Farmland hedgerows can provide benefits ranging from reducing wind and soil erosion to biological control of insects and weeds and are drawing interest among growers on California's Central Coast, says Sam Earnshaw of the Community Alliance with Family Farmers.
Earnshaw, Central Coast regional coordinator for the Davis-based group that promotes sustainable agriculture, described what the linear plantings can do during a recent meeting of growers and PCAs in Salinas, Calif.
Hedgerows are defined generally as lines of trees, shrubs, annuals, perennials, grasses or other vegetation in, across or around a field.
They can be tall or short, and they can be designed for specific, local needs and conditions by selecting native plants which require only minimal care once they are established. In addition to farmland uses, they can supply weed control and landscaping to roadways and other non-culti vated spaces.
Among examples of farmland applications are in-field insectary plantings and trap crops. The white blossoms of alyssum rows interspersed with the crop draw beneficial insects to the crop. Alyssum is also used as a groundcover for weed control.
Trap crops include plants, such as alfalfa, clovers, various other legumes and wildflowers that attract pests and are then mowed or otherwise removed along with the pests.
Earnshow said a mix of species having different flowering periods can provide a year-round source of food and habitat for beneficial insects. Willows and ceanothus species start blooming in January and February, while buckwheat species bloom from April through December.
A Gilroy grower having problems with control of poison hemlock on berms, he said, found a solution by planting creeping wild rye, a native species, and irrigating it by drip to overwhelm the weed.
Earnshaw also listed precautions and concerns associated with hedgerows. A wise step to avoid difficulties later is to consult with local biologists before making selections about which species will truly benefit the particular crop or crops.
A frequent pitfall is using non-native species that could eventually harm the local ecological balance. Local biologists can advise on whether a plant is non-invasive and appropriate for your location.
Species must be selected on the basis of the particular insects they attract, which may or may not be beneficial to the crop and location. Where deer, rodents or birds may be problems, species can be selected that are not food for wildlife.
The same applies for diseases that hedgerow species may support. Some plants also are hosts of Pierce's Disease, sudden oak death, eutypa, or other pathogens that damage crops.
Irrigation, either too little or too much, can be a factor in the success in establishing hedgerows. Plants should be selected on the basis of their needs and ability to supply them with water.
“One of the big problems with getting a hedgerow established is managing it to avoid damage by tractor drivers and other workers who think the plantings are weeds,” Earnshaw said. Reminders to workers and signs indicating the plants are helpful in getting the hedgerow off to a good start.
Costs of hedgerows vary widely, from $1.20 per linear foot to $4 per linear foot, plus maintenance costs.
Earnshaw said dense, perennial hedgerow species do attract birds, rodents and other wildlife, and that means food safety issues for some growers.
Those who produce salad vegetables are fearful of liability if disease or fecal contamination from wildlife were to be found in their produce.
“This needs much more scientific research to find out if their concerns are justified. However, we are helping a lot of farmers who don't have a problem with food safety and want hedgerows. These growers do not have mechanically harvested crops like spinach or a salad mix. Or, they are growers who have those crops but grow celery or some other manually harvested crop next to the hedgerows.”
Practically any grower, he said, can find a place for hedgerows with some juggling of field rotation.
Earnshaw said the pros and cons are being discussed among interested parties, and the Monterey County Resource Conservation District has held meetings to exchange information on hedgerows.
Meanwhile, he added, state water quality regulations require growers to take steps to curtail irrigation water runoff and soil erosion, which hedgerows can help accomplish.
In his observations on insectary crops this year, Franklin Dlott, University of California Cooperative Extension research assistant for Monterey County, said he has concentrated on how manage species for blooming to attract beneficial insects at the opportune time for lettuce crops. The objective is to attract syrphid flies that will prey on lettuce aphid and eventually develop a strategy for managing them. “Visits” by syrphids were tallied for each plant species.
In small plots at Hartnell College, Dlott planted a “low profile blend” of flowering species, including alyssum, clovers, California poppy, phacelia, yarrow, cornflower and others. He also seeded plots of each individual species for comparison.
“The idea with the blend is that something in it will do well and attract insects,” he said. “And we found that the blend is more difficult to manage than individual species.”
Some blends, while good for weed suppression or soil erosion control, are not necessarily the best attractants for beneficial insects.
Dlott also noted that how well insectary plantings do the job is dependent on the soils and irrigation practices of the field and he warned that they may not perform the same way every year.
In the trials this year, he said, alyssum bloomed earlier and longer than the others and showed good attraction for syrphids.
Phacelia, which has been reported a good host for syrphid in Australia, rapidly established itself in Dlott's trial. “But the problem,” he said, “is it also attracts bees, which syrphid flies avoid.”
Nitro-persian clover, he added, was a good performer for weed suppression, but it did not attract syrphids.