Five problems in yam cultivation and production

In recent years, by analysing my own 3 years of practice growing twin-tuber trellis-free yams and surveying more than ten thousand local yam growers, I have found that no matter which variety is grown, five problems commonly exist in yam production that affect quality to varying degrees.

1. Yam red spot disease. Commonly known as rusty yam. Yam red spot disease is a disease caused by nematodes. If infected during the growing period, it affects tuber development, making tubers small and light in weight. The nematodes mainly infect the underground tubers. Initially, reddish-brown, nearly round, slightly sunken spots form on the tubers. On severely affected tubers, the spots are dense and merge with one another, forming large dark brown patches. Control method: at sowing, apply 1 bottle of root nematode control liquid per mu together with 250 kg of 50% carbendazim, applied into the sowing furrow along with fertiliser and irrigation water. After that, apply once every 1-1.5 months in the same way.

2. Yam anthracnose. This disease is the main disease that causes early vine death in yams. Anthracnose mainly harms leaves and stems. On infected leaves, the spots are round to oval, greyish-white to dark grey in the centre with dark brown edges. The boundary between diseased and healthy tissue is obvious. Control method: start spraying the first treatment when seedlings emerge uniformly, using chlorothalonil at 600 times dilution, then spray once every 10-15 days. After initially infected spots are found on the leaves, switch to alternating sprays of copper hydroxide at 600 times dilution and thiophanate-methyl at 600 times dilution for control.

3. Yam brown rot. Commonly known as "rotten yam". Young yams show decay-like symptoms when infected, with irregular brown spots or deformities. After slight rotting, the diseased part becomes soft. When cut open, the browned part of the tuber is often larger and deeper than the external spot. It is controlled incidentally during anthracnose control.

4. Yam forking. There are two main causes of yam forking: (1) the meristem at the tip of the young yam tuber is bitten by insects, causing forking; (2) fertiliser burning the roots, or root damage from human or other causes, causing the yam to fork. The first cause is solved through the pesticide treatment used to control red spot disease; for the second cause, care must be taken not to damage the yam root system during fertilisation and cultivation management.

5. Flat yam. The root cause of flat yam formation is lack of water. Yams should be watered during the peak period of shoot and leaf growth and during drought. There is a folk farming saying that "drought produces flat ones, moisture produces round ones"; the larger the yam, the more severely it flattens. In my area there is also the farming saying "yams are tormented by dryness, taro is tormented by wetness", which also affects drought-resistant watering of yams. It is worth noting that in yam fields where a no-deep-ploughing soil conditioner is used instead of ridging the soil, even more attention should be paid to drought-resistant watering in the later stage of yam growth. A no-deep-ploughing soil conditioner can only fully exert its effect under the premise of sufficient water. However, yam fields must not accumulate water either. Only by ensuring that every ditch is connected can high quality and high yield of yams be ensured.