Evaluation of foliar application of caffeine in almond (Prunus dulcis) cultivation as an alternative to chemical pesticides: Minimizing chemical residue in almond hulls for sustainable use of almond by-products

Almonds are universally recognised as a highly nutritious and economically valuable edible nut. However, the 2023/2024 global Almond production of 1.51 million metric tons generated a significant amount of waste, mainly in hulls, totalling about 5.03 million metric tons. Addressing the sustainable disposal of this waste is crucial to ensuring the industry's long-term viability. Whilst Almond hulls are a valuable source of crude protein and dietary fibre for livestock feed, when using them as feed for dairy and beef cows, it is essential to consider the possibility of carry-over pesticide residues resulting from chemical pathogen control during production. These residues have the potential to enter the food chain and appear in dairy and beef products. This study tests the hypothesis of using natural caffeine as a replacement for chemical pesticides, which could help to reduce the chemical residue levels in Almond hulls. There were three different concentrations of caffeine, 0.01, 0.1, and 0.5 % (w/v), used as foliar applications for three common Almond varieties. Caffeine treatments have been found to effectively control Almond fungal diseases like Hull Rot and Shot-Hole in commercial agriculture production, and they also show some effectiveness in reducing damage from insect pests. The treatments have been shown (i) to have a positive impact on increasing kernel weights and enhancing nut sets, not significantly affecting the plant's absorption of nutrients or the distribution of plant nutrients, and (iii) they have a neutral effect on leaf chlorophyll levels. These results indicate the potential of caffeine to address pesticide Maximum Residue Limit (MRL) issues and support its use in combination with suitably Integrated Pest Management (IPM) approaches.