Assessing the Use of Farm-Made Foliar Biostimulants and Microbial Inoculants for Cut Flower Production

Production of specialty cut flowers has surged in the United States in the last two decades, driven by increased consumer demand for local products and interest in diverse floral crops that cannot be successfully packaged and shipped from overseas (Redman et al., 2002). In the Northeast alone, the number of operations growing cut flowers and foliage has nearly doubled between 2002 and 2022 (USDA NASS, 2022).

The presence of disease and the feeding and secretions of insect pests can reduce crop vigor, harvestability, and storage life. Unsurprisingly, diseases and insect pests have ranked among the top production challenges for the specialty cut flower industry in the United States and Canada (Loyola et al., 2019). For flower crops, whether they are bound for the farmer’s market stand, farm share bouquet, florist, or wholesaler, aesthetic quality is paramount and the threshold for visible damage from insect pests and pathogens is very low. Additionally, customers expect that the product will maintain its quality in the vase for a week or more post-purchase. Since vase life can be significantly reduced by the presence of disease and insect damage, it is of the utmost importance that growers minimize these impacts to ensure crop quality (Maree and Van Wyk, 2020).

Conventional methods of managing insect pests and diseases, which rely upon the continued use of insecticides, fungicides, and other synthetic pesticides, present challenges for many of today’s specialty cut flower growers. Pesticides can constitute a significant production cost that may be difficult for small producers to shoulder. Many operations producing cut flowers and foliage in our region are small; the average acreage in most Northeast states is between 0.7 and 2 acres (USDA-NASS, 2022). These small farms, likely representing a significant portion of cut flower operations in the country, may not have the financial capacity to purchase pesticides with regularity.

Furthermore, past overuse or misuse of pesticide products in agriculture, particularly fungicides, has led to growing resistance among target organisms, causing these products to be less effective over time. This has been documented with powdery mildew, a common fungal disease of many crops, including cut flowers (Bettiol et al., 2008).

In addition, some growers have moral or environmental objections to the use of synthetic pesticides, preferring regenerative practices that sustain healthy soils and ecosystems to those associated with industrial agriculture (Frankel-Goldwater et al. 2024). Many cut flower growers in the United States, particularly new growers, are dedicated to or interested in sustainable and regenerative production practices (S. Crone, personal communication, 2024). For these growers, the use of synthetic pesticides does not align with their farming philosophy. Commercially available, OMRI-approved products exist to address many of the same pest and disease issues that conventional pesticides target. In many cases, these products do provide viable alternatives for farmers concerned about the environmental toll of synthetic pesticides. However, this does not address the issue of cost; organic pesticides can be equally, or more, expensive when compared to their synthetic counterparts (McCoy et al. 2020). Additionally, even organic pesticides can be sublethal or lethal to non-target organisms. For example, pyrethrin, an organic insecticide, is highly toxic to bees (Adamson et al. 2021). For farmers concerned about the impacts of production on biodiversity, even some organic products do not coincide with their values.

There is a need for affordable, sustainable solutions to common pest and disease issues in cut flower production. Biologically derived products that boost a plant’s growth rate and ability to fight infection and infestation, many of which derive from materials readily available to farmers at low or no cost, have been used in agriculture for centuries. Growers dedicated to ecological farming methods have shown a renewed interest in systems like Korean Natural Farming (KNF). With roots in Japanese and Korean traditional farming practices, KNF utilizes recycled and fermented farm wastes to produce inputs that are rich in beneficial microorganisms, to be applied to plant foliage, soil, seeds, or compost (Reddy, 2011).

The farm-made inputs in KNF and other natural farming systems are used as foliar fertilizers to boost plant nutrition at different plant growth stages, as microbial inoculants and biocontrols to compete with pathogens, and as general biostimulants to boost plant vigor and resistance to pest and disease pressure. For instance, lactic acid bacteria or Lactobacilli (LAB) cultured from rice and milk, is used by farmers as a microbial inoculant to compete with undesirable pathogens on plant leaf surfaces and in soil. Vermicompost extract (VCE), made by earthworm-processed composts mixed with water, is used as a crop biostimulant. Water-soluble calcium (WCA), made from roasted eggshells steeped in vinegar, and kelp solution, are used as calcium- and potassium-rich foliar feeds, respectively.

Research is needed to capture how and to what extent natural farming inputs aid in production, and under which conditions they are most effective. In this project, we intend to test the efficacy of foliar-applied LAB, VCE, kelp solution, and WCA as pest and disease management tools for cut flower crops in Philadelphia and Butler, PA. Both sites are proximal to the largest urban areas in Pennsylvania and have a high concentration of cut flower operations. We’ve chosen to focus on zinnia and dahlia, two of the most commonly grown specialty cut flowers in the United States and Canada (Loyola et al. 2019) that commonly succumb to disease and pest pressure, as well as spirea, a woody perennial crop used in floral arrangements that is prone to aphid infestation. We plan to trial two rates of LAB against a water-only control to assess powdery mildew incidence on zinnia, addressing one of zinnia’s most insidious disease challenges. For dahlia and spirea, we will assess the use of vermicompost extract, kelp solution, and WCA on the incidence of and damage caused by insect pests, including cucumber beetle, spider mites, and aphids. If these inputs can be shown to be effective in reducing disease and pest damage, they can provide a low-cost, user-friendly, and ecologically sustainable alternative to the use of pesticides to maintain crop quality.