Habitats on Farm
A. Why plant habitats?
Growers plant habitats on site to increase biological diversity. Diversity of plants provides diversity of microorganisms, insects, and spiders both in and out of the soil. These diverse organisms regulate pest populations in natural balance and reduce the need for costly inputs such as pesticides. Therefore, sustainable productivity is dependent on a high level of diversity (Metcalf and Luckmann, 1975). Symptoms of low level diversity are: plant productivity decreases, plant productivity will be spotty and easily susceptible to pest and disease pressure, soil water holding capacity and organic matter is reduced, input costs increase, such as fertilizer, fungicide and pesticide costs, erosion occurs, farming communities decrease, farms go bankrupt.
A habitat on site is a tool growers can use to increase biodiversity. How does one know if they need to plant habitats? The age-old saying of, "what is the strength of a chain?. . . . . Its strength is equal to the weakest link" is applicable (Savory, 1991). A grower must recognize if their weakest link is low diversity in order to decide if they should spend time and money establishing habitats. In this chapter, case studies of farmers who planted habitats will be highlighted.
2. Holistic View
Wildlife managers no longer promote protecting a single species as has been discussed in debates regarding the Endangered Species Act. Wildlife biologist now accept that species need habitat in order to survive and, therefore, their objectives are to preserve and create habitat to protect endangered species. For example, there is no logging allowed in old growth forests where spotted owls live because of habitat protection. This same concept applies to beneficial insects, arthropods and soil organisms. Beneficials need habitat to survive and thrive so they can exist in large enough numbers to protect crops.
3. Insect Ecology Pattern Development and Monitoring
Habitats attract the complex of insects which provides food for beneficial insects. These beneficial insects will forage out into the market crop and provide the most cost- effective, environmentally sound pest control. Without a refuge, an area with growing plants and blooming plants which is not sprayed, beneficial insects cannot survive on site for sustained periods. During fallow times or early crop cycles these habitats are the only places where beneficial insects can survive. Furthermore, these habitat areas are the only place where there is tolerance for pests which are providing food for beneficial insect reproduction.
Refuges also attract migrating pests. They can effectively trap migrating pests by providing a highly desirable area for certain pests and their natural enemies. For example, rapidly growing alfalfa provides a great attractant for migrating aphids and aphid parasites. Migrating cucumber beetles (Diabrotica sp.) were trapped effectively in the Naturfarm pest break strips which had an insectary blend of flowers, grasses and alfalfa (Dietrick, 1995).
Habitats also provide an excellent place to monitor for early pest outbreaks and insect ecology (see Chapter III). In habitats, pest damage is tolerable. Pests and their natural enemy complex can be observed and documented over several seasons. Growers can check on the progress of beneficials to pests and develop insect ecology patterns for their own operations.
4. Augmentation Locations
Habitats are great places to augment natural biological control. Purchased insects can be released in habitat areas where there is food and shelter so that they will multiply and forage out into the market crop. Corn is especially good as a release point in a habitat because of its deep whorl and insect attracting ability (see Corn the King insert).
5. Soil fertility
Soil biodiversity increases in habitat areas as well as beneficial insects. Roots build soil by increasing soil organic matter and by supporting microbial populations which are responsible for providing plant available nutrients. Habitats usually produce a larger, more developed rhizosphere (aggregation of microbes around roots) per square foot than in cropped areas and, therefore, provide diverse microbial populations. A good example of a great soil building habitat is cover crops.
B. Managed habitats
Beneficial insect habitats must be managed alongside crops. Habitats which support a crop-protective population of beneficials will not occur simply because a manager chooses not to spray or not to weed. Habitat management techniques will be different for every grower, however, there are some principles to help with management decisions.
1. Habitat Plant Species
Research is ongoing in plant/insect and plant/microorganism relationships which is providing valuable information on choosing habitat plants. An array of articles referring to plant/insect interactions is refereed to in the bibliography of this manual.
Insects and plants evolved together through time and have developed exceptional relationships (e.g. bees and pollination). Furthermore, their interactions with each other cause selection of attributes whereby successful races become dominant. The plant/insect interactions are the very reason why there exists such great plant and insect diversity in the world today (Jolivet, 1998). Therefore, supplying habitat areas for many plant and insect relationships to occur, ensures continued biodiversity and selection for environmental stability.
Nectar and pollen sources support key predators and parasites for crop protection. Therefore, planting successive blooming plants and pollen shedding plants is essential in keeping beneficial insects on site. The floral architecture is important as well because some key beneficials have a hard time accessing nectar and pollen in some flowers (Patt, Rutgers). Umbel flowers such as dill, carrots, and onions have well exposed nectar and pollen. Perennials that attract beneficials are listed in this chart:
Habitats must contain pest attracting plants. Ideally, the habitats should attract pests which are similar to a key crop pest but which do not harm the crop. These non-market crop pests act as a surrogate host to natural enemy complexes. The natural enemies build up around the non-pest as would build up around the key pest and be in place if the key pest should increase. For example, corn attracts western flower thrips which in turn attracts orius, a key greenhouse and scirto thrips predator. Corn also attracts the corn earworm which provides host eggs for Trichogramma and other parasites of army worms, cut worms and fruit worms. Corn also attracts aphids which draws lady bugs, lacewings, aphid parasites, etc.
"CORN KING OF THE INSECTARY REFUGE PLANTS"
Corn or maize, Zea mays L., sparsely interplanted in hills, using a mix of corn seed with differing maturity periods (e.g. early to 120 days and longer development times) will help attract and nurture sets of predatory and parasitic insects beneficial to biological control of many different market crops. These hills of corn act like pheromone or black light traps that attract and grow pests of corn. Where hills are sparsely distributed, one or two per acre, they provide plant food for primary consumers of corn and habitat to grow the general predators and parasites known to be useful in many market crops.
Mixing corn with other grasses--sorghum, sudan or cereals--will create even more diversity of food and habitat. Farms with heavy pest pressure may benefit from an upwind hedgerow that could include a corn-sorghum mixture in addition to the interplanted hills. The first couple of years of transition from chemical to biological farming is an especially important time to use border and strip refugia. Some sorghum varieties grow to 14 feet adding extra mass and height to present physical barriers against wind, insects and cross-pollination. Varying heights of plants enhances the architecture for orb-weaving spiders.
Corn (and sorghum) will grow minute pirate bugs, several species of ladybugs, many diverse parasites that attack armyworms and cutworms, corn rootworms and leafhoppers. Many species of Tachinid fly parasites and a dozen or more parasitic wasps that attack corn earworms and rootworms and other common pests are found in corn (unless it has been treated with pesticides). Some predatory mites survive well on pollen in these refuges until their favorite meal of spider mites and/or thrips move in. A few hills will enhance beneficial insects and guarantee their timely presence when migrations of pests begin. The hill functions as a "hot spot" of pests that will grow the key biological control insects naturally. As the beneficials consume their prey in the corn, they move into the market crop looking for more insects and mites. Additional inundative releases of beneficials into the market crop, timed for pest invasions into the market crop, are made more effective by the greater diversity of biological control organisms.
Corn is a hardy, easy to grow annual providing a sequence of pollen producing tassels offering a steady flow of insect food, pollen, corn silk, corn ears and seed that act like a pheromone beacon. Corn pollen provides food for flower thrips that is an ideal food for minute pirate bugs: corn earworms. army worms, stalk borers, for lacewings and lady bugs and diverse sets of parasites: of beetles like the corn root worms and flea beetles: moth egg hosts for Trichogramma spp.; continuous new growth for several species of corn aphids and their parasites, and others. There are other plants such as sunflowers/collards and various legumes, alfalfa, that are often used in refuges, but they are not as easy to use as corn.
Many of these corn pests prefer the corn refuge plantings to any of the alternative host crops, such as cotton, tomatoes, and beans. Orchard crops benefit as well. Walnuts almonds, pecans and most stone fruits that are conventionally grown in monoculture are not attractive to many biological controls. The corn refuge is an economical way to guarantee the presence of beneficial insect work animals, ready to suppress sudden invasions of aphids, mites, moth and butterfly larvae and pupae and possibly root infesting beetle larvae and other soil pests, such as walnut husk fly, flea beetles and Diabrotica beetles
Corn plants that are relatively free of pests attract green lacewing adults to feed. Many beneficials feed on the water of gutation (nutrient-laced droplets of plant water that bleeds from the leaves) even when no insect honey-dew is present. Trichogramma adults have been observed to survive extremely high temperature by hanging out near transpiring stigmata. Wasps, like Trichogramma, can live up to four times longer when there is a carbohydrate food source in the field. Tiny wasps like Trichogramma can be found running along the corn silks looking for corn earworm eggs to parasitize so the next generation of wasps will be present to attack eggs of moths invading the market crop.
Corn should be planted in small amounts in succession plantings. Maintaining a sequence of small plantings is more important than fewer plantings of more plants. When corn matures and no new plants are shedding pollen, the corn pests will no longer stay in old corn and may enter the market crop. Corn starts pollinating in about 20 days from planting and there is about a three week window of shedding pollen. Some, like Black Aztec, are more variable in ripening. A long (100 day) season may shed pollen longer and should stay attractive for insects well into September. Planting sequences of corn refuges through to harvest of the market crop will protect against this possibility. Planting successions of both early and late varieties further assures a continuous food supply for beneficials.
The amount of land required is minimal, because the insectary plantings are located outside or at the edge where there is a need for protection of the outside rows of crop from dust and infrared radiation. A diverse, well-planned perennial hedgerow may be possible along drive roads leaving space for sparsely planted hills of corn and sorghum in between or in front of the perennials. A more diverse flowering annual insectary mix can be added in corners and single rows along roads or in the roads where they help compete with weeds. No extra land is needed for interplantings of hills of corn in skips that appear in the market crop during the season.
The focus of the habitat enhancement is on the entire natural enemy complex system through adding plant biodiversity in a cost-effective way. The great thing about this new paradigm of habitat diversity is its flexibility. Each farmer can decide the best plan for his or her cropping system. A variety of resources are available from Fish and Wildlife and the Resource Conservation Districts to provide the latest knowledge to help you design the best habitat building program and turn your pest management budget into a beneficial insect management budget.
Along with the decision of which plant species to choose for a habitat, managers must decide on how to water the habitats. The habitats which are most successful are irrigated the same way the crop is and will survive with that watering regime. For example, perennial or annual grasses planted in sunny orchards must be able to survive and reseed themselves with deep, infrequent irrigations.
Habitats with mowable plant species must be alternatively mowed so that a diversity of plant growth stages is present (Dietrick, 1950s). Alternative mowing can act as a trapping technique for some key pests. For example, young lygus emerging from eggs laid in freshly mowed alfalfa will be quickly eaten by a complex of natural enemies surviving in adjacent uncut alfalfa (Dietrick, personal contact). The mowed alfalfa area is a trap for the young lygus. Mowing also provides new growth which is attractive to aphids and their natural enemy complex.
4. Weed Control
Weeds often add to diversity, however, they can harbor overwintering pests and can be more damaging than good. Managers must research the species of weeds they have and determine how detrimental they are to overall pest management of the farm. Then a cost-benefit analysis can be done to ensure that money and time spent weeding will be regained by more productivity. Habitats may also provide weed suppression by covering the soil and reducing habitat for many weed species.
C. Examples of Habitats
1. Cover crops
Cover crops improve soils and help build natural enemy complexes in and out of the soil for pest and disease resistant plants. They also act as a nutrient sink, taking up excess fertilization compounds so that they are not lost by leaching or volatilization and releasing the nutrients slowly after being incorporated.
Cover crops can be either permanent or present for a short time. There are custom species mixes available now which are based on crop, cost, fertilization plan, soil characteristics, irrigation schedules, climate, beneficial insects and other factors. Cover crops should include more than 3 species to increase the chances of survivability and to attract a natural enemy complex. Pollen and nectar is a necessity for predator and parasite reproduction, therefore, the cover crop species mix should include blooming species. Legume/grass mixes are often preferred in row crops due to their high nitrogen levels. Perennial grasses and alfalfa are preferred in some orchards.
Cover crops in row crop management are usually thoroughly incorporated into the soil prior to planting. However, taking out all of the cover crop leaves no habitat for beneficial insects. Beneficials should be in place when the crop germinates and, therefore, need habitat to perpetuate during fallow and pre-germination. Growers can keep a section of the cover crop or have another planted habitat area near by to sustain beneficials (check the following types of habitats for ideas).
Case Study-cover crop
Larry Acin farms hundreds of acres of lima beans, pumpkins and banana squash in the Santa Ynez Valley near Lompoc, CA. He farms adjacent to the Santa Ynez river in sandy, low fertile soils.
In the fall of 1997 Mr. Acin decided to plant an oat grass cover crop for the first time. The fall was wet making ground work impossible. So he simply broadcast oat grass seed on the soil surface and hoped for germination.
In the beginning he was not sure how the cover crop would benefit him or how well it would grow. However, by March the oat grass had grown 6-12 inches uniformly. Furthermore, after a winter of torrential, El Nino rains, he felt the oat cover crop protected his soil from eroding into the river. He also noticed how the previously fertilized ground grew the lushest oats. He realized the oat grass cover crop was preventing nitrates from leaching into the river and was holding nutrients until spring disking when it would become available for the next squash crop.
Not only did the cover crop exceed his expectations in erosion control and as a nutrient sink, the oat grass harbored thousands of overwintering ladybugs (Cycloneda spp.). These lady bugs were foraging in the adjacent broccoli field he had leased out over the winter. Mr. Acin decided to leave 2 strips of cover crop habitat so that the ladybugs would stay during the ground working and planting time. He did not have the need to buy pesticides or beneficial insects for aphid control in 1998. He plans to plant a cover crop every year.
2.Pest Break Strips
In 1991 the California Energy Commission granted Mr. Dietrick funds to do research on an organic farm on what has been called pest break strips. Pest break strips are "strips" of mixed plant species planted down the middle of the market crop. Often they are present well before the market crop germinates. In the Naturfarm study, pest break strips were perennial. However, on other farms pest break strips have been strips of corn or annual insectary blends. The objectives are to provide an on-site insectary where pests can grow and provide for the beneficial enemy complex and to act as a trap crop for pests.
Pest Break Strip case study-The Naturfarm, Lompoc
The Naturfarm, a 100 acre mixed organic vegetable farm, planted 5% of its land into quarter-acre pest break strips. These strips were interplanted along field rows. They were planted with alfalfa and perennial grasses and were irrigated to allow for growth year-round. Half of the each strip was mowed every 2 weeks during the growing season. Crops which were protected effectively due to the pest break strips were lettuce, tomatoes, peppers, potatoes, summer squash, winter squash and carrots. Crops which were moderately protected were cucumbers, greens, cole crops, green beans, and red beets.
Total number of beneficial insects per acre in the pest break strips was 2,326,000 which equated to a US $ value of 17,208. Extra mowing and watering costs was off set by a reduction in pest control costs and a premium organic price.
3. Greenhouse and Nursery Habitats
Greenhouse and nursery managers have special pest management objectives. Because plants are grown mostly indoors or in semi-sterile areas, a large population of beneficial insects cannot exist naturally. In enemy free space, pests can reproduce extremely fast. Explosive pest reproduction perpetuates fear of total crop loss and the complete reliance on chemicals for pest eradication. Furthermore, greenhouse and nursery plant distributors have extremely low tolerances for pests. Without any pests, the few natural enemies present will not have enough food to reproduce. Therefore, greenhouses and nurseries usually spray pesticides on a timely basis not on a as needed basis. Pesticide costs become the second largest costs after labor. However, because a lot of nurseries and greenhouses are in urban centers, human health and environmental concerns are great.
Greenhouses and nurseries need to establish habitats where there is tolerance for pests and where beneficial insects can grow and be released. Several nurseries have already created habitats in a variety of ways. Blooming annual flowers placed in pots on pallet sleds are used in one nursery on the central coast. The blooming habitats are moved adjacent to crops that need pest protection and are watered and maintained regularly. Also many nurseries and greenhouse make their own potting soil so that they can easily incorporate beneficial microbial products to help boost plant health and pest resistance.
A unique idea of habitat for beneficial insects and natural pest control is occurring at Monrovia nurseries in Azusa, California. Monrovia typically holds 1 gallon plants for over a year for their production cycle. Often these younger plants can harbor a small level of pests and their natural enemies without risk of pest explosion or product damage. These young plants act as the habitat for beneficial insects and harbor released beneficials as well. These areas are not sprayed often and have time to grow out of any pest damage which may occur. Beneficials are able to forage on adjacent older plants and have a refuge when pesticide use occurs.
In 1996 Underwood Ranches planted a 1000 long perennial hedgerow down a busy roadside bordering a lemon field. The perennials planted were chosen due to their noted abilities to attract beneficial insects which are key predators to citrus pests. Jeff Chandler of Cornflower farms chose the plants and designed the hedgerow. The plants were transplanted from small tubes in the fall. They were on a drip watering system.
5. Resident Vegetation
Many growers leave weeds in the field as habitat for beneficial insects. This often is the most cost-effective method to ensure plants are growing and providing habitat. No seeding, watering, or special care is needed to allow certain weeds to grow and bloom. Often this is the preferred method in orchards where shade seems to select out only a few tolerant plants. Noxious weeds should not be encourage such as puncture vine. However, we have found sow thistle to support aphids and their parasites as well as many aphid generalists like ladybugs and lacewings. Malva also has provided the only home during the winter for the hooded beetle in a fallow pumpkin field.
6. Clump or hill planting
Many berry growers are planting small clumps of beneficial insect habitat at the end of each row or in-between rows. These small areas break up the monoculture and provide islands for beneficial insects to take cover and forage out from.
case study of salinas berry grower alfalfa
Mulch provides a great habitat for ground beetles and spiders. These large predators devour soil insects many of which are common pests. Many pests pupate in the soil and spend long periods of time there. During this time they are immobile and susceptible to predation by the ground dwelling predators.
case study of Dr. Schlingers
Compost habitat for beneficial soil microorganisms. It provides organic mater for the organisms to live and reproduce. Compost is the end product of raw materials which have been digested and fermented by microorganisms. Compost needs to be placed in and around a plants roots so that the microorganisms are near the plant root.