Ligustrum lucidum brown spot fallen leaf disease

A few years ago, Ligustrum austrophylla was widely planted because of its advantages of easy reproduction, drought resistance, few pests, pruning resistance, long golden leaf period and good effect of large color blocks, especially for modeling patterned flower bands and large color blocks. However, due to high planting density and inadequate conservation and management, brown spot and deciduous disease will occur in rainy season every year (August to September in Luoyang area), resulting in leaves falling one after another, new leaves and buds can not be taken out in time, and even plants die in pieces, seriously damaging the landscape effect. In view of this situation, we observed and recorded the growth and incidence of Ligustrum lucidum in 2003, and invited experts to identify pathogenic bacteria and take comprehensive measures to prevent it. In the peak period of rainy season, the harm of this disease was effectively reduced.

symptoms

At the early stage of leaf disease, small round spots of water stain and chlorosis appeared, then turned purple or brown, gradually expanded into round, oval, semicircular or irregular spots, the size of 5~10 mm ×3~5 mm. At the later stage, the center of the spot on the front of the leaf was light brown or grayish white, slightly convex, the edge was brown, the color was darker than the center, obvious ring patterns appeared on the spot, and irregular light brown rot appeared around the spot. The center of the spot on the back of the leaf was sunken, and the color was lighter than that on the front. In wet weather conditions, there are many small black mold spots scattered on the back of the leaves, and there are a few black mold spots on the front of the disease spots when it is serious. The disease first occurs in old leaves, leaf tips, leaf margins and leaf bases, and then gradually develops to the middle. In severe cases, the disease spots are connected together, reaching 1/2~2/3 of the whole leaves. At this time, only touch the plants gently, and the leaves will fall one after another.

pathogenic

After identification, the pathogen of the disease was Alternaria, belonging to the subphylum Semiphylum, Hyphomycetes, Fungiales. Alternaria.

occurrence regularity

The pathogen overwinters in the form of mycelia and conidia on fallen leaves and branches, the conidia are transmitted by air flow and rain, invaded by wounds and stomata, the incubation period is 10~20 days, the optimum temperature for pathogen growth is 25℃, and the optimum temperature for conidia germination is 20℃~29℃.

Partial application of nitrogen fertilizer, lack of phosphorus and potassium fertilizer, soil hardening, poor drainage, over-dense planting, poor ventilation, insufficient fertilizer and water in summer, poor growth of trees, and excessive rainfall in autumn will aggravate the occurrence of this disease.

integrated control

1. Good planting: planting land should be selected slightly higher in the middle and lower around the terrain to prevent water accumulation; planting density should be 36 to 49 plants per square meter. Not too dense. As seedlings grow, should be timely thinning, pruning, picking leaves.

2. Reduce infection sources: remove diseased leaves and dead plants in autumn; spray 5 - 7 degree sulfur mixture before germination in spring to kill overwintering bacteria sources; combine pruning, comb out diseased branches, diseased leaves and dense seedlings and random long branches affecting ventilation and light transmission.

3. Strengthen maintenance and management: apply proper amount of compound fertilizer in spring, topdressing potassium dihydrogen phosphate, potassium sulfate and other phosphorus and potassium fertilizers in early summer, insist on sufficient irrigation in summer, irrigate thoroughly, avoid sprinkling irrigation from the top of plants; pay attention to drainage in rainy season in autumn.

4. Chemical control: spraying once every 10 days from mid-May, twice in succession; once every 7 days from mid-June to mid-August; once every 10 days from early September to late September, twice in succession.

Through experiments, we screened out several drugs with remarkable control effect: before the disease onset, spray systemic fungicides such as carbendazim 300 - 500 times, thiophanate-methyl, nikacin, methylphenamine 700 - 1000 times; Protective fungicides such as 1% lime equivalent Bordeaux mixture, 50% mancozeb WP300~500 times, 50% dihydantoin WP 700 ~1000 times, chlorothalonil 500~700 times should be used in order to avoid drug resistance of pathogenic bacteria. Protective agents and systemic agents should be used alternately.

5. Biological agents control: such as Trick, X8, although the current application range is not too wide, but has shown obvious advantages, practice has proved that the effect is better.