Pests and Birds 105
Root-knot nematodes are one of the most important nematodes associated with
papaya (Coveness 1967).
9.8.1 Root-Knot Nematode................................................
A root-knot nematode infestation under irrigated conditions primarily caused by M.
javanica and M. incognita has been reported from many countries (Morton 1987).
These nematodes attack the root systems of the plant and impair water and nutrient
uptake. Heavy nematode infestations can cause wilting, stunting, decreased plant
vigor, reduced yields and shortening of the productive life of a papaya tree. Young
plants of papaya are severely damaged as compared to the mature trees. The larvae
of these nematodes can travel short distances in soil, finding and attacking papaya
roots only, near the tips. When female larvae feed near the water conducting core
of the roots, the plant cells increase in number and size until readily visible swell-
ings, called galls or ‘knots’ are formed. Small to large swellings (galls), which are
produced as a result of the feeding process of the nematode, interfere with the proper
functioning of the roots. Severe attack of this nature causes retarded root growth and
a subsequent reduced root system for the plant (Figure 9.5). Secondary symptoms
which may be seen in the above ground portion of the tree are like those associated
with trees suffering from malnutrition or water stress. Leaves of papayas that are
affected appear pale green or slightly yellow and may fall prematurely. Infected
plants are sensitive to slight moisture stresses and wilt more readily than the non-
infected plants. Fruits produced are smaller than normal, may be slightly insipid and
more likely to have an off-flavour. These nematodes are principally spread through
cultivation and surface runoff or irrigation.
9.8.2 Management
Summer ploughing and exposing the soil to sunlight for one or two months dur-
ing April–May reduce the nematode and pathogen load in soil. Crop rotation with
onions, baby corn, sweet corn, maize, millet, sorghum, sesame, cassava and sudan
grass reduces nematode incidence for the next crop (Dobson et al. 2002). Mixed
cropping with marigold or Indian mustard as trap crops, can also minimise root-knot
nematode damage. Purchase of nematode-free papaya seedlings for transplanting in
orchards, application of farmyard manure (FYM), neem cake, pressmud and car-
bofuran 3G at 8.0, 1.0, 3.0 and 10.0 g, respectively, per plant at the time of planting
in the pits are very effective (Singh et al. 2010a,b). Application of carbofuran 3G at
40.0 g/tree before flowering is also an effective method of its management. Use of
resistant cultivars, namely, Solo, Pusa Majesty, Washington and Coorg Honeydew
against R. reniformis and CO-2 and CO-3 against M. incognita (Ram 2005) are
recommended in susceptible areas.
Use of chemicals as preplanting soil fumigation is effective (Ahmad and Sultana
1981) but recent concerns about their indiscriminate use necessitates a careful
approach. These were also known to affect beneficial microflora and, thus, disturb
the ecological balance. Control of nematodes using plant-based material is suggested
which increases soil fertility (Muller and Gooch 1982) as well as causes considerable