Causes, Symptoms and Control Methods of Garlic Leaf Blight

Garlic leaf blight is a common disease in the garlic cultivation process, especially in open-field cultivation, and is simply a nightmare for growers. This is because garlic leaf blight not only causes the quality of garlic to deteriorate, but also reduces yield. Let's take a look below at the causes, symptoms and control methods of garlic leaf blight.

I. Causes of garlic leaf blight

Garlic leaf blight is caused by infection by the fungus Pleospora herbarum (Pers.ex Fr.) Rabenk, an ascomycete of the subphylum Ascomycota. The pathogen mainly overwinters in the soil as mycelium or perithecia with diseased residues. The following year, ascospores are produced to cause primary infection, after which conidia produced on diseased parts are spread by airflow and raindrop splash to cause secondary infection. After autumn-sown garlic emerges, conidia produced on the diseased residues are spread by airflow and raindrop splash, land on garlic leaves, and cause infection and disease.

The pathogen has strong adaptability to temperature, but requires relatively high humidity. Rainfall and high humidity in the field are necessary conditions for the disease to become epidemic. The susceptible growth period of garlic is the mature plant stage.

Generally, the disease is severe in fields that are low-lying, poorly drained, overly supplied with nitrogen fertilizer, mixed-cropped with onion and garlic vegetables, where plants are injured, where plants grow weakly, and where continuous cropping is practiced. In years with frequent fog and rain, the disease is severe.

II. Symptoms of garlic leaf blight

Garlic leaf blight mainly damages leaves, leaf sheaths and bolt stems, with leaf damage being predominant. After leaves are infected, 4 types of disease symptoms appear: tip blight type, stripe spot type, purple spot type and white spot type. When the disease is severe, lesions on the leaves can extend through the leaf node to the leaf sheath, causing the leaf sheath to wither and turn yellow. When the field is humid, a brown to black mold layer forms on the surface of the lesions. In the tip blight type, the lower leaves first show white round spots, which gradually expand, after which the leaf tip becomes dark brown and necrotic, with faint purplish-brown diagonal streaks on both sides. The stripe spot type mainly occurs on the middle and lower leaves. When leaves are infected, brown stripes running the entire length of the leaf are produced, developing along the midrib or located on one side of the leaf. The stripe spot type can be seen throughout the entire growth period and is the main lesion type in the field. When leaves are damaged, the lesions are elliptical or irregular, with a darker dark brown center, light brown edges, and withered yellow necrotic lines at both ends; after expansion and spread, they can cause the leaves to wither and turn yellow. In the white type, during the bolting stage, dense round and oval white small lesions with distinct edges appear on the upper leaves. Some white spots later develop into purple spots.

III. Control methods for garlic leaf blight

1. Clean the field. After garlic harvest, promptly remove diseased residues from the field to reduce the number of pathogens overwintering.

2. Practice crop rotation. Garlic fields should as far as possible not be continuously cropped or mixed-cropped with onion crops; rotation with wheat, corn, beans or cucurbit vegetables is recommended.

3. Strengthen field management. Prepare the land finely, plant at a reasonable density, apply sufficient base fertilizer, increase phosphorus and potassium fertilizer, avoid flood irrigation, and drain promptly after rain.

4. Chemical seed dressing. Before sowing garlic, dress the seed with 50% carbendazim wettable powder at 0.3% of the weight of the garlic seed bulbs.

Chemical control. In the early stage of disease in the field, you may choose 80% mancozeb wettable powder at 600 times dilution, 75% chlorothalonil wettable powder at 500 times dilution, 25% azoxystrobin suspension concentrate at 1000 times dilution, 10% difenoconazole water-dispersible granules at 1500 times dilution, 2.5% fludioxonil suspension concentrate at 1200 times dilution, 64% oxadixyl · mancozeb wettable powder at 600 times dilution, 50% procymidone wettable powder at 1000 times dilution, 50% prochloraz wettable powder at 1000 times dilution, 50% carbendazim wettable powder at 1 000 times dilution, etc. Every 7 to 10