A Detailed Guide to the Latest Control Methods for Corn Brown Spot

Corn brown spot is a corn disease that has occurred severely and spread rapidly in China in recent years, and in serious cases it can destroy the entire crop. It occurs in all corn-producing regions across the country, with the most severe damage in Hebei, Shandong, Henan, Anhui, Jiangsu and other provinces, mainly occurring on corn leaves, leaf sheaths and stalks. Now let us take a look at the control methods for corn brown spot!

Damage Symptoms

Corn brown spot occurs on corn leaves, leaf sheaths and stalks. It first appears at the tips of the upper leaves, with the most lesions at the junction of the leaf blade and leaf sheath, often densely arranged in rows. Initially they are yellow-brown or red-brown small spots; the lesions are round or oval to linear, and the leaf tissue near the raised areas often turns red. Small lesions often merge together, and in severe cases several sections or even the entire leaf is covered with lesions. Larger brown spots appear on the leaf sheaths and veins. In the later stage of the disease, the epidermis of the lesions ruptures, the leaf cell tissue becomes necrotic, and brown powder is released. The diseased leaf partly splits, with the veins and vascular bundles remaining like threads. On the stem, the disease mostly occurs near the nodes.

Occurrence Pattern

For corn brown spot, if temperatures are high, humidity is high and there are many rainy days in July and August, the disease is favored. On plots with poor soil, leaves turn yellow and the disease occurs severely; on plots with higher soil fertility, corn grows robustly, the leaves are dark green, and the disease is milder or does not occur at all. The disease generally occurs easily when corn has 8 to 10 leaves, and after corn has 12 leaves this disease generally no longer occurs. In addition, according to surveys, corn varieties whose parents contain the Tangsipingtou component are susceptible, such as Shendan 16, Shandan 911, Yuyu 26 and others.

Agricultural Control

1. After the corn harvest, thoroughly remove diseased plant residues and plow the soil deeply. Select disease-resistant varieties and implement crop rotation of more than 3 years. Plant at a suitably sparse density (3500 plants per mu for large-eared varieties, and no more than 5000 plants per mu even for density-tolerant varieties) to improve field ventilation and light penetration.

2. Apply sufficient base fertilizer and topdress in a timely manner. Generally, seedling fertilizer should be applied at the 4 to 5 leaf stage of corn, with 10 to 15 kg per mu of urea (or nitrogen, phosphorus and potassium compound fertilizer). If disease is found, topdressing should be carried out immediately, paying attention to the combination of nitrogen, phosphorus and potassium fertilizers. Apply compost fermented with Japanese enzyme bacteria or fully decomposed organic fertilizer, topdress in a timely manner, and carry out intertillage and weeding to promote robust plant growth and improve disease resistance.

Chemical Control

1. Early prevention: At the 4 to 5 leaf stage of corn, spray the leaves with 25% triadimefon 1000-fold solution or 25% tebuconazole 1500-fold solution per 667 square meters to prevent the occurrence of corn brown spot.

2. Timely control: When corn first shows the disease, immediately spray the stems and leaves with 25% triadimefon wettable powder 1500-fold solution or spray with fungicidal agents. To improve the control effect, an appropriate amount of foliar fertilizer can be added to the spray solution, such as potassium dihydrogen phosphate, diammonium phosphate aqueous solution (the urea mentioned in the original text contradicts the quick-acting nitrogen fertilizer topdressing described later), blue crystal multi-element microfertilizer, Zhuanghan liquid fertilizer, etc. Combined with topdressing of quick-acting fertilizers, this can control the spread of the disease, promote robust corn growth and improve corn's disease resistance. According to the rainy climate characteristics, fungicidal sprays should be applied 2 to 3 times at intervals of about 7 days; if it rains within 6 hours after spraying, re-spray after the rain.