Causes and Control Methods of Fungal Leaf Spot Disease in Corn

Corn northern leaf blight, southern leaf blight, and gray leaf spot are the main diseases in corn production (collectively called leaf spot disease), often occurring together as a mixed infection, with a moderate level of incidence. At present, large areas of corn in some regions have entered the vigorous growth stage, and with excessive rainfall this year, it is expected that in August there will be widespread epidemic occurrence and damage with a trend toward severe incidence. Therefore, active efforts should be made to carry out control of corn leaf spot disease to ensure a bumper corn harvest.

Causes

1. Cold and humid conditions easily trigger the disease.

2. The base level of pathogen inoculum is large, various corn varieties have different levels of resistance, and susceptible varieties are widely planted.

3. Most farmers in mountainous areas have a low level of management, and combined with the frequent rainy weather from July to August, the favorable climatic factors very easily cause recurrent infection of corn leaf spot disease.

4. August is precisely the tasseling stage for most corn, and also the peak period for corn leaf disease occurrence; all the above factors favor the occurrence of corn diseases.

Control Methods

1. Agricultural control: promptly remove diseased leaves from the lower part of diseased plants, strengthen mid-to-late stage management of corn fields, carry out cultivation and weeding, pay attention to drainage in low-lying areas, improve the microclimate environment of corn fields, and enhance plant disease resistance.

2. Timely fertilization: from the jointing stage to the tasseling stage, appropriately apply 10--20 kg of chemical fertilizer as a top dressing to improve variety resistance, so as to control and reduce the damage of northern and southern corn leaf blight.

3. Chemical control: prevention of corn leaf spot disease should be carried out early, with key prevention for susceptible varieties and fields with a history of the disease. Generally, in corn fields, once scattered diseased plants are found, chemical control should be carried out to control the disease center and reduce spread and epidemic. The main control agents include: timely chemical control at the early stage of disease onset, and the following agents can be used in rotation: 100 g of 25% triadimefon per mu, 50% carbendazim wettable powder at 500-600 times dilution, 75% chlorothalonil wettable powder at 600-800 times dilution, 65% zineb wettable powder at 400-500 times dilution, as well as thiophanate-methyl (Topsin-M), propiconazole, difenoconazole (Score), and other agents, diluted with water and sprayed. Spray once every 7-10 days, for 2-3 consecutive treatments. Choose sunny days for application; after application, it must not rain for more than 5 hours for the treatment to be effective.

4. Increase phosphorus and potassium fertilizer: for corn plots showing phosphorus deficiency symptoms, spray potassium dihydrogen phosphate to supplement trace elements and improve corn resistance; for severely affected fields, after the disease is brought under control, potassium dihydrogen phosphate or other foliar fertilizers can also be sprayed to help corn recover growth as quickly as possible and ensure a good harvest.

5. Promptly collect diseased plant residues and burn them.