How to control Cascuta and moon vine, the enemies of your trees

There are two parasitic weeds that agroforestry farmers have to beware of due to their devastating effects on trees.

These are Cascuta campestris or Dodder plant and Ipomoea alba, which is also called moonflower or moon vine.

Both are noxious climbers with no serious insect or disease problems. They kill trees by suffocating them.

Moonflower has been around since the colonial days and is widespread in the eastern part of the country, which comprises the larger Ukambani and the former Northeastern region. In Kikamba, it is known as Windia.

It produces sweet-scented white flowers that open in the evening and close when touched by the morning sun.

It is perhaps this attribute that made colonialists to introduce this tree assassin to Kenya from Queensland, Australia.

Dodder, which is native to the Americas, is a recent invader but it has spread so fast that it is now present in nearly all the regions of Kenya.

I have seen this killer weed in many places across the country – Busia, Kisumu, Bungoma, Kakamega, Uasin Gishu, Elgeyo-Marakwet, Kajiado, Machakos, Makueni, Nairobi and Kilifi.

Initially, it was limited to public forests but increasingly, it is attacking private plantations. My Cypress, Grevillea and Blue gum trees in Webuye were attacked in 2018. 

Both weeds start their destructive lives as seedlings in the soil before attaching to a host plant, usually a tree.

For Cascuta, once it is united with its host, the first portion of its stem withers and the weed is no longer connected with the ground. It obtains all its food and water from its host.

It kills by suffocation and starvation. Once it attaches itself to a tree, it grows rapidly, completely covering its branches and leaves.

This prevents photosynthesis – the process by which the energy of sunlight is used by plants to grow – from happening. “It is becoming a nightmare,” says Dr Eston Mutitu, a research scientist at the Kenya Forest Research Institute (Kefri).

In Ukambani, a number of farmers have lost plantations of Melia volkensii (mukau) trees to moon vine, according Bernard Kigwa, a Kefri environmental scientist based at the Kitui station. 

How they spread

According to scientists, the weeds spread mainly through contaminated crop seed, although vegetative spread is also possible.

Some people who are yet to understand the weeds’ danger spread it willingly by planting it in their homes, especially on their hedges.

The moon vine is attractive because of its sweet scent while Cascuta has bright yellow and orange colours.

Thus public awareness is critical to fight them. Birds and strong winds also spread their seeds far and wide.

How to control them

Kefri has been analysing Cascuta to understand the biology of host plants, among other issues, with a view of coming up with a mitigation strategy.

Among the possibilities under consideration is chemical and biological control.

The challenge scientists face is that hundreds of plants, including crops, are hosts.

In the meantime, how do you control it if it attacks your trees? These are some of the measures I deployed in Webuye:

1. Manually pluck it from the affected plant. Do this regularly. Do not allow it to establish itself. This takes time and resources but it is much better than allowing it to kill your trees. It does not wither easily but you can put it together with other dry matter and burn it. Kigwa also advises that one way of doing this is to plant other crops in your tree farm. “This way, as you weed your crops, you also weed the trees, removing any harmful weeds. Most of the farmers who have lost their trees to the parasite left their land to lie fallow,’’ he said.

2. Uproot the affected tree or cut off branches and burn them together with the weed. This will save the other trees by stopping its spread.

3. Regularly inspect your hedge and the ground under your trees. This way you can catch them before they attach to them or in early stages, which is much easier to deal with.

4. Chemical control. A range of chemicals may work against Cascuta and farmers should seek advice from experts on how to apply them.

Mr Wanyonyi is Managing Partner at Storylines Kenya,