Aculops lycopersici Tryon (Acari: eriophyoidea) monitoring, control options and economic relevance in German tomato cultivation
by Alexander Lars Pfaff
Date of Examination:2023-06-26
Date of issue:2024-02-02
Advisor:Prof. Dr. Michael Rostás
Referee:Prof. Dr. Michael Rostás
Referee:Prof. Dr. Rainer Meyhöfer
Referee:Dr. Elias Böckmann
Referee:Prof. Dr. Stefan Vidal
Sponsor:This work was financially supported by the German Federal Ministry of Food and Agriculture (BMEL) through the Federal Office for Agriculture and Food (BLE), grant number 2816ERA01L
Persistent Address:
http://dx.doi.org/10.53846/goediss-10291
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Abstract
English
The tomato russet mite Aculops lycopersici Tryon (Eriophyoidea) is a damaging pest in commercial tomato production in many countries, including Germany. This mite feeds on the surface cells of leaves, stem and fruit. This feeding behaviour leads to plants and fruit taking on a russeted appearance, the plant dropping leaves, and in severe cases it can lead to the death of the plant. In dry and warm conditions, A. lycopersici populations are able to grow rapidly, and in high numbers they are able to cause extensive damage. Infestation is usually detected when first symptoms become visible, at which point a large population of A. lycopersici has already built up. Currently in Germany, the number and efficacy of available acaricides is limited. A. lycopersici is very small and it can move freely between the trichomes of tomato. The mite’s small size serves to partially protect it from the beneficial arthropods who are usually larger and therefore struggle to navigate the trichomes when preying on this species. To date, research looking at A. lycopersici control has mostly taken place under laboratory conditions; comparatively little research that has been conducted under practical conditions. Prior to this work, no research had investigated the dynamics and spread of A. lycopersici populations in the widely-used layer cultivation method of tomato in detail. There was also room for improvement of the detection methods for A. lycopersici, such that infestations might be identified at an early timepoint. The main goal of this dissertation was to contribute to an improvement of A. lycopersici management in commercial tomato cultivation. The first study, detailed in Chapter 1, addressed the lack of efficient early detection methods. In this study, repeated non-imaging fluorescence measurements were taken from the stems of tomato plants grown under semi-practical conditions. Via a machine learning algorithm, it was possible to differentiate between infested and healthy plants based on stem fluorescence. After 20 dpi (days post inoculation) correct classification rate was above 90 % and reached up to 99 % in consecutive measurements. In comparison, visual assessment of plants reached a correct classification rate of above 90 % after 22 dpi. A simple sticky tape imprint method revealed infestations much earlier but this method was considered too time consuming for large scale monitoring and instead could be used to verify suspected infestations. In addition to testing non-imaging fluorescence as a detection method, this study further supported the hypothesis that population growth of A. lycopersici was accelerated on plants that were in a state of drought stress. A second study (two trials), detailed in chapter 2, investigated (a) how A. lycopersici spread in layer tomato cultivation under practical conditions, given the opportunity to disperse unhindered and (b) how A. lycopersici respond to a barrier method that restricts their movement on the plant. The development of the barrier method that was implemented was partly based on the observations that were made in the first trial of this study. Under practical conditions, when small numbers of A. lycopersici arrive on a previously uninhabited plant, it takes between 4 and 6 weeks for symptoms to become visible. A. lycopersici populations will usually feed and grow in the area where they first arrive on the plant, until at some point the population begins to move upwards. This leads to many A. lycopersici individuals becoming trapped on the highest points of leaves and fruit trusses, where they begin to accumulate. The only remaining route to crawl upwards to colonise fresh, undamaged, plant material is via the stem. In the second trial of this study, the plant stem was blocked using insect glue that was applied weekly 15 cm below the tip of plants grown in layer cultivation. Only small numbers of A. lycopersici were able to reach the next higher level above a glue ring. This meant that the population was reset to a low number and it first had to grow for several weeks before plant damage occurred at this higher point on the stem. As a result, glue ring treated plants grew new plant material faster than the pace in which A. lycopersici damaged these plants. In the untreated control plant damage was significantly higher. Additionally, fruit damage was avoided entirely on the treated plants. In a third study (chapter 3), a survey of 50 tomato producing farms in Germany was conducted. One aim of the survey was to examine whether there was a link between A. lycopersici incidence and severity and cultivation practices. A second aim was to capture the farmers’ perspective on the impact of A. lycopersici, and to identify any countermeasures that might have established in practical cultivation. The survey revealed that A. lycopersici occurrence was not limited to specific areas of Germany; 33 of the 50 surveyed farms reported infestations. Twenty-four of the 33 farms reported repeat infestations, with A. lycopersici present every year following the year of first incidence. The yearly number of farms with first A. lycopersici incidence increased between 2014 and 2019. This study revealed that A. lycopersici occurred significantly more often on farms implementing high intensity cultivation methods (a short cultivation break, heating during cold months, use of an artificial substrate and a large production area). Occurrence could not be linked to a single intensification factor due to autocorrelation. A. lycopersici was considered the most important pest by participating farmers in terms of plant protection effort exerted.
Keywords: Aculops lycopersici; Tomato russet mite; Monitoring; crop protection; horticulture; spectroscopy; tomato
