Comprehensive Control Methods for Damping-Off Disease in Spruce Seedlings Grown in Greenhouse Tunnels
In high-cold mountain areas, greenhouse tunnel seedling cultivation is usually adopted to shorten the cultivation period of spruce seedlings and enable earlier out-planting. The special environment of the greenhouse tunnel creates conditions for the breeding and spread of various pathogenic bacteria and organisms that cause damping-off in newly sown spruce seedlings, and improper control can lead to failure of seedling cultivation. To control damping-off in newly sown spruce seedlings in greenhouse tunnels, the policy of "prevention first, comprehensive control" must be adhered to.
1 Damping-off symptoms
The symptoms of damping-off mainly manifest in 4 types: (1) After sowing but before emergence, seeds and ungerminated sprouts rot and die in the soil, and spiderweb-like mycelium is often present around the seeds; (2) Within 30d of seedling emergence, the stem base near the ground surface becomes water-soaked, rots and constricts, and seedlings collapse and die in patches; (3) The tender leaves and stems of seedlings rot, sometimes producing white filamentous material, and the stems and leaves wilt and rot; (4) After the stem base of seedlings becomes lignified, the roots rot and the seedlings die standing upright.
2 Damping-off pathogens
Damping-off is a major enemy of newly sown spruce seedlings. The causes of damping-off in greenhouse spruce can be divided into one category of infectious pathogens including fungi (mainly Rhizoctonia, Fusarium, Pythium), bacteria, mycoplasma-like organisms, and viruses; and another category caused by nutritional conditions, temperature, humidity, toxic substances, light, gases and other factors unsuitable for the growth of spruce seedlings.
3 Control techniques
3.1 Seed treatment
When purchasing seeds, strict control should be exercised over the place of origin and source of spruce seeds, and seeds that have not undergone quarantine inspection and have no origin marking should not be used. It is best to use plump, high-quality seeds collected in the current year or the previous autumn. Seeds are disinfected with dexon, potassium permanganate, etc., then subjected to snow storage or warm water soaking for germination, and the soil should be kept moist before emergence.
3.2 Soil treatment
The soil of greenhouse seedbeds must not be sticky-heavy soil or soil previously used for crops. Where conditions permit, it is best to improve the nursery soil with loose and fertile forest humus soil to a thickness of 20-30cm, then disinfect the soil with 2g dexon + 3g quintozene per sq m; alternatively, 20g ferrous sulfate powder can be spread per sq m, and 50kg potassium phosphate fertilizer can be applied per 667 sq m at a 3:1 ratio, and plant ash can also be added, which can promote seedling growth and improve the lodging resistance of seedlings.
3.3 Sowing period
In high-cold mountain areas with greenhouse seedling cultivation, sowing can be carried out in all four seasons. In middle and low altitude areas, practice has proved that sowing from early February to mid-March in spring, and from early September to early October in autumn, gives newly sown spruce seedlings the strongest lodging resistance.
3.4 Management methods during the seedling stage
(1) Through many years of production practice, newly sown seedlings in areas treated with chemical herbicides have stronger lodging resistance than seedlings in manually weeded areas. The specific method is: after sowing and covering with soil, compact the bed surface, then use prometryn at an effective rate of 60g/667 sq m, diluted in 40kg water, and spray evenly on the bed surface with a sprayer; the weeding effect is over 90%. After emergence, the seedlings grow more robustly than those in untreated areas, and lodging resistance is greatly enhanced.
(2) After sowing, cover with yellow subsoil, with a thickness of 2cm being appropriate; after emergence, spray the seedlings evenly with 0.5%-1% Bordeaux mixture 2-3 times every 10d, using 60kg of solution per 667 sq m each time.
(3) When lodging is observed in seedlings, immediately pull out the affected seedlings, sprinkle a 0.1%-0.2% dexon solution, and at the same time spread plant ash between the seedling rows, which can effectively control damping-off in seedlings. Within 1-2 months of emergence, high temperature and high humidity; low temperature and high humidity; and dry, hot air inside the greenhouse are the main triggers of seedling lodging. Therefore, artificially controlling environmental factors such as light, heat, water, and air inside the greenhouse and strengthening ventilation can prevent and control seedling lodging.
The key to controlling damping-off in newly sown spruce seedlings in greenhouses lies in raising the technical level of seedling cultivation, managing the greenhouse scientifically, strictly controlling each link, and always adhering to the guiding ideology of "prevention first, comprehensive control," so that damping-off in newly sown spruce seedlings can be effectively controlled. (Xie Yun, Zhao Bo, Xia Jinchun)