The mole rat (Tachyoryetes splendens) is one of the most devastating underground rodents that attack various plants that include annual crops (like maize, beans, wheat and barley), vegetables, pasturelands, compound lawns, perennial crops like tea and coffee and large trees crops like mangoes and paw paws.
The rodents are more devastating in perennial crops like tea and coffee because the crops take long in the field.
The mole rat is a mammal that lives and develops its own extensive tunnel system underground, by digging a burrow and a network of superficial foraging tunnels, a deeper nest complex with a toilet area, and often, a food store.
The holes or burrows are sealed from the surface, except when disposing excavated soil on the surface which occur as mounts of soils on beautiful lawns or farmlands.
The rodents are dangerous because they attack roots of crops from below the soil. And they use all their body parts to survive. Its sharp teeth cuts through the soil as the front feet digs it. The dug soil is pushed behind using the hind feet and tail and the animal uses its chest to push the soil that comes out onto the surface.
WHY THEY LIVE UNDERGROUND
The underground burrows offer protection from predators like snakes, birds and small carnivores but water is a big challenge, especially floods.
Therefore, the mole rats live in a subterranean micro-habitat that is buffered from the extremes in terms of temperature and humidity. To live underground, the rats have anatomical adaptations that include:
i) Short limbs, which make them occupy small space.
ii) They have bodies that are cylindrical.
iii) The necks are muscular and indistinct from head to body.
iv) They are able to move backwards and forward with equal ease in the narrow confines of their burrows due to their streamlined shape and short limbs.
v) They have well-developed eyes (suitable for living underground) which are very small and at best can only detect light and darkness. The eyes are also protected from injury and soil.
vi) They have ears that are very small and lack the external pinnae that restricts hearing to movement above ground only and less underground for effective detection of predators. Since they live in burrows, the sense of touch is important to them.
vii) Their hair is thicker than those of rats, short and easily reversible. This is critical when moving in and out of the burrow.
viii) Mole rats have a pair of large and ever-growing and forwardly-directed incisors, which lie outside the mouth for cutting through the soil and also for protection.
There are both male and female moles which produce young moles called litter rodents. When they mate, they produce up to five litter rodents weighing about 9g each, which is higher than those of larger rats. Mating takes place at any time of the year.
What are the management options of moles?
TRAPS
Trapping of rodents is an early development in human culture and it has been used as a preferred mode of killing or capturing even before the invention of pesticides. Trapping is the most effective and environmentally sustainable way especially when skills and experience are not available.
This method, however, is limited because it is tedious and requires a lot of patience. One uses factory made traps or local materials that include wooden stick about a metre long fixed into the ground. A piece of soft thin wire noose is suitably placed in the burrow and the stick is pulled to curve to form a loop ’spring’ over the burrow entrance and held in place by a string ‘trigger’ system.
The noose wire is then tied to the upper end of the stick spring and as the mole rat tries to seal the burrow or forage, it cuts the string trigger system and is then trapped. This method requires a lot of patience and skill to use, however, it is also the most effective way to get rid of mice. Another option would be to have professional mice exterminators who can take care of the problem for you.
USE OF RODENTICIDES
This method is not recommended unless trapping is difficult or when there is an epidemic of moles in home lawns or farmlands. Use of traps is preferred because it is effective for low infestation of rodents even in large-scale plantations of cashewnuts, tea, coffee, maize or grasslands.
Rodenticides may be baits or fumigants depending on mode of action, which provide an immediate solution to mole control. They need right environment like soil moisture and temperatures at the time of application to be effective.
Many agrovets in Kenya sale the products as powders to be mixed with food as baits or fumigants. Examples that are commonly used but in different trade names are zinc phosphide, which is applied as bait, and aluminium phosphide used in fumigation of burrows and tunnels.
Depending on poison levels, (lethal dose-LD50), these rodenticides can be applied many times, thus called multiple-dose anticoagulants (low levels of poison) or only once, in this case called single dose anticoagulant poisons (high concentrations).
Generally, coagulants are much less dangerous to humans than anti-coagulants. Moles need to ingest over a long period to get a lethal dose.
For the single dose rodenticides and fumigants, though more effective, they are dangerous and generally unavailable for direct sale at agrovet counters since they must be applied by qualified personnel.
High field efficacy of aluminium phosphide (a fumigant) can achieve success rates ranging from 80 per cent to 100 per cent in the control of mole activity when well-applied in the field.
In most formulations, the table is sold as 3g (with 1g active ingredient) which is able to release 1g hydrogen phosphide gas that suffocates the moles inside the tunnels or furrows. To be more effective, it is advisable to increase dosage (two to three tablets) depending on the size of the tunnel and burrow.
Aluminium phosphide can also be used to control other underground rodents like porcupine but dosage needs to be increased from three to five tablets per hole depending on sizes. To have effective control, the tablets should be placed in each active borrow (which has fresh soil mounds or damaged crop) at about 10 to 15cm into the tunnel and immediately sealed with soil.
The farmer should then wait for fumigant to act on moles for five to seven days, then come back and re-examine for mole activity in fumigated area by checking damaged crops or having fresh soil moulds pushed outside the surface or you open tunnels and check if they will have been closed 12 to 24 hours after opening.
If mole activity is still on, it is advisable to apply fumigants again until success rate is over 90 per cent. Since fumigants are poisonous, proper care is required and the person applying should use hand gloves and put on appropriate nose masks.
For successful use of gassing tablets and sufficient concentration of gas reaching the animal before it can respond by blocking off the tunnel, high moisture is required since efficiency of the phosphine gas is faster with the availability of moisture, therefore, the method may be more effective during wet than dry periods.
CULTURAL METHODS
The most common practice in many communities is using a mixture of cow dung and pepper. It is placed in the burrows and then burnt to smoke the rodents out.
In areas where other crops grow, damage by moles could be reduced by planting on mounds rather than ridges for root crops like cassava and sweet potatoes.
Intercropping food crops like maize, sweet potatoes with deep rooted, poisonous shrub Tephrosia vogeliiin will also help.
Mole rats can also be killed or chased away by pouring fermented cattle or pig urine (one week old) into their burrowing holes which create a stinging smell that keep moles away. This is one of the cheapest and most reliable environmentally recommended method.