Just in time for the season, we’ve got a horde of scary black and orange monsters rampaging through our fields. Unfortunately, they are not cute kids dressed in costumes, but rather unwanted insect visitors. And they are feasting not on candy, but on our broccoli, cabbage, kale and cauliflower.
Bagrada bugs are “stink bugs” — large, shield-shaped insects with a hard shell and a long proboscis that they use to suck the life out of plants. There are several native stink bugs to California, all of which cause damage to crops and are difficult or impossible to control. But Bagradas are an invasive species from Africa via China with no natural predators. And unlike their local cousins, whose solitary nature limits the amount of damage they do, Bagradas are gregarious and quickly multiply.
They are also very picky eaters. Bagrada bugs’ favorite food is mustard, or rather, plants in the mustard family. Also known as “brassicas”, this famly includes many of the crops we grow — arugula, broccoli, cabbage, cauliflower and kale — as well as others such as bok choy, brussel sprouts and mustard greens. Bagradas can smell these crops from far away and they actively seek them out. After a few weeks of feeding on their favorite food, they develop the hormones that cause them to start breeding. A happy pair of Bagradas bugs living in a broccoli field can produce 3 or even 4 generations in just a few months, and each pair has dozens of offspring. If that sounds scary, it is: don’t click this photo linkif you are an insectaphobe.
Unfortunately for the plants in question, and the farmers who grow them, Bagrada bugs cause severe damage. When they suck the juice from a leaf, they cause a sort of allergic reaction that makes the attacked plant stop growing. Cabbages that are attacked by bagradas, for example, do not form heads. Damaged plants are dwarfed and fall victim to attack by other insects.
Later, when populations build, a hundred or more Bagradas will colonize a single plant — doing massive damage that usually kills it.
Our first experience with Bagradas was back in 2015, when they came in on a batch of transplants from our nursery in Gilroy. They caused extensive damage for one season, and then disappeared…until this year. In the three years that have passed, no one has come up with any effective organic control for them.
It is still unclear to scientists who are studying their spread in California why there were so few or no Bagradas last year or the year before. They don’t like cold weather or rain, and they tend to burrow into the soil when winter arrives. The stormy weather in 2016 and 2017 might have kept them in check. Unfortunately, the long-term forecast this year looks a lot more like winter 2015 — warm and dry. And climate change could make those conditions even more common.
The appearance of the Bagradas on our farm is even more unfortunate given that research continues to point to brassicas of all kinds as a huge win/win for humans — healthy food that provides tremendous benefits to the soil while reducing the need for agricultural chemicals and fertilizers (I wrote a newsletter about that last year).
We are cooperating with researchers in any way we can to help find natural and organic solutions to the Bagrada problem. But it’s also critical to educate the people who enjoy and benefit from the crops that the bugs are damaging — you! If we can’t find a solution to this problem, fewer and fewer organic farmers will grow broccoli, kale, cabbage, etc And prices will have to rise to compensate for the 10-20% yield loss the bugs cause. Meanwhile, conventional growers will spray their fields more heavily and more often.
Invasive species in agriculture is a huge issue that impacts everyone who eats, not just the farmers who grow the crops.