Some of the biggest threats to humanity’s survival are so tiny that it can be hard to take them seriously — Covid is a pretty good example. Thrips are insects that can barely be seen with the naked eye, yet they are the single most costly agricultural pest worldwide. The average person has no idea they even exist. And they love climate change.
Thrips literally suck the life out of the plants they love. They are attracted to flowers, particularly yellow flowers, but they feed on basically any plant material that provides them with nutritious sap. If they find a plant when it is small, they can severely damage or kill it as their populations increase quickly under the right conditions. But they also transmit damaging viruses from plant to plant, greatly exacerbating the potential for massive crop loss.
Like many insects, thrips populations are weather dependent. They love hot, dry weather and breed quickly in it. Rain or wetting irrigation drowns them, washes them off plants, and keeps their populations low. But long periods of wet weather create lush growth of foliage that can support large numbers of thrips if it is followed by hot, dry weather. They tend to move out of wildlands or weedy areas en masse when that vegetation dries out, and usually end up in irrigated crops. If you pay attention, you can actually see this happen. Many of our fields border on unmanaged land, and after a wet winter you can watch the foliage turn color as the thrips cut a swath through it.
Onions are particularly sensitive to thrips, as they have a limited amount of leaves and can easily sunburn if even a smaller percentage of them die. When we see the symptoms of thrips feeding on them in the spring — “bronzing” of the leaves — we spray an organic oil made from cloves and rosemary that kills a portion of them and keeps the damage under control. Some years we have to spray the onions every week for two months.
In 2021, we didn’t get the wet winter nor the heavy growth of weeds. So we didn’t see many thrips in the spring, and we didn’t do much spraying. But with our fields being the only green in a mostly brown landscape, they eventually found our fields. And with the intense summer heat, their populations blew up.
Which brings us to the other threat these pests pose: virus. A few years ago, a new tomato virus called “Spotted Wilt” began to show up the Central Valley. It causes stunting and deformation of tomato plants and fruit, as well as extensive plant death. We had seen a few individual plants here and there in previous years, but this year it essentially wiped out our late tomato plantings.
All it takes is a single thrip to transmit a virus to a plant, and there is no cure you can apply to the plants once they are infected. The only solution is to prevent the virus from infecting the plants. There is no such thing as a “plant vaccine”, but you can breed plants that resist particular viruses.
Like with any virus, the more extensive it becomes, the more likely humans are to prioritize it. With Spotted Wilt Virus spreading rapidly around the world, plant breeders isolated a tomato gene that confers resistance to it and have begun developing varieties that contain it. This is not genetic modification, but rather combining advanced gene-detection technology with good old fashioned plant breeding to cross different varieties to confer the desired trait. In the not-to-distant future, Terra Firma and other farms in California will likely only let tomato varieties onto the farm if they are “vaccinated” against Spotted Wilt.