By Molly Shaw
Biocontrol is simple, in concept that is. The good bugs eat the bad bugs so the bad bugs don’t damage our crops. Give the good bugs safe places to live, and they work overtime for you, resulting in happy farmers, happy bugs, and happy customers.
Right, that’s the rosy picture, but we all know it’s not that simple. Successful biocontrol can be likened to artisan bread making—again, a simple concept of adding yeast to flour which together transform tasteless flour into a savoury loaf of bread…..if the recipe and process is followed correctly, and the baker has developed that experienced “feel” for the dough. The first time you try the recipe it seems like a million and one complicated steps with elaborate timing. That initial batch might not come out so well, but with a bit of practice you can get spectacular success. So, too, with biocontrol.
There are three “genres” of biocontrol. One is called “conservation biocontrol,” where farmers enhance and protect the good insects that are already there, such as leaving diverse hedgerow plants to provide food and shelter for beneficial insects. Another is termed “classic biocontrol,” where introduced predators eat pests (like introduced stoats were supposed to eat the rabbits, but we all know what happened there). The last is called “augmentative biocontrol,” where the farmer boosts the good guy population with reared insect releases until there are enough present to get the job done. Much of the biocontrol work in agriculture settings has been done with insects, so for this discussion we’ll focus our attention there.
Biocontrol tends to work best with:
1. Processed crops, or crops where the pest attacks the non-edible part. In other words, where <100% pest control is acceptable.
2. Simple pest complex (crops with only a couple of main pests). Biocontrol tends to be economical if farmers can save a whole spray trip out to the field, rather than just omitting one ingredient from the spray tank.
3. Controlled environment (like a greenhouse). Some predator insects have narrow environmental conditions where they thrive, and it can be easier to maintain those conditions in protected greenhouse culture. In addition, greenhouse crops are high value, in some cases justifying the use of biocontrol even if that option is more expensive than a traditional spray.
4. Committed/interested practitioner. It takes persistence to make biocontrol work.
Everyone has a heard a failed biocontrol story, so let’s spend a minute analyzing one of them.
A greenhouse grower in New York state put up a high tunnel (unheated greenhouse where plants are grown in field soil) for raspberries. The reason for a high tunnel was to protect the flowers and fruit from rain, avoiding botrytis and increasing yield and quality. He had heard from other raspberry growers that spider mites could be really bad in the warm, protected tunnel environment, so from the outset he kept an eye out for them on the plants. He had heard that predator mites could be used on spider mites, and was interested in giving them a try (augmentative biocontrol). Mid-summer a consultant stopped at the farm and offered to scout for spider mites. Sure enough, the population was building to high levels down low in the plant canopy, but since it was the first time the grower had scouted for the mites, he hadn’t recognized the telltale speckled signs of feeding damage. By the time the grower ordered the beneficial mites from the insectary, waited a week for them to arrive, and dispersed them in the greenhouse, the spider mite population was damagingly high and still increasing rapidly. Conventional spray options were pretty limited once the beneficial mites were in place, since most insecticides that would work on the pest would kill the beneficial too. To boot, it was a busy time of year and the raspberry tunnel wasn’t front and center in importance. Consequently, the spider mite population exploded, seriously decreasing fruiting potential. The next year a new pest, a fruit fly that lays eggs in the berries, arrived on the scene. Predator mites don’t prevent maggots in the fruit, so the grower had to spray for the fruit flies anyway, and decided to throw a little miticide into the spray tank to take care of the spider mites at the same time. Biocontrol failed.
Now let’s analyze this story, looking at the 4 parameters that make biocontrol more likely to work. The spider mite that was targeted by the biocontrol was, at the time, the only significant pest of greenhouse raspberries (there was a simple pest complex). The spider mite also attacked plant leaves, rather than fruit, so the grower could tolerate some low level of damage. A high tunnel is a more controlled environment than the open field, an environment where the beneficial mites had a good chance of surviving. So far so good. The farmer was a little bit interested in biocontrol, but his customers weren’t going to pay any extra for “greener” growing methods (such as organic), so there wasn’t a big incentive to make the biocontrol work. Also, it was the first time the grower had experienced spider mites on raspberries, his first time “through the recipe,” so to speak. So by the time he recognized the pest, it was already beyond the stage where predatory mites could keep the population at bay. The next year he could have ordered his predator mites in two batches to place in the tunnel before spider mites had caused damage, therefore preventing their population from exploding. Unfortunately, a new serious pest turned up that had no proven biocontrol options, so the grower was back to spraying. Sad, but at least the grower had a marketable crop of raspberries.
Now let’s look at a successful biocontrol story closer to home. Steve Wratten, professor of ecology at Lincoln University, has worked with several vineyards in the Waipara Valley to implement biocontrol measures in their vines. The only insect pest these growers spray for is the leafroller (unlike in Hawkes Bay, where mealy bugs are increasingly a problem), so they have a simple pest complex to contend with. In addition, the leafroller does not attack the fruit directly, and growers can tolerate up to 5 leafrollers per 100 bunches of grapes. The vineyard isn’t a protected environment, but even so there are tiny naturally occurring parasitoid wasps that prey on leafrollers (a conservation biocontrol opportunity). The wasps lay their eggs in leafroller caterpillars, then the wasp larvae eat the caterpillars from the inside out. It turns out that female parasitic wasps live only three days if all they have to survive on is water, but 40 days if they can feed on nectar. Longer life translates into more eggs laid, more leafroller caterpillars eaten, and higher populations of parasitoid wasps. Researchers have found that the wasps can fly 20 meters looking for leafroller caterpillars in which to lay their eggs, so if vineyard growers can give these wasps a good food source every 10-15 vineyard rows, they’ll hang around in high enough numbers to keep the leafrollers at a tolerable (low) level.
Jean-Luc Dufour at Waipara Hills has been using buckwheat between every 10th row of vines, and has successfully controlled leafrollers without insecticide sprays since he began this practice. Buckwheat is a great nectar producer but has a relatively short flowering window, so seeds are drilled three times (monthly, Dec-Feb) in order to keep up the nectar resource for the parasitoid wasps. Economically, the vineyard saved roughly $250/hectar in insecticide costs, and at the time they had a cheap source of buckwheat seed so those plantings were low cost to establish. Jean-Luc was also interested in biocontrol because his vineyard workers don’t like to use pesticides, and it matches the company philosophy (and marketing image) of the vineyard using environmentally friendly practices.
Systems where biological control of pests is possible are becoming more researched and gaining traction, not only because of environmental concerns, but also because new pesticides are becoming rarer and old broad-spectrum insecticides are becoming more restricted. Perhaps there’s an opportunity in your farming system to try it out, gain the expertise required, and become a leader in the field.