Researchers plot against coffee thrips invasion

Researchers are urging coffee farmers to mulch and irrigate their crops to address rising levels of the plant pest thrips, last witnessed at current levels some 15 years ago and now set to knock out an estimated 10 per cent of the country’s coffee output this year, but posing a bigger risk for next year if left unaddressed.

The surge in the pest is not yet at alarming levels, but has been rising visibly since March, said Dr Harrison Mugo an agricultural entomologist with the Coffee Research Foundation (CRF).

Yet countering the problem only requires a greater awareness of soil moisture levels, say scientists.

Though thrips attack berries, they are largely concentrated under the leaves. The leaves turn irregularly grey, with silvery patches and black spots. They then fall leaving a stunted coffee plant.

Thrips are brown in colour with feathers that look like birds wings. The surge in their numbers has been caused by the dryness since March, which is expected to last until September’s short rains, prompting the CRF alert to coffee farmers.

If rains fall before September, the problem will diminish, but if they don’t all coffee areas could see surging thrip numbers and need to use pesticides, said Dr Mugo. 

Nearly half of all coffee farms in Kenya have thrips on their crops, but the pest is most prevalent in the main coffee growing zones in the Upper Midlands. However, the pest is only considered a threat if it rises above the stipulated Economic Injury Level (EIL) of 2 to 3 thrips per leaf. In well tended coffee plantations most fall under the EIL threshold. Hence “they are not a major worry factor for the farmer,” said Dr Mugo

Indeed, coffee researchers don’t normally rate thrip as a major coffee pest, but following the surge in numbers this year they have moved to outline measures farmers can implement to control or eradicate them. The CRF is advising farmers to mulch their coffee trees to conserve moisture and if they have an irrigation kit, to irrigate their plantations in dry spells.

As a long term measure, CRF is also encouraging farmers to plant the Cordia tree and intercrop it with coffee to provide shade in dry spells. The tree matures in 2 to 3 years if the rains are good and is spaced 30 by 30 metres. Once its leaves fall, it provides organic matter that helps conserve moisture in the soil.

The mulch from fallen Cordia leaves also encourages the multiplication of predator mites that feed on thrips. The predator mites are inherent in coffee farms but organic matter ups their numbers. Introducing Cordia “is a bio pest control measure,” said Mugo.

Coffee plants are additionally more immune to thrips attack when they getting extra nutrients from the organic matter. “The same as when a person is healthy, he is less likely to fall sick,” said Dr Mugo.

Nonetheless, where the thrips reach or surpass the stipulated EIL of 2 to 3 thrips per leaf, spraying with pesticides is mandatory.

When the level of infestation becomes high, thrips can cause total crop loss in the following season. This is likely where leaves fall and coffee plants are left bare by the pests. The plants then fail to flower the following year leading to a barren coffee season.

According to a report by Bloomberg News, the Coffee Board of Kenya now projects thrips will reduce coffee yields this year to 40,000 metric tons, compared to last year’s 45,000 tons.

Written By James Karuga for African Laughter

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