How to prevent and control northern leaf blight in Sudan grass? These methods are worth mastering

Sudan grass, also known as wild sorghum, is an annual herbaceous plant that can adapt to the same environment as sorghum, only maturing earlier. It has fibrous roots and a well-developed root system, with roots penetrating more than 2 m deep, distributed on average across 75 cm, and about 60-70% of the root system distributed in the plough layer. Sudan grass has good regrowth capacity, which is an important reason for its multi-cut nature and high yield. After cutting, regrowth shoots can arise from three sites: the tillering nodes, the first stem node at the base, and shoots whose growing points have not been damaged, but more than 80 percent of the regrowth shoots are formed from the tillering nodes, with the rest formed at the first stem node at the base of the stem. The cutting height of Sudan grass is directly related to its regrowth capacity; generally a stubble height of 7 to 10 cm is appropriate, and too low a stubble affects regrowth.

Sudan grass is not demanding about soil; as long as drainage is unobstructed, it can be grown on sandy loam, heavy clay, slightly acidic and mildly saline soils (soluble sodium chloride at 0.2 to 0.3 percent), and it grows best on fertile black calcareous soil and dark chestnut soil. It grows poorly on overly wet, poorly drained, or overly acidic or overly alkaline soils. It can also be planted on sandy soil, but yields are low.

Geographical distribution of Sudan grass

Sudan grass originated on the Sudan Plateau in Africa. It is widely cultivated in Europe, North America and the Asian continent. It was already introduced into China before liberation, and now there is fairly large-scale cultivation in all provinces north and south. After many years of cultivation trials and small-area promotional planting, it has been proved that suitable growing areas are: Sudan grass has broad adaptability and can be cultivated from Hainan Island in the south to Inner Mongolia in the north of our country.

How to prevent and control northern leaf blight in Sudan grass?

Northern leaf blight is an important disease of Sudan grass, widely distributed at home and abroad, and it also infects corn and plants of the genus Sorghum, causing serious damage. Symptoms of northern leaf blight in Sudan grass:

It mainly damages leaves. Leaf lesions are long fusiform, sized 20-60mm×4-10mm, with water-soaked margins, yellowish to brown centers, and later purple margins. Black mold-like material, namely the pathogen's conidiophores and conidia, can be seen on both the front and back of the leaf spots, and in severe cases the whole leaf dies. Lesions can also occur on leaf sheaths and bracts. Pathogen of northern leaf blight in Sudan grass:

Bipolaris turcicum (Pass.) Shoemaker, called Exserohilum turcicum, synonym Helminthosporium turcicum Pass., belongs to the Deuteromycotina fungi. It does not produce a sexual generation in nature. Conidiophores emerge from the stomata, in clusters of 2-6, olive-brown, with 2-6 septa, sized 12.5-188.7μm×7.5-10.0μm, swollen at the base, with obvious spore scars, borne at the apex or at geniculate bends. Conidia are fusiform, olive-brown, straight or slightly curved, with a distinct protruding hilum on the basal cell, with 2-8 septa, mostly 4-7, sized 45-140.6μm×15-25μm; spores germinate from the cells at both ends to produce germ tubes. Occurrence characteristics of northern leaf blight in Sudan grass:

The pathogen overwinters as dormant mycelium and conidia on diseased plant residues, becoming the source of field infection in the following spring. Spores are spread by wind and rain and invade through the epidermis or stomata. The optimum temperature for mycelial growth is 27-30℃, with a temperature range of 5-35℃. The temperature for spore formation is 11-30℃, with an optimum of 23-27℃. The optimum temperature for field epidemics is about 25℃. After spores invade, they can produce spores on lesions in 10-14 days. Spore germination requires rainy and foggy weather, with relative humidity of at least 60%-70% or more, and a liquid water film on the leaf surface. New leaves are more disease-resistant than old leaves, and seedlings or young plants are less affected than adult plants after heading. Control methods for northern leaf blight in Sudan grass:

1) Select and plant disease-resistant varieties according to local conditions.

2) Strengthen grassland management.

Sow early at the appropriate time, avoiding high-temperature and rainy periods as much as possible; plant at a reasonable density to prevent lodging from overcrowding; manage fertilizer and water scientifically to improve plant disease resistance; graze moderately, harvest in time, and thoroughly remove field residues after harvesting.

3) Chemical control.

For research plots and seed fields, fungicides such as carbendazim, chlorothalonil, thiram, thiophanate-methyl, or zineb and thiram can be used for protection.

Commonly used agents: carbendazim, chlorothalonil, thiram, thiophanate-methyl, zineb, thiram.