Using red nets to cover crops could prove an effective deterrent against certain pest insects causing serious damage to crops, reducing the need for pesticides, research in Japan suggests.
Scientists carried out laboratory experiments using a prolific pest, the onion thrips (Thrips tabaci) exploring the deterrent effect of combinations of red, white and black threads in meshes covering Welsh onion. As well as directly feeding on plant tissues, the thrips species is a known vector of iris yellow spot virus and tomato spotted wilt virus, which cause disease affecting several types of vegetable.
The research team found that the covers using red threads all performed better than those using white and black, reducing the number of the pest entering the crop significantly, even when larger sized meshes were used.
Field tests validate colour theory
They then went on to test the meshes in two field experiments. In one, they used 0.8mm coverings coloured all-red, red-white and all-white, and applied no chemical insecticides. They monitored for direct damage by the thrips, as well as signs of disease infection. In the second, they tested the effect of different approaches to covering the crop with all-red 0.8mm mesh in equal-sizes plots, as well as an uncovered plot. Pest pressure on the uncovered plot meant that they also applied insecticides twice.
Analysing the results of the tests, they saw that the invasion of the pest into the crop can be significantly halted using the nets, and damage to leaves reduced. Insecticide applications can also be reduced by 25-50% by using the nets, compared to uncovered plots.
“We report that the effectiveness of the conventional insect net can be greatly advanced by changing their colour to red that helps significantly reduce pesticide use,” the researchers wrote in the journal Nature Scientific Reports.
Seeing the light
The effects seen in the work suggest that thrips visually discriminate nets containing red fibres, they noted, with blue and green photoreceptors in the insects’ compound eyes likely to be involved in this mechanism.
While using crop nets is a well-known preventative approach against small pests as part of integrated pest management strategies, testing nets in different colours had not been done before, said the team.
Small pests such as T. tabaci are becoming increasingly difficult to tackle using conventional insecticides due to the development of resistance, meaning growers are seeking novel interventions. Investigations are needed to see if using red nets can help in the case of other pests of crops grown in greenhouses, they added.
Previous research had shown that the manipulation of light using coloured nets has had positive knock-on effects. Some work has shown that covering fruit with red nets can improve quality and nutrient quality, though the impact on onions is as-yet unknown.
A potential downside of covering crops in greenhouses with nets is possible overheating and reduced breathability. However, the researchers noted that any such issues could be addressed by using red nets with larger mesh, which performed better than meshes of the same size but in other colours over the course of the work.
