Understanding Mealybugs; A Pest Causing Havoc To Crops In Kenya
Farmers in different parts of the country are grappling with an outbreak of mealybugs, an insect that is attacking various kinds of crops, including fodder.
The soft-bodied wingless insects that belong to the family Pseudococcidae live in clusters and feed by inserting their long sucking mouthparts into the plants and drawing the cell sap out from tissues.
The insects then excrete honeydew, which makes the plants sticky and encourages the growth of black sooty moulds on leaf surfaces that inhibit photosynthesis while at the same time acting as vectors for viral plant diseases.
Mealybugs thrive in warm, dry weather, with the female being wingless while the males are smaller with wings. The pest appears as cottony masses on the leaves, stems and fruits.
The insect is not a new pest in the country, but the intense attack on crops is blamed on the lengthy dry spell in parts of the country, with the warm weather providing a conducive environment for their fast multiplication.
Farmers in Tharaka-Nithi, Embu, Meru, Kisumu and Kajiado are among those battling the insects that are attacking tomatoes, potatoes, citrus fruits like oranges, peas, pomegranates, bananas and fodder.
Other crops the bugs feast on are beans, cassava, coffee, cocoa, cotton, sugar cane, sweet potato, apples and groundnuts.
Coming at a time when farmers are still grappling with fall armyworms, the insects are not only the newest threat to food security, but are also increasing the cost of production for growers.
Julius Mutembei, who farms papayas on an acre in Tharaka-Nithi, is counting losses estimated at Sh500,000.
Mr Mutembei tells Seeds of Gold that three weeks ago, he found some of his fruits covered with a whitish substance and did not think much about it. Some later turned black before he tried to remedy the situation in vain.
Nancy Kagendo from Tunyai in Tharaka South sub-county lost half an acre of pawpaw fruits and an acre of peas to the insects in less than two weeks. The peas were at the flowering stage.
“I first noticed some flowers had dropped on the ground and when I looked closely, I realised the crop had been infested with insects covered by a whitish substance,” says Kagendo.
SPREAD TO OTHER CROPS
Nicholas Mokaya, an agricultural officer in charge of Chuka and Igambang’ombe sub-counties, says the mealybug outbreak is as a result of the failed rains. He terms the insects dangerous to crops.
Charles Odira, a farmer in Kisumu County, says he started seeing the mealybugs early last year, but their severity has increased in the last weeks.
“The white cotton-like bugs usually appear under the leaves. They have attacked my pawpaws,” says Odira, who has 60 plants.
But he says it is easy to control the bugs by spraying a combination of detergents and insecticides.
“Mealybugs have a white coating made of waxy and fibre layers, which makes it difficult for insecticides to penetrate.
I mix soap, water and insecticides and spray,” he says, noting the soapy water dissolves the white coating while the insecticide kills the bugs.
“We plant vegetables, onions, oranges, avocados and pomegranates under irrigation. But so far, the mealybugs have attacked mainly oranges and pomegranates. I fear they may spread to other crops,” he says, blaming it on the dry spell.
According to him, the pest attacks all parts of plants, from fruits, leaves and stems, making them die if not contained on time.
Desperate farmers are spraying crops with baking powder, tobacco and washing detergents. But the solutions are not working.
In Tharaka-Nithi where the pests are most severe, governor Muthomi Njuki has declared the mealybugs attack an emergency and ordered agricultural officers to visit farms and train farmers on the appropriate measures to take in battling the insect before everything is lost.
He notes that the region has received very little rainfall this season and that if the few crops on the farms are destroyed, there is a risk of a famine worse than the one experienced in 1984.
PROVIDING EXTENSION SERVICES
County Agriculture executive Jasper Nkanya this week convened an urgent meeting with 60 agricultural officers from across the county and came up with ways of battling the pest.
The officers resolved to conduct 600 demonstrations across the county where farmers will be taught on how to control the pest.
The county has drafted a message that is being sent to farmers’ mobile phones alerting them of the pest invasion and the appropriate pesticides to use.
They advise farmers whose crops have been completely destroyed to uproot and burn them to avoid spread.
“The main challenge in controlling the pest is that it is even in the bushes making it impossible to spray with pesticides,” says Nkanya.
Agriculture PS Hamadi Boga says the pest infestation should not be treated as an outbreak since mealybugs and other bugs are always in the tropics which have warm to hot and moist climate.
“What we need is the usual management to ensure that crops remain healthy,” says Prof Boga.
He says that since crop husbandry issues have been devolved, it is the responsibility of the county to manage the bug infestation as the national government only offers technical support.
“We have national government bodies that deal with prevention and management, authorisation of chemicals to deal with pests and development of resistant seeds among others. The counties then have a role of providing extension services to the farmers and teach them about management,” he says.
Get it Quick
How the pests destroy crops
Adults and nymphs suck the sap from plant tissue, which occurs at all stages of crop development.
The infestation leads to crinkled and twisted leaves, reduced flower development, distorted and stunted plants with a bushy appearance.
Losses range from 5 -20 per cent if contained but they can hit 100 per cent in case preventive measures are not taken.
In ideal situations, mealybugs are controlled by practising crop rotation, and most importantly maintaining farm hygiene
Ways of controlling the insects
Mealybugs can cause 100 per cent crop loss if not controlled. They attack crops grown in the field and also in protected structures like greenhouses.
They have a wide range of host crops, including vegetables, ornamentals and fruit trees like pawpaw, citrus, mango, pineapple and passion fruits.
The pest injects toxic substances into the plants as it feeds, leading to yellowing and withering of leaves.
There is also stunted growth of the crop, attacked fruits shrivel and there is premature fruit drop.
Mature females lay about 300-600 eggs on various plant parts. The eggs are small and develop in three to nine days. Under normal conditions, they take 30 days to go through all the nymphal stages. In warm conditions, the insects remain active and reproduce throughout the year.
Management of mealybugs
Practice crop rotation with crops that are not attacked by the mealybugs. This will help to break the life cycle of the pests.
Remove infected crops from the field to prevent spread of the pest. Weeding should be done because some weeds may harbour the pests.
Chemical control is done using a systemic insecticide. According to Greenlife Crop Protection Africa, chemicals like Emerald, Loyalty, Amazing Top and Lexus can be used.
Mix the insecticide with a sticker like integra to make sure that the chemical sticks on the leaves of the crops. For biological control, parasitic wasps, ladybird beetles (Cryptolaemus montrouszieri), hover flies and lace wings are used.
Before applying biological control agents, make sure you control ants because they feed on the honey dew produced by the mealybugs.
Apply oils like vegetable oil, neem oils and mineral oils or soapy solution to suffocate the mealybugs. This should not be done on a sunny day because it will lead to discolouration of the leaves. Neem oil also has antifeedant and repellent properties.
Use of pheromone traps: Planococus is a mealybug lure impregnated with a synthetic replica of the mealybug female pheromone.
The traps will attract the males and they die, leaving the females to lay eggs that are infertile. Planococus is available from Dudutech Company.
Practice field sanitation. Use of a biological pesticide called ‘Campaign’ also helps. This is a biopesticide developed by RealIPM. The product is based on the fungus Metarrhizium and is effective against papaya mealybug.
Overhead irrigation will wash away the mealybugs.
Avoid excessive use of nitrogenous fertilisers and overwatering as this will encourage lush growth and thus attract mealybugs.
Regular monitoring and scouting of the pest should be done to ensure successful management.
-By Carol Mutua