Occurrence and Control Methods of Potato Tuber Rot Nematode

Fengning and Weichang counties in the north of Chengde City plant more than 40,000 hectares of potatoes annually, producing more than 800 million kg of seed potatoes and commercial potatoes per year, with about 120 million kg stored in winter, making it one of the four major potato production bases in the country. In recent years, the damage caused by the potato tuber rot nematode has led to great losses in stored potatoes. In 1994, it caused 5%-7% loss of stored potatoes, and in severely affected potato cellars, losses reached as high as 20%-30%. According to the currently retrieved data, this nematode is widely distributed in potato-growing areas of Asia, Europe, the Americas and Africa, has a wide host range, and poses varying degrees of threat to potato storage. Through two years of work, the occurrence patterns and control measures have been identified as follows.

1. Pathogen and damage symptoms

1.1 Pathogen Microscopic identification confirmed it as the potato tuber rot nematode.

1.2 Symptoms This nematode only infects the tubers during the potato growing period, with no special symptoms on the aboveground parts. The initial visible symptom is the appearance of small pale white spots on the tubers. Severe disease of the tubers occurs during storage. The infected tuber tissue dries up and becomes granular. When the entire tuber is infected, the tuber skin becomes as thin as paper and cracks, the tuber dries out, and weight loss exceeds 80%. Moreover, tissue infected by the nematode is susceptible to secondary infection by fungi.

2. Infection cycle

2.1 Overwintering There are mainly three pathways for overwintering: (1) widely surviving in the soil, living saprophytically after potato harvest; (2) parasitizing weeds and various crops; (3) overwintering with seed potatoes entering the cellar, and returning to the field with the tubers the following year.

2.2 Infection After potatoes are planted, the nematodes enter the young potato tubers through lenticels and the epidermis near the eyes. In the early growth stage of potatoes, only a small number of nematodes invade the subepidermal tissue of the tubers. During tuber enlargement and maturity, very small white spots form on the tubers, and large numbers of nematodes exist at the boundary between diseased and healthy tissue. The tissue beneath the lesions softens and becomes granular. After the tubers are harvested, the nematodes enter the cellar with the tubers. Once the tubers are placed in the cellar early or the storage quantity is too large, a large amount of respiratory heat is produced, causing the temperature to rise, and the nematodes then develop severely, more tuber tissue is damaged, and this leads to secondary infection of the tubers by pathogens such as Penicillium and Aspergillus.

2.3 Suitable temperature and humidity (1) Temperature. This nematode can develop within the range of 5-34°C. Under field conditions, it can still survive at a low temperature of -28°C. (2) Humidity. The suitable relative humidity is 90%-100%. When the relative humidity is below 40%, this nematode basically causes no damage.

3. Control measures

3.1 Sowing with pesticide Use 5% Du'er granules at 4-5 kg per 667 sq m, adopting the hole application method, applied to the field at the same time as planting the potatoes.

3.2 Crop rotation Rotate with corn, @#@245@#@, broad beans, etc., which can purposefully change the ecological environment for nematode survival and can play a role in reducing the pest population base.

3.3 Late cellaring This method allows the field heat and respiration-released heat of the tubers to be released outside the cellar, avoiding a temperature rise after cellaring, which would cause excessive nematode activity and reproduction and cause serious losses to stored potatoes.

3.4 Ecological control of disease occurrence

When nematodes occur severely due to early cellaring and extensive management, the temperature and humidity can be reduced by increasing ventilation. The specific method is as follows: keep the temperature fluctuation inside the cellar within the range of 0.5-4°C. When the temperature is higher than 4°C, open the air holes or cellar opening for ventilation; when the temperature is lower than 0.5°C, close the ventilation opening. In winter, repeating ventilation in this way during the day can bring the pest damage under control in about 7 days.