Helen Atthowe, Biodesign Farm
Alex Stone, Oregon State University
This article is part of the Biodesign Farm Organic System Description
Biodesign Farm's goal was to build and manage habitat for biological control organisms (insect predators and parasites, birds, bats, soil and foliar microorganisms), thereby suppressing pests, minimizing the use of insecticides, and producing high-quality crops.
Biodesign's insect pest management system (Table 1) included the following:
- Landscape-level diversity, provided by small crop fields bordered on four sides by native grassland/pasture: pasture (75%), native grassland/dryland shrub–steppe community (15%), and riparian areas (10%)
Reduced tillage using seasonal (1990s) and permanent (2000s) living mulch row middles, minimum primary tillage, and no tractor-based weed cultivation. According to the results of 2006 on-farm research, reduced tillage may have enhanced survival of ground-dwelling predators, such as carabid beetles and spiders, which are rarely found in tilled vegetable crop systems.
- Perennial and annual living mulch groundcover in row middles to provide in-field/interspersed plant diversity, season-long pollen/nectar/seed food sources, and winter cover
- Selective mowing of the perennial living mulch to avoid disturbance of natural enemies at key pest pressure times
Irrigation management to discourage certain pests
- Organic soil amendments to maintain balanced crop growth, thus suppressing insect pests
- Three-year crop rotation by crop family (Solanaceae, Brassicaceae, Fabaceae)
- Sprays only when necessary (Table 2): From 1993 through 2000, reduced rates of organic insecticides were applied to avoid killing beneficial insect predators and parasites. No insecticides were applied from 2001 through 2010. Five percent pest damage was tolerated to maintain a food source for natural enemies.
- Use of selective organic insecticides such as Bt and M-pede (soap)
- Field scouting of pests, with farm-specific action thresholds
- Pest-resistant varieties: Red cabbage was more resistant than other brassica crops to aphids and flea beetles at Biodesign.
- Crop diversification: Solanaceous (60%), brassicas (30%), alliums (5%), other crops (5%)
- Allowing some crops to mature and flower
- Allowing certain weeds to grow in the living mulch to provide winter cover, early spring bloom, and summer groundcover for beneficial insects, birds, and fungi
- Floating and hooped row covers: Used early in the season on brassicas and solanaceous crops for frost control and flea beetle protection
- Inorganic mulches: Black plastic and paper mulch used in solanaceous crops
- De facto beetle banks (undisturbed grassy fencerow and pasture) on four margins of both Old and New fields; one 30-ft x 600-ft undisturbed grassy beetle bank in the center of the 5-acre New field
- 2005–2010, New field: Woody plant hedgerow on the south margin—one 600-foot hedgerow (flowering/fruiting native shrubs and small trees)
- 2005–2010, New field: Flowering insectary—one 10-ft x 100-ft grass insectary (native, mostly perennial wildflowers) in the center of New field
Crop yield and quality losses to insects mostly decreased over 18 years, according to Helen. This observation is supported by spray records showing reduced use of insecticides 1995- 2000 (Fig. 1). Sprays for aphids, cabbageworms, and Colorado potato beetle were eliminated 2001-2010. Nonetheless, total insect damage to broccoli, cabbage, brussels sprouts, tomato, and pepper crops averaged less than 5% from 2004 to 2010 (Fig. 2 and Fig.5). In contrast, insect damage to unsprayed brussels sprouts in a no-till 2006 experiment averaged 11.5%.
Biodesign was known at local farmers markets for high-quality tomatoes and peppers. See the eOrganic video: Organic no-till living mulch introduction: Weed Em and Reap.
Lower grade tomatoes and peppers (seconds) were sold by the box at farmers markets for canning. Seconds were small, misshapen, or insect-injured fruits that generally amounted to 5—10% of the total crop yield. Only premium-grade brassica crops were counted in yield/harvest evaluations.
General field monitoring in Old field (1993–2004) revealed a diversity of beneficial insects, including an abundance of ground-dwelling predators such as ground beetles (Carabidae) and several spider species (Araneae) in the living mulch. See the eOrganic video Organic no-till living mulch beneficials: Weed Em and Reap. On-farm research in 1996 recorded predator incidence in the living mulch, including damsel bugs (Nabidae), syrphid fly adults and larvae (Syrphidae), green lacewing adults and larvae (Chrysopidae), ground beetles (Carabidae), many species of spiders (Araneae), lady beetles (Coleoptera:Coccinellidae), and predaceous stink bugs (Perillus species).
In New field, monitoring from 2004 to 2010 and on-farm experiments in 2006 revealed relatively high season-long diversity and population densities among predator and parasite species (Fig. 3, Fig. 4):
- Ground-dwelling predators such as carabid beetles (Carabidae) and several spider species (Araneae) were found in high numbers during the growing season, both in the living mulch and under crop plants (Fig. 4).
- Predaceous stink bugs (Perillus bioculatus and Podisus maculiventris) were prevalent in the later years, feeding on Colorado potato beetle (Leptinotarsa decemlineata) (Photo 1).
- Several species of syrphid flies (Diptera:Syrphidae) were regulars all season. They seemed to prefer nectar of clover flowers and fanweed (Thlaspi arvense); both occurred in the living mulch in an interspersed pattern between crop rows.
- Other common generalist predators observed were lady beetles (Coleoptera:Coccinellidae), lacewings (Neuroptera:Chrysopidae), assassin bugs (Reduviidae), nabid bugs (Nabis spp.), and aphid midge (Aphidoletes aphidimyza).
- Parasites included wasps in the Aphidiidae, Braconidae, and Aphelinidae families. Specific aphid parasitoid wasps were observed attacking several species of aphids (Aphidius and Aphelinus species) and cabbage aphids (Diaeretiella rapae) (Photo 2).
Photo 1. Predaceous stink bug (Perillus bioculatus) attacking Colorado potato beetle larva (Leptinotarsa decemlineata) on Biodesign eggplant leaves. Photo credit: Helen Atthowe.
Photo 2. Parasitoid wasps (Aphidius and Aphelinus species) and aphid midge larvae (Aphidoletes aphidimyza) attacking green peach aphid (Myzus persicae) on Biodesign pepper leaves. Photo credit: Helen Atthowe.
Pesticide applications were significantly reduced over 18 years (Fig. 1). Bt-K (Bacillus thuringiensis kurstaki) was sprayed on brassicas for cabbageworms from 1994 through 1998. M-Pede (soap) was sprayed on peppers for aphids from 1995 through 2000. Bt-SD (Bacillus thuringiensis San Diego) was sprayed on eggplant for Colorado potato beetle in 1995 and 1997. No sprays were applied on any crops from 2001 through 2010.
Biodesign's solution to insect pest problems was to create interspersed habitat for generalist predators and parasites within crop fields. Knowledge and monitoring of ecological relationships among crops, habitat, and pests were part of the insect pest management system (Table 1).
In the early years (1993-2004), habitat building at Biodesign did not include common strategies such as installed insectary plantings, woody hedgerows, or grassy beetle banks. Instead, the farm was designed as small crop fields bordered on four sides by native grassland/pasture. Cover and food sources for beneficial organisms were distributed within fields and in close proximity to crops, using living mulches, rather than in blocks or rows on field edges.
In 2005, 5 years after pesticide spraying ceased due to decreased pest pressure, Biodesign began to add other habitat-building strategies to New field, including a native plant hedgerow and insectary. See the video Conservation Farming and Sustainability, Missoula, Montana.
Biodesign planted annual living mulches each year from 1993 through 2004. Between 2005 and 2010, perennial living mulches were maintained between crop rows. The living mulch was tilled each spring in Old field. In New field, it was left undisturbed from 2005 through 2010. Living mulches provided the following:
- Cover and sequential, season-long sources of nectar, pollen, sap, and seed for beneficial organisms. The living mulch bloom sequence extended from early April (fanweed—Thlaspi arvense) through late September (grasses and clover, including flowering white and red clover).
- Diverse above-ground habitat (different plant heights, flower shapes, and colors)
- Diverse below-ground habitat (different rooting types and root architecture)
- Reduced need for tillage
- Living mulches were 50% of the total area in New field and 30% of the total area in Old field. During field monitoring, predators and parasites were found within crop rows and in the living mulch between crops.
Certain weeds were left growing in the living mulch to provide winter cover, early spring bloom (Thlaspi arvense), and summer groundcover for beneficial insects, birds, and fungi. A specific weed, Solanum nigrum, was preferred by solanaceous flea beetles at Biodesign and acted as a de facto trap crop.
The living mulch was a mixture dominated usually by white clover (Trifolium repens) in Old field and by red clover (Trifolium pratense) in New field. Within 2 or 3 years after first planting in both Old and New fields, the living mulch became a naturally diverse mix of clover, weeds, and grass species that was allowed to flower (Photo 3). Species included:
- Old field: white clover (Trifolium repens), common mallow (Malva neglecta), chickweed (Stellaria media), pigweed (Amaranthus retroflexus), nightshade (Solanum nigrum), fanweed (Thlaspi arvense), lamb's quarter (Chenopodium berlandieri), prickly lettuce (Lactuca serriola), and purslane (Portulaca oleracea)
- New field: red clover (Trifolium pratense), fanweed (Thlaspi arvense), lamb's quarter (Chenopodium berlandieri), common mallow (Malva neglecta), white campion (Silene alba), dandelion (Taraxacum officinale), and quackgrass (Agropyron repens)
Photo 3. Flowering weeds in broccoli, such as fanweed (Thlaspi arvense), provided early season nectar and pollen sources for predators and parasites. Photo credit: Helen Atthowe.
Helen Atthowe's mowing practices evolved since the first living mulch planting in 1993, when she mowed the living mulch regularly to facilitate farm work and reduce competition with crops. Following experiments in 1995 and 1996, she began to let the groundcover grow taller and wilder; beginning in 1998, she allowed the living mulch to flower and produce seed in some rows before mowing. Helen particularly avoided spring mowing in order to provide wind/cold protection for young crop transplants and to avoid disturbing predators and parasites of green peach aphid. Aphid populations were highest and most damaging to pepper transplants in the spring. Helen also managed the groundcover so that some areas (at least 50%) were undisturbed and blooming throughout the season. See the eOrganic video Organic no-till living mulch mowing: Weed Em and Reap.
Biodesign created mostly interspersed diversification from 1994 through 2010, including living mulches between all crops, partial weediness, and reduced tillage. With interspersed habitat, cover and food sources for beneficial organisms were distributed randomly within and in close proximity to crops, rather than in blocks or rows around crops or on crop edges. Hence predators and parasites did not have to move far from cover and food sources to reach crops. Biodesign also created some aggregated or blocked diversification in New field from 2005-2010, including one non-crop insectary planting and one hedgerow.
Some crops were allowed to mature and flower each year, particularly brassica crops, which made up about 30% of the cropping area. Broccoli crops usually flowered from July through November (Photo 4).
Photo 4. Mid-season broccoli in full bloom (right) as red cabbage heads begin to size. Photo credit: Helen Atthowe.
Table 2 shows strategies, biological control organisms, supplemental pesticides, and outcomes for specific pests.
No insecticides were ever applied to manage cabbage aphids. Aphids were a problem and managed with soap (M-Pede) on pepper transplants from 1995 through 2000; high populations occurred where soap was not applied. No insecticides were applied to manage aphids on peppers after 2000, due to low aphid incidence and high numbers of aphid predators and parasites (Photo 2). Nonetheless, pepper yields were stable and/or increased until the farm was sold in 2010 (Fig. 2).
CPB feeding on eggplant transplants was a problem in the early 1990s. Field scouting records from July 1996 show CPB present on 48% of eggplant transplants, with an average of 3 larvae and 2 adults per plant (10 leaves each from 10 plants). Adult beetles were hand picked from 1993 through 1996. CPB larvae were sprayed with Bt San Diego in 1995 and 1997. No insecticides were applied to manage CPB after 1997 due to low CPB incidence and high numbers of CPB predators. Natural populations of predaceous stink bugs (Perillus spp.) were observed feeding on CPB in 1996 (Photo 1). Predaceous stink bugs (Perillus bioculatus and Podisus maculiventris) were observed feeding on CPB from 2005-2010. Lady beetles, Carabid beetles and spiders were observed near solanaceous plants during on-farm research in 2006 and 2007.
Flea beetles were occasional problems throughout the 1990s. They were not sprayed, but all brassica and solanaceous transplants were covered with Reemay for 2 to 3 weeks following transplanting from 1993 through 2010 (mostly for frost protection).
Bt (Bacillus thuringiensis kurstaki) was applied regularly from 1994 through 1998. Beginning in 1999, no insecticides were applied to control cabbageworms. By 2010, cabbageworms occurred at low levels, likely due to the presence of high numbers of worm predators.
Despite regular (although fluctuating) populations of imported cabbageworm adults, broccoli and cabbage yields were stable from 2004—2008, with less than 5% damage (Fig. 5). During 2006 on-farm research in no-till plots, unsprayed brussels sprouts produced an 88.5% marketable crop, with 0.48 pounds of sprouts harvested per plant (Fig. 6).
In most biologically diverse native plant communities, natural enemies (e.g., insect predators and parasites, microorganisms, birds, and bats) regulate plant pest populations. Diverse plant landscapes, as compared to monoculture agriculture, are correlated with increased diversity and density of biological control organisms (Thies and Tscharntke, 1999).
Systems management for insect suppression aims to reintroduce into farm systems some of the ecological relationships and functions found in undisturbed plant communities. It has been hypothesized that conserved or introduced natural enemies might reduce agricultural insect pests. In some crop/farm systems, natural enemies do provide enhanced pest management (Thies et al., 2003). However, this is not always the case, since pest populations may also respond positively to landscape and farm diversity (Thies et al., 2005).
Using natural plant communities as a model, systems design for economically acceptable insect pest suppression has four components:
- Learning about the pests and biological control organisms in a particular farm landscape
- Building and managing habitat to shift the ecological balance toward natural enemies
- Tolerating low levels of pests in order to support healthy populations of biological control organisms
- Using selective pesticides only when pest populations exceed the tolerance of farm economics and ecology
Building and managing habitat includes providing food and sheltered areas for biological control organisms to mate, reproduce, and overwinter. Nectar, pollen, sap, and seed are important alternative food sources that fuel predator and parasite survival, flight, and reproduction (Wilkinson and Landis, 2005).
Biodesign built and managed habitat through a variety of practices. The primary long-term strategies included:
- A diverse perennial and annual living mulch in an interspersed pattern between crop rows to enhance food and shelter for natural enemies. The living mulch was selectively mowed. It occupied 30—50% of the field area and thus may also have interfered with host selection by some insect pests.
- No-till/reduced tillage
- Wild margin habitat (native grasslands and pasture)
These practices supported an assemblage of mostly generalist natural enemies that may have contributed to lower pest damage. In 2006 on-farm research, predators and parasites were monitored over the entire growing season using sweep nets and pit-fall traps (Fig. 3 and Fig.4). Biodesign's pattern of interspersed habitat distributed within crops may have been one key to its success. Some evidence indicates that predators and parasites move no more than 60–100 meters from undisturbed habitat into crops (Morandin et al., 2014; Long et al., 1998; Thomas et al., 1991, 1992a, 1992d, 2002). Reduced tillage may also be key because at Biodesign, an undisturbed living mulch in close proximity to crops supported a large population of ground-dwelling predators (Fig.4). This theory is supported by field research in which fewer ground-dwelling predators were found as tillage increased (Halaj et al. 2000, Zehnder and Linduska 1987).
Insect problems and crop damage diminished over time, and Biodesign stopped spraying for insect pests in 2000, with no decrease in crop yields and quality.
Specific predators and parasites, such as syrphids, spiders, lady beetles, lacewings, earwigs, parasitoid wasps (Aphidius and Aphelinus species), and aphid midge (Aphidoletes aphidomyza) were observed feeding on aphids at Biodesign (Photo 1) and may have been part of the observed suppression (Fig. 2).
There is support in the literature for these observations. All of these observed predators are listed as aphid predators in the University of California Natural Enemies Handbook (Flint and Dreistadt, 1998). Syrphids were found to be strong aphid predators in an Oregon study (Ambrosino, 2006). Greater vegetation complexity, created by allowing weeds to grow between cabbage rows, was associated with lower cabbage aphid abundance and enhanced populations of generalist natural enemies (Bryant, 2013). Both cabbage and green peach aphid populations were lower on broccoli (Costello, 1994; Costello and Altieri, 1995) and zucchini (Frank and Liburd, 2005; Hooks et al.,1998) where crops were grown with clover living mulches, as compared to clean-cultivated crops.
Natural populations of predaceous stink bugs (Perillus species) were observed feeding on CPB in 1996 (photo 2). Predaceous stink bugs (Perillus bioculatus and Podisus maculiventris) were observed feeding on CPB larvae from 2005 through 2010. It has been reported that releases of these predators have suppressed CPB density by 62% (Biever and Chauvin, 1992), reduced defoliation by 86% (Hough-Goldstein and McPherson, 1996), and increased potato yields by 65% (Biever and Chauvin, 1992), when compared to an untreated control (no predator release).
Lady beetles, carabid beetles, and spiders were observed near solanaceous plants at Biodesign from 2005 through 2010. According to some researchers, these predators attack CPB (Hough-Goldstein et al., 1993). Fourteen species of carabid beetles, three species of lady beetles, and one spider species (Xysticus kochi) were reported to feed on CPB (Sorokin, 1976). Adult ground beetles (Lebia grandis) were shown to feed on CPB eggs and larvae, while larvae of the same species parasitize CPB pupae (Weber et al., 2006). Another ground beetle, Pterostichus chalcites, reportedly feeds on CPB (Heimpel and Hough-Goldstein, 1992). The daddy longlegs (Phalangium opilio) has been observed feeding on CPB eggs and small larvae (Drummond et al., 1990). A lady beetle (Coleomegilla maculata) reportedly consumes eggs and small larvae (Groden et al., 1990; Hazzard et al., 1991), killing up to 37.8% of eggs for the first CPB generation and up to 58.1% of eggs of the second generation (Hazzard et al., 1991).
Reduced tillage may have helped to manage CPB. Adult beetles were reduced in no-till tomatoes planted into killed ryegrass compared with tilled tomatoes (Zehnder and Linduska, 1987).
Flea beetles were occasional problems throughout the 1990s in Old field, but were never a problem in New field, where tillage was further reduced and high populations of ground beetles and spiders were observed (Fig. 4). Flea beetles spend a large portion of their life cycle as larvae in the soil and hence may be vulnerable to ground-dwelling predators whose populations diminish with increased tillage. There is some evidence to support this theory. Flea beetle incidence and damage to broccoli foliage was lowest in strip-till/living mulch plots compared to conventionally tilled plots (Luna and Staben, 2000). Ground beetles and spiders reportedly feed on crop pests with subterranean life stages (Brust, 1994; Snyder and Wise, 2001; Halaj and Wise, 2002).
Living mulch row middles at Biodesign, and the reduced tillage they provided, may have enhanced flea beetle predators, especially carabid beetles and spiders. Plant residues increase the density of ground-active predators, both by providing cover on hot days and by providing food for detritus-feeding insects. Spiders and ground beetles in turn feed upon these insects when pests are not available (Settle et al., 1996; Landis et al., 2000; Symondson et al., 2002).
Several studies have demonstrated the negative impact of tillage on pest predators and parasites. Spring cultivation reduced the numbers of one species of carabid beetle (Pterostichus melanarius) by 80% (Cárcamo, 1995). Spider populations declined when fields were tilled (Halaj, 1998). Spider and carabid ground beetle densities increased when conservation tillage practices were adopted (House and Stinner, 1983; Kladivko, 2001; Altieri et al., 2005). Altieri and Gliessman (1983) found that populations of brassica flea beetles were greater in weed-free collard monocultures than in polycultures intercropped with beans and left weedy for 2 or 4 weeks after transplanting.
No insecticides were applied after 1999 to control cabbageworms at Biodesign. By that time, cabbageworms occurred at low levels, likely due to the suppressive system and resulting high numbers of worm predators.
Despite regular (although fluctuating) populations of imported cabbageworm adults, less than 5% damage was recorded on unsprayed broccoli and cabbage, and yields were stable over the 15 years of production, even when spraying was stopped after 1999 (Fig. 5). During 2006 on-farm research in no-till plots, unsprayed brussels sprouts produced an 88.5% marketable crop, with 4.8 pounds per plant of salable sprouts (Fig. 6), and large populations of generalist predators were observed in unsprayed treatment plots (Fig. 3) (Fig. 4.)
Possible insect pest suppression due to Biodesign's system strategies is supported by other research. A number of carabid beetles eat imported cabbageworm larvae (Allen, 1979) and reduce lepidopteran pest populations (Brust et al., 1985). The density of all taxonomic groups of soil arthropods, including carabid beetles and spiders, was higher in weedy cropping systems than in conventional tillage systems (McGrath, 2000). More carabid beetles of a specific species (P. melanarius) were caught in plots where brussels sprouts were growing in white clover living mulch than on bare ground (O'Donnell and Coaker, 1975).
Greater vegetation complexity, achieved by allowing weeds to grow between cabbage rows, was associated with lower cabbageworm abundance and enhanced populations of generalist natural enemies (Bryant, 2013). Imported cabbageworm mortality was higher in weedy plots compared to weed-free plots (Dempster, 1969). Cabbageworm egg and larval densities and damage to broccoli at harvest were significantly lower in broccoli undersown with clover living mulches compared to broccoli grown without living mulches and cultivated for weeds, and spider counts were significantly higher on broccoli in living mulch habitats than in cultivated broccoli plots. Despite competition from living mulches, total broccoli yields were not lower in living mulch plots undersown with strawberry clover (Trifolium fragiferum L.) or white clover (Trifolium repens L.). However, yields were lower in yellow sweet clover (Melilotus officinalis L.) living mulch plots when compared to monoculture treatments (Hooks and Johnson, 2007). In two other studies, cabbageworm damage was also lower in crops grown with living mulches (Theunissen, 1994; Brandsæter et al., 1998).
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