Some facts about Dodder

Dodder is a major threat to Sericea, and demands rigorous control. Neglecting the problem can lead to a drastic reduction in forage yield.

Sericea strangled by dodder.
Photo: John Fair

Livestock farmers on the Highveld who have planted Sericea on a large scale have found this legume to be of immense value. Some say it has revolutionised their farming. This is no hyperbole. Sericea is a non-bloating legume pasture that is drought-hardy, disease-tolerant and long-lived. It produces a considerable amount of forage on medium- and low-potential soils, makes protein-rich hay, and does not require nitrogen fertilisation.

All of this results in increased production at lower forage costs. Unsurprisingly, demand for seed is growing. But the easy days in Eden are over. The devil, in the form of dodder (genus Cuscuta) has moved in, with devastating effect on forage yield. (The Afrikaans name for this weed, duiwelsnaaigaring, translates as ‘devil’s sewing thread’.)

Key facts
Prof Charlie Reinhardt and Dr Wayne Truter of the University of Pretoria published an article on dodder in 2012, entitled ‘Dodder, die plantdoder’ (‘Dodder, the plant killer’). They highlight three facts that farmers should know in order to manage this threat effectively:

Dodder is a parasite
It feeds on most legume pastures, potatoes, tomatoes, carrots, onions and sugar bean. It does not parasitise grasses, which, of course, include maize, sorghum and winter grains. It is totally dependent on the host plant
After germination, dodder entwines itself around the host plant with long, string-like tentacles that suck nutrients out of the host. It must do this within five to 10 days of germination or die of starvation.

Dodder does not have chlorophyll, so is unable to convert sunlight energy into plant energy (carbohydrates). Once it has attached itself, the base of the dodder, and its start-up roots, die off. It then becomes dependent on the host for all of its food. Its seed spreads rapidly and effectively Dodder seed is extremely small – 1kg contains 1,2 million to 1,8 million seeds. This means that if you sow Sericea seed contaminated with only 0,001% of dodder seed, at a seeding rate of 20kg/ ha, you can end up with more than 350 dodder plants per hectare.

This may not sound like much, but dodder spreads rapidly and the infestation can become serious. The problem is compounded by the fact that dodder has hard seeds that can lie in the soil for 10 years or longer before germinating.

Prevention
Fortunately, dodder can be managed effectively. To begin with, prevention is better than cure. In South Africa, most Sericea seed is produced by farmers. Top producers are taking steps to avoid contamination by reaping seed only from lands free of the parasite. They have also developed sophisticated cleaning equipment capable of removing weed seeds.

Purchasing certified seed is thus the first step towards managing the problem. But this is by no means a guarantee of dodder-free Sericea. As one farmer pointed out, dodder has been around for many years and has survived by feeding on other weeds such as cosmos. It is already in the ground and is stimulated to germinate by the planting of Sericea.

Control
One method of fighting dodder is to cut off its supply of nutrients. I know of one farmer who pulled out the few Sericea plants that had dodder attached to them within the first few months of planting. The plants died, but so did the dodder! Grazing and mowing infested Sericea before the dodder flowers are also effective ways to eliminate the threat.

Spot-cutting with a hand-held brush cutter is another option. Most of the contamination that I have seen in Sericia lands has been limited to isolated patches easily picked out due to the weed’s yellow colour. Deal with these patches before they produce seed. It is important to cut or graze below the point at which the dodder is attached to the Sericea plant.

John Fair heads up Fair’s Biofarm Assist.