By Ruth Vaughan
The decomposers’ heroic deeds in farms are fast being replaced by a trail of destructive activities
Have the beneficial worm Millipede turned predatory? This is the question scientists and some potato farmers are grappling with as the worms feed on tubers dealing a major blow to farm productivity in parts of Meru. Farmers have courted millipedes since time immemorial due to the insects’ role in cycling nutrients in the soil through consuming microorganisms, dead plant residues and animal waste and moisturizing food with their secretions. Even in death they continue replenishing soils through decomposition-the breakdown of organic materials.
The docile decomposers are credited with turning the iconic Haller Park in Mombasa from the industrial wasteland that had a barren quarry floor that was hard as a rock in the 70s to the thriving wildlife sanctuary that it is today. The millipedes feasted on the casuarina trees needles that lay on the forest floor with nothing to decompose, turning them into humus which formed the first layer of soil in the park.
But the decomposers’ heroic deeds in farms are fast being replaced by a trail of destructive activities as they now feast on the same crops they have long assisted to flourish. Potato farmers in prime growing areas of Meru, Timau, and Laikipia are raising alarm over the increasing number of millipedes that have started feeding on the tubers, taking a toll on yields. This has caused jitters at a time when potato has gained importance and focus from farmers, the private sector and government as a viable alternative to the staple maize which has taken a hammering from climate change, market dynamics and poor varieties. Potato on the other hand has gained traction, due to its superior nutritional value and adaptation to various production environments. The millipedes are threatening to reverse these gains.
Why have millipedes turned predators?
By being root crops potatoes are prone to attack by millipedes which thrive deep inside the soils. The roots crops are easy prey especially when the seeds are not from a credited sources or are from previous harvests. Millipedes lay the eggs on the potato or any other root crop fanning their reproduction.
Lack of crop rotation
As is the case with all crops, planting the same crop time after time causes a build up of insects and diseases to levels above economic thresholds including insects that would previously not be considered pests. This applies to millipedes too.
As rains fail and farms become dry, millipedes which are known to survive in moist and wet conditions are migrating in search of water. Such movements land them into crops.
Millipedes are known to build tunnels under the ground that facilitate their movement and reproduction. Increased tillage and turning of the soil exposes the millipedes to birds and animals which eat them therefore reducing population. Lack of tillage however keeps them under the soil where they reproduce fast.
Reduced use of class 1 broad spectrum insecticides
This means that the millipedes that were previously being killed by these chemicals when they were in use for other problems like nematode control are now not, creating a population build up.
Movement of seed from one growing area to another
Seeds might move from one area to another through trade or farmers who share the seeds among themselves. This allows the pests to move around with a likelihood of finding favourable conditions in the new area increasing their population. With millipedes being an emerging pest, there are no registered pesticides for their control. Those interested would need to petition KEPHIS or Pest Control Poisons Board and chemical suppliers to get the products registered.
So how can farmers tame the spread and destruction caused by millipedes?
Monitoring the population and movement is at the heart of the control. Because millipedes are nocturnal or hide in dark places they are difficult to spot during normal crop scouting. Farmers are advised to be on the look out for signs of millipedes: small underground tunnels and holes, surface scraping, fragments of white exoskeleton from dead millipedes, damage in sample roots and live millipedes in organic waste. Millipedes can come to the surface after dark, examine your crop at night with a torch.
The best way to find millipedes is by using traps and baits. Corn bait traps can be made by placing a hand full of corn seed in a net pouch and soaking in water for 12 hours. A useful bait is a big juicy potato cut in half. Baits should be buried 15 cm deep and left for two to three days before examining and replacing with fresh bait. Another excellent monitoring tool is a ‘pitfall trap’. This can be made from a plastic cup buried in the ground with the rim just protruding from the soil. For small scale farming baiting, trapping, chickens and collecting millipedes after dark might be sufficient to reduce crop damage.
Millipedes frequently attack crop tissue that has already been weakened by poor nutrition, high salinity, diseases, nematodes or other insects. Farmers are therefore advised to test their soils and fertilize to optimum levels. Rotate crops. Keep pests, diseases and nematodes to a minimum. Always wash soil off seed potatoes before planting to avoid transferring millipedes or eggs to new fields
Ruth Vaughan is the Technical Director at Crop Nutrition Laboratory Services Ltd. (CROPNUTS). Ruth is also a contributing author to Kenya’s leading horticulture magazines such as the HortFresh Journal, HortiNews and Floriculture. Ruth is a great believer in soil health, organic matter, biochar and carbon sequestration as a way to alleviate climate change and increase food security. Loves visiting farmers and seeing all the different farming methods