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A late frost occurred in the Southland region of New Zealand in November 1995 when many winter wheat (Triticum aestivum L.) crops were at early grain fill, and resulted in a large number of insurance claims for frost damage. In this study, frost damage was characterised. Spikes in affected crops were sharply tapered from a point half to two-thirds from their bases. Grains were as much as 80% lighter in upper parts of affected spikes. Overall yield losses as a result of frost of between 13 and 33% were calculated in affected crops. Grains were sectioned and examined with a scanning electron microscope. Whereas in healthy grains, the layers making up the pericarp and testa were compressed, in frosted grains these layers comprised loosely compressed and unstructured networks of cells. The aleurone layer was less ordered in frosted than in normal grains, and was not always readily distinguished from the starchy endosperm. Rehydration of frosted grains was accompanied by expansion of pericarp and testa cells, whereas little cell expansion occurred in normal grains. Blisters were common in frosted grains, where the outer layers were detached from the remainder of the pericarp.

Since the discovery that the plant immune system could be augmented for improved deployment against biotic stressors through the exogenous application of chemicals that lead to induced resistance (IR), many such IR‐eliciting agents have been identified. Initially it was hoped that these chemical IR agents would be a benign alternative to traditional chemical biocides. However, owing to low efficacy and/or a realization that their benefits sometimes come at the cost of growth and yield penalties, chemical IR agents fell out of favour and were seldom used as crop protection products. Despite the lack of interest in agricultural use, researchers have continued to explore the efficacy and mechanisms of chemical IR. Moreover, as we move away from the approach of ‘zero tolerance’ toward plant pests and pathogens toward integrated pest management, chemical IR agents could have a place in the plant protection product list. In this review, we chart the rise and fall of chemical IR agents, and then explore a variety of strategies used to improve their efficacy and remediate their negative adverse effects. © 2021 The Authors. Pest Management Science published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.

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