Dr. Richard Freeman
In this brief presentation, I overview a strategy for reducing pest problems by planting carefully selected flower varieties.
This presentation will following this sequence:
1. I’ll begin by discussing some key principles.
2. Then I’ll discuss management objectives that reflect these principles.
3. Next, I’ll outline some easy-to-do practices for implementing these objectives.
4. I’ll conclude by tying this presentation into other presentations I will be offering to the public.
Section 1. Important Concepts and Principles
A key concept is the ecosystem. In the most general terms, an ecosystem is “the environment” – the physical, chemical and biological world around us. For research or management, we define boundaries based on our goals. Any garden zone or farm zone can be an ecosystem, depending on your perspective.
Ecology is another important concept. Ecology is the study of ecosystems and ecosystem components and how they function and interrelate through time, with special emphasis on energy flows.
Another fundamental concept is biodiversity, short for biological diversity. Biodiversity describes the diversity of the organisms in an ecosystem. Ecologists describe three types of biodiversity, including diversity of composition, diversity of structure and diversity of function.
Biodiversity is key to effective horticulture, even at a small scale. The most robust, resilient ecosystems exhibit high diversity in function, structure and composition. With the smallest organisms – nematodes, microbes, etc. – more species representation is better than less. The vast majority of the smaller organisms are beneficial or neutral to gardens and crops. A biodiverse ecosystem with high species representation will usually deter the small minority of pest species that are present and keep damage within a management comfort zone.
The term biodiversity refers to one of more of the following analytical categories.
The term composition refers to the species and higher taxonomic groups that are present in an ecosystem. Taxa, short for taxonomic groups, include individual species, genera and families, all the way to kingdoms and domains. The term composition also encompasses the population patterns of the taxa that are present. So, compositional diversity refers to the diversity of species, families, etc. in an ecosystem.
The term structure describes the spatial and temporal distribution of organisms and taxa in terms of volume, mass and shape. So, structural diversity refers to diversity of organisms and taxa in physical, spatial terms.
The term function describes the biological processes at work. Functions contribute to net productivity in an ecosystem. More specifically, functions refer to the effects of organisms on each other and how these effects determine productivity. One species can affect another species or it can affect an entire family and so on. Likewise, a family can affect another species or another family, and so on.
Furthermore, organisms can affect other organisms in various ways, among them behavior, physiology and/or metabolism. In combination, these effects, or functions, determine the net productivity of the entire ecosystem.
So, functional diversity refers to diversity of functions that contribute to productivity in the ecosystem.
1.4. Ecological Pest Management
Ecological pest management involves two components: 1) altering habitats to suppress pests, and 2) promoting plant health and pest resistance. A key component of the first component, habitat manipulation, is planting flowers that will either confuse and distract pests or promote arthropods that will kill them.
1.5. Resource Concentration
Pests, especially the plant-eating arthropods, favor areas with intense concentration of food supply, such as found with monoculture crops, which grow only one plant variety. Monocultures attract pests and suffer infestations far more than diversified crops. In contrast, diverse plantings confuse and distract pests with the scents of volatile oils called terpenes, and they physically block and divert pests from crop plants.
1.6. Pest Enemies
Several types of organisms prey upon, parasitize or infect plant pests. For this presentation I will focus on five types of insect: syrphid fly larvae, parasitic wasps, predatory beetles, flower bugs and lacewings.
1.6.1. Syrphid flies
Syrphid fly larvae feed heavily on aphids and aphid larvae and other insect larvae. Syrphids, also known as hover flies, are part of the Syrphidae family in the insect order Dipthera (flies).
1.6.2. Parasitic wasps
Parasitic wasps deposit eggs into plant pests and other insect larvae. Many families in the Hymenoptera (wasp) insect order are parasitic.
1.6.3. Predatory beetles (lady beetles)
Predatory beetles, or lady beetles, adults and larvae, feed on a wide variety of arthropods. Lady beetles make up the Coccinillidae family of the insect order Coleoptera (beetles).
1.6.4 Flower bugs
Flower bugs, also known as minute pirate bugs, prey upon a range of arthropod pests. These bugs make up the Anthocoridae family in the insect order Hemiptera (true bugs).
Lacewings, which include green lacewings and brown lacewings also prey upon a range of arthropod pests. These flying creatures with gossamer wings make up the insect order Neuroptera.
1.7. SNAP benefits
Each of these insect types requires flowers to survive and reproduce, and many require grasses for overwintering habitat. Flowers benefit these insects in four primary ways, known as SNAP benefits: shelter, nectar, alternative prey/hosts and pollen.
Our beneficial insects use plants for shade (cooling and humidity), ovipositing (egg-laying) and hiding.
Many adult beneficial insects require nectar as a primary source of energy, especially the flying insects (parasitoids and syrpids). Nectar is generally the preferred plant-hosted resource for pest enemies.
1.7.3. Alternative prey/hosts
Many of these insects require diverse prey or multiple hosts for oviposition.
Many adult beneficial insects require pollen as a primary source of protein and energy, especially for reproduction.
2. Section 2. Practices for Managing Pests by Planting Flowers
2.1. Plant flowers that provide SNAP benefits
Our target organisms concentrate on plants that offer the easiest and safest access to SNAP benefits. Much of this has to do with access to pollen and nectar, which depend upon the size of the flower parts in relation to the size of the insect parts, so access varies per plant and insect species. In general, these target insects prefer small yellow flowers, though many exceptions exist to that rule.
Prominent plant families contributing floral benefits include Apiaceae, Asteraceae and Polygonaceae, but others like Boraginacea offer them, also.
Most species in the Apiaceae family, which form umbel flowers, provide nectar and pollen to several pest enemies. Daucus carota, Heracleum sphondylium, Angelica sylvestris and Oenanthe crocata provide nectar to hymenopteran parasitoids. Researchers have found that that dill (Anethum graveolens L.) and coriander (Coriandrum sativum L.) flowers are compatible with the head morphology of some species of ladybeetles (Coleomegilla maculata, Coleoptera: Coccinellidae) and green lacewings (Chrysoperla carnea, Neuroptera: Chrysopidae).
Several members of the Asteraceae family, which form composite flowers (pseudoanthems), provide nectar and pollen to several pest enemies. Sunflower (Helianthus annuus) provides SNAP benefit to several pest enemies, including predators of thrips (Thysanoptera). Marigolds generally increase predators and parasitoids in some food crops.
Flowering plants in the Polygonaceae family provide nectar and pollen to several pest enemies. Buckwheat, Fagopyrum esculentum provides floral benefits to several pest enemies, including predators of thrips (Thysanoptera). Buckwheat improved longevity, fecundity and sex ratio of at least one species of parasitic wasp (Dolichogenidea tasmanica) in the braconid family.
The Boraginacea includes several genera that provide SNAP benefits, including Phacellia spp. Phacelia tanacetifolia in strips among farm fields has increased abundance of syrphid flies and other aphidophagous predators and reduced aphid populations. However, Phacelia’s deep corolla makes the nectar unavailable to some short-tongued insects, such as some syrphids. Some hymenopteran parasitoids feed off Phacelia as well.
Allysum flowers have extended longevity for female parasitoids in the Braconidae family.
2.2. Build special zones to provide habitat and travel corridors
These zones provide beneficial insects with abundant SNAP resources, especially in non-cropping seasons. They also provide access to other special zones and natural ecosystems. Designating 5% or more of the growing space to special zones should offer plenty of protection, given an adequate off-site reserve. Otherwise, a higher proportion of blocks and strips would be beneficial.
Reserves are nearby or adjacent natural zones from which beneficial insects can migrate into cropping zones. Reserves are biologically diverse and rich in SNAP services
2.2.2. Blocks and Strips
Blocks are zones within the cropping zones with plantings designed to offer SNAP services. Strips are blocks that run parallel to rows in row-cropping systems or between rows in orchards.
Corridors are areas configured to offer continuous passage between reserves and blocks and strips.
2.3. Plant for a continuous display of flowers.
Plant combinations of flower species and varieties that bloom successively from early-season through late season, so one or more species are blooming at an given time throughout the entire season. Dandelions are often the first beneficial flower to bloom.
Pesticide use, including so-called organic pesticides, will kill friendly arthropods. Use them only in the context of an integrated pest management plan.
Enhancing and protecting biodiversity by providing a diversity of plant taxa for SNAP benefits can confer additional benefits, as well. Increasing diversity of crop plants, especially perennial species, assures a harvest even in the face of failures of one or two crops. Generally, even under harsh conditions, the gardener will get a harvest from the majority of crops in a diversified garden.
Though highly important, floral design is only one component of ecological pest management. Equally important is building a robust and sustained soil food web to maintain plant health and pest resistance. I talk more about this topic in other presentations.
With an ecological pest management plan in place, the gardener can employ an integrated pest management plan, which I also cover in another presentation. Several of my presentations focus on various topics directly pertaining to ecological gardening. Especially relevant to this presentation are my talks on integrated pest management, eco-intensive gardening and perennial polycultures.