Controlling Fall Armyworms and Grubs on Lawns


Armyworm. file photo | nmg

We all dream of having a picture perfect lawn with thick, rich and lush foliage that resembles a layer of premium carpet picked from the shop.

While this is an attainable goal, it calls for a little more effort than just the occasional watering and trimming. Frequent mowing, fertilisation, irrigation and weed control are vital.

But even with all this care, the problem of a lawn grub — a collective term that describes caterpillars—remains inevitable.

Collective term

In mid-January, Kenya was unfortunate enough to join countries facing the fall army worm invasion.

Unlike the true army worm, the fall army worms feed day and night, are most active during early morning hours and late evening, damaging plants in patches. 

Grass and grain crops

Originally from Brazil, the fall army worm has caused havoc in southern African countries and invaded East Africa in December last year.

Typically, the worms prefer grass and grain crops such as wheat, maize, sorghum and an estimated 80 other types of crops including Irish potato, tomato and spinach. The female fall army worm can lay up to 1,000 eggs at a time and can produce multiple generations very quickly without pause in tropical environments.

As is the case with most caterpillars, the juvenile fall army worms are small, meaning that feeding damage may largely go unnoticed in the beginning.

Feeding damage becomes more noticeable as the pests mature and start to march in their numbers across lawns, leaving behind dead patches of brown turf grass.

Every gardener should be on the lookout for the first signs that indicate the lawn is under an army worm attack.

Watch out for brown spots that appear slightly shorter and thinner, as well as an increase of the number of birds in your yard.

Invasive moth

Plant experts reckon that close surveillance and early detection are the best remedies in tackling the fall army worm attack.

“Early detection and rapid response are the immediate actions that could control the pest from spreading and damaging more crops,” said Joe DeVries the Vice President at Alliance for a Green Revolution in Africa (AGRA).

The invasive moths which have ability to spread 100 kilometres a day, feed as they march, eating the tops of grass blades. The larvae of the pest proliferate mainly due to wind dispersal and on host plants from eggs laid by the moths.

Intervention measures that can be taken depend on the stage of the life cycle of the army worm. The worm has a life cycle of between 35 and 61 days Mathews Matimelo, a research expert from Zambia, said a population of three or four fall army worms per square foot is a responsible treatment threshold.

“The best results are achieved when the egg masses are present on five per cent of the plants or when 25 per cent of the plants show damage symptoms and live larvae are still present,” he said.

Controlling larvae

Controlling larger larvae typically after they are hidden under the frass plug (droppings of the caterpillar) is more difficult.

Aside from application of pesticides, a host of natural predators such as birds, insects and other larvae can also be used to tackle the fall army worms.

Some beneficial insects such as lacewing, lady bugs and minute pirate bugs parasitic wasps and flies feed on army worm eggs and the larvae.

Experts agree that no single method or pesticide has been found to completely eradicate the invasive pest that move in.

To be on the safe side, the scientists advise that gardeners and smallholder farmers combine the various intervention methods in order to build resilience against the fall army worm.