Think of it as one step beyond cover crops.
Many conventional growers have now implemented soil saving practices such as no-till or cover cropping. Cover crops provide habitat for beneficial insects and pollinators, conserve soil moisture, reduce weed growth, enhance carbon sequestration, prevent nutrient leaching and protect soil fertility and erosion.
The ecosystems benefits gained by utilization of cover crops can benefit all growers, reducing the need for chemical inputs, increasing soil organic matter, positively impacting water infiltration and vastly improving soil physical, chemical and biological properties.
All this good stuff provides the optimal stage for a healthy cash crop. And healthy crops, grown in a diverse, vibrant ecosystem, should show a decrease in pest and pathogen pressures.
Could living mulches be a next step in disease defense?
Could a cover crop – a living mulch – that is not terminated prior to planting, and which grows alongside the crop, provide growers (organic or conventional) a way to decrease or eliminate the use of synthetic pesticides? By deterring pests and pathogens, living mulches could reduce the need for on-farm inputs for fertility and pest and weed control.
Ongoing Living Mulch Vegetable Research
Researchers at South Dakota State University have been studying the effect of living mulches on a variety of vegetable crops in several ongoing studies. Broccoli, squash, peppers and cabbage are all being studied, and research on grafted cucumbers and tomatoes is underway.
Weed suppression, pest control and pathogen reduction, soil health benefits, crop nutrition and yield are being examined in multiple studies in order to provide specialty crop growers data on the impacts living mulches can have on crop production.
Joslyn Fousert, a SDSU graduate student, has focused on the use of living mulches to deter weeds and to serve as a tool in integrated pest management techniques. Fousert is researching the effect of three different perennial clovers – red, white and a white x kura cross – on five different varieties of cabbage, spanning early, mid and late season, under both till or no-till management and either using fabric weed barriers or not.
“We are looking at different practices to allow organic farmers to work better with land,” she explained.
Cabbage is planted directly into the clover living mulches. Data on soil moisture throughout the growing season have been studied, and while the clover living mulch does tend to compete with the crop for water, cabbages planted in the bare ground control plot wilt even more under the same water management.
Further studies examining the amount of applied water needed across different treatments to ensure adequate soil moisture for the crop are needed. The quality and yield of the cabbage, the biomass of the clover vs. the weeds and soil health and overall properties are also being examined.
The trials also include a study of insect damage from cabbage looper and white cabbage butterfly worm. Preventing worms when the heads are forming is important for crop quality. Beneficial flowers were planted into guard rows to attract pollinators and deter the common cabbage worm pests. The zinnias, marigolds and nasturtium have been working.
“My big picture IPM … is to utilize beneficial flowers, crop scouting and application of Dipel DF (Bt),” Fousert said.
“I’ve been noticing that the beneficial flowers have been helping. However, when I do crop scout, the [number of] cabbage loopers and the white butterfly worms have been above the economic threshold levels, which are two or more worms per plant,” and application of Bt are needed, Fousert said. “The key is to keep it at a lower level, to where the cabbage plants don’t start to become stressed with becoming defoliated.”
Grafting for Yield
Dr. Sean Toporek, plant pathologist at SDSU, will be researching the impact of living mulches on grafted cucumbers and tomatoes. Living mulch is “a way of integrating cover crops into the space that is in between your vegetable beds,” he said, and the purpose is to enhance ecosystem improvements – including pest control – that these systems bring to the farm.
In past studies, researchers determined both that marigold and sunhemp used as a living mulch in cucumbers seemed to decrease pest damage but also significantly decreased yields. In tomatoes planted with a hairy vetch living mulch, yield suppression was also seen.
“The issue with grower adoption is that living mulch reduces cash crop yield,” Toporek said.
By grafting more vigorous rootstocks to desired cultivars, yields have been proven to increase. Toporek wants to determine if grafting would “offset the losses that the growers don’t want to stomach and maintain the yields we would have without the living mulch.”
He is enthusiastic about living mulches as pathogen deterrents. Prior studies show that pest and pathogen pressures are reduced in vegetable crops grown in conjunction with a living mulch.
“A lot of these cover crop choices actually have some insect deterrent properties to them,” he said.
In data from other trials, sunhemp was shown to decrease the cucumber beetle population as compared to bare ground in zucchini. Zucchini planted in a buckwheat living mulch has also been seen to have a reduction in the number of plants with symptoms of cucurbit leaf crumple virus, a thrips-vectored disease, when compared to the control.
Toporek is interested in the insect-vectored cucurbit yellow vine disease, vectored by squash bug and caused by the Serratia marcescens bacteria; as well as bacterial wilt, which is caused by the pathogen Erwinia tracheiphila and vectored by the cucumber beetle.
In his upcoming living mulch trials with grafted cucumbers and tomatoes, he hopes to demonstrate insect – as well as their vectored pathogen – reduction in living mulch systems while also reducing the cash crop yield losses typically associated with living mulches.
“Maybe these cover crops that we choose will also have the added benefit … of blocking out these bacteria-vectoring insect pathogens,” Toporek said.
Living mulches have been studied before. It isn’t a new idea. But perhaps the time is ripe for finding ways to beneficially utilize this management system on a wide scale, across multiple crops.
By providing benefits to farming ecosystems – and doing so without much yield loss – living mulches might just bring more to the farmers’ table than a profitable cash crop.
