Identification of Clover Powdery Mildew Symptoms and Introduction to Control Methods

Clover is actually quite common in our daily lives, and it has high ornamental value. In China it is generally used for lawn construction in landscaping. Clover has strong vitality and very low soil requirements, so it is one of the more easily surviving plants.

What Is Clover

Clover, also known as trefoil, is a perennial herbaceous plant. There are mainly 2 types, namely white clover and red clover. Clover is a high-quality leguminous forage, with soft stems and leaves, abundant leaf mass, high crude protein content, and low crude fiber content. It can be used both for grazing livestock and for feeding herbivorous fish. Among them, white clover (Triofliumrepens), because of its low plant height and strong adaptability, can serve as an excellent plant for establishing lawns in urban landscaping.

Growth Habits of Clover

Growth stops but it remains green. Therefore, the green period is very long. It is not strict about soil requirements and can adapt to various soil types, growing well on slightly acidic soil. It prefers warm, sunny environmental conditions with good drainage. Under drought conditions growth is slow, and in high-temperature seasons some plants die back. It tolerates pruning and trampling, and has strong regeneration ability; within 10d after pruning, new small leaves can grow. After high-intensity trampling or rolling, it can recover in 3 to 5d. Under strong shading it is prone to leggy growth, resulting in poor growth. It has strong resistance to harmful gas pollution and strong resistance to pests and diseases.

Clover has strong cold resistance. When the temperature drops to 0°C, some old leaves turn yellow, and the small leaves on the main root cling close to the ground, stopping growth, but they still remain green. Within 10 days after pruning, new small leaves can grow. After high-intensity trampling or rolling, it can recover in 3 to 5 days. It has strong resistance to harmful gas pollution and strong resistance to pests and diseases. The type that bears red flowers opens during the day, with five petals, and at night the flowers close into a bundle; through comparison it was found that after blooming at the turn of spring and summer, the stems and leaves begin to turn yellow and then wither. It is commonly cultivated in China, and in moist grasslands, riverbanks, and roadsides it appears in a semi-wild state.

Introduction to and Control of Clover Powdery Mildew

Powdery mildew is a common disease on clover. It occurs commonly in various planting areas across the country, seriously affecting hay yield and quality. 1. Symptoms of clover powdery mildew:

In the initial stage, white powdery spots composed of the pathogen's hyphae and conidia reappear locally on both sides of the leaves, then rapidly cover most or all of the leaf. When the disease is epidemic, the entire grassland looks as if it has been sprayed with white powder. In severe cases, the leaves may turn yellow or wither and drop, and the seeds are unfilled or shrunken and inferior. In the later stage, many dark brown small black dots are produced on the white diseased spots, namely the pathogen's cleistothecia. 2. Pathogen of clover powdery mildew:

ErysiphepisiDC., called pea powdery mildew, belongs to the Ascomycota fungi, synonym Polygonum powdery mildew (E.polygoinDC.). The conidiophores grow from external hyphae, erect, colorless, with conidia borne in chains at the apex; conidia barrel-shaped, or cylindrical with bluntly rounded ends, single-celled, colorless, size about (22.9)25.4-38.1(43.2)μm×(11.4)12.7-17.8(18.3)μm; cleistothecia flattened spherical, dark brown, diameter about (72)92μm-120(130)μm, occasionally reaching 150μm; appendages numerous, hypha-like, length about (0.5)1-3(5) times the diameter of the cleistothecium, brown at the base, gradually lighter toward the apex until colorless; asci multiple, oval, elliptical, a few nearly spherical, with short stalks to nearly sessile, (43.2)55.9-76.2(86.4)μm×(30.5)35.6-43.2(48.3)μm; internally bearing (2)3-5(6) ascospores; ascospores single-celled, pale yellow, oval or elliptical, (17.8)20.3-25.4(27.9)μm×(11.4)12.7-15.2(16.4)μm. Among leguminous plants its parasitic range is relatively broad, but it adapts to different hosts and differentiates into many physiological races. As far as the three clover genera are concerned, it occurs relatively commonly on red clover, and is occasionally also seen on white clover, crimson clover, alsike clover, and others.

3. Disease characteristics of clover powdery mildew:

The pathogen mainly overwinters in the host body as dormant hyphae. In most clover planting areas, the conidial stage (Oidiumsp.) is the main disease-causing agent. For example, in Guizhou, China, red clover does not produce the sexual stage cleistothecia, and in Xinjiang wild white clover also rarely forms cleistothecia. Conidia are spread by wind, and multiple reinfections can occur during the growing season, causing disease epidemics. Moist conditions combined with hot days, cool nights, and windy conditions are favorable for the epidemic of this disease. Rainy or overly humid conditions are unfavorable for the occurrence of the disease. Excessive application of nitrogen fertilizer or phosphorus fertilizer aggravates the occurrence of the disease. Increasing potassium fertilizer can inhibit the growth of hyphae and reduce the severity of the disease.

Control Methods for Clover Powdery Mildew

1. Select and plant disease-resistant varieties according to local conditions.

2. Strengthen field management. Sow at the appropriate time and plant at a reasonable density; fertilize scientifically, increase phosphorus and potassium fertilizer, and improve plant disease resistance; irrigate at the appropriate time and pay attention to drainage after rain; use the grassland reasonably, cut at the appropriate time, and graze moderately to prevent the spread of the disease.

3. Chemical control. In research plots or seed propagation plots, fungicides such as carbendazim, thiophanate-methyl, and triadimefon can be used for control. Mixing the above fungicides with disease-prevention high-lipid film agents can significantly improve the control effect. Commonly used fungicides: carbendazim, thiophanate-methyl, triadimefon

Although clover is relatively easy to keep alive and does not have very high requirements for its living environment and soil, and its vitality is relatively tenacious, it can still sometimes get sick. Timely prevention of clover diseases is the most critical factor in growing clover. Even though it is easy to grow, you must not become careless.