Possible new uses for UV LEDs

[enricosavazzi]

http://luxreview.com/article/2017/04/led-could-remove-need-for-pesticides-in-farming?cmpid=enl_leds_horticultural_lighting_newsletter_2017-08-07

 

This is being studied, as far as I understand. The above link is not a scientific reference on the subject (which so far I have been unable to find).

[Andy Perrin]

It sounds like he will present it at the conference, so there may not be a paper yet. Presumably in the coming months his group will write it up.

[aphalo]

The idea is not that new. UV radiation from lamps is being used commercially in greenhouses to some extent in central Europe to control the same pathogens. Special greenhouse cladding polythene films with high UV transmittance have been in the market for about a decade, and UV-transparent acrylic channel sheets for greenhouses for over two decades. There is potential, but also complications: dealing with many organisms simultaneously involves many interactions. Some are: although UV radiation may be detrimental for some pathogenic fungi it may induce or increase sporulation in others. Some insects like white flies, navigate by means of UV vision, so cladding that absorbs UV radiation has been shown to delay the spread of white flies in greenhouses. On the other hand in many cases UV and blue radiation induce the accumulation of secondary compounds in plants, which then may act as chemical defences against some pathogens, deterrents for generalist insect herbivores, and also as atractants for specialist herbivores. Furthermore, one of the current problems for the adoption of use of UV in greenhouses and "plant factories" is exposure of workers.

 

In the last few years we have learnt that plants can acquire and use a lot of information from their environment and communicate with each other. Light and UV radiation play a very important role as well as volatile and soluble metabolites. My view is that it is true that we can control the growth, morphology and defences of plants through changes in the light environment, but as the signalling from different photoreceptors (14 and counting in Arabidopsis) is combined through signalling, any unnatural spectrum can lead to very unexpected responses. Of course, these responses cannot be expected to be the same in different organisms, even different plants species... There are simple things like getting shorter plants, darker red lettuce, and more intensely coloured flowers that can be manipulated rather easily. Even the taste of rocket and some herbs can be drastically changed by playing with the visible spectrum using LEDs. When we get into inter-organism interactions, things get a lot more complicated, and there are all sorts of things to consider when using illumination with spectral composition targeted to a given group of organisms. Say one could try to optimize plant defences, or plant growth (there is usually a trade-off), or produce yield, or produce quality, or total market value of the production, but then we have herbivore insects interacting with the plants, but also pollinator insects that need certain wavelengths for navigation. And then pathogenic and non-pathogenic fungi and bacteria, some of which will be competing with each other on the surface of the plant (those are the ones which UV could directly affect)...

 

So to me, "ending" the use of pesticides will not come from LEDs, but instead we can drastically reduce their use through integrated pest management. LED light sources with variable, or at least, tailored emission spectra are one tool, as is biological control, and even simpler things like controlling irradiance, humidity and temperature play a huge role. Biological control by introduction of predator insects in greenhouses is in commercial use and possibly changing the light spectrum could make it more or less effective. Of course crop breeding can also play a very important role in reducing the use of pesticides when it is targeted in this direction.

 

A book that I frequently recommend to my students is: Chamovitz, Daniel (2013) What a plant knows : a field guide to the senses of your garden - and beyond.

This book shows how complex plant interactions with their abiotic and biotic environment are, and how much plants use sensory mechanisms.