Occurrence patterns and control methods of pear tree crown gall
Damage symptoms
The pathogen is a bacterium, namely Agrobacterium tumefaciens. Galls form on the roots and root crown of affected trees, varying greatly in size, from as small as a bean to as large as a ball, hard in texture, lignified, with a rough surface. Diseased trees are stunted, appearing as small old-man trees, with yellowed leaves that drop early and low yields. The disease causes severe damage to nursery stock and young trees.
Occurrence patterns
The bacterial cells overwinter in diseased parts, residual roots and soil. Infection occurs mainly through wounds (insect wounds, mechanical injuries, etc.), and the transport of diseased nursery stock can spread the disease. Poor soil management is an important factor inducing crown gall. Soil compaction and long-term waterlogging can lead to poor aeration. Poor, thin soil and improper fertilizer and water management cause nutritional deficiency in the tree, which can lead to poor root development and reduced disease resistance, favoring infection and spread of crown gall. At the same time, the bacterial cells can expand the scope of damage as soil water flows.
Control methods
(1) Strengthen nursery stock quarantine and treatment
Try to avoid transporting nursery stock from diseased nurseries. For disinfection treatment of nursery stock, use 2% limewater, or 0.5% copper sulfate solution, or 50% amobam aqueous solution at 1000 times dilution, soaking the stock for 15 minutes.
(2) Strengthen cultivation management
Apply more organic fertilizer, dig ditches for drainage and otherwise improve the soil, which is beneficial to root growth and enhances the disease resistance of the tree.
(3) Scrape off diseased spots
Dig open the root crown to locate the affected parts, thoroughly scrape off the diseased spots with a small knife, and apply 2% limewater to the wounds to sterilize; the scraped diseased spots should be collected and destroyed. Larger wounds should be covered with mud or wrapped in plastic sheeting for protection.
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Occurrence and control of pear tree crown gall
Damage symptoms
The pathogen is a bacterium, namely Agrobacterium tumefaciens. Galls form on the roots and root crown of affected trees, varying greatly in size, from as small as a bean to as large as a ball, hard in texture, lignified, with a rough surface. Diseased trees are stunted, appearing as small old-man trees, with yellowed leaves that drop early and low yields. The disease causes severe damage to nursery stock and young trees.
Occurrence patterns
The bacterial cells overwinter in diseased parts, residual roots and soil. Infection occurs mainly through wounds (insect wounds, mechanical injuries, etc.), and the transport of diseased nursery stock can spread the disease. Poor soil management is an important factor inducing crown gall. Soil compaction and long-term waterlogging can lead to poor aeration. Poor, thin soil and improper fertilizer and water management cause nutritional deficiency in the tree, which can lead to poor root development and reduced disease resistance, favoring infection and spread of crown gall. At the same time, the bacterial cells can expand the scope of damage as soil water flows.
Control methods
(1) Strengthen nursery stock quarantine and treatment
Try to avoid transporting nursery stock from diseased nurseries. For disinfection treatment of nursery stock, use 2% limewater, or 0.5% copper sulfate solution, or 50% amobam aqueous solution at 1000 times dilution, soaking the stock for 15 minutes.
(2) Strengthen cultivation management
Apply more organic fertilizer, dig ditches for drainage and otherwise improve the soil, which is beneficial to root growth and enhances the disease resistance of the tree.
(3) Scrape off diseased spots
Dig open the root crown to locate the affected parts, thoroughly scrape off the diseased spots with a small knife, and apply 2% limewater to the wounds to sterilize; the scraped diseased spots should be collected and destroyed. Larger wounds should be covered with mud or wrapped in plastic sheeting for protection.
Integrated control of common winter diseases and pests
To reduce the occurrence of diseases and pests in the following year, integrated control is carried out in combination with winter pruning according to the different overwintering sites of diseases and pests. This not only reduces the severity of diseases and pests on landscape plants, but also has advantages such as saving labor, saving pesticides and good effectiveness.
Disease control
1. For diseases such as Euonymus japonicus leaf spot, Ligustrum sinense var. aureum leaf spot, Ligustrum sinense var. aureum sooty mold, crape myrtle sooty mold, rose sooty mold, rose black spot and ornamental peach shot hole disease. Since their pathogens mostly overwinter on dead branches and fallen leaves, in winter promptly remove fallen leaves and weeds from garden green spaces and collect them for deep burial, burning or high-temperature composting, which can eliminate a large number of overwintering sources of disease.
2. For diseases such as Euonymus japonicus powdery mildew and anthracnose, their pathogens mostly overwinter parasitizing branches and leaves. In combination with winter pruning, cut off branches damaged by the pathogen, and after pruning spray once with 5 to 8 degrees Baume lime sulfur mixture.
3. For diseases with alternate hosts such as crabapple-juniper rust and pear-juniper rust, after entering winter the mycelium forms spore horns on juniper and overwinters there. The control method is to cut off the spore horns on juniper; when the telial horns mature in late winter and early spring, spray 1:2:100 lime double-strength Bordeaux mixture to inhibit the telial horns from swelling and cracking after rain to produce sporidia.
4. For diseases such as turfgrass powdery mildew, rust and brown patch, their pathogens overwinter on diseased leaves. The control method is to remove fallen leaves, thatch and diseased residues from the lawn to reduce sources of inoculum.
5. For Euonymus japonicus scab and Ligustrum sinense var. aureum wilt, the pathogens usually overwinter in the soil, and mole crickets, click beetles and nematodes can all carry the pathogens and expand the damage. The control method is to cut off diseased branches and leaves and dispose of them centrally; manure, compost and other organic fertilizers applied during winter irrigation must be fully decomposed, or mixed with pesticides, which can kill overwintering mole crickets and click beetles to reduce the spread of disease; in late winter spray 5 degrees Baume lime sulfur mixture for prevention.
6. For Populus tomentosa crown gall, rose crown gall and Paulownia witches' broom, their pathogens overwinter in diseased plants, within galls or on diseased residues in the soil. Control methods: in combination with pruning, remove galls and witches' brooms, then disinfect the wounds with 1000 units of agricultural streptomycin or oxytetracycline; dig out and remove dead diseased trees, and disinfect the tree pits with 50 g to 100 g of sulfur powder, ferrous sulfate or bleaching powder applied to the soil.
Pest control
1. Pests that overwinter as cocoons
Slug moths mostly overwinter as cocoons. For example, the yellow slug moth overwinters as a cocoon spun by mature larvae at branch forks and other places; the flat slug moth overwinters as a cocoon in crevices underground; the brown-edged green slug moth overwinters as a cocoon in branches, trunks and shallow soil around roots; the two-toothed green slug moth overwinters as a cocoon at the base of trunks, in scars or in cracks of rough bark, etc.
Control methods
In combination with winter pruning, cut off branches bearing cocoons and burn them centrally.
During the winter cocoon-forming period of slug moths, remove or crush the cocoons on branches (yellow slug moth, two-toothed green slug moth), and dig out cocoons in the shallow soil around tree bases (brown-edged green slug moth), to reduce overwintering pest sources.
2. Pests that overwinter as larvae
(1) Tussock moths mostly overwinter as young larvae in bark crevices, dead branches and fallen leaves, and tree holes; the brown-banded tortrix, peach fruit moth and peach pyralid moth overwinter in bark crevices, raised bark, tree scars or pruning and saw cuts of affected plants; the boxwood leafroller overwinters in a thin cocoon in a nest made from two host leaves; the pear starmoth overwinters as a cocoon in the bark crevices of branches and main limbs of affected plants.
Control methods
In winter thoroughly clean up fallen leaves, cut off dead branches and burn them centrally. In winter scrape off insect cocoons in bark, branches and crevices, and whitewash tree trunks. Eliminate overwintering pest sources.
(2) The pale sword noctuid and cotton bollworm overwinter as larvae in loose soil.
Control methods
In combination with plowing and turning the soil, eliminate overwintering larvae. On lawns, in combination with winter irrigation, broadcast carbofuran or phoxim granules to kill overwintering larvae.
(3) Pests that damage branches and trunks as larvae, such as the rose stem sawfly, the ash Hartig stem sawfly, the fragrant carpenter moth and the poplar clearwing moth, generally overwinter as larvae inside damaged branches; the pagoda tree small leafroller overwinters in damaged branches and seeds.
Control methods
(1) For the rose stem sawfly, in combination with winter pruning, cut off damaged branches; if the pest body is found to have bored into the roots, use a syringe to inject 5 ml to 10 ml of 50-times diluted imidacloprid emulsifiable concentrate into the bore hole, and immediately seal it with mud to kill the remaining larvae.
(2) For the ash Hartig stem sawfly, cut off damaged branches and burn them centrally.
(3) Carpenter moths mostly bore tunnels at branch forks, rough bark and wounds; larvae in the tunnels can be killed with a wire hook.
3. Pests that overwinter as pupae
(1) Hawk moths and geometer moths, such as the frost hawk moth, grape hawk moth, bean hawk moth, pagoda tree geometer moth, pagoda tree prominent moth and Euonymus geometer moth, all overwinter as pupae in the soil.
Control methods
In combination with plowing and turning the soil, clear weeds. Dig pupae by hand to kill overwintering pupae. Spray 50% phoxim on the ground around host plants to kill pupae in the soil.
(2) Tiger moths and prominent moths, such as the fall webworm, the crimson-speckled flunkey, the red-edged tiger moth, the pagoda tree prominent moth and the poplar prominent moth. They mostly overwinter as pupae under old bark on trunks, in building crevices, under eaves, in holes, among bricks and debris and other places; the citrus swallowtail pupates suspended on branches and trunks.
Control methods
Thoroughly remove weeds and debris from green spaces and the surrounding environment. Destroy the habitat of overwintering pupae, and in combination with plowing and turning the soil, eliminate overwintering pupae.
4. Pests that overwinter as eggs - aphids mostly overwinter as eggs in bark crevices and between bud axils, for example the autumn four-veined cotton aphid overwinters as eggs on branches and trunks; mites mostly overwinter as eggs or fertilized female adults, for example the hawthorn spider mite and the Shi's start mite overwinter as eggs or fertilized female adults in bark crevices or under the soil; the wheat rock mite overwinters as adults under eaves of buildings near lawns, under raised tree bark, in weed clumps and other places; the four-legged mite that causes Populus tomentosa leaf curl disease overwinters as eggs between the bud scales of Populus tomentosa, and so on.
In addition, the gypsy moth overwinters as fully developed larvae inside eggs, with egg masses on the shaded side of trunk bases, bark, stone crevices and other places; the spotted lanternfly generally lays eggs on the sunny side of trunks.
Control methods
In winter remove diseased and pest-infested branches, clear weeds and burn them centrally. Scrape eggs by hand; scrape off rough bark and raised dead bark to kill overwintering eggs. Whitewash tree trunks to kill overwintering eggs in the bark layer.
5. Pests that overwinter as adults
Stink bugs mostly overwinter as adults, for example the tea bug, the brown-marmorated stink bug, the bean bug and the red-backed long stink bug overwinter as adults in grass clumps, dead branches and fallen leaves, under eaves, in wall crevices and in haystacks. The elm green flea beetle and the blue willow leaf beetle also overwinter as adults in hidden places such as under eaves, in wall crevices, in soil, under bricks and stones and among weeds.
Control methods
Remove dead branches and fallen leaves, weeds and debris, dispose of them centrally, and kill overwintering adults. Capture and kill adults by hand
6. Pests that overwinter in protective cases
The great bagworm moth and the small bagworm moth overwinter as larvae in protective cases hanging on branches; the camphor silk moth generally also overwinters on branches as a pupa in a cocoon hanging there.
Control methods
After leaf fall in winter, remove the bags and cocoons by hand to eliminate larvae and cocoons.
(The author's affiliation is the Landscape Plant Protection Center of Huajia Comprehensive Service Office, Huabei Oilfield)