‘Universal’ spray droplet adhesion model – accounting for hairy leaves

The adhesion of a spray droplet upon initial contact with a leaf surface is extremely important to spray efficacy and is dependent on dynamic interactions between droplets (formulation, size, velocity) and leaf (micro‐topography, surface chemistry, veininess, hairiness and orientation). A ‘universal’ spray droplet adhesion model has previously been developed, using 50% aqueous acetone contact angles as a measure of leaf surface properties; this model satisfactorily predicts initial adhesion over a range of formulation surface tensions, droplet sizes and velocities. However, it failed to fit data from hairier leaves. This study investigates initial spray droplet adhesion on hairy leaves. Two categories of hairy leaves were identified by how the droplets penetrate the leaf hairs, Wenzel (hairy) and Cassie–Baxter (super hairy). For the Wenzel‐type, a simple constant accounted for the increased droplet shatter caused by the hairs. For the Cassie–Baxter‐type, a cushioning factor was introduced to account for the absorption of kinetic energy at impact by the hair mat. The cushioning factor was estimated by measuring the relative height of the hair mat. By including these two parameters, the new model successfully predicted the mean adhesion of non‐hairy, hairy and super‐hairy plants (R² = 0.96). This model and the underlying principles determining hairy leaf adhesion developed in this article will help develop spray formulations effective at targeting hairy‐leaved weed and crop species.     

Feeding‐deterrent activity of α‐asarone isomers against some stored Coleoptera

All isomers of α‐asarone [(E)‐4‐prop‐1‐enyl‐1,2,5‐trimethoxybenzene] were tested for their feeding deterrent activity against adults of Sitophilus granarius and Tribolium confusum and larvae of Trogoderma granarium and Tribolium confusum. (E)‐2‐prop‐1‐enyl‐1,3,5‐trimethoxybenzene exhibited the strongest deterrent activity against all the species tested. The total coefficients of deterrency for this compound were 140.6 and 169.7 for Tribolium confusum adults and larvae, respectively, and 144.9 and 104.6 for larvae of Trogoderma granarium and adults of Sitophilus granarius, respectively. © 2000 Society of Chemical Industry     

Callose and β‐1,3‐glucanase inhibit Phytophthora cinnamomi in a resistant avocado rootstock

Phytophthora root rot (PRR) of avocado, caused by Phytophthora cinnamomi, is a significant threat to sustainable production wherever the crop is grown. Resistant rootstocks in combination with phosphite applications are the most effective options for managing this disease. Recently, the mechanisms underpinning PRR resistance have been investigated by the avocado community. Here, biochemical assays and confocal and scanning electron microscopy were used to investigate early defence responses in PRR resistant and ‐susceptible avocado rootstocks. Zoospore germination and subsequent hyphal growth for the pathogen were significantly inhibited on the surface of resistant avocado roots. When penetration occurred in the resistant R0.06 rootstock, callose was deposited in the epidermal cells, parenchyma and cortex of roots. In addition, β‐1,3‐glucanase was released early (6 h post‐inoculation, hpi) in response to the pathogen, followed by a significant increase in catalase by 24 hpi. In contrast, susceptible R0.12 roots responded only with the deposition of lignin and phenolic compounds incapable of impeding pathogen colonization. In this study, PRR resistance was attributed to a timely multilayered response to infection by P. cinnamomi.