Thrips are currently the bane of my greenhouse.
Thrips are a tiny, long and narrow shaped insect which love to attack flowers and also the growing point of plants (especially cucumbers, though thrips are not too fussy). They often damage the fruit when it is still close to microscopic-sized, killing part of the fruit, and causing it to become misshapen. That reduces the price that growers can get for their fruit. Also, infestations of thrips will kill leaves and even whole plants.
The good news is that there are a lot of biologicals that work very well on thrips. The bad is that companies have only developed biological controls because the pests (like thrips) have become immune to chemicals faster than the chemical companies can develop new chemicals and get those through their country’s val system. Biological controls are much easier to get approved and so that industry is taking off and everyone gets vegetables that are less likely to have been sprayed.
You can check for thrips in several ways. First, you can look for damage by thrips. Often the damage they do appears silvery. I believe that this is because thrips have a mouthpart that is like a rasp, so when they feed, it is like sandpaper and sort of smooths out the cells that they rasp–or at least that’s what it looks like. Also, you can blow into flowers on your plant and thrips will tend to move around and come out of hiding. Others have told me that this is because thrips don’t like the carbon dioxide, but I don’t know if that’s true or not. Finally, you can use yellow or blue sticky cards and watch for the tiny adult thrips to get caught while flying around.
For the last decade or so, growers used several predators to deal with the thrips (I’m sorry that I don’t know a common name for most of these organisms). These are the ones that I use:
1. Steinernema feltiae is a nematode (the fancy name for a microscopic worm) that one can spray on crop leaves, flowers and soil. The nematode kills thrips that it lands on. Personally, I’ve had very good success with nematodes.
2. Hypoaspis miles is a mite that lives in the growing media and eats thrips as they pupate (thrips pupate in the growing media). They won’t provide 100% control, but they certainly contribute. They also live for a long time, so they are a good investment early in the season.
3. Amblyseius cucumeris is another mite–one that lives on the leaves, stem and flowers of plants. They are decent predators, especially if they are introduced fairly early in the crop cycle.
4. Minute pirate bugs (Orius spp.) is a true bug and an aggressive predator of thrips. It is the only predator that does a decent job against adult thrips (all of the others work much better on juvenile thrips). The problem with orius, traditionally, is that they are aggressive predators, but need other food when they run out of pests to eat. Some flowers, like peppers, have pollen that makes a fine substitute for orius, so they can live on the pollen while they hunt for thrips but some other crops (like cucumbers) do not have pollen which is that good as food for orius, and so they often die early.
The emerging solution to keeping thrip populations down to begin with, is to grow plants for the thrips to live on in addition to the crop plants. (Plants grown specifically for beneficial organisms to live on are called banker plants). So a greenhouse that specializes in cucumbers might have a few small, ornamental pepper banker plants to provide pollen for the minute pirate bugs. This also creates an easy way to allow the insects to live from one season to the next inside the greenhouse.
Using banker plants for minute pirate bugs is the emerging technology in greenhouse growing. It’s a simple technology for small greenhouses also, and potentially a very interesting project for children. I’m not sure how easily it can be adapted to being used in a home (I can imagine that most people would balk at purposefully introducing bugs into their home) but it is a huge step in the direction of moving away from dependence on chemicals–something that should be applauded by everyone.
Thrips are a huge problem in greenhouses for almost every crop (and especially cucumbers). They damage fruit and, in enough numbers, kill plants. Traditional control included a cocktail of chemicals which thrips have become immune to. Out of this resistance to chemicals, people began to use biological controls like insects, mites and nematodes. Although this was somewhat effective, adopting banker plants as a new technology catapults biological controls from a decent technology to the best practice–more effective than even chemical controls. As this develops, it will hopefully become more accessible to the household market as well.
This is an emerging technology, and we recently planted banker plants for minute pirate bugs in our greenhouse. Those bugs are supposed to arrive next week, so hopefully they will help us turn back the growing tide of thrips in our cucumbers.