Identification of cucumber leaf spot disease

Cucumber leaf spot disease, also known as brown spot and target spot disease, has become increasingly serious in many vegetable growing areas in recent years. Because the field symptoms are easily confused with cucumber downy mildew, bacterial angular spot, and anthrax, it is difficult to identify and control correctly.

Symptom recognition

The disease mainly damages the leaves, and it mostly occurs in the middle and late stages of the growth of cucumbers. It develops upward from the middle and lower leaves. The young leaves are light and spread to petiole and stem vines when serious. Field symptoms can be divided into three types:

Small spots: easy to appear at low temperatures and low humidity. The lesions are 0.1-0.5 cm in diameter and appear yellow-brown dots. After the lesions spread, the lesions on the front of the leaves are slightly sunken, the lesions are nearly round or slightly irregular, the lesions and junctions are distinct, brownish, the peripheral color is slightly darker, the central part is slightly lighter, and the yellowish color is slightly raised. Yellow white.

Large spots: easy to produce at high temperatures and high humidity. The lesions are round or irregular in shape, 2-5 cm in diameter, overall brown, grayish white in the center, translucent, rough lesions on the front of the leaves, vaguely ringy, and when the humidity is high, the front and back of the leaves can produce a lot of grayish black Hair floe.

Angular spot: more than a combination of small spots, large spots, and downy mildew. The lesions are yellow-white, polygonal, and diseased and healthy. The diameter is 0.5-1 cm.

The above three symptoms can continue to spread development, the late lesions in the foliage a large number of scattered or connected into a piece, resulting in leaf perforation, withered, shedding.

Differences between cucumber downy mildew, bacterial leaf spot and anthrax

(1) The symptoms of keratoconus are easily confused with cucumber downy mildew, and they are called “pseudo-fermented mildew” and “small downy mildew” by vegetable farmers. The difference is: the lesions on the front and back sides of the leaf are of the same size and can produce ash. Black mold layer, diseased and healthy junctions are obvious and the lesions are rough; the downy mildew leaves are chlorotic and yellow on the front, and the diseased and healthy junctions are not clear. The lesions are more integrated and the lesions are flat, limited by veins. It is a polygon with a gray moldy layer on the back of the leaves when the humidity is high.

(2) The symptoms of keratoconus are easily confused with bacterial keratoses. The keratoderma leaves are similar in color on both sides. When the humidity is high, there will be gray-black moulds. Bacterial keratoses have no mold layer on both sides, and the humidity on the back side. White pus is produced when large, and white marks are formed after drying.

(3) Large spots are easily confused with anthrax, with the difference being that pink stickies are produced on the lesions of anthrax.

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