Pest and Disease Management-Organic Ecosystem : Avoidance Techniques

Avoidance Techniques

To manage pests and diseases effectively, producers need to understand the biology and growth habits of both pest and crop. The type and concentration of pests are often responses to previous crop history, pest life cycles, soil conditions and local weather patterns.

Crop Rotations

Crop rotation is central to all sustainable farming systems. It is an extremely effective way to minimize most pest problems while maintaining and enhancing soil structure and fertility. Diversity is the key to a successful Crop rotation program. It involves:

• rotating early-seeded, late-seeded and fall-seeded crops

• rotating between various crop types, such as annual, winter annual, perennial, grass and broadleaf crops; each of these plant groups has specific rooting habits, competitive abilities, nutrient and moisture requirements. (True diversity does not include different species within the same family - for example, wheat, oats and barley are all species of annual cereals.)

• incorporating green manure crops, into the soil to suppress pests, disrupt their life cycles and to provide the additional benefits of fixing nitrogen and improving soil properties

• managing the frequency with which a crop is grown within a rotation

• maintaining the rotation's diversified habitat, which provides parasites and predators of pests with alternative sources of food, shelter and breeding sites

• planting similar crop species as far apart as possible. Insects such as wheat midge and Colorado potato beetle, for example, are drawn to particular host crops and may over winter in or near the previous host crops. With large distances to move to get to the successive crop, the insects' arrival may be delayed. The number that find the crop may be reduced as well.

Diverse rotations are particularly effective in regulating flea beetles, cabbage butterfly, wheat midge, wheat stem maggot and wheat stem sawfly.

Rotations are also effective in controlling soil-and stubble-borne diseases. The success of rotations in preventing disease depends on many factors, including the ability of a pathogen to survive without its host and the pathogen's host range. Those with a wide range of hosts will be controlled less successfully. For example, sclerotinia stem-rot is a common disease in conventionally grown canola on the Prairies, but it can also infect at least a halfdozen other field crops. Rotations will not have much effect on pathogens that live indefinitely in the soil, but will shorten the life span of pathogens that can survive only brief periods apart from their hosts. Other situations that limit the benefit of crop rotations include: the transmission of pathogens via seed, the presence of susceptible weeds and volunteer crops that harbour pathogens, and the invasion of pathogens by wind and other means.

Rotations should be used with other cultural practices to achieve the greatest benefit.

Field Sanitation/Crop Residue Management

Reducing or removing crop residues and alternate host sites can be used to control some insects and many diseases. Incorporating the residue into the soil hastens the destruction of disease pathogens by beneficial fungi and bacteria. Burying diseased plant mate rial in this manner also reduces the movement of spores by wind.

Insects most affected by tillage will be those that overwinter in crop residue (for example, European corn borer and wheat stem sawfly) and those that lay their eggs in the residue. Conversely, fields where residue has not been disturbed may have higher levels of some beneficial predaceous insects, which may reduce levels of insect pests such as root maggots in canola. Reduced or zero-tillage may also reduce the damage by certain pests, as the crop residue creates a micro-climate less preferred by some insects (for example, flea beetles).

It is important to maintain a balance between crop sanitation and soil conservation. Lighter soils and those prone to wind and water erosion may require postponing tillage until just before seeding to ensure stubble cover for as long as possible.

Alternate host sites, such as field margins, fence lines, pastures, shelterbelts and riparian areas, will usually contain weeds and natural vegetation that may serve as reservoirs for disease, vectors of disease and insect pests. Left uncontrolled, these insect and disease pests can be transmitted to healthy crop plants. Insects may use these plants as alternate habitat until an appropriate crop occurs in a nearby field. However, these areas may also host many beneficial insects and predators, therefore the grower must carefully assess the potential threat from pest insects in these areas before mowing or removing any plants. The ecological importance of areas such as sloughs, wooded bluffs, road allowances, railroad rights-of-way, abandoned farmyards and schoolyards must also be included in long-range planning

Seed Quality

The use of high-quality seed is especially important in preventing disease. The seed supply should be free of smut, ergot bodies or other sclerotia, and free of kernels showing symptoms of Fusarium head blight infection.

Seed analysis by a reputable seed testing laboratory will help determine specific diseases in the seed supply.

Relatively few diseases are exclusively seed-borne, and it is more common for pathogens to be transmitted from soil, stubble, or wind, as well as with the seed.

Planting physically sound seed is also important. In crops such as flax, rye and pulses, a crack in the seed coat may serve as an entry point for soil-borne micro-organisms that rot the seed once it is planted.

Image courtesy : wikipedia

Weed Management

Although weeds need to be controlled to reduce their impact on crop yield and quality, a field completely free of weeds is not necessarily the best objective. In many cases, weeds provide food and shelter for beneficial insects. Parasitic wasps, for example, are attracted to certain weeds with small flowers. Field experience has shown that the number of predators attacking insects increases and the number of aphids and leafhoppers decreases on certain crops as the diversity of weeds (that act as host plants) increases. Research has shown that outbreaks of certain crop insect pests are more likely in weed-free fields. 

Insects that are generalist feeders, such as beet webworm, thistle caterpillars and grasshoppers, may prefer to feed on weeds rather than some crops, only damaging the crop after the weeds are eaten. 

 

Each field situation should be considered separately, as weed competition must always be taken into account. Sometimes mowing weeds at the edge of the field results in beneficial organisms moving into the crop where they are needed.

Forecasting

Producers should pay attention to the forecasts for various pest and disease infestations for each crop year. Maps of these forecasts are usually available for many of the major destructive insects such as grasshoppers and wheat midge, as well as some diseases . Agro meteorological warning and forecast can help in this way.

Record-Keeping

Keeping diligent field records can provide very useful information. A complete history of each field should include any insect or disease infestations, which management methods worked and which did not, and a list of management techniques to try in the future.

Info courtesy : TNAU Agritech Portal