The nymphal duration lasts for about 60 days. The pest causes about 40% damage by way of feeding on the inflorescence (Prakash and Sudharshan, 2002).
Management of H. picus includes monitoring of the bug during November– February and removal of egg mass and first-instar nymphs that are seen on the lower surface of leaves. Spray of Monocrotophos at 0.1% a.i. controls the nymphs, if the infestation is high.
Nezara viridula (Pentatomidae) occurs throughout the tropics; the bug lays eggs on leaves and stalks; the nymphs suck the sap of flower buds and stalks. The pest is reported to occur on vanilla in Karnataka and Kerala but its incidence is very low (Varadarasan et al., 2002a).
The bug was reported to occur on vanilla in Kerala and Karnataka as a minor pest. The nymph and adult suck the sap from beans and leaves (Varadarasan et al., 2002b).
This insect found in Idukki district, Kerala, sucks the sap from the leaves, vines, and inflorescence. Ants are found to be associated with this sucking insect and the pest incidence occurs during January–February (Varadarasan et al., 2002b). Control measures with Monocrotophos at 0.1% a.i. is warranted only if the pest is serious.
Coleopoteran Pests
Three species of Coleopteran pests are recorded in vanilla. Among them a weevil, Sipalus sp. occurring in Idukki district of Kerala, causes serious damage to young shoots, vines, and leaves.
The weevil lays eggs singly along the length of the vine and the emerging grubs feed on the inner core of the stem by boring a tunnel, the entire length of vine shreds, rots, and falls down (Varadarasan et al., 2002a).
The adult weevil is 8–10 mm long, 2–3 mm wide, and is light to dark black with two wavy white cross bands on the elytra. They feign death upon approach or touch (Thanatosis). The adult female is larger than the male. Adults mainly feed on shoots by inserting the snout; the injured area becomes necrotic within a day, leading to rotting of the shoot tip/vine. The weevil also feeds on leaves by scrapping upper or lower epidermis with mesophyll tissue, leaving a thin transparent epidermis on the lower or upper surface of leaves (Figure 20.9).
FIGURE 20.9 Vanilla vine weevil, Sipalus sp. (Left: egg deposited with necrosis; right: grub tunneling the vine).
After copulation, females lay eggs singly, 2–4 mm below the epidermis on the vine or shoot tip. The egg is capsule like 5–6 mm long, 0.8–1.0 mm wide, white and subsequently turns to yellow before hatching. The site of egg deposition develops necrosis. Eggs are laid only on tender vines and not on the leaves. The emerging grubs feed on the necrotic tissue by making tunnels in the vine.
The first-instar grub is yellow and the final-instar grub is white with brown head capsule. The grub (larva) period lasts for 35–40 days. The grubs tunnel the vine by feeding and the entire length of the affected vine becomes necrotic. The mature grub pupates inside the tunnel with fibrous material; pupation lasts for 19–21 days. The adult weevil emerges from the vine by making a small slit in the dried vine.
Extensive damage by the grubs and the adult weevil on the vine is observed mostly in open areas where shade is less. The adult weevils are seen in the field during November–January, and can easily be located. The weevils are not very active, and, hence, they may be hand picked and destroyed to reduce the damage on the crop (Varadarasan et al., 2002a).
This beetle, found in Wynad and Nilgiris in India, cuts through the leaf from the lower surface, eating the entire leaf tissue, except for the thick translucent cuticle of the upper epidermis. The damaged leaves rot as a result of fungi infection. The pest may be managed by keeping the garden weed-free and in severe cases by application of Malathion 0.1% (Rai and Nayar, 1976).
Holotrichia (Scarabaeidae): Roots of vanilla are damaged by white grubs in Idukki and Thiruvananthapuram districts of Kerala. Drenching Chlorpyriphos 0.05% a.i at the plant base during May or application of entomopathogenic nematodes controls the pest.
Lepidopteran Pests
The caterpillar of the moth occurring in Idukki, Kottayam, Ernakulam, and Thrissur, districts of Kerala, feeds on the vegetative shoots; these pale green caterpillars are seen in between the shoot bud and the first leaf, forming a web and feeding the shoot that leads to rotting of the terminal bud (Figure 20.10). Incidence of the caterpillar was recorded in January and February. The adult moth is reddish brown with a broad bright yellow band across forewings, gray hind wings, and body. The pest may be controlled by spraying Monocrotophos at 0.1% a.i. if the incidence is high (ICRI, 1996).
FIGURE 20.10 Shoot tip damage by webber caterpillar, Archips sp.
The yellowish ash-colored caterpillars with brown heads are very agile and damage the inflorescence and flower buds by feeding (Figure 20.11). The late instar caterpillar is light brown and pupates in between the damaged inflorescence. The pest was recorded in Chemannar in Idukki district of Kerala during February–March. Monocrotophos 0.075% or Lambda cyhalothrin 0.004% control the pest efficiently.
FIGURE 20.11 Left: Egg deposit on flower bud, right: damage on a flower bud by semi-looper, Nemoria sp.
Noninsect Pests
Among these, mites, snails, and avian pests cause considerable damage.
This mite is found to infest beans in storage in India (Sasikumar et al., 1992).
Snaiclass="underline" Achatina sp: They were found to feed on the chlorophyll tissues from the base of the vine and were recorded in Nagercoil in Tamilnadu, where coconut fronds were used for mulching on the plant base. The snails hide in the mulch during daytime, and come out in the night to feed on vanilla. The snails are also found to feed on leaves (Figure 20.12). The management of this pest includes avoiding mulching with coconut fronds or any other planting materials that do not decompose fast. The snails may be collected from the mulch and destroyed (Varadarasan et al., 2003b).
FIGURE 20.12 Damage on leaves by snail, Achatina sp.
Chicken cause much damage by scratching among the mulch and thus exposing and damaging the roots.
Vanilla Scab
Longitudinal corky formations on the beans of vanilla have been observed, which are commonly referred as “vanilla scabs.” It was suspected to be caused by insects or fungi or due to abiotic factors such as dew drops or higher light intensity. Experiments conducted at the ICRI, Kerala, indicated that scab formation in vanilla is not due to insect or fungus or due to any other abiotic factors. It was found that the mechanical injury at the early stage of the beans caused scab. Close observation on beans, leaves, and internodes showed that wherever the early stage of plant parts come in contact with hard objects, such as bamboo or dry twig or even mature leaf lamina, scab formation was observed on the point of contact. Subsequently, experiments with nail injury on the ovary during pollination show scabs on the beans. Any minute injury on the early stages of the ovary is stretched longitudinally with the elongation of beans, and thus scabs are formed (Varadarasan et al., 2005).