Strategies for the protection of macrophytes from Tetranychus urticae invasion and fungal infections in hydroponic systems – a case study

Abstract

This article analyses biotic threats in laboratory hydroponic systems using the example of a cascading infestation by the two-spotted spider mite (Tetranychus urticae) and subsequent fungal colonisation. The original aim of the study was to assess the ability of selected macrophyte species – Juncus effusus, Alisma plantago-aquatica, Pontederia cordata and Typha angustifolia – to regulate nutrients in a liquid medium. This aim was revised following the T. urticae infestation. The revised objective was to restore the phytoremediation potential of the macrophytes and to assess the rescue measures undertaken. The procedure included mechanical removal of pests, emergency spraying with Agrocover and Agricolle preparations, and transfer of surviving plants to soil substrate previously exposed to UV radiation. The use of UV radiation in the laboratory coincided with an intensification of fungal symptoms; this temporal association supports only a hypoth esis that changes in microbial balance may have contributed to fungal development. During the fungal-infection phase, final survival was 13% (3 of 23 plants), corresponding to 87% mortality. During the initial phase of the spider mite attack, Pontederia cordata showed the highest infestation, whereas Juncus effusus had the highest survival rate. Juncus effusus did not survive the subsequent fungal-infection phase. The observations indicate that microclimate control and monitoring of plant condition are important for maintaining the stability of phytoremediation processes. The results provide a preliminary assessment of the response of selected macrophytes to combined biotic and thermal stress.