Diseases and insect

Diseases and insect pests of lawn

The lawn must have the suitable condition, can carry on the normal growth development, the reproduction offspring. When the lawn is affected by unsuitable environmental conditions, or by other pests, it can not carry out normal growth and development, if the disease is serious, it will cause the death of lawn. On the one hand, lawn diseases are caused by unsuitable environmental conditions, known as non communicable diseases, also known as physiological diseases; on the other hand, they are caused by the infection of other harmful organisms, known as infectious diseases.

1. Rust

Rust damage the vast majority of lawn grass, occurring anywhere in the world, is a serious fungal disease. It mainly damages Kentucky bluegrass, perennial ryegrass, bermudagrass and tall fescue. Under suitable environmental conditions, it will happen within a few days, causing serious losses.

In the early stage of rust occurrence, light yellow spots appeared on the leaves and stems. With the development of the disease, the number of spots increased, and the epidermis of leaves and stems ruptured, and thick spores of yellow, orange, brown, chestnut brown or pink were emitted from the leaves and stems. At the later stage of disease development, rust colored and black winter spore piles appeared in the diseased part. The most typical symptom is to rub the diseased leaf with your hand, and there will be a layer of rusty powder on your hand. These are the summer spores and the winter spores of rust. Due to the damage of rust, the damaged lawn grows badly, the leaves and stems bend into abnormal colors, the growth of turfgrass is short, the photosynthesis is decreased, and even the lawn is dead.

In the diseased area, 150 times Bordeaux solution or 400-500 times carbendazim solution should be used in advance during the turning green period of grass. When the disease occurs, it can be used as dirust sodium and stone sulfur mixture, mancozeb, chlorpyrifos, Triadimefon, 25% Triadimefon 1000-2500 times, 12.5% teprazole 2000 times.

2. Powdery mildew

Powdery mildew (powdery mildew) is a common disease of grasses, which is distributed all over the world. Poa pratensis, Festuca arundinacea and bermudagrass were the most serious diseases in turfgrass. The varieties were susceptible to the disease, and the habitats were covered. The disease was especially serious when the light was insufficient, which led to the poor development and premature senescence of the lawn and the destruction of the landscape.

In the early stage of the disease, there is a layer of white powder on the surface of leaves, leaf sheaths and branches, which are conidia, conidiophores and mycelium of the pathogen. The pathogen grew rapidly and quickly expanded and covered the whole leaf surface. The mould layer became thick and gray and light brown. In the late stage of the disease, many yellow to brown spots, namely the closed capsule shell of powdery mildew, were produced. Generally, the damage of old leaves is more serious than that of young leaves. Because the plant surface is covered by powdery mildew, it leads to the decline of photosynthesis, respiratory disorder and asphyxia. Green spots appeared on the surface of the plants, and the plants grew poorly and withered. In serious cases, the plants withered and died, and the lawn became sparse, and finally a large lawn was destroyed.

The effective insecticides include 500 times of carbendazim 25% WP, 1000-1500 times of 70% thiophanate methyl WP, 1000-1500 times of 50% abamectin WP and 2000-3000 times of 25% Triadimefon WP.

3. Brown spot of lawn

Brown spot is an important and common fungal disease on turfgrass. On the cold season turf, when the lawn is low, the air humidity is high, and the weather is warm, the disease spots begin to appear on the lawn infected by Rhizoctonia solani, and the disease spots develop rapidly from the initial few centimeters to dozens of centimeters, and the black purple or gray brown edge of smoke ring appears around the disease spots. This ring is the mycelium of a fungus. In the cold season turf, the stubble is high. On the perennial ryegrass, Kentucky bluegrass or tall fescue, the main cause is light brown ring disease spot, rarely forming smoke ring, the diameter of the disease spot is 15 cm. In dry conditions, the lesion can be as large as 30 cm. The damaged lawn often shows the symptoms of depression, forming annular spot, also known as frog eye spot.

Bordeaux solution or 25% carbendazim WP 500 times, 70% thiophanate methyl WP 1000-1500 times, 50% abamectin WP 1000 times were used.

4. Anthrax

Colletotrichum gloeosporioides is a worldwide disease that occurs in most turfgrasses. It is a common leaf disease mainly caused by conidia of asexual generation of fungi. Especially, the damage to Poa pratensis and creeping scissor is very serious.

Under the cold and humid conditions, the pathogen mainly infected the root, root neck and stem base, especially the stem base. In the later stage, the black small wart spots grew on the spot, which were the conidial plates of pathogenic bacteria, and there were black brown setae in the plates. When the root neck and stem base were seriously affected, the whole plant or part of tillers grew poorly and turned yellow and died. The disease of leaf is premature aging. Oval and oblong reddish brown spots were found on the leaves, and the diseased leaves turned yellow, brown and even died. On the diseased lawn, there are withered spots of several centimeters to several meters in diameter, which are reddish brown at first, withered yellow later, and finally turned brown.

In terms of prevention and control, we should strengthen the management of lawn, remove the diseased body, balance the application of nitrogen, phosphorus and potassium fertilizer, avoid fertilizing in hot and dry weather, reduce the frequency of irrigation, and do not irrigate in the afternoon and evening, so as to reduce the environmental humidity. Planting immune or high resistance varieties of Poa pratensis, spraying fungicides when necessary.

5. Cercospora leaf spot

It occurs in grass lawns such as scissor glume, tall fescue, bermudagrass and blunt leaf grass. The leaves and sheaths were oval and irregular, brown to purplish brown, 4 mm × 1 mm in size. In the later stage, the inner part of the lesion was yellow to gray, with gray white mold layer. In severe cases, the diseased leaves died and the lawn was thin.

Control measures: rational use of fertilizer is conducive to the control of the disease. Improve the lawn environment, remove the trees and shrubs around the grassland to keep the grassland ventilated and have sufficient sunlight. At present, varieties resistant to Cercospora leaf spot have been bred, such as Blumea. The use of fungicides can effectively control the occurrence of leaf spot disease.

6. Red silk disease

It is an important disease of lawn, which damages scissor glume, ryegrass, Kentucky bluegrass and many other lawn grasses. There were round or irregular diseased spots on the diseased lawn, with the diameter ranging from 5 to 50 cm. The diseased grass was waterlogged and died quickly. It is one of the early recognition features that dead yellow leaves appear on grassland. On the leaves and leaf sheaths of the diseased plants, water stained spots gradually withered from the leaf tip to the leaf stem. Under saturated humidity, the diseased part is covered with pink, orange red to dark red hyphae, forming red filamentous filaments up to 10 mm long and cotton flocculent node conidia clusters up to 10 mm in diameter. At this time, the withered grass spot is reddish brown and easy to identify.

Control measures: to prevent and control the disease, we should balance fertilization and increase nitrogen fertilizer. The disease resistance of grass varieties is different, so we should avoid planting highly susceptible varieties. Spraying mancozeb, thiram or other fungicides on the diseased lawn when necessary.

7. Pythium

Almost most turfgrasses will be damaged by Pythium, especially the cold season turf. This is a devastating disease. Under suitable conditions, the disease can occur in one day and destroy the lawn.

The seeds were infected by Pythium in the process of germination and emergence. The apical part of young roots showed typical Brown wet rot. The leaves of light diseased seedlings turn yellow and slightly short, and then the symptoms may disappear.

Control method: improve the site conditions of lawn. The soil should be leveled before planting, and the soil with heavy clay or high sand content should be improved. Underground or ground drainage facilities should be set up to avoid ponding after rain and reduce groundwater level; lawn management should be strengthened. When the thickness of the dead grass layer is more than 2 cm, the grass should be removed in time, and the grass should not be cut when there is dew in the high temperature season, so as to avoid the spread of the pathogen. Balanced fertilization, avoiding excessive nitrogen topdressing, increasing phosphate and organic fertilizer; planting disease-resistant varieties. The results showed that the resistant varieties had strong physiological compensation effect, and the loss was reduced by enhancing the root development after the disease; the seeds were treated with chemicals to prevent rotten seeds and seedling collapse. In high temperature and high humidity season, spraying fungicides on lawn should be done in time. The effective Fungicides against Pythium, such as ethylphosphide, metalaxyl, chlorothalonil, metalaxyl manganese zinc, and alum, can control the disease.