M.G. Venkatesha


White stem boi~r has been recorded on arabica coffee as early as 1867 in India. Though intensive research has been carried out on the pest for more than five decades by scientists of Coffee Board, the borer still poses serious problem in arabica plantations. The severe damage of the borer in spite of adoption of several management practices in plantations is due to various reasons.

1. Why white stem borer is serious pest in arabica coffee ecosystems?

Among a few serious insect pests on coffee such as white stem borer, coffee berry borer, shot hole borer, mealybugs and green scale damage caused by white stem borer is always considered to be economically important as it affects health of the plants or kills the plants whereas, coffee berry borer can only damage crop, mealybugs and green scale can damage crop and tender leaves and twigs and shot hole borer can affect a few fruiting twigs.

Thc various reasons for serious nature of white stem borcr damage in arabica plantations arc as follows.

A. Arabica coffee is a principal host plant: Though stcm borer known to attack othcr plants such as robusta coffee and tree coffee (which are weakened by other causes), olea (kalsadle) and teak in India, it can successfully breed only on arabic a coffee. Supposing an equally suitable alternate host plant like arabica exist in nature, then some amount of the borer attack would have been diverted from arabica plantations to them. In the absence of such a host plant entire pressure of pest attack is exerted only on arabica coffee. Resent observations have revealed that the borer can multiply fast only on dead/drying teakwood. Hence, one should not keep dead/drying teak branches on the tree or ground in plantations.

B. Large scale monoculture of arabica coffee: A highly suitable host plant for stem borer breeding is arabica coffee, which is made easily available to the borer through large scale monoculture. When we are copiously supplying the suitable food for stem borer to breed in nature, the pest population automatically rises in plantations owing to successful multiplication. Before the introduction of arabica coffee to India, the borer survived on some wild plants and its population was under check in mixed forest ecosystem. A large scale monoculture of arabica coffee tilted the balance of natural ccosystcm and enhanced the borer population by providing sufficient food for its breeding.

C. Mode of behaviour of the borer : Stages of the stem borer life cycle such as eggs, larvae and pupae are not easily availablc for natural enemies (predators or parasites). Eggs of the borer are laid in canneries of the bark on tbe main stem and thick primaries. Hidden eggs in canneries are not easily accessible to any predators like ens, birds, spiders, etc. and unfortunately there has been no efficient egg parasites repotied on coleopteran pests in general and white stem borer in particular. The eggs will hatch in 1-2 weeks and tiny larvae bore in the cambium region for about two months and then get into hard wood. The pupation of the borer is also inside the wood. As eggs (to certain extent), larvae and pupae of the pest are well protected in coffee plants, establishment of any efficient predators or parasites is curtailed in nature. Whatever the predators and parasites have been recorded so far on the borer are occasional ones. As indigenous (native) natural enemies are unable to establish on their own in the field and contribute high morality of the borer, their multiplication in the laboratory and further release in the field will not be useful. Since there is no efficient natural enemies on the stem borer to check the population in the ficld unlike in the case of many other agricultural pests, the borer incidence remains serious in coffee ecosystem.

The above are the main reasons for persistent white stem borer havoc in Arabica plantations.

II. Reasons for failure in successful control of the borer

The present recommendations by Coffee Board such as tracing, uprooting and destruction of the borer infcsted plants to rcducc the pcst inoculum, maintenance of medium share on the estate to reduce flight and egg laying activities and application of chemical (Lindane 20 EC) in the beginning of flight (emergence) periods i.e., in October

and April to kill fresh hatched out larvae will help to contain the borer population. However, during many surveys it could be noticed that uprooted borer stems were stored in the estates in which pest completes its development fast and emerged adults of the borer infest plants in the field. This practice will defeat the very purpose of tracing operations. In several estates it could be generally seen that shade has been reduced to minimum level to boost production in view of boomed price in the market. This has enhanced the level of borer incidence in such estates. It was also true in many estates that chemical application do not coincide with flight periods of the borer. These are some of the reasons contributing for build up of the borer population in estates in spite of meticulous adoption of control methods. They are as follows.

A. Shade management

Maintenance of optimum shade on the estates is beneficial to individual growers, as pest will move to another estate where shade level is low. If optimum shade is maintained in every estate, the borer is forced to lay eggs under shaded condition. This behaviour of the borer has been observed in the laboratory. Therefore only optimum shade in an estate will not help to check the pest population. B. Chemical application:

In several estates it was observed that planters do apply chemical at appropriate time. However, the flight periods of the pest coincide with the premonsoon (April-May) and nOlih east monsoon (Oct-Dec,_ showers which usually wash off the chemical applied against the borer. This is the main disadvantage as far as chemical control of the borer is concerned. C. Problem in tracing:

Tracing will help to bring down the borer population effectively by removing and subsequent destruction of borer infested plants. However, in many cases the borer infested plants will be as productive as healthy noninfested plants and yield difference between non-infested plant and borer infested plant is not significant unless the plant is severely damaged by the presence of several borer larvae in the main stem. The plants infested with a few grubs can yield productively for many years. Besides this, in some occasion bore grubs after feeding under the bark region, which could be seen by appearance of ridge, will die in the hard wood region. Hence, several plants showing ridge may not be having damage inside, as larvae die during the process of tunnelling. Uprooting of such productive plants with heavy crop will have negative impact in plantation management. Therefore, whatever the plants infcsted with borer (this many be 3-4 plants per acre in well managed estates) can be covered cylindrically with nylon net prior to start of flight periods for preventing escape of emerged beetles. The cut edges of nylon net have to be joined and stitched/stapled and both top and bottom ends can be tied with thread as shown in figure. Nylon net should not be wrapped on the stem tightly as beetle will cut the nylon during the process of cutting emergence hole in the stem. Once the beetle falls into the nylon cage after making an exit hole, it cannot cut the net. If main stem of coffee plant is with fewer primaries around 1-2 feet from the ground level, it is easy to cover the stem with nylon net. Crop can be harvested from such plants as long as they are found to be productive. If possible, primaries also can be covered like this. Only in the case of plants showing dying symptoms (yellowing and wilting of leaves) due to borer damage can be uprooted. It was also found that uprooted borer plants could be stored for any purpose after immersing them in water for about seven days. III Tactful management of white stem borer

The borer can be effectively kept well below the economic injury level by following estate specific management in general and block specific management in particular.

Wherever shade is less especially in eastern and western aspects of an estate, borer tracing and chemical application should be strictly followed in such blocks. If borer management is adopted in particular . block of an estate where pest build up/breeding is likely to be more due to less shade, automatically the pest incidence will come down in entire estate as one is hitting the hot spot of the pest. As mating and egg laying activities of the borer are vigorous in the morning (9-1 lAM) and again in the afternoon (4-5 PM) whatever the blocks exposed to sunlight during these particular hours, borer incidence will go up. Therefore, in borer vulnerable blocks adoption of control methods is very important and also economical in bringing down the pest level. Supposing chemical applied is washed off due to rain, immediately chemical may by applied for second time only in borer vulnerable blocks which may be hardly a few square feet to a few acres depcnding upon extent of holding. In eastern and western aspects of an estate where the borer build up is expected to be high, shade lopping may be done in such areas in the month of June after summer flight period. Only certain blocks can be considered like this as shade lopping in June in entire estate is not possible in pre-monsoon period. Moreover, shade lopping during June will-affect the already set flower buds. Chemical application in most of the estates is done by sponging (swabbing) on the main stem and thick primaries of the plants. However, sponging by hand will not be that effective due to physical fatigue after a few hours of work. Moreover, in sponging, establishing a contact between chemical and dried bark of the plant is difficult. Hence, spraying of chemical is effective than sponging as chemical contact with the plant and spray coverage are found to be satisfactory. Besides this, spraying is economical than swabbing as less manpower and chemical will be utilized. Spraying also helps to avoid health hazard posed in sponging by hand. It is important is spraying that only suitable nozzle should be used to target spray mainly on the main stem and thick primaries of the plants. Indiscriminate chemical application not only causes serious environmental hazard but also kills various kinds of natural enemies occurring on all types of coffee pests. IV. Importance of smoothening of the main stem and thick primaries

Smoothening of arabica plant against stem borer attack is popularly known as bark scrubbing. Bark scrubbing has been in practice against stem borer since about five decades, The term bark scrubbing is wrongly understood 111 stem borer management and deep scrubbing using hard implements resulted in death of plants. Though bark scrubbing has given good control of the borer, the method did not become popular, as it is labour intensive and cumbersome to adopt in large area. If the main stem and thick primaries are meticulously smoothened using coir it will give excellent control of the pest. The purpose of stem smoothening is to remove cannaries of bark for preventing the borer beetles from laying eggs on the plants. First year stem smoothening is a bit laborious process as bark has to be removed completely and about 35 workers are required per acre. In subsequent years, as bark will not develop immediately about 16 workers are required per acre to polish the already smoothened plants. Since scrubbing is labour intensive it can be adopted in phased manner in large areas. Under tactful management practice for white stem borer control, the plant smoothening can be implemented in borer vulnerable blocks of an estate where usually borer breeding is expected to be high due to more sunshine. Plant smoothening can be adopted during October when bark will be neither hard nor very smooth. It is difficult to remove dried bark in summer and removal of wet bark during monsoon will injure green portion of the plants. Moreover, plant smoothening in October also helps to kill deposited borer eggs as well as just hatched larvae. Unlike chemical sprays if plant smoothening is skipped in one season due to unavoidable reasons. Existing smooth conditions of the plant can cheek the pest attack. V. Pheromone technology

Male white stem borer beetle is known to attract female bcetle by rei casing some chemical (Pheromone) from its body for mating. Once the female is fertilized, it will deposit eggs on coffee plants. Using a chemically synthesized male pheromone in sticky traps whether female beetles of stem borer can be attracted and trapped has' recently been tried in the field by Coffee Board scientists in collaboration with Greenwich University, UK. Preliminary results of pheromone experiments are found to be encouraging. However, this advanced technology in the borer control has to be verified carefully for a few more sea'sons to understand whether it can be used as one of the tools in white stem borer management. VI. Conclusion

As coffee white stem borer is a well adapted pest in coffee ecosystem, easy suppression of the borer is impossible. Once w~ clearly understand the bioecology of the borer it is difficult to blame either scientists or planters for failure in bringing down the borer incidence. Among all major pests of coffee, white stem borer will continue to be a challenging one in future. However, one should not expect complete eradication of the borer, as it is not possible with any insect pest. In addition, if the stem borer is completely eradicated in nature, then another similar type of borer which is minor now in coffee ecosystem could take an upper hand. So our aim should be to keep the white stem borer at economically acceptable level by sensibly adopting integrated management methods. We hope that only nature can find some solution if the pest attack go out of hand.

M.G. Venkatesha, Department Of Zoology, Bangalore University, Janana Bharathi. Bangalore-56.

* The author himself a planter had earlier worked on coffee white stem borer management for about a decade at CCRJ, Balehonnun.

Source.' Featured in Indian Coffee, April, 1999.

Current Issue              Archives