Harm and Control Methods of Dodder in Potatoes

[Host crops] Potato, tomato, eggplant, pepper, Chinese onion, soybean and many other crops. [Disease diagnosis] It occurs sporadically or in patches in the field. Dodder twines its vine stems around the stems of the plants, coiling around them, and at the point of contact with the potato plant it grows haustoria that penetrate into the stem or petiole tissues, absorbing the plant's water and nutrients, causing the affected plants to grow weakly. The plants are stunted, with bent and slender stems, small and yellowing leaves, and few and small tubers. In severe cases, the stems and leaves of the plant are completely covered with dodder, and the whole plant stagnates and stops growing until it dies. The pathogenic dodder is Chinese dodder (Cuscuta chinensis). The dodder stem is slender and yellow, without chlorophyll; after its stem contacts the host stem, haustoria grow at the contact point, attaching to the host surface to absorb nutrients and water. The flowers are small and white, with two styles, capitate; the sepals have ridges, the ridges running longitudinally, the sepals showing angular edges, the dorsal surface of the sepals bearing longitudinal ridges; the stamens alternate with the corolla lobes; the fruit is a capsule, completely enclosed by the corolla at maturity, dehiscing circumscissily when it splits, and the seeds are round.

[Occurrence pattern] After the dodder seeds mature, they fall into the soil, or are mixed among the host seeds and overwinter with organic fertilizer. The following spring, when conditions are suitable, the dodder seeds overwintering in the soil germinate, producing a 6-10 cm long sprout (young stem) standing in the field, whose tip constantly circles or sways; once it touches a plant it can parasitize, it immediately twines around it. At the contact point between the dodder stem and the stem of the host plant it has twined around, haustoria grow and firmly wedge into the interior of the host plant; after establishing the parasitic relationship, the dodder and its underground portion immediately separate, and it begins its parasitic life. The haustoria of dodder are formed by protrusions of the vascular bundle sheath, and the portion extending into the host tissue differentiates into vessels and sieve tubes, which connect respectively with the vessels and sieve tubes of the host plant, thereby continuously absorbing large amounts of water and nutrients needed for its growth and development from the host. In the field, dodder twines around one host plant after another, continuously spreading in all directions. Throughout its entire growth period, dodder keeps flowering; although the flowers are small, they are extremely numerous and produce a large quantity of seeds. After the seeds mature, most fall into the soil; the seed coat is hard and highly resistant to adverse conditions, and the seeds can survive in the soil for 5-10 years. In low-lying, humid areas with dense plant cover, dodder damage is severe.

[Control measures] (1) Carefully select seeds to prevent dodder seeds from being mixed in and brought into the field. (2) In plots where dodder occurs, immediately carry out deep plowing to a depth of more than 20 cm after harvest, turning the dodder seeds into the deep soil layers so that they cannot germinate and emerge. (3) Manure mixed with dodder seeds must undergo thorough fermentation treatment, so that the dodder seeds lose their germination capacity or are rotted. (4) Plastic film mulching cultivation can significantly reduce the incidence of the disease. (5) Intertillage and weeding should be timed when dodder has germinated but has not yet twined, so that it is promptly hoed out and destroyed. (6) When scattered dodder twining is first seen, it is necessary to act before it flowers and sets seed, thoroughly removing the dodder vines and carrying them out of the field to be burned or deeply buried. When removing, be sure not to leave any broken stem stubs behind. (7) Chemical control: the most effective agent is spraying Bacillus thuringiensis preparation No. 1 (Bao No. 1), with a concentration requirement of no fewer than 30 million viable spores per milliliter of water, at 2-2.5 L per 667 sq m. Spray after rain or in the evening and on cloudy days. If the dodder stems are broken with a stick to create wounds before spraying, the control effect is even more pronounced.