Plant growth and morphology can be modified with light quality, but could plant pests be affected too? For example narrow bandwidth UV-B light can be used directly and efficiently against the growth of powdery mildew fungi, as thorough investigations in a collaborative project by Cornell researchers and colleagues in Norway have shown. However, the UV-B treatments must be applied at night, so that the wavelengths in natural light can’t repair the damage caused by UV-B light to powdery mildew genome.
Aphids are a tricky problem in lettuce, hiding between the leaves. There they are protected against chemical pesticides as well as natural enemies used against aphids. Aphids can be thwarted with systemic pesticides, that are transported in plant vascular tissues and foliage. But fresh edible plants would be safer, if pests could be under control without pesticides. There would be no need to worry about waiting periods or anyone exposed to chemicals during their use.
In recent experiments done by Irene Vänninen at the Natural Resources Institute Finland, aphid reproduction rate (glasshouse-potato aphids Aulacorthum solani) was monitored on iceberg lettuce seedlings grown under different spectra for three weeks. In all, conditions were good for the aphids, that multiplied their numbers. At the same time, plant growth performance remained on a good level as well, as was demonstrated by plant dry weight, that was not reduced due to the aphids. Detailed analysis of the results is ongoing and it is clear that both direct and indirect effects (through production of plant protective compounds) of light quality will remain an interesting field of study in controlled environment pest management.
Photos by Ari Eskola, LUKE.