Pesky pests blight exports for local avocado farmers

Glady's Chebet at her avocado farm in Mulot,Narok West.The over 200 farmers have ventured into avocado for export after disappointment in Maize crop after the deadly Maize Lethal Negrosis Disease afffected their crop in the year 2012.[FILE,Standard] Gorge Menge, a farmer in Borabu, Nyamira County, never suspected the golden spots dotting the leaves of his avocado plants could spell doom for his thriving enterprise. Menge is among local avocado farmers who are making a killing from the export of Hass avocados to international markets. Menge ventured into avocado farming seven years ago and has, over time, doubled the number of trees on his 10-acre orchard from an initial 1,200 to 2,400. For the past three months, he has been worried by the premature shedding of flowers and leaves from most of his avocado trees, leading to an overall reduction in yields. After consulting a local agronomist, Menge's worst fears were confirmed: his crop had come under a serious Persea mite attack. The tiny insects ravage the leaves of avocado trees, causing them to fall off. Persea mite is believed to have originated in Mexico and Central America but has since spread to places like California, Spain, and Israel. Experts say it likely reached Kenya through imported plant material or contaminated nursery stock, slipping past quarantine checks. Menge counts himself lucky to have arrested the problem early enough before it spread through the entire crop. The mites infest the underside of the leaves, where they lay eggs and feed on the chlorophyll, which is a key substance that enables leaves to carry out their functions of manufacturing nutrients for the plant, according to Jacob Keror, Nyamira County's crops director, who is also an expert in plant health. According to Keror, Persea mites on avocados are first noticed by the formation of circular spots along the midribs and veins of the leaves, as well as the underside of the leaves. "With time, the spots enlarge and inhibition of photosynthesis of the plant starts, making the leaves start turning yellow due to reduced efficiency of the two important life functions of leaves," he says. And just when he thought he had the Persea mite under control, Menge woke up to a new threat - the false codling moth. His avocado trees have been exhibiting signs of premature ripening while still very green, besides showing signs of scars on the rinds. Both the False Codling Moth and Persea mites have been the primary culprits behind catastrophic harvest drops for many farmers. Unlike Menge, who took about three months to notice the effects of the Persea mites and false codling moth, Joseph Soti, an avocado farmer in Nakuru County, was unaware of them until a friend brought them to his attention. His friend observed that a significant portion of the fruits Soti supplied to an exporting agent were being rejected. "I used to sell around 50 tonnes of Hass avocado every fortnight," Soti recounts. "But the shock of my life started when nearly a quarter of my fruits were rejected due to poor quality, which was attributed to poor health. I only came to realise it was due to the moths' infestation." According to Menge, his early, proactive measures saved him from a wider infestation. For the mites, he successfully smeared tree stems with pyrethrin powder. For the moths, he used a physical trapping method. He laid out tapes coated with pheromones to attract the male moths hovering near the trees. "After getting falsely attracted to the traps, the opportunity for mating is intercepted and, as a result, their reproduction cycle is broken," Menge explains. Keror emphasises that an integrated pest control management strategy must be effectively employed to prevent these moths. "The measures range from cultural practices and monitoring with pheromone traps to disrupting mating, employing biological control-especially by killing larvae-and using licensed insecticides judiciously," Keror advises. For Persea mites, Keror recommends regular monitoring of avocado leaves, particularly during dry spells, to detect early infestation. The effective use of miticides is another method for eliminating the mites. For farmers using irrigation, it is advisable to thoroughly spray the underside of affected leaves to weaken the mites or wash them off. Additionally, avocado fields should be kept free of other crops and weeds that could host the insects. As with Menge's use of pyrethrin, chemicals can also serve as preventive measures. All growers should contact crop officers at their respective county extension services whenever they suspect a plant health issue. For instance, contacting a Nakuru County government crop health officer helped Soti solve his problem before it could spread. Experts warn that if left uncontrolled, Persea mites and the false codling moth can cause losses of up to 70 per cent, in addition to the long-term impact of farmers being quarantined from international markets. "If large quantities of avocados marked for export are found to be of low quality and disease-infested, then the country may as well be quarantined," Keror cautions. "This can have a huge negative impact, especially on the farmer." For example, by the time Soti discovered the problem, he had lost about 50 per cent of his regular income-an estimated Sh1.5 million. "If the fruit trees don't flower well or the premature fruits fall off, then it means reduced earnings," Soti says. "It is even worse when the mature fruits are found to be infested with the false codling moths."

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