How to prevent and control root rot and stem rot in ginkgo seedlings

Ginkgo seedling cultivation is the foundation of developing the ginkgo planting industry,  and whether it succeeds depends on the effectiveness of root rot and stem rot prevention and control. These two major diseases of ginkgo seedlings not only have a high infection rate,  but are also difficult to control once infected,  often causing large numbers of seedling deaths and even total loss. The pathogens of ginkgo seedling root rot and stem rot fall into 2 categories: infectious pathogens and non-infectious pathogens. Infectious pathogens refer to diseases caused by pathogenic fungi,  while non-infectious pathogens refer to diseases caused by certain abiotic factors,  mainly excessive or insufficient soil moisture, weed damage, chemical damage, and so on.

The prevention and control of these two types of disease generally uses seedling cultivation technical measures and chemical control technical strategies. Among these, prevention and control through seedling cultivation technical measures addresses the root cause,  because it can prevent the occurrence of both infectious and non-infectious root rot and stem rot. For example, if drainage and irrigation are unobstructed and the nursery site and seedbed do not accumulate water, non-infectious root rot can basically be prevented from occurring,  and shading can reduce infectious stem rot caused by high-temperature sunscald to a minimum. Not only that,  it can also greatly reduce production costs.

Seedling cultivation technical measures

Meticulously select the ginkgo sowing and seedling nursery site: select plots with convenient drainage and irrigation one by one, and former rice paddies or virgin dry land with obvious elevation differences,  among which sandy loam or light clay loam plots are best.

Apply sufficient base fertilizer:Base fertilizer directly affects the growth of ginkgo sown seedlings,  and its effect is much more significant than soil topdressing and foliar spraying.

Make great efforts to dig deep ditches:  the rainy season runs from June to mid-to-early July,  and ginkgo seedlings are most intolerant of waterlogging,  which is one of the main causes of root rot,  so great efforts must be made to dig deep ditches. Each field plot is required to have nursery ditches 0.5 m deep,  and middle ditches 0.3  m deep. In addition,  seedbeds must not exceed 10  m in length,  and seedbed height must be 0.3  m or more. If these standards are not met,  seedlings will inevitably develop infectious or non-infectious root rot.

Covering seeds with plastic film:Covering seeds with plastic film enables seedlings to emerge earlier,  and their rapid growth phase accordingly comes earlier,  making the seedlings relatively robust with a higher degree of lignification, thereby enhancing the seedlings' resistance to pathogenic fungi.

Lining seedbeds with subsoil and covering seeds with subsoil:Taking subsoil from more than 1  m deep on hillsides to line seedbeds and cover seeds  not only greatly reduces weed growth in seedbeds and saves a great deal of labor,  but more importantly, subsoil contains few substances usable by pathogens and can effectively inhibit pathogen production.

Timely weeding: In spring, weeds compete with ginkgo seedlings for water,  and also make field plots poorly aerated and stuffy,  causing ginkgo leaves to rot from heat and moisture under prolonged rainy conditions. In addition,  weeds spread pathogens,  for example, chewing and piercing-sucking insects hiding in weeds create wounds on seedlings,  allowing pathogenic fungi to invade and cause stem rot. Therefore, after ginkgo seedlings emerge, weeds must be removed early and when small,  saving labor and money for later field management,  and laying the foundation for full stands of strong seedlings.

Handling diseased seedlings:In the early stage of infectious root rot and stem rot in ginkgo seedlings,  a firm decision should be made to pull out diseased seedlings and destroy them in a centralized manner,  disinfect the soil at the pathogen's root zone and the surrounding soil, and spray fungicides on healthy seedlings.

Shading:Ginkgo seedlings are relatively shade-tolerant,  and shading accordingly creates good environmental conditions for their growth. After mid-July, sustained high temperatures and drought can last for months,  and shading can greatly reduce surface temperature,  preventing ginkgo seedling root collars from sunscald and subsequent stem rot or physiological death.

Chemical control strategies

Chemical control is a technical measure that must be taken after root rot and stem rot occur in ginkgo seedlings,  and as long as the right remedy is applied promptly and pesticides are applied scientifically,  the disease can be effectively controlled.

Seed disinfection:Chemical disinfection of ginkgo seeds  can kill pathogens on the seed kernel surface and also protect seeds from soil-borne pathogens after sowing. During seed storage, seeds can be soaked in a 500-fold carbendazim solution for 5 minutes, removed, air-dried, and then stored by mixing with sand in layers.

Prevention and control of ginkgo stem rot

Prevention and treatment of ginkgo stem rot

        This disease occurs commonly in all ginkgo seedling cultivation areas. It mostly appears in 1- to 2-year-old ginkgo seedling stock, and is especially severe in one-year-old seedlings, often causing large numbers of seedling deaths.

       2 Symptoms: In the early stage of the disease, the base of the seedling turns brown, the leaves lose their normal green color and droop slightly downward, but do not fall off. The infected area rapidly spreads upward, until the entire plant dies. The cortex at the base of the diseased seedling shrinks, and the tissue inside the bark rots into a spongy or powdery form, grayish-white in color, mixed with many tiny black sclerotia. The pathogen of this disease can also invade the xylem of the seedling, so small sclerotia are sometimes also seen in the brown hollow pith. Afterward the pathogen gradually spreads to the roots, causing the root cortex to rot. If a diseased seedling is pulled by hand, only the xylem can be inserted, while the root cortex remains in the soil. In ginkgo cuttings under high or low temperature conditions, stem rot can also occur, causing the cutting bark to form a tube-like sheath around the xylem, while all the parenchyma tissue of the phloem turns black and rots.

       3 Pathogen: The pathogen of ginkgo stem rot is the charcoal rot fungus Macrophomia phaoli Maubl Ashby, of the order Sphaeropsidales, family Sphaeropsidaceae, genus Macrophoma. This fungus prefers high temperatures, with a suitable growth temperature of 30-32°C; it has no strict pH requirements and grows well between pH 4 and 9.

        4 Disease occurrence pattern: The stem rot pathogen usually lives saprophytically in the soil and is a weakly parasitic fungus. Under suitable conditions it invades through wounds on seedlings. Therefore, disease occurrence is related to the host and site environmental conditions. The fundamental cause of seedling damage is excessively high surface temperature, with the seedling base injured by high temperature and then invaded by the pathogen. The lower the degree of lignification of the seedling, the higher the incidence of this disease. When the seedbed is low-lying and water accumulates, the incidence also increases markedly. In ginkgo cuttings, in June to August when the seedbed temperature reaches above 30°C, the disease begins 10-15 d after insertion, and in severe cases large areas of scions turn black and die. Experiments have proven that antagonistic actinomycetes can effectively inhibit the spread and diffusion of this disease pathogen.

       5 Control methods: Based on the causes of ginkgo stem rot, prevention should currently be the main approach.

       A. Harvest early - aim to sow as soon as the soil thaws; this measure helps seedlings lignify early and enhances their ability to withstand high surface temperatures.

       B. Sow densely at a reasonable rate - dense sowing helps give play to the population effect of seedlings and enhances resistance to adverse external conditions. Experiments have proven that the lower the seedling density, the higher the incidence; the higher the density, the lower the incidence. Practice has also proven that where previously 25-40 kg of seeds were harvested per mu, if changed to a harvest rate of 80-100 kg of seeds per mu, not only is the incidence reduced, but the number of seedlings produced per unit area also increases, saving land while reducing disease.

       C. Control underground pests - after seedlings are damaged by underground pests, they are extremely susceptible to infection by the stem rot pathogen; therefore, before and after harvest, close attention must always be paid to eliminating underground pests.

        D. Prevent mechanical damage to seedlings - for current-year harvested seedlings or one-year-old transplanted seedlings, during loosening soil and weeding or during lifting and planting of seedlings, great care must be taken not to damage the root crown of the seedlings, otherwise stem rot is very easily triggered.

       E. Shade and cool down - to prevent solar radiation from raising ground temperature, nursery land should adopt measures such as building shade frames, covering grass between rows, planting corn, and inserting branches for shade to reduce damage to seedlings.

       F. Irrigation and spraying - in high-temperature seasons, irrigation and spraying should be done in a timely manner to lower surface temperature; where conditions permit, sprinkler irrigation can be adopted, which is even more helpful in reducing disease occurrence.

       G. Combine chemical and biological control with irrigation - various fungicides such as thiophanate-methyl, carbendazim, Bordeaux mixture, etc. can be sprayed. Antagonistic actinomycetes can also be added in mid-June when applying organic fertilizer, or wood ash/superphosphate (1:0.25) can be applied with antagonistic actinomycetes added.