Carol Shennan: We try and address issues of pests and diseases and nutrients all in the same rotation systems, and that’s really what CalCORE—the core of CalCORE—is. And then we are also interested in the biological control of important pests, and most of that work focuses on either strawberry pests or pests of broccoli.
Chapter 1.1: Lygus Bug in Strawberry
Diego Nieto: Lygus bug is one of the two sort of key pests of strawberry in this region. If you look at the organic acreage in Santa Cruz County, it is worth about $23 million for strawberry. A conservative, very conservative, estimate for losses with respect to lygus damage is about 5%. That means annually there is over a million dollars of yield that is lost due to this particular pest just in organic strawberries in this county.
Tim Campion: The lygus bug feeds on the flower, and you can't visually see that the flower has been damaged until it starts developing into fruit and it will result in a fruit that they call cat-faced. It is kind of gnarled and unmarketable.
Jaime Lopez: The way we control our lygus bug and from the Extension’s outreach, is the best management practice right now is using vacuums, aspirators, that will come into the field and suck up the bugs and just grind them to pieces.
Chapter 1.2: Alfalfa Trap Crop: A Prevention, Scouting, & Management Tool
Diego Nieto: So lygus bug is a generalist feeding pest, which is to say that it doesn’t become problematic in strawberry because it loves strawberry, but rather because it is sort of available when the hillsides and all of the native plants have become dry as spring turns to summer. If we can utilize that polyphagous feeding behavior and take advantage of it by providing a plant host that is in fact preferred, then you can prevent pest establishment in a strawberry field. And of course with organic agriculture, prevention is steps 1, 2, and 3 in a good pest management program. So what we have done is implement alfalfa trap crops to attract lygus bugs.
In addition to the preventative component, alfalfa trap-cropping also provides a very efficient and effective means of scouting and management. So rather than scouting a very large strawberry field, with alfalfa trap crops you know exactly where to look. With respect to management, again there is lots of efficiency built into the system. The lygus bug pest pressure tends to be concentrated in this little three-row universe, which is one alfalfa trap crop and then the immediately adjacent strawberry row on either side. So these tractor-mounted vacuums can go through the three-row area and get the majority of lygus bugs and you can in that way conserve the beneficial insects, the predators, and the parasitoids that are in those strawberries.
Chapter 1.3: Identifying Lygus Bug Predators
Diego Nieto: Part of the aim here was to distinguish, identify, and characterize how predators operated in this trap crop system. So we were able to collect predators in commercial strawberry and look at their gut contents to see which ones had actually consumed lygus bug. We were able to identify 14 different predator groups that we found evidence of lygus predation. This included 8 different types of spiders, 3 true bugs, and 2 beetles. So there is a very big predator community that is in strawberry that is consuming lygus bug.
Chapter 1.4: Increased Predation Rates in Alfalfa Trap Crops
Diego Nieto: We were able to collect a significant amount of evidence that predation increases with increased prey abundance in alfalfa relative to strawberry.
Ultimately, when you look at yield in strawberry that are adjacent or associated with alfalfa trap crops compared to strawberry by themselves, what's exciting is you do get a yield improvement. So there is definitely an economic benefit to alfalfa trap crops.
Chapter 2.1: Cabbage Aphid in Brassicas: Improving Knowledge of the Beneficial Syrphid Community
Steve Pedersen: As far as brassicas are concerned, the cabbage aphid is by far the number one problem.
Diego Nieto: If you unofficially survey growers who deal with this pest on a routine basis, it sounds like there is about 15% yield loss in the form of contamination where these aphids get into the florets or the heads of a particular brassica.
More often than not the syrphid community will come in in a timely fashion and will effectively manage these cabbage aphid communities. But there is inconsistency and unpredictability with how these syrphids move in in terms of the quantity or the timeliness of their establishment. So the timing of when syrphids come in and establish in a field ends up being incredibly important and influential to the ultimate yield outcome of a particular organic brassica crop.
Some of our goals with respect to cabbage aphid and the syrphid community that is found in cole crops on the Central Coast involves distinguishing and characterizing the species in that syrphid community, determining how they interact with the timing of a broccoli growing season, particular aphid densities, how they complement possibly one another with those dynamics, and then to try and illustrate, communicate how those species operate—making sure people understand the differences between one species versus another and especially those species versus caterpillars so that no one is confusing a beneficial insect with a pest.
I think the management implications might be tailoring beneficial insectary habitats that have the most utility for these particular species. Some of these species they vary from smaller flies to larger flies and correspondingly from smaller larvae to larger larvae and so it is important to figure out which flowers—the flower types, the flower shapes, how accessible the nectar and pollen is—how that corresponds to particular syrphid species to make sure that we are getting the full benefit out of these insectary habitats.
Steve Pedersen: Identifying the roles of specific predators in organic systems is very exciting and that’s a really neat component of the CalCORE project.
This is an eOrganic article and was reviewed for compliance with National Organic Program regulations by members of the eOrganic community. Always check with your organic certification agency before adopting new practices or using new materials. For more information, refer to eOrganic's articles on organic certification.