damage could occur:
- Flowering, when acidic ash could burn plant tissues, reduce pollination and reduce bunch fill.
- Fruit development, where ash deposits would block sunlight and reduce quality.
- Harvest, where ash deposits would be a contaminant with the extra acidity of the ash possibly having a significant impact on wine quality. Ash would have to be removed prior to harvesting by washing and allowing bunches to dry (not economically feasible in Etna case study).