The Latest Technical Guide to Tomato Powdery Mildew Prevention and Control

Tomato powdery mildew mainly damages leaves, and petioles, stems and fruits can sometimes also be affected. White mold spots first appear on the leaf surface, scattered, then gradually expand into white powdery patches and merge with each other into powdery mildew patches of varying sizes. In severe cases, the entire leaf surface is covered by white powder, as if a thin layer of flour had been sprinkled on it. Now let us take a look at tomato powdery mildew prevention and control techniques!

Symptoms of Tomato Powdery Mildew

Tomato powdery mildew commonly has two manifestations. The first is that small radial powdery patches first appear on the upper side of the leaf, namely the mycelium, conidiophores and conidia, which later expand into round powdery patches, and the white powdery material gradually becomes denser and larger, covering the whole leaf in severe cases. In the other symptom, the powdery patches on the upper side of the leaf are not obvious at first, but there are yellow patches with indistinct edges, and a sparse mold layer can be seen on close inspection. Later, the lesions expand and join together, the white mold layer gradually becomes obvious, and it covers the entire leaf, causing the whole leaf to turn brown and die in the later stage.

Occurrence Pattern of Tomato Powdery Mildew

In northern China, the pathogen mainly overwinters as asexual spores on winter-grown tomatoes. In addition, cleistothecia can also overwinter with diseased residues on the ground. When conditions are suitable, the ascospores released from the cleistothecia spread through the air, and later conidia are produced on the diseased parts. After the mature conidia detach, they cause secondary infection through air currents. In areas of southern China where tomatoes are grown year-round, the pathogen has no obvious overwintering phenomenon, and conidia are continuously produced, causing damage in successive cycles. The optimum temperature for conidial germination of Oidium lycopersici is 20-25°C, and for Leveillula taurica it is 15-30°C. In open fields it mostly occurs in June to July or September to October, while in greenhouses or plastic tunnels it is mostly seen in March to June or October to November.

Prevention and Control Techniques for Tomato Powdery Mildew

1. Select and breed powdery mildew-resistant varieties, and strengthen temperature and humidity management in greenhouses and tunnels. After harvest, promptly remove diseased residues to reduce overwintering sources of the pathogen. In the early stage of the disease, dust or smoke methods can be used in greenhouses and tunnels. In the evening, dust with 10% Duobai dust at 1 kg per mu each time, or apply 45% chlorothalonil smoke agent at 250 g per mu each time, ignite it with a smoldering flame and fumigate overnight.

2. In open fields or greenhouses and tunnels, the following can be used: 15% triadimefon (Fenxiuning) wettable powder at 500 times dilution, 40% Fuxing emulsifiable concentrate at 10000-8000 times dilution, 10% Shigao water-soluble granules at 1500 times dilution, 30% Tefulin wettable powder at 1500-2000 times dilution, 50% sulfur suspension concentrate at 200-300 times dilution, or 50% qinamine emulsifiable concentrate at 500-600 times dilution, 2% Wuyi mycin aqueous solution or 2% Nongkang 120 aqueous solution at 150 times dilution, 25% diliduo emulsifiable concentrate at 3000 times dilution, 15% triadimefon (Fenxiuning) wettable powder at 2000 times dilution plus 25% diliduo emulsifiable concentrate at 4000 times dilution, once every 7-15 d, for 2-3 consecutive applications.