This year, there has been frequent and heavy rainfall, coupled with high temperatures, creating ideal conditions for the outbreak and spread of maize large spot disease.

The CCTV meteorological station predicts that most of northern China will experience above-average rainfall in the coming week, benefiting soil moisture; however, localized heavy rainfall and strong convective weather may cause crop lodging and flooding; and waterlogging damage to farmland in northern and eastern Heilongjiang will worsen.

Currently, maize large spot disease has been reported in 41 counties and 156 monitoring points in Heilongjiang, with an average disease incidence rate of 10.7% in affected plots.

On August 3, Northeast Net reporters learned from the Heilongjiang Provincial Plant Protection Station that the overall occurrence of maize large spot disease in the province is expected to be moderate, with some counties experiencing severe outbreaks, and the central and western regions being the key affected areas. Currently, maize large spot disease has been reported in 41 counties and 156 monitoring points, with an average disease incidence rate of 10.7% in affected plots.

In areas such as Hulan, Zhaozhou, Shuangcheng, Lindian, Hailin, and Baiquan, the disease incidence rate in severely affected plots exceeds 20%, with individual plots in Baiquan and Hailin reaching 63% and 66% respectively. Lesions are mainly concentrated on the lower leaves of maize plants; other counties show sporadic occurrences.

Maize large spot disease is also known as stripe disease, coal streak disease, leaf blight, leaf spot disease, etc. It mainly harms the leaves, leaf sheaths, and bracts of maize. In recent years, with the promotion of no-tillage technology and large-scale agricultural machinery, the number of overwintering pathogens in the field has increased year by year, resulting in a gradual increase in the occurrence of maize large spot disease, which has become a major disease in maize production.

Diseased leaves initially show water-soaked grayish-green spots, which then expand along the veins to both ends, forming large spots with dark brown edges and light brown or grayish-green centers. In later stages, the spots often crack longitudinally. In severe cases, the spots merge, causing the leaves to turn yellow and die. A large amount of grayish-black mold layer appears on the spots when wet. Lower leaves are affected first. On single-gene resistant varieties, it manifests as chlorotic spots, which are smaller, parallel to the veins, yellowish-green or light brown in color, with a dark brown border. Some show necrotic spots.

Transmission Pathways

The pathogen overwinters as mycelium or conidia attached to diseased plant debris, serving as the primary inoculum for the following year's infection; seeds can also carry a small amount of the pathogen. In the field, it invades maize plants, and conidia are produced on lesions after 10-14 days, spreading through air currents for secondary infection. The prevalence of maize large spot disease is related not only to the susceptibility of maize varieties but also to environmental conditions.

Disease Development Conditions

Temperatures of 20-25℃ and relative humidity above 90% are conducive to disease development. Temperatures above 25℃ or below 15℃, and relative humidity below 60% for several days, will inhibit disease development. In spring maize areas, during the period from jointing to heading, suitable temperatures and continuous rainy days lead to rapid disease development and easy outbreaks. Nitrogen deficiency during maize tasseling and heading stages results in more severe disease. Low-lying areas, high planting density, and continuous cropping are prone to disease.

Control Methods

The control of maize large spot disease should focus on planting resistant varieties, strengthening agricultural control, and supplementing with necessary chemical control.

(1) Selection of resistant varieties: Select resistant varieties based on local dominant pathotypes, paying attention to preventing changes and spread of other pathotypes, and using varieties with different resistance levels and combined resistance.

(2) Strengthen agricultural control: Timely early sowing to avoid disease outbreaks. Apply sufficient base fertilizer and increase phosphorus and potassium fertilizer. Improve soil cultivation, weeding, and hilling, remove the bottom 2-3 leaves to reduce field relative humidity, make plants strong, and improve disease resistance. After maize harvest, clean the field, concentrate and process the straw, and use it as compost after high-temperature fermentation. Implement crop rotation.

(3) Chemical control: For high-value breeding materials and high-yield maize fields, 50% carbendazim wettable powder 500 times liquid, 50% methyl thiophanate wettable powder 600 times liquid, 75% chlorothalonil wettable powder 800 times liquid, 25% benomyl emulsion 800 times liquid, 40% validamycin emulsion 800-1000 times liquid, or agricultural streptomycin 120 water agent 200 times liquid can be sprayed from the late heart leaf stage to the pollen shedding stage or the initial stage of disease. Spray every 10 days for 2-3 consecutive times.

Generally, prevention and control should be carried out before the disease expands, that is, around the maize pollen shedding stage, when the disease incidence rate reaches 70% and the disease leaf rate reaches about 20%, spraying should begin. Effective agents include: 50% carbendazim wettable powder, 50% carbendazim wettable powder or 90% mancozeb, 80% methyl tobuzin, etc.