AFRICAN White coffee stem borer (Monochamus leuconatus), is one of the most notorious insect-pest of coffee in Tanzania. The adult beetle of the pest is about three centimetres long and dark brown in colour, with the largest part of the wing cases appearing greyish white. The antennae are about as long as the body in females and about twice as long as the body in the males.
It lays eggs on the trunks of coffee trees, usually at the base near the ground level. A female beetle has been observed to lay about 23 eggs. According to the Integrated Pest Management ((IPM) Specialist with the Tanzania Coffee Research Institute (TaCRI), Mr Fredrick Magina, the damaging stage is the whitish, legless larva that barrows into the bark and the wood of the trunk and main roots.
He points out that the attack causes serious damage, particularly if the trunks are almost ring barked. Mr Magina says that young trees of one to two years may therefore be killed quite rapidly, but older trees wilt, turn yellow and produce a poor crop.
Incidentally, this pest attacks Arabica coffee that contributes to over 80 percent of the total coffee produced in Tanzania, which supports livelihood and income security to coffee growers in 14 regions in the country and about four percent of the GDP. The IPM Specialist says that Robusta coffee is not attacked by the pest.
The pest has a number of alternative hosts to harbor; wild Rubiaceae and shrubs such as Keetia venosa, Oxycnthus speciosus, Randi sp., Mviru (Vanguera sp.), Pavetta oleveriana and Rytigynia schumanii. As the plants confined in Tropical Africa, the pest is also confined in these areas. “Larvae of white coffee stem borer feeds on coffee tree barks and finally bore into the stem, weakening the plant andcausing yellowing and chlorosis of leaves, which then wither and fall (die-back).
Presence of wood shavings from the bark or the roots just below the soil level and entrance or exist holes on the stem of about 1 cm is normally observed. Infected trees that are less than two years old are inevitably killed, while mature or old trees are not usually killed outright, but they continue to produce weak roots and suckers and eventually die.
Dry woods will finally be attacked by termites or fungi,” says the specialist. In the past, he unveils, the African coffee stem borer was effectively controlled by using Aldrin and Dieldrin (Organochlorine pesticide) mixed with methylated blue as a marker and applied to the trunks of trees from the ground level to a height of 90 cm.
Mr Magina says this mixture was applied before the onset of rains in October/November across coffee regions. Despite their effectiveness, Aldrin and Dieldrin were removed from the list of pesticides used on coffee due to their effect to the environment and potentially to human health. The Aldrin and Dieldrin were widely used pesticides for several crops, including management of white coffee stem borer since 1950s to 1970s, and was banned in 1974.
Mr Magina says that after banning of Aldrin and Dieldrin, there was no effective chemical to manage the pest, very serious resurgence emerged and became notorious to manage.
Damages of the pest resulted crop loss ranging from 5 – 25 percent, therefore coffee cultivation was uneconomical. As TaCRI’s mission is to develop and disseminate appropriate technologies to improve coffee productivity and quality in the country, knowing that there is a problem of white coffee stem borers, the institute initiated trials in April 2015 in farmers’ fields.
The trials were held in Mbinga (Ruvuma), Buhigwe (Kigoma), Burka (Arusha) and Karatu (Manyara). It involvedevaluating the efficacy of Fipronil 200SC (Regent 50 SC) against the pest by spraying or banding different dosages. The trials were conducted for duration of three seasons, from April 2015 to March 2018.Mr Magana unveils that results indicated that at a rate of 20 mls of Fipronil per 20 litres of water, the chemical is able to kill the pest.
In order for the pesticide to be effective, it should be applied at the beginning of short rains and long rain (estimated two weeks before). “This prevents and/or repels the adults from laying the eggs of the pest on the trunk. Low infestation levels were observed in coffee fields treated with Fipronil adopting this spraying regime,” he says.
TaCRI has also investigated tainting effect of the product on cup quality of the coffee samples harvested and processed from the coffee trees applied with the chemical in all locations of the trials. “Results indicated no tainting effect of the product assurance of marketing coffee from fields treated with Fipronil. In addition, Maximum Residue Level (MLRs) of beans processed was done by TPRI but nil or minimal effect was observed,” says the specialist.
Mr Magana notes that after the research findings, a technical paper was prepared and presented to the Tropical Pesticides Research Institute (TPRI) for registration consideration. The 28th meeting on Pesticide Approval and Registration Sub-committee (PARTS) that was held at the National Carbon Monitoring Centre (NCMC) – Sokoine University of Agriculture (SUA), Morogoro from September 27-29, 2018 fully approved the product (Fipronil 200SC/Regent 50 SC) for use by farmer for management of the white coffee stem borer, Monochamus leuconatus, Coleoptera: Cerambycidae. “Now Fipronil has been registered by TPRI.
TaCRI and Bajunta Chemical Company (owner of the product) is in preparation for launching, then will be followed by introducing the product in all Arabica coffee growing areas in the country and sensitize growers. TaCRI is hereby informing coffee farmers in all areas prone to white coffee stem borers to use the product,” says Mr Magina.