Crop safety of UV-C applications in Tomato

From June 13th 2023 to June 30th 2023 a trial was carried out by Botany BV on their site in Horst-Meterik to test the crop safety of the UV-C treatments on tomato. The trial was set up with 4 treatments:
1) Untreated control - UV Robot did not drive in this part of the trial
2) Lights-off control - UV Robot drove this part of the trial with the lights off
3) Application of UV-C at a normal dose (50 J/m2)
4) Application of UV-C at extreme dose (250 J/m2)
Applications with the UV-C robot were performed during the night and were carried out three times a week. Assessments were performed on the leaves of the tomato plants, on the fruits of the tomato plants and on de flowers of the tomato plants. The flowers were present in the layer of the crop which was higher than the top of the UV-C robot. The observed leaves and fruits were in the same layer of the crop as the lights of the UV-C robot.

After the first applications with UV-C, no effect was observed on the crop. On June 16th 2023 all leaves, fruits and flowers that were assessed were scored as 100% healthy/vigorous. At this assessment timing, 2 applications with UV-C were executed.
On June 19th 2023, the first symptoms of phytotoxicity on the leaves of the tomatoes were observed in treatment 4 (12.8%). At this time, no negative effects on fruits and flowers were observed. At this assessment timing, 3 applications with UV-C were executed.
On June 26th 2023, after 6 applications with UV-C were performed, leaf damage (61.3%) was observed in treatment 4, the extremely high dose application of UV-C (Picture 1). There was no leaf damage observed in the other treatments (Picture 2). In all treatments, there was no negative effect observed on the fruits of the tomatoes or on the flowers of the tomatoes.
The data of assessments on the tomato leaves is presented in Figure 1.


Picture 1: Extreme high dose UV-C (treatment 4)                    

Picture 2: Normal dose UV-C (treatment 3)

Applications on assessed leaves and assessed fruits were direct applications, applications on assessed flowers were indirect applications.
After 3 applications, negative effects on the leaves of tomato were observed in the extreme high dose of UV-C (250 J/m2). This effect was even larger after 6 applications of UV-C. All other treatments showed no negative effect of UV-C treatments.
Based on these results, in this trial, under these conditions, application of UV-C on a normal dose (50 J/m2) is safe to the tomato crop.


Figure 1: Observed leaf after 1, 2, 3 and 6 applications with UV-C

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