A Detailed Guide to the Prevention and Control of Root Rot and Stem Rot in Ginkgo Seedlings

Root rot and stem rot in ginkgo seedlings often occur in 1- to 2-year-old ginkgo seedling stock, and are especially severe in one-year-old seedlings, often causing large numbers of seedlings to die. So what are the prevention and control methods for root rot and stem rot in ginkgo seedlings?

1. Symptoms of root rot and stem rot in ginkgo seedlings

1. Root rot in ginkgo seedlings

In the early stage of root rot, the root cortex rots, and in the later stage the xylem is damaged. Many pathogens can cause root rot, and the symptoms caused by different pathogens differ. The main pathogens causing root rot are Armillaria mellea and fungi of the genus Phytophthora.

(1) Root rot symptoms caused by Armillaria mellea

In the early stage of the disease, dark brown water-soaked lesions appear on the cortex of the root crown. After they gradually expand, the root cortex turns black, the phloem readily falls off, and the xylem becomes brown and rots, accompanied by a smell of distillers' grains.

In the later stage of the disease, the lesions spread downward and the entire root system rots. When the soil environment is moist, the diseased tissue is filled with white to pale yellow fan-shaped mycelial layers, which can emit blue-green fluorescence in a dark environment. Later, clusters of honey-yellow small umbellate basidiocarps sometimes form on the diseased roots. The aboveground parts turn yellow and drop their leaves, some branches dry up, or the whole plant wilts and dies.

(2) Root rot symptoms caused by fungi of the genus Phytophthora

The pathogen first invades from the root tip or root crown, then gradually spreads inward. In the early stage of the disease, leaf growth in the aboveground parts weakens, turns yellow, curls, and becomes smaller. When the disease is mild, the root system grows weakly; when severe, the cortex of the main root rots. In more severe cases, early leaf drop begins in July, and in August the leaves of individual plants all fall off, or even the entire plant dies. Older trees are more susceptible than young trees.

2. Stem rot in ginkgo seedlings

In the early stage of stem rot, the base of the seedling turns brown, the leaves lose their normal green color, and they droop slightly downward, but do not fall off. The infected area rapidly spreads upward, until the whole plant dies. The cortex at the base of the diseased seedling shrinks and wrinkles, and the tissue inside the bark rots into a spongy or powdery form, grayish white in color, and interspersed 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. After that, the pathogen gradually spreads to the roots, causing the root cortex to rot. If a diseased seedling is pulled up by hand, only the xylem can be pulled out, while the root cortex remains in the soil. In ginkgo cuttings under high or low temperature conditions, stem rot can also occur, causing the epidermis of the cuttings to remain like a tube around the xylem, while the parenchyma tissue of the phloem all turns black and rots.

2. Prevention and control methods for root rot and stem rot in ginkgo seedlings

1. Prevention and control methods for ginkgo stem rot

(1) According to the causes of ginkgo stem rot, prevention should currently be the main approach.

(2) Sow early and aim to sow as soon as the soil thaws. This measure helps the seedlings become woody early and enhances their resistance to high surface soil temperatures.

(3) Reasonable dense sowing. Dense sowing helps give play to the collective effect of the seedlings and enhances resistance to adverse external conditions. Experiments have shown that the lower the seedling density, the higher the disease incidence; the greater the density, the lower the disease incidence. Practice has also shown that where previously 25-40 kg of seed was sown per mu, if this is changed to a sowing rate of 80-100 kg of seed per mu, not only does the disease incidence decrease, but the number of seedlings produced per unit area also increases, saving land while reducing disease.

(4) Control underground pests. After seedlings are damaged by underground pests, they are highly susceptible to infection by the stem rot pathogen. Therefore, before and after sowing, always pay attention to eliminating underground pests.

(5) Prevent mechanical damage to seedlings. For current-year sown seedlings or one-year-old transplanted seedlings, be sure not to damage the root crown during loosening the soil, weeding, or lifting and planting seedlings; otherwise, stem rot is very likely to occur.

(6) Shade and cool the soil. To prevent solar radiation from raising soil temperature, the seedling bed should adopt measures such as building shade frames, covering the rows with grass, planting corn, and inserting branches for shade to reduce damage to the seedlings.

(7) Irrigate and spray water. In hot seasons, irrigate and spray water in a timely manner to lower the surface temperature. Where conditions permit, sprinkler irrigation can be used, which is even more helpful in reducing the occurrence of disease.

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

2. Prevention and control methods for ginkgo root rot

Root rot generally occurs in June. The prevention and control methods are:

(1) Remove diseased plants in a timely manner and burn them in a centralized manner;

(2) Spray with a 70% thiophanate-methyl 1000-fold solution.