How to prevent and control soybean phytophthora root rot? Detailed explanation of occurrence patterns and control methods

After soybean phytophthora root rot was introduced into our prefecture with the transfer of soybean seeds in July 2005, our station immediately established a soybean phytophthora root rot monitoring leading group and dispatched professional and technical personnel to carry out field monitoring work in Gongliu County.

1. Disease investigation

In 2005, the affected area was 2239 hectares, and in 2006 the affected area was 2858 hectares.

1. Disease situation in Xinyuan County

The soybean planting area was 0.67 million hectares, the investigated area was 0.3 million hectares, and the affected area was 0.23 million hectares, of which the sporadic occurrence area was 0.21 million hectares, and the area with a diseased plant rate of 1% was 267 hectares. The distribution areas of soybean phytophthora root rot were mainly in Halabula Township, Xiaorbulak Town, Taleide Town, Xinyuan Town, and Biesituobie Township; the main susceptible varieties were Kesuo and Shidadou No. 2.

2. Disease situation in Gongliu County

The spring-sown soybean planting area was 0.43 million hectares, and the replanted area was 0.58 million hectares. The main spring-sown cultivars were Xindadou No. 1, Shidadou No. 2, Xiangwen-88, Wangzhongwang, Hefeng 47, and Yidadou No. 1, mainly distributed in 10 townships and farms in Gongliu County, including Agaersen Township, Dongmaili Township, Tasitobie Township, Tikeareke Township, Aketubieke Township, the town area, Cattle Farm, Sheep Farm, Comprehensive Farm, and Liangfan Farm.

According to a preliminary investigation, the affected area of spring-sown soybean phytophthora root rot reached 325 hectares. It mainly occurred in several townships (farms), including Cattle Farm, Sheep Farm, Agaersen Township, Tasitobie Township, and Tikeareke Township. No occurrence has been found so far in replanted soybeans. Among the susceptible varieties, the varieties introduced from Northeast China were severely affected, including Xiangwen-88 and Hefeng 47; the varieties with milder occurrence included Xindadou No. 1, Wangzhongwang, Yidadou No. 1, and Shidadou No. 2. Because Heinong 39 was severely affected in 2005, it was not planted in 2006.

3. Disease situation in Regiment 71

The soybean planting area was 667 hectares, and the affected area was 200 hectares. Heinong 39 was the main cultivar of the regiment, with an area of 200 hectares. The original seeds were transferred from the Shihezi Academy of Agricultural Sciences, and the disease incidence rate in 2006 was 1%-5%.

2. Disease symptoms

In our prefecture, the symptomatic period of soybean phytophthora root rot is mainly at the flowering stage, causing root rot, stem rot, plant dwarfing, wilting, and death. The main root of diseased seedlings turns dark brown, and the lateral roots are almost completely rotted. Water-soaked lesions appear on the diseased stem from the soil surface to the first branch, after which the stem rots and the plant lodges. Leaves of susceptible varieties turn yellow, wilt, and die. When affected at the adult plant stage, the main and lateral roots rot, and dark brown ulcer-like lesions appear at the stem base. The affected site expands upward, and in some cases appears intermittently on the stem, with affected nodes reaching as high as the 4th to 8th nodes. The pith of the diseased stem turns black, and the cortex and vascular bundle tissues become necrotic. The base of the petiole near the lesion turns black and sunken, and the leaves droop and wilt, forming a splayed shape, but the leaves do not fall off. The leaves of affected plants turn yellow from the bottom upward, and then the entire plant wilts and dies. Plants infected later can set seed, but the base of the pod is water-soaked, and the diseased area gradually expands toward the tip, causing the entire pod to turn brown and dry up. When moist, black mold appears on the pod skin. Seeds in diseased pods are also infected; the seed surface is light brown, brown, to dark brown, lusterless, shrunken and shriveled, and the seeds become smaller.

3. Conditions for disease occurrence

The key factor affecting disease occurrence is soil temperature. Soybean phytophthora root rot is spread by the pathogen, with soil or diseased residues being the main source of the pathogen, and the pathogen spreads through rainfall and irrigation water. Therefore, sufficient moisture is a necessary condition for infection and epidemic development of the disease.

4. Affected plots

The disease mainly occurs in night-tide land with a relatively high groundwater table, waterlogged land, and low-lying land. In plots with a relatively high groundwater table, the severely affected plants were all at waterlogged spots and water outlets.

5. Prevention and control measures

1. For plots where the disease has occurred, organize labor to pull out and destroy diseased plants.

2. Practice crop rotation. Soybeans are strictly prohibited from being planted again in plots where soybean phytophthora root rot has occurred, and seed production units are required to be strictly prohibited from privately transferring seeds from other provinces.

3. Temporarily define epidemic areas, and prohibit soybean seeds from epidemic areas from being @#@136@#@ to non-epidemic areas.

4. For seed fields where soybean phytophthora root rot has occurred, under no circumstances may the seed be used for planting, and no origin quarantine certificate may be issued.

5. At the early stage of disease occurrence, use 58% metalaxyl-mancozeb wettable powder at 100 grams/667 sq m mixed with water for spray control. The plants in the disease center were affected by the fungicide and soil temperature, and the disease severity was somewhat reduced.