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Scientists battle deadly tomato pest

Friday July 25 2014

David Maina tends to tomato crops in a green house at a farm at Honi area in Nyeri county on June 26, 2014. PHOTO | JOSEPH KANYI

David Maina tends to tomato crops in a green house at a farm at Honi area in Nyeri county on June 26, 2014. PHOTO | JOSEPH KANYI 

Imagine investing more than Sh500,000 in tomato farming hoping to get it all back in six months only for the plants to start browning too soon.

You try everything you know to treat the crop but the situation seems to get worse. And so you watch helplessly as the plants wither and eventually die. This is the tribulation of tomato farmers in Kirinyaga County.

“I noticed that my tomatoes were being eaten by some kind of a caterpillar. The pest wasn’t responding to any chemical we know,” says Elijah Gitari from Mwea.

Evanson Gachoki, who was among farmers taught how to curb the disease during a recent workshop in Kirinyaga, says when he first saw it on the 15-acre farm that he manages, he thought it was “the normal cold-associated disease that tomatoes often suffer from because they dry up the same way.”

These are the deadly effects of tuta absoluta, a virulent tomato pest which originated in Peru in 1917 and spread to Spain and across Europe like wildfire.



It entered Africa in 2008 through Morocco and by last year, it had already reached Ethiopia. Now it is in Kenya with Kirinyaga County being among the worst hit. Others are Isiolo, Meru, Embu, Garissa, Marsabit and Wajir.

“It looks like a moth, a very small one, about 2 to 3cm long,” Nayem Hassan, the head of research and development at Russell Integrated Pest Management in London, explains.

“You might even confuse it with a potato tuber bolt. How you’ll know for sure that it is tuta is to look at the larvae when they are feeding on the leaves. They have a dark red colouring on the head.”

Rangaswa Muniappan, the director for Integrated Pest Management at Virginia State University says the pest flies during the night, and hides during the day.

“It lays eggs on the leaves, sometimes even on the fruit. And when it hatches, the tiny caterpillar mines the leaf and then the whole plant turns brown.”

“It actually looks like someone lit a fire and burnt down your tomatoes,” says Lusike Wasilwa, the Assistant Director of Horticulture and Industrial Crops at the Kenya Agricultural Research Institute.

“We are getting up to 100 per cent yield loss, because symptoms look like those of late blight so when farmers see it, they start to spray fungicides, which don’t help.”

Gitari says from the two acres on which he had planted tomatoes, he managed to harvest less than 100kg.

Gachoki’s employer wasn’t as lucky. He lost everything.

“This pest affects the crop at all stages from germination to maturity,” says Wasilwa.


The farmer must pay special attention to the leaves closer to the ground, and if the temperatures there feel a little higher and humid, then it is likely that tuta is present.”

Kirinyaga has more than 1,900 hectares under tomatoes, which earn the county over Sh1 billion annually.

And with nearly all the crop affected, the prices of tomatoes are beginning to rise. If the pest isn’t brought under control, tomatoes will be the most expensive vegetables by the end of this year, experts warn.

To manage the pest, allow at least six weeks fallow break from one crop harvest and next planting to prevent carry-over of the pest from previous crop. “In between this planting cycle, cultivate the soil and cover with plastic mulch.”

One should control weeds to prevent multiplication in alternative weed hosts.

Other measures include seal greenhouses with high quality nets, inspect crops to detect first signs and destroy attacked plants.

One should also vary insecticides for effective control. More importantly, farmers should seek help from agricultural officers.