Farmers are facing serious plant protection issues and phytosanitary risks, in particular in the tropics. Such issues are food insecurity, lower income in traditional low- input agroecosystems, adverse effects of pesticide use on human health and on the environment in intensive systems and export restrictions due to strict regulations on quarantine pests and limits on pesticide residues. To provide more and better food to populations in both the southern and northern hemispheres in a sustainable manner, there is a need for a drastic reduction in pesticide use while keeping crop pest and disease damage under control. This can be achieved by breaking with industrial agriculture and using an agro- ecological approach, whose main pillar is the conserva- tion or introduction of plant diversity in agroecosystems. Earlier literature suggest that increasing vegetational biodiversity in agroecosystems can reduce the impact of pests and diseases by the following mechanisms: (1) resource dilution and stimulo-deterrent diversion, (2)

https://link.springer.com/content/pdf/10.1007%2Fs13593-011-0022-4.pdf

Plant species diversity for sustainable management of crop pests and diseases in agroecosystems: a review

Intercropping, the simultaneous cultivation of multiple crop species, has been used throughout history and remains common among farmers of small landholdings in the tropics. One benefit of this practice may be disease control. In phenomenological research comparing disease in monocrops and intercrops, primarily due to foliar fungi, intercropping reduced disease in 73% of more than 200 studies. Nematodes are the primary pathogen for which disease increases are reported, but variability in disease impacts among studies can be high for all types of diseases. The mechanisms by which intercrops affect disease dynamics include alteration of wind, rain, and vector dispersal; modification of microclimate, especially temperature and moisture; changes in host morphology and physiology; and direct pathogen inhibition. The effect of intercropping on host density is a factor underlying many of these mechanisms. By synthesizing our growing understanding of mechanisms and their interactions with phenomenological studies, we may develop a theoretical grounding that allows us to improve the application of intercropping for tropical smallholders and industrial farmers alike.

Diseases in Intercropping Systems

Until recently, conservation biological control has been the least well studied area of biological control (Ehler, 1998). During the 1990s, however, several important texts dealing with conservation biological control were published (Boatman, 1994; Barbosa, 1998; Pickett and Bugg, 1998). These suggest a growing level of international research. However, unlike classical biological control, where databases such as BIOCAT (Greathead and Greathead, 1992) exist with which to analyse levels of success, and inundative biological control, where sales figures provide at least a measure of uptake, the performance of conservation biological control has received little attention. This contribution will consider the factors that are relevant in this branch of biological control and, using recently published examples, consider the extent of success that has been achieved. We shall conclude by proposing how the future success of conservation biological control attempts may be maximised.

Success in Conservation Biological Control of Arthropods

Clover as a cover crop for weed suppression in an intercropping design: II. Competitive ability of several clover species

Clover as a cover crop for weed suppression in an intercropping design: I. Characteristics of several clover species

Leek (Allium porrum L.) is an Important field vegetable in most of western and central Europe. Infestations of onion thrips (Thrips tabaci Lindeman) cannot be controlled with the range of insecticides now available in The Netherlands. Leek rust (Puccinia allii Rudolph) is now also difficult to control. Experiments in which no insecticides or fungicides were applied, were carried out to assess the effects on thrips populations and infection by leek rust when leek crops were undersown with subterranean clover (Trifolium subterraneum L.). To evaluate the economic aspects of this approach, both the quality and quantity of the leeks produced in the two systems were compared. Undersowing leeks with clover drastically reduced thrips infestations which was reflected in improved quality of leeks at harvest. Leek rust incidence was also reduced slightly by undersowing with clover and the quality of the leeks at harvest was also better. Although the quality of the leeks was improved when the crop was unders...

G. Schelling

Papers

Pest and disease management by intercropping: suppression of thrips and rust in leek.