Main Pests and Diseases of the Deciduous Large Tree Ginkgo: Damage Patterns and Control Methods of Spider Mites
The ginkgo tree is a deciduous large tree with a trunk diameter of up to 4 m. The fruit of the ginkgo tree is commonly known as white fruit, so ginkgo is also called the white fruit tree. The ginkgo tree grows slowly and has an extremely long lifespan. Under natural conditions, it takes more than 20 years from planting to bearing ginkgo fruit, and only after 40 years can it bear fruit in large quantities. Therefore, some people also call it the “grandfather-grandson tree”, with the meaning that “the grandfather plants it and the grandson gets to eat”. It is the longevity star among trees and has ornamental, economic, medicinal and other values.
Although the ginkgo tree can live for a thousand years, it often suffers from spider mite infestation.
1. Damage patterns of spider mites:
The spider mite that damages ginkgo locally is mainly the hawthorn spider mite. After overwintering, the spider mites emerge from dormancy in March-April and cause damage, with very small numbers early on. Because some courtyard ginkgo trees have many natural enemies, which often eat the spider mites completely, some courtyard ginkgo trees have no overwintering spider mites; the spider mites first damage other fruit trees and then move from other fruit trees to ginkgo trees to cause damage. In June, spider mite damage can be seen on the leaves of courtyard ginkgo trees. July-August is the peak period of damage, and the damage can last until September. In September-October, the spider mites overwinter in various life stages. After the leaves are damaged, they turn pale white, and in severe cases become scorched and dry, falling early. This affects the growth, fruiting and tree vigor of ginkgo.
2. Control methods
1. Manual control: On ginkgo trees with relatively light damage in summer, the spider mites overwinter late, generally overwintering in soil cracks and other places on the lower part of the trunk. In winter, use fresh soil to cover and bury the spider mites in the ground around the trunk to prevent them from emerging from the soil and climbing the tree in spring. In autumn and winter, clean up dead branches, fallen leaves and weeds under the trees in the courtyard, sweep them outside and burn them to reduce the overwintering population base of spider mites.
2. Chemical control: For ginkgo trees with overwintering spider mites, after the spider mites emerge from dormancy in spring, spray 0.3°Be lime sulfur mixture 1-2 times to kill the spider mites. In July-August, when spider mite damage is very serious and natural enemies cannot effectively control the spider mite damage, spray a 3000-fold 20% clofentezine suspension. When there are many natural enemies of spider mites on the tree, but there are pests such as slug caterpillars and bagworms damaging the leaves on the tree, do not spray highly toxic pesticides that kill natural enemies. Biological pesticides or other low-toxicity pesticides that do not harm natural enemies can be used to control other pests.
3. Biological control: There are many kinds of natural enemies that control spider mite damage locally, including Scolothrips takahashii, green lacewings, Stethorus punctillum, spiders, etc. Based on many years of observation, the dominant natural enemy controlling spider mite damage locally is Scolothrips takahashii.
In some years, spider mite damage on ginkgo is relatively severe while Scolothrips takahashii is scarce. The method of augmenting Scolothrips takahashii can also be used by transferring large numbers of Scolothrips takahashii occurring on crops such as kidney beans and eggplants in farmland onto the parts of ginkgo with more spider mites. Pick some leaves with large numbers of Scolothrips takahashii and place them on the ginkgo tree, which can promptly control spider mite damage.
3. Precautions for spider mite control: When spider mites are damaging ginkgo and Scolothrips takahashii are preying on the spider mites, do not spray highly toxic pesticides on the ginkgo that kill natural enemies. In addition, only after spider mites have been damaging and reproducing on ginkgo for a period of time can natural enemies eat them completely. In June-July, spider mite damage causes some damage to the leaves, but before it causes serious damage, do not rush to spray. Observe the activity of the spider mite natural enemies. When the ratio of the natural enemy Scolothrips takahashii to adult spider mites is 1:5, spraying is not necessary. If natural enemies are few and spider mite damage is becoming more severe, chemical control can be used to promptly control spider mite damage.