Yam dry rot. It is also known as yam nematode, yam dry rot nematode. 

Scutellonema bradys.

Asia (India, Pakistan), Africa, North, South and Central America, the Caribbean. It is NOT recorded from Oceania.

Dioscorea species. The main species are Dioscerea rotundata-cayenensis, Dioscorea alata, Dioscorea dumentorum, Dioscorea esculenta, and others. The following in other plant families are also main hosts: cowpea, melon, and sesame.

BIOSECURITY
The risk of introduction is high, especially associated with the trade in yam tubers. Small numbers of nematodes may be present in yams after harvest without noticeable signs of their presence. For this reason, and also because there is evidence of different strains of Scutellonema bradys the unrestricted movement of varieties of yam from one country to another should be prohibited, and transfer made only as sterile, pathogen-tested plants, following the FAO/IBPGR (1989) Technical Guidelines for the Safe Movement of Yam Germplasm.

 CULTURAL CONTROL

Before planting:

• Carefully check tubers for dry rot symptoms by scraping away small areas of skin; it is easier to check for dry rot if tuber cuttings or mini-sets are used for planting rather than whole tubers.
• Wipe the knife used to cut the sets with a cloth soaked in bleach, especially if the knife has cut infested tubers.
• Coat the sets in wood ash; even it will not significantly reduce nematode numbers, it may add beneficial potassium.
• Avoid planting yams in fields where previous crops were any of the following alternative hosts of the nematode: cowpea, sesame, green gram, pigeon pea, kenaf (Hibiscus cannabinus), okra, tomato and melon. Preference should be given to maize, groundnut, chilli, Indian spinach or sorghum.

During growth:

• Ensure healthy growth. Add cow dung to the mound to reduce nematode populations, or add applications of NPK fertilizer, but nitrogen alone may increase populations.
• Keep weeds to a minimum, especially those that are hosts of yam nematode, e.g., Eupatorium, Synedrella and Chromolaena.

After harvest:

• Collect all undersized and rotten tubers after harvest and bury deeply or burn.
• Ideally, plant yams after a fallow period; this is often difficult as pressure on land is intense and increasing; nor is it always obvious to farmers what crops to use as Scutellonema has a wide host range. However, restorative fallows using legume cover crops reduce nematode populations and the following are recommended: Aeschynomene histrix, Pueraria phaseoloides, Mucuna puriens and Centrosema species.

RESISTANT VARIETIES
No varieties of either Dioscora cayenensis-rotundata or Dioscorea alata with nematode resistance are yet available. The main methods of controlling dry rot are by cultural methods, the most important of which is the use of clean, nematode-free planting material. Nematode resistance is an object of the yam breeding program at the International Institute of Tropical Agriculture.

CHEMICAL CONTROL
This is not an appropriate method for the control of this disease as most nematicides are dangerous to use without training, they are expensive and mostly unavailable to smallholders. By contrast, hot water treatment is inexpensive and beneficial. Yams should be immersed in water at 51°C for 10 minutes. As a thermometer is needed to ensure the water is kept at the required temperature, this may not be a viable method for smallholders unless they are trained. If used, farmers should test it on a few sets first, as a method to produce nematode-free planting material for the next season’s crop. Treatment should be applied near the end of dormancy, but before shoots develop, not immediately after harvest.