Eric Brennan, USDA Agricultural Research Service, Salinas, CA
A natural all-you-can-eat buffet keeps beneficial organisms working on the farm year-round. Hedgerows, cover crops, and insectary plants provide this biodiversity which helps farmers control pests without pesticides and makes the farm more sustainable and beautiful. This fun video by USDA-ARS scientist Dr. Eric Brennan explains how this works at the Agricultural Research Service's organic farm in Salinas, California in high-value production systems for vegetables and strawberries. It provides some details on drought-tolerant, native perennial hedgerows for California and describes some challenges and novel strategies to make intercropping vegetables with a common insectary plant (alyssum) more efficient.
See also another video by Eric Brennan: Efficient Intercropping for Biological Control of Aphids in Transplanted Organic Lettuce
Hedgerow Control. This is Hoverfly 742, maintaining 2000. Heading 180. Requesting land clearance. Hoverfly 742 turn left. Heading 090. Descend to 1000 until established on the ILS runway. Coyote Brush 32 approach. Cleared to land. Hoverfly 742. Turning left. Heading 090. Descend to 1000 until established on the ILS runway. Coyote Brush 32 approach. Cleared to land.
So you've probably figured out by now that I'm not your typical air traffic controller. I don't direct airplanes in and out of airports, but you might think of me as an organic air traffic controller or a biological air traffic controller. What I mean is that, as I've managed the airspace above this organic farm since 2001, I've tried to encourage a diversity of beneficial organisms to come here to help us to control our pests. And the three main components of our farm that help with this are hedgerows on the farm edges, cover crops that we usually grow when our fields don't have cash crops, and insectary plants that we interplant with our vegetables and strawberries. I like to think of these three components as providing a buffet of food options for beneficial organisms on our farm.
Over the next few minutes I'll give you a short tour of our 22 acres of high value land and explain how our conservation biological control program here works to control pests as we conduct and share cutting-edge, commercial-scale research on organic vegetable and strawberry production. I'm fortunate to have great collaborators here with lots of practical farming experience and a passion to think out of the box and develop new and creative sustainable farming strategies that apply to organic and conventional systems.
To help you understand our farm let's fly up to get a bird's eye view. The cool Pacific Ocean is about 15 miles that way as Salinas Valley opens to Monterey Bay. Our organic farm is connected to about another 150 acres of conventional USDA research land. A simple way to understand the layout of our organic farm is to divide it into four main sections that include strawberries in one section each year, and vegetables and cover crops in the other sections. For example, this section had broccoli this last summer and was just planted to strawberries. Our new strawberry planting also includes a novel cover-cropping strategy in the furrows.
Okay, so let me now provide a few details about these three critical biological control components starting with my favorite place on the farm, the hedgerow. In some ways it reminds me of the biologically diverse tropical forests in Papua New Guinea where I grew up, and which surrounded many of the agricultural fields there. Our hedgerow is a fun place to explore that's filled with biodiversity and is just a relaxing place to take a break when you need one. I consider it a sacred place, because it reminds us of the balanced natural ecosystem that once dominated this landscape and that has so much to teach us to help us to improve our agricultural systems. The hedgerow is essentially the supporting backbone of our biological control system. What I mean by supporting backbone is that the hedgerow is the most stable, complex, and permanent part of our farm. And it's a refuge for beneficial organisms when we disturb our fields with intense tillage between crops. The hedgerows are then the major source of beneficial insects to recolonize our new plantings.
I remember the fun and productive day that our hedgerow was planted in 2003 with the help of volunteers and our local hedgerow guru, my friend Sam. Since then, our hedgerow has been low-maintenance because it includes a diversity of drought tolerant, native perennials, which were irrigated only during the first year. Now a key benefit of the hedgerow and the adjacent berm with flowering annuals is that the diversity of plants ensures that there's always something flowering to provide beneficial insects like hoverflies with the pollen and the nectar that they need to reproduce and thrive. For example, the coyote brush plant where Hoverfly 742 landed—it flowers in the fall and the winter when there are few other sources of food for adult hoverflies on our farm.
Now there are some challenges with hedgerows. For example, some people think that hedgerows increase the risk of food safety problems from rodents, and try to minimize this with fences and toxic baits along the borders with neighboring hedgerows. But I've not seen any compelling scientific evidence to support this concern about food safety. In fact, recent research suggests that removing non-crop vegetation, like hedgerows, may actually increase food safety pathogens. Now one clear challenge with hedgerows is from leaf-eating birds like the White-crowned Sparrow. They like to overwinter in the hedgerows and eat leaves of some crops right next to the hedgerow. Ironically, these same birds may actually help us though, because they can also eat weed foliage under the canopy of some of our cover crops.
Speaking of cover crops, let's now consider their role in biological control on our farm. We grow lots of cover crops in rotation with our vegetables and strawberries and have seen huge benefits. This bumper sticker is one that I designed a few years ago, and it does a pretty good job of summarizing some of the benefits of cover crops in terms of their ability to reduce runoff and improve soil quality, and boost crop yields with fewer fertilizer inputs. But it doesn't say anything about cover crop benefits for biological control. So here's another bumper sticker I just designed to help clarify this. It's got a few common beneficial insects that I often see in our cover crops. I've also seen other beneficial organisms like gopher snakes. Now just like the cover crop provides the gopher snake with a good habitat to hunt for gophers, the cover crop also provides beneficial insects with a source of insects to eat—like aphid species that are usually different from the aphids that are on our cash crops.
Flowering weeds in our cover crops can also provide pollen and nectar for adult hoverflies and parasitic wasps. But the problem with many of these weeds is that they produce seeds quickly, and therefore can increase the hand weeding costs in our subsequent cash crops. So we carefully manage our cover crops to suppress weed growth and flowering. Although wild radish is one weed that we really don't mind in our winter cover crops, because it doesn't flower until late in the spring when the cover crops are usually ready to be mowed down and incorporated back into the soil.
Allright, now for the last part of our biological control buffet, the insectary plants. There are many different types of insectary plants in our region, but I'll just briefly describe two ways that my research has improved the efficiency of using one popular insectary plant, sweet alyssum. First, I'll describe it for transplanted lettuce and then also for direct-seeded lettuce. Alyssum flowers are a great source of pollen and nectar for adult hoverflies, and encourages them to move through lettuce fields. In the process, the female hoverflies lay eggs on lettuce that has aphids. And the larvae that hatch from these eggs eat the aphids, live! When I started working with transplanted lettuce in 2004, farmers here usually gave up about 5 to 10% of their field to grow alyssum in strips or as randomly scattered plants through the field. But I found that a far more land-efficient approach to get plenty of alyssum flowers into the field was simply to insert alyssum transplants between the regularly spaced lettuce, without displacing any lettuce. In other words, you don't need to give up space for alyssum. We call this additive intercropping.
The last method I'll describe is a simple, efficient, and novel way that I've been working on to help farmers plant alyssum seeds with the same precision seeder that they use to plant pelleted lettuce seed. These seeders provide very uniform and regular spacing of the pelleted seed. To achieve this, I teamed up with a local seed treatment company that was able to pellet the alyssum seed to the same size as a pelleted lettuce seed. This was a complicated process because the alyssum seed is much smaller than lettuce seed and therefore the alyssum seed had to be coated in much more pelleting material than the lettuce seed. But it's worked beautifully! And it means that farmers here can now mix just a few teaspoons of pelleted sweet alyssum into their pelleted lettuce seed, and the alyssum will be scattered randomly through the field. The lettuce thinning and weeding crews are then trained to easily identify alyssum seedlings and leave these to flower for the hoverflies. It's a great system!
That's our biological control buffet here at the USDA organic research farm in the Salad Bowl of America—Salinas, California. Our system isn't perfect but we're pretty happy with it. We're always trying to fine tune it—make it a little bit better, more efficient. So I hope you'll stay tuned as we do that. And I also hope that you can find ways that you can support farmers that are using the types of techniques that I described here today.
You know what.... I got to get back up there to hedgerow control tower because Hoverfly 742 that landed on this Coyote Brush plant right here has already fueled up with pollen and nectar and is ready to take off on another mission out there to look for aphids. So I don't want to delay her. I want to encourage her, and I want to keep her safe.
Hedgerow Control. This is Hoverfly 742. Requesting take off clearance. Roger, Hoverfly 742. You are cleared for takeoff!
MUSIC (Fly me to the moon)
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