How do you prevent and control root-knot nematode disease in wax begonias?

The pathogenic nematodes of root-knot nematode disease in wax begonias damage the lateral roots and fine roots of the plant, stimulating the root tissue to form giant cells and causing excessive cell division and proliferation, resulting in the production of many tumors of varying sizes ranging from 1 to 10 mm in diameter. The tumors are smooth at first, then rough on the surface later, and often produce many fibrous roots; they may grow singly or join together in strings. Cutting open a fresh gall reveals pear-shaped transparent small white spots, which are the female nematode bodies. Because root growth is hindered, water and nutrient uptake is affected, the plant becomes stunted, the leaves become smaller, yellow and wilted, the internodes shorten, and finally the plant dies.

Root-knot nematode disease in wax begonias is caused by infection by the southern root-knot nematode of the class Nematoda. The pathogenic nematode is sexually dimorphic; the female adult is pyriform, visible to the naked eye, 0.4 to 1.4 mm long and 0.3 to 0.8 mm wide. The wax begonia root-knot nematode overwinters as eggs and larvae within eggs or as males in diseased residual roots and soil. When the soil temperature rises above 10°C the following year, the eggs hatch into larvae, which infect the tender roots. The nematode's own range of activity is not large, and it generally spreads through irrigation water, surface runoff, seedling transplanting, and human activity. A soil temperature of 22 to 30°C is the peak period for nematode infection, when tumors form in large numbers. The most suitable soil temperature for growth and development is 25 to 30°C, with a soil moisture content of about 40%. The larvae stop activity below 10°C. At a temperature of 35°C, they die after 5 minutes.

Control methods: (1) When raising seedlings by cuttings or planting in pots, disease-free soil must be used, avoiding taking soil from places where the previous crop was infected with nematodes. In hot summer weather, the soil can be sun-exposed to kill the nematodes. (2) Use chemicals to disinfect the soil. Dig holes or ring trenches in the potting soil, then apply 5 to 10 ml of undiluted dichlorvos per pot, immediately cover with soil and press flat; after fumigating for half a month, planting can begin. Alternatively, use a 200- to 300-fold dilution of 80% dibromochloropropane, applying 300 to 400 ml per pot, in the same way as above. (3) For diseased plants, apply 10% fenamiphos granules, 1 to 2 g per plant, once every 30 days, for 2 consecutive applications.

Control methods for root-knot nematode disease in begonias

Wax begonias damaged by root-knot nematodes show weakened, stunted growth of the entire plant, wilting leaves, and in severe cases drying up and dying. Tumor-like growths of varying sizes form on the roots (lateral roots and fibrous roots).

The growths are milky white to yellowish white, covered with a layer of brown membrane, and rough on the surface. The tumor-like growths are the proliferations formed after root-knot nematodes parasitize the plant.

The pathogen is the root-knot nematode [Meloidogyne incognita (Kofoid et White) Chitwood]. This nematode survives as eggs and larvae in the soil and on host plant residues. It can infect when the soil temperature is above 20°C and humidity is 40%. Most females enter the host tissue before sexual maturity and can reproduce by parthenogenesis, stimulating the plant tissue to form tumor-like bodies and severely hindering the plant's physiological functions. This nematode can occur year-round in greenhouses, but is most severe in May and June.

Control methods for rhizosphere nematode disease in wax begonias

Rhizosphere nematode disease in wax begonias:It mainly damages the root system, causing yellowish-white tumor-like growths to form on the roots, shortening the plant's internodes and making the leaves smaller; in severe cases the plant dies.

Control methods:The potting soil must be disinfected before use.