Disease Management

An integrated disease management involving cultural, chemical and biological control is recommended (Ramachandran et al. 1991, Sarma et al. 1988, 1992b, Anandaraj and Sarma 1995, Sarma and Anandaraj 1997).

Cultural control

Provision of drainage: Population build-up of P. capsici is dependent on weather and is positively correlated with soil moisture (Anandaraj 1997). High precipitation during rainy season leads to water logged conditions. Such conditions predispose plants to Phytophthora infections. During water stagnation, temporary anaerobic conditions result in low oxygen and together with increased root exudation stimulates germination and growth of pathogen propagules. Such conditions enhance host susceptibility due to decreased production of phenol oxidases, reduced phytoalexin production, suppression of mycorrhiza and reduction in nitrogen fixation (Drew and Lynch 1980). Thus adequate drainage is essential to reduce the population build-up of P. capsici and subsequent infection of pepper plants.

Phytosanitation

Pepper Phytophthora is reported to survive up to 19 months in plant debris. The initial occurrence and spread of the disease is also non-random and tend to cluster around the previously infected plants (Anandaraj 1997), hence the infected plants serve as the foci of infection (Zadocks and van den Bosch 1994). Removal of infected plants would reduce the inoculum level and spread of the fungus.

Shade regulation

Pepper is trailed on live supports like Erythrina indica, Garuga pinnata, Glyricidia sepium etc. During monsoon season the canopies of the support trees also grow and generate a microclimate under their canopies with high humidity and low temperature, which is ideal for P. capsici to multiply and infect. Lopping of the branches during rainy season is essential to facilitate penetration of sunlight and reduction of high humidity thereby altering the microclimate. The lopped branches could be used as mulch to prevent soil splashes.

Cover crops

The main source of initial inoculum of P. capsici in pepper plantation is the contaminated soil. Infection on the foliage occurs through soil splashes often initially to the tender shoots trailing on the ground, and from these shoots to other parts of the canopy through rain splashes (Ramachandran et al. 1990). To prevent soil splashes live mulch in the form of legume and grass cover are suggested (Ramachandran et al. 1991, Sarma et al. 1992c). But, recent studies have shown that population of P. capsici increases under weed cover and death of plants is faster with weeds than without weeds (Anandaraj 1997). Although weed cover reduces soil splashes and restrict movement of propagules along with soil, it also supports the population build-up of P. capsici. In Malaysia, studies with Desmodium trifolium as cover crop for pepper has indicated that plants showed faster and better growth in clean weeded plot than with cover crop and concluded that it was economical to grow pepper in clean weeded plot (Ahmed 1993). In India, after the monsoon, there is a prolonged drought from November to May. During this period weeds compete for soil moisture and the population of P. capsici also survives longer. Hence, after the rainy season it is better to remove the weeds in pepper plantations and rake up the top soil. Removing weeds and turning the top soil would help to conserve soil moisture, as the capillary pores are broken (Brady 1984, Russell 1973) and soil moisture removal by weeds during summer is also reduced. Once weeds are removed the saprophytic survival of P. capsici on weeds would also be reduced. In view of this, a post monsoon clean cultivation is suggested (Anandaraj 1997). Root exudates of some of the plants such as Allium spp. are inhibitory to zoospores of Phytophthora (Manohara et al. 1992). Aqueous extracts of P. colubrinum, Azadirachta indica, Strychnos nuxvomica, Lantana camera extract and Chromolaena odorata (Eupatorium) were tried on P. capsici and C. odorata extract was found toxic to P. capsici (Anandaraj and Leela 1996). Mulching with this plant has been reported to increase the yield in Cambodia (Litzenberge and Lip 1961). Although the mulching was done to reduce the nematode infestation on pepper, there was no reduction in the nematode population but recovery of plants have been reported.

Chemical control

Although the disease occurs every year during rainy season, a fixed fungicide scheduling is advocated against both aerial infection and collar infection. The control measures include: spraying of Bordeaux mixture 1 per cent (BM), pasting the collar with BM and drenching the basins with either BM or with copper oxychloride (Ramachandran et al. 1991, Sasikumaran et al. 1981, Nair and Sasikumaran 1991, Malebennur et al. 1991, Lokesh and Gangadarappa 1995). Based on the epidemiological studies and nature of occurrence of collar infection, the practice of pasting the collar with Bordeaux mixture is discouraged (Anandaraj et al. 1994, 1996a, 1996b, Sarma et al. 1992c). Among the systemic fungicides, several formulations of metalaxyl such as Ridomil granules and Ridomil-ziram have been reported to be effective against foot rot of pepper (Ramachandran and Sarma 1985, Ramachandran 1990, Ramachandran et al. 1988b, 1991, Sarma et al. 1992c, Kueh and Sim 1992a, Kueh et al. 1993). In experiments with granular formulations of Metalaxyl, Ridomil 5G at 50 g per plant gave protection up to seven weeks and granular formulations were better than foliar spray (Kueh et al. 1992, 1993). However, owing to the cost of systemic fungicides and the poor socioeconomic conditions farmers seldom use them. While reviewing the control of four soil-borne Phytophthora diseases, doubts about the success of chemical control of Phytophthora foot rot was expressed by Coffey (1991). Studies with various concentrations and frequency of application revealed that it is safe to apply the chemical six months prior to harvest to prevent the traces of metalaxyl residues in the final product (Sarma et al. 1992c).

Use of beneficial microorganisms

Several beneficial organisms like vesicular arbuscular mycorrhizae (VAM) are associated with pepper (Ramesh 1982, Manjunath and Bagyaraj 1982). Incorporation of VAM alone or in combination with other beneficial microorganisms like Azotobacter and Azospirillum enhance rooting and growth of pepper (Govindan and Chandy 1985, Bopaiah and Khader 1989). VAM inoculation has been found to enhance rooting, growth and suppress root damage caused by P. capsici, R. similis and M. incognita under artificial inoculation and under field conditions (Anandaraj and Sarma 1994a, Anandaraj et al. 1991a, 1991b, 1996c, Sivaprasad et al. 1990a, 1990b, 1995). Occurrence VAM has been a rule rather than an exception in crop plants (Harley 1989). Colonization of mycorrhiza alters the nature of root exudate and the rhizosphere microflora due to the influence of mycorrhizosphere effect (Dehne 1982, Linderman 1988, Graham 1982,1988).VAM fungi have been reported to suppress the root rot caused by Phytophthora in citrus (Davis and Menge 1981, Davis et al. 1978, 1980). VAM fungi not only enhance growth but also suppresses diseases caused by soilborne pathogens (Ewald 1991, Graham and Egel 1988). Colonization by VAM is described as a prelude to biological control. Realizing the importance of this, incorporation of VAM in the nursery is recommended both for enhancing growth and suppressing root infection (Sarma et al. 1996).

Organic amendments

Organic matter such as neem oil cake (Sadanandan et al. 1992, Nair et al. 1993) soyabean meal, ground nut cake, coconut cake and chicken manure are added to the soil to supplement nutrition and enhance the growth of saprophytes (Kueh and Sim 1992a). In soils amended with organic matter the saprophytic activity is enhanced and P. capsici population drops to undetectable levels (Anandaraj 1997).

Biological control

Soil borne pathogens are amenable to biological control (Cook and Baker 1983). In the rhizosphere of pepper several antagonistic microorganisms belonging to Trichoderma and Gliocladium occur (Dutta 1984, Anandaraj and Sarma 1994b, Anandaraj and Peter 1996). P. capsici being soilborne, and the main source of inoculum is contaminated soil, growth of antagonistic fungi would prevent the population build up. The competitive saprophytic ability of P. capsici is very low and addition of organic matter to the soil containing P. capsici promotes the growth of saprophytes and reduces the population of P. capsici (Anandaraj 1997). Several strains of biological control agents effective in protecting pepper against P. capsici have been isolated, screened and mass multiplied on inexpensive carrier media and applied in the field with promising results (Anandaraj and Sarma 1995, Sarma et al. 1996). Mature coconut water, which is an agricultural waste, supports good growth of Trichoderma and Gliocladium and could be used for the mass multiplication of these antagonistic fungi (Anandaraj and Sarma 1997).

Thus integrated control involving phytosanitation, cultural, chemical and biological controls are being followed to check Phytophthora infections in pepper (Ramachandran et al. 1988a). Attempts are also being made to incorporate resistance in the cultivars by adopting biotechnological means. For this the necessary regeneration protocols have already been developed (Shaji et al. 1995a, 1995b, 1996).

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