Other Considerations

Weather
Perennial vs. Annual
Healthy Soil Ecology
Insectary Plant Characteristics
Mulches & Trap Crops

Weather

Weather variations from year to year may cause a particular management practice to be beneficial one year and problematic the next. A flexible approach is needed in order to adjust beneficial habitat according to weather variations. An observant eye is the grower’s most valuable tool in this respect.

Perennial vs. Annual

The type of cropping system, perennial vs. annual, is an important factor in farmscaping. Perennial systems such as orchards possess an inherent ecological stability derived from the variety of tree-based habitats, which are not harvested or destroyed as in annual systems. Adding a cover crop to an orchard can increase and complement the biodiversity of the system.

Ideally, cover crops (CCs) in orchard systems should be selected and managed for the following attributes (1) :

• CCs should not harbor important orchard pests
• CCs should have some ability to divert generalist pests from the orchard crop
• CCs should confuse specialist pests visually or olfactorily (by smell) and thus reduce their colonization of orchard trees
• CCs should be capable of altering host-plant nutrition (without negatively impacting the crop) and thereby reduce pest success
• CCs should reduce dust and thereby reduce spider mite outbreaks
• CCs should change the microclimate and thereby reduce pest success
• CCs should increase natural enemy abundance or efficiency, thereby increasing biological control of arthropod pests.

Studies of commercial pecan orchards in Oklahoma (2) and almond plantations in California (3) have demonstrated the efficacy of managing cover crops for pest control in orchard systems. In all instances, this farmscaping technique resulted in significant reductions in pesticide applications.

Annual cropping systems are much less stable than perennial ones. Depending on the amount of tillage involved, the ecology of annual systems, both above and below ground, is dramatically altered every year. To help anchor the ecology of an annual system, consider planting “permanent” insectary strips or hedgerows in or along an annual crop field.

The idea of undisturbed beneficial habitat distributed at intervals in or around crop fields is a theme common to many farmscaping techniques. Depending on the plant species, these “perennial islands” provide food resources for beneficial organisms as well as overwintering sites from which crops can be colonized in the spring. Kenny Haines, a vegetable grower in North Carolina who practices farmscaping, notes that his insectary strips provide a “meetin’ place” for the beneficials. Springtime environments of annual cropping systems are characterized by extremes of temperature, sunlight and humidity—conditions in which colonization and survival of beneficials is unlikely without good habitat nearby. For details on how some farmers (including Kenny Haines) incorporate a “permanent” component into their annual fields, see Appendix D.

Healthy Soil Ecology

Many organisms, including pest insects associated with both perennial and annual crops, spend part of their life cycle in the soil. A diverse soil ecology maintained with regular additions of organic matter helps to regulate populations of both pest and beneficial organisms (4, 5, 6).

Insectary Plant Characteristics

Experimentation is the key to finding a successful combination of planting systems, ground covers/mulches, and management practices that work best for the unique soil and environmental conditions of a particular farm and crop.

As a first step, the producer should choose plants that provide good habitat for the desired predators or parasites, and at the same time, do not harbor insects that are likely to become pests. For example, subterranean clover harbors many beneficials like big-eyed bugs, and also harbors relatively few Lygus species. pests. Avoid aggressive, invasive plants and those that may act as reservoirs for diseases that attack surrounding crops.

The Nature Conservancy runs a website that has a comprehensive list of invasive plants using both scientific and common names. Pictures as well as tips for managing the plants are also included:

http://tncweeds.ucdavis.edu.

Cover crops that are good insectary plants include buckwheat, sweet clover, faba beans, vetch, red clover, white clover, mustards, and cowpeas. Herbaceous plants that are good insectary plants and which may be planted in strips include species in the carrot (Apiaceae=Umbelliferae), sunflower (Asteraceae=Compositae), and mint (Lamiaceae) families. (Refer to appendices A, B, and C for detailed information on pests, beneficials, and seed blends for plants that attract beneficials.)

In many instances, floral structure is an important consideration. Beneficials with short mouthparts, such as the tiny parasitic wasps, find it easy to obtain nectar and pollinate plants in the parsley and sunflower families because of the small, shallow flowers these species provide. Plants that possess extrafloral nectaries (nectar sources outside the flower), such as faba beans, cowpeas, vetch, and several native ground covers, provide beneficials with easy access to an important food source in addition to the nectar and pollen of their flowers.

Recent work in Georgia investigated the importance of different food sources—extrafloral nectaries, honeydew (a liquid emitted by whiteflies, aphids, scales, and leafhoppers, composed of unused portions of plant sap as well as certain waste products of the insects), sucrose, or no food sources—on Microplitis croceipes, a parasitoid of the corn earworm in cotton (7). Important findings included:

• Retention of the wasp and parasitization rates were highest in cotton plots in which wasps were able to feed on extrafloral nectar.
• Retention of the wasp and parasitization in patches with honeydew was comparable to patches without food—probably due to the rapid decrease in quality of honeydew as it dries, combined with low quantity per site and general low detectability of this food by the parasitoid. Honeydew is scattered about randomly within a field and on a plant. Extrafloral or floral nectaries, on the other hand, are always found at the same location on a particular plant, making it easier for beneficials to locate this food source.
• Important characteristics of an ideal food source in the field are high quality, high quantity per site, high detectability, and high predictability of the food location. Nectar sources possess all these qualities.

To summarize this research, some species of parasitic wasps will stay in an area with nectar sources—either floral or extrafloral—and this results in a higher parasitization rate of host pests in that area. This makes sense, because the wasp can spend more time hunting for hosts and less time hunting for food. Many crop plants do not provide sufficient food for hungry parasitoids. As a consequence, parasitoids will disperse from target areas in search for food. After feeding, parasitoids may not return to original target areas, especially when the distance between food and host locations is too great or when the food locations also harbor hosts (7). Because nectar sources are so important to many beneficials, non-invasive plants with floral or extrafloral nectaries might be considered prime candidates for use in farmscaping.

A study in California (8) revealed that beneficials in fact do feed on nectar and pollen provided by insectary plants, and will move up to 250 feet into adjacent crop lands. Further research is needed to determine the optimum spacing of insectaries within a particular crop and ecosystem so that parasites spend most of their time controlling pests (as opposed to searching for food) and producers know how much land insectaries will require and where they are most effectively placed.

The appearance of beneficials should be timed to coincide with peak need for biological control of pests associated with the main crop. Another way of looking at this is that an insectary crop should grow and bloom at a time that best meets the needs of beneficials for pollen, nectar, or alternate hosts. Strategies to prolong bloom include planting cover crops in strips on successive planting dates. Planting a mix of plants, particularly perennials, that bloom in succession and that meet the habitat needs of desired beneficials is another farmscaping option. It may be helpful to develop a diagram, such as the one in Appendix F, when planning habitat that will have something in flower year-round.

The migration of certain species of beneficials from the cover crop(s) to the main crop is sometimes associated with senescence (or post-bloom period) of the cover crop. In these instances, mowing the cover crops in alternate strips may facilitate their movement while the remaining strips continue to provide refuge for other beneficial species. Sickle-bar mowers are less disruptive to beneficials than flail mowers and rotary mowers.

Mulches

Although this publication generally focuses on living habitat, clearly some beneficial organisms, such as spiders and ground beetles, benefit from mulches (or a habitat that mimics some of the effects of mulches, such as that found in “no-till” fields). Much of the benefit lies in the fact that mulches provide overwintering habitat for these organisms in a moderated microclimate (9).

Trap Crops

A related strategy in farmscaping is the selection of plants that attract pests. These “trap crops” can then be plowed down or managed in some fashion that takes advantage of a vulnerable stage in the crop pest life cycle. See Appendix D for examples of farmers using trap crops.