Anthracnose of Impatiens

Shanghai, Hangzhou.

[symptoms] both branches and leaves can occur, mainly on branches and leaves. At the initial stage of the disease, withered yellow or brown spots appeared on the leaf surface, and then gradually developed into round to nearly round, light brown to brown, with dark edges, not obvious wheel lines, and small black spots scattered on the disease spots; with the development of the disease, the adjacent disease spots are connected to form irregular large disease spots, which make the leaves shrink and wither, resulting in shedding.

In wet weather, pink gel gushes from small black spots, which can occur from June to September, and sometimes cause blackening and decay on branches.

[pathogen]

The pathogens are fungi, Gloeosporiumimpatientis, Vermiculariasp.; conidia, the former is oval, long oval, primary color, containing 1 to 2 oil globules; the latter is crescent, single cell, large, generally light grayish brown; antennae serrated, each node has tufts, gray to brown; forewings gray to brown; forewings gray-brown, outer margin line composed of semilunar dots, middle chamber markings white, surrounded by dark brown circles.

[occurrence regularity] 4-5 generations a year, and overwintering with mature larvae pupating in the soil. In early summer of the following year, the infection was spread by wind and rain. The overwintering adults appeared in April of the next spring, which lurked in dark places or between branches and leaves during the day, came out and laid eggs at night, laid eggs scattered in the stems and leaves of the plant, and the first instar larvae spun silk and drifted with the wind, but the larvae were not very active, but had mimicry, and often perched on the stem of the plant, similar to tender branches, but not easy to find. Complete one generation in 40 days in summer. The egg stage is 5 days, the larval stage is 18 ~ 21 days, and the pupal stage is 9 ~ 10 days. The adults pupated 3 days after emergence. In general, the disease is serious in the leaves of the lower part of the plant. The disease is the most serious in the hot and rainy season.

[prevention and control methods]

(1) artificial prevention and control: to find the victim, that is, to search and kill carefully, not to be confused by its mimicry.

(2) Horticultural control: combined with soil preparation, overwintering pupae are eliminated. Strengthen the management of fertilizer and water and enhance the disease resistance of plants. At the initial stage of the disease, the diseased leaves and plants should be removed in time. Diseased leaves and diseased plants were destroyed at the end of autumn, and potted impatiens were not allowed to use old soil to reduce the source of infection.

(3) Pesticide control: at the initial stage of the disease, 50% Dysenamine 500 Mel 600 times solution, or 50% anthrax Fumei magnesium wettable powder 500 times solution, 75% chlorothalonil wettable powder 600 times solution alternately sprayed. During the larval damage period, 50% phoxim EC 1000 times or 20% fenvalerate EC 1500 Mel 2000 times can be sprayed.