Control of black spot disease of growing soybean

Soybean black spot is a common disease. The disease harms pods and stems, resulting in stem death, pods are not fruiting, and in serious cases, plants die. The bean grains in the diseased pods were thin and small, which affected the yield and quality, and the commodity value and oil yield of diseased beans decreased.

1) symptoms: soybean black spot initially appeared grayish brown, long strip or oval spot on the base and lower branch of the stem, especially near the branch, the edge was red, and then the spot was sunken and reddish brown. In the later stage, the disease spot is enlarged and can fill the stem, on which there are black spots in the rows, that is, the parting apparatus of the bacteria, which is the obvious feature of the disease. The diseased plant withered early and the stem rotted easily. The disease spot on the pod was brown at the beginning, nearly round or irregular, and gradually connected into large spots. In the later stage, the disease spot is grayish white, the disease pod is dry, and there are small black spots scattered above. That is, the meristematic embracing apparatus of the pathogen. There are white hyphae in the diseased pods. All the diseased pods can be killed, and the damaged beans are atrophied and stiff, with white hyphae on them. Infected seeds generally cannot sprout, and even if they sprout, the seedlings are very weak.

2) pathogen: soybean black spot disease is caused by fungi. The meristematic embracing apparatus of the pathogen was originally born under the epidermis, and then broke through the epidermis to form small black spots visible to the naked eye, spherical or oblate in shape, with an orifice at the upper end and a dark brown wall. Pedicel bottle-shaped, colorless. There are two kinds of clasps, one is oval or long ovate, unicellular, colorless and transparent, and the other is slender hooked, slightly curved, colorless and transparent, unicellular.

3) Control methods: ① selected seeds, eliminated diseased seeds, and mixed seeds with 0.3% seed quantity of 50% Fumishuang wettable powder. ② rotates with Gramineae crops. Increase the application of phosphorus and potassium fertilizer to improve the disease resistance of the plant. After harvest, the disease and residue in the field were removed and the source of bacteria was reduced. When ③ was sprayed in the year of onset, 65% of mancozeb wettable powder or 50% benzoate wettable powder was sprayed again 10 days later.