What are the common pests of canna lilies? A detailed guide to control methods

Canna lily

Canna lily is a plant that does not demand much from its growing environment, is easy to cultivate and easy to propagate, and has a long flowering period. It is a common greening and eco-friendly plant along roadsides, and is used in many courtyards to beautify the surroundings. Generally, as long as there is plenty of sunlight and plenty of water, it can be grown anywhere. But no matter where canna lilies grow, they cannot avoid being troubled by pests. So what are the common pests and diseases of canna lilies?

I. Mosaic disease

Symptoms

On the leaves of infected plants, mosaic patterns or mottling of alternating yellow and green appear; the petals become smaller and develop variegation. When the plant is severely affected, the leaves become deformed and curl inward, and the blotches become necrotic.

Control methods

1. Because canna lilies are propagated by division of the roots, the virus is easily passed on year after year. Therefore, when propagating, it is best to select virus-free mother plants as propagation material. If diseased plants are found, pull them out and destroy them immediately to reduce the source of infection.

2. This disease is spread by aphids, so use insecticides to control aphids and reduce the transmission vector. Spray with 40% omethoate at 2000 times dilution, or 50% malathion, 20% diazinon, or 70% pirimicarb each at 1000 times dilution.

II. Whiteflies

Pests of the family Aleyrodidae in the order Homoptera. The insects are relatively small and the whole body is covered with a white powdery waxy substance. They usually gather in groups to harm plants. They are prone to occur when cultivation is poorly ventilated. They often harm the young leaves and flower buds of canna lilies. When feeding, they insert their piercing-sucking mouthparts from the underside of the leaves and suck the sap from the plant tissues, causing the leaves to turn yellow and wither, and they often excrete large amounts of honeydew at the wound sites, inducing other diseases such as sooty mold and fungal infections. Because whiteflies have strong reproductive capacity, they can reproduce 9 to 10 generations a year in a greenhouse, and can form huge numbers in a short time.

Control methods

Because the adult whiteflies have a white waxy powdery substance on their bodies, this makes control difficult, so control must be timely. Chemical control is better during the nymph stage. Commonly used options are 2.5% deltamethrin, or 10% permethrin, or 20% fenvalerate diluted 2000 times, which give good results; 40% dimethoate, or 80% dichlorvos, or 50% malathion emulsion can also be used once every 5 to 6 days, sprayed continuously 2 to 3 times. Natural enemies such as Encarsia formosa can also be used and have a certain effect.

III. Bud rot

Symptoms

Before canna lilies unfold their leaves and bloom, the bud rot bacteria invade through the stomata of young leaves and flower buds and cause damage. When the leaves unfold, many small spots appear on the leaves and gradually expand, connecting to each other along the leaf veins to form large blotches; sometimes the lesions form stripes. The lesions initially appear grayish white and quickly turn black. Infected flower buds turn black and die before flowering. The lesions can extend downward along the petiole, causing the young stems and buds to die. When old leaves are affected, the lesions expand slowly, are irregular in shape, yellow, with water-soaked edges.

Control methods

1. Select healthy rhizomes as propagation material. For rhizomes suspected of carrying bacteria, soak them in streptomycin at 500 to 1000 times dilution for 30 minutes before planting; this can both prevent disease and promote the growth of buds and branches.

2. It is best to plant in a location with plenty of sunlight, fertile and moist soil, and good drainage, and avoid planting too densely.

3. In the early stage of the disease, spray Bordeaux mixture (1:1:200) or 77% copper hydroxide wettable powder at 500 times dilution, 14% copper ammonia complex aqueous solution at 400 times dilution, etc.

4. Remove severely diseased plants and diseased plant debris at any time and burn them.

Canna lily

IV. Canna leaf roller

The adult canna leaf roller lays eggs on the leaves, tender stems, and petioles of canna lilies. After the larvae hatch, they crawl to the leaf edges, bite and feed on the leaves, and spin silk to glue the leaves into rolled bracts. In the morning and evening they crawl out of the bracts to bite and feed on nearby leaves. In severe cases, the plants show numerous leaf bracts and incomplete, ragged leaves, affecting growth and ornamental effect.

Control methods

Remove the leaf bracts promptly and kill the larvae;

Before the larvae hatch and form leaf bracts, use 90% trichlorfon at 1000 times dilution to kill the larvae, or use chlorfluazuron at 1000 times dilution and spray in the morning or evening.

V. Black cutworm

The black cutworm, also known as the cutworm or black soil cutworm, is the larva of a moth. Its body is yellow-brown to dark brown, with a distinct dorsal line and rough skin. It can reproduce 4 to 5 generations a year. Its adult is a medium-sized moth, with brown front wings bearing reniform markings and black wedge-shaped spots that are very distinct. When it causes damage, holes can be seen on the plant leaves, and in severe cases it damages the flower buds, resulting in plants without flowers.

Control methods

During cultivation and management, clear the surrounding weeds and keep the environment clean. Black light traps or sugar-vinegar bait can be used to trap and kill adults, and grass piles or poison bait can be used to trap and kill larvae. For example, mix 90% crystalline trichlorfon with wheat bran or bean cake crumbs at 1:50, add an appropriate amount of water, stir, and scatter it at the root zone in the evening to trap and kill. You can also pour 50% phoxim, or 40% dimethoate, or 80% dichlorvos at 1000 times dilution at the root zone or on the seedbed to kill black cutworms.

Whether raising animals or plants, what growers worry about most is disease. Generally, ordinary diseases can be treated once the cause is found and the right medicine is identified, but infectious diseases are beyond the grower's control, so prevention is crucial.

Pests of canna lilies and control methods

Pests of canna lilies: leaf roller

Symptoms

In summer and autumn, the larvae spin silk to bind leaves into rolled or stacked leaves, and the larvae hide inside and chew the leaf mesophyll, leaving the veins and upper epidermis, forming a transparent gray-brown film that later breaks into holes, known as "open skylights."

Although canna lilies are highly adaptable, from May to August each year, attention must be paid to the damage caused by leaf rollers to canna lilies so as not to damage the tender leaves and inflorescences.

Control methods

In autumn and winter, promptly capture and kill overwintering larvae in fallen leaves, cracks, or near buildings; in summer, promptly capture and kill newly hatched larvae, and if necessary remove the damaged leaves.

You can spray 50% dichlorvos at 800 times dilution or 50% fenitrothion emulsion at 1000 times dilution for control.

Pests of canna lilies: canna leaf roller

Symptoms

The adult canna leaf roller lays eggs on the leaves, tender stems, and petioles of canna lilies. When the larvae hatch, they crawl to the leaf edges and bite and feed on the leaves. The canna leaf roller also spins silk to glue the leaves into rolled bracts. In the morning and evening, they crawl out of the rolled bracts and bite and feed on nearby leaves.

Plants severely infested by the canna leaf roller show large numbers of leaf bracts and incomplete leaves, seriously affecting the growth and ornamental effect of canna lilies.

Control methods

When leaves infested by the canna leaf roller are found, remove the leaf bracts promptly and kill the larvae.

Before the larvae hatch and form leaf bracts, use 90% trichlorfon at 1000 times dilution to kill the larvae, or use chlorfluazuron at 1000 times dilution and spray in the morning or evening.

Pests of canna lilies: cutworm

Symptoms

The cutworm is a polyphagous pest. It mainly harms canna lilies as larvae. The larvae bite through the stem near the ground of the seedlings, causing the entire plant to die.

Control methods

When cutworm damage to canna lily plants is found, manual capture can be carried out, or 600 to 800 times dilution of trichlorfon can be used to drench the root soil for control.

Control of boring pests in August

I. Damage symptoms and main characteristics of boring pests

Damage symptoms of longhorn beetles: They mainly harm the host's phloem and xylem as larvae. Newly hatched larvae bore vertically from the phloem into the sapwood, tunnel horizontally along the spring wood portion of the outermost annual ring of the branch or trunk, and then bore inward. The tunnel is "Z"-shaped. Adults feed on the tender bark of new shoots to supplement nutrition; the edges of the fed areas are neat. They are not good at flying and easily fall to the ground when disturbed. They make egg-laying chambers in bark cracks and other places to lay eggs, then cover the eggs with a grass-green secretion. (Images of the main characteristics and damage symptoms of longhorn beetles).

Damage symptoms of jewel beetles: The larvae tunnel vertically and horizontally between the cambium and xylem, destroying the conductive tissues, causing the tree to weaken, the trunk to gradually die, and eventually the whole tree to die. Generally, trees under extensive management, with weakened vigor and many wounds, suffer more damage, while vigorous trees suffer less. (Images of jewel beetles)

Damage symptoms of the dahlia stem borer: The larvae bore into and feed on the stems of garden ornamental plants such as dahlia, chrysanthemum, Populus cathayana, canna lily, gladiolus, palm, and hemp. In severe cases, almost the entire stem is bored and damaged, and the plant cannot bloom. The stems of affected plants break easily, the plants cannot bloom, and the upper part of the stem turns yellow and dies. (Images of the dahlia stem borer).

Damage symptoms of the rose stem sawfly: The larvae bore into and feed on the stems of ornamental flowers, often causing breakage and wilting from the bore holes, causing great harm to roses. (Images of the rose stem sawfly)

II. Control measures for boring pests

(1) Control measures in August:

1. Pay attention to inspection. When branches of flowers and trees damaged by the dahlia stem borer or rose stem sawfly are found, they should be cut off promptly with pruning shears and burned together to kill the larvae; longhorn beetles and jewel beetles mainly harm the main trunk of trees. When the larvae are still boring and feeding under the cortex at the root crown, or have not bored deep into the xylem, hook and kill them promptly.

2. Chemical poisoning of larvae. When the larvae have bored relatively deep into the xylem, chemical agents can be used for poisoning.

Inject 80% dichlorvos, 40% omethoate, or 50% phoxim into the bore holes, then seal the openings with poisoned mud made by mixing chemicals, which can poison and kill the larvae.

Insert poison sticks into the bore holes to poison and kill the larvae (the poison sticks can be made by yourself using zinc phosphide, peach gum, oxalic acid, and bamboo sticks).

In the early stage of larval damage, you can use 5% beta-cypermethrin or 50% methamidophos emulsion at 5 to 10 times dilution, or 80% dichlorvos emulsion at 5 times dilution, or a 1:20 dichlorvos-kerosene solution to brush the epidermis of the damaged part (the damaged area is slightly sunken and blackened) or the trunk. The effect of poisoning and killing larvae is very good.

(2) Other control measures

1. Strengthen quarantine when transporting nursery stock. For insect-infested logs in transport, use methyl bromide, sulfuryl fluoride, or 56% aluminum phosphide tablets for fumigation treatment, with dosages of 20-30 g/m³and 12-15 g/m³, fumigating for 24 h and 72 h; or soak the pest-infested wood in water for more than 1 month; after peeling the logs, dip thin branches in 20% fenvalerate emulsion at 20 times dilution, or 40% omethoate emulsion, or 2.5% deltamethrin emulsion at 10 times dilution, and insert them into the insect holes to poison and kill the pests.

2. Strengthen management and improve tree vigor; during the dormant period, scrape off the coarse and raised bark on the main trunk and main branches, and prune branches with insects. Eliminate some overwintering insect sources; promptly remove dead trees and dead branches and burn them to reduce insect sources.

3. Manual control

a. Manually capture adults. Late June is the peak period of adult emergence. Before the emerging adults bite through the emergence holes and fly out, use a screwdriver to poke them to death; when adults have just emerged from the emergence holes, they crawl on the trunk and are gregarious, so they can be caught directly at this time.

b. Manually kill eggs and newly hatched larvae. Late June to early July is the adult egg-laying and hatching period. Newly laid eggs are green and easy to identify; newly hatched larvae are on the outer layer of the bark and easy to remove, so manual egg removal and larval capture can be organized at this time.

c. Egg trapping control: Use woven bags such as those for packaging chemical fertilizers. After washing them clean, cut them into strips 20-30 cm wide. Before the star longhorn beetle lays eggs, wrap the main trunk area where eggs are likely to be laid with the cut woven strips for 2-3 turns, leaving no gaps at the connections between turns, then tie them with hemp rope. The control effect is very good. Through this wrapping barrier, the longhorn beetle can only lay eggs on the woven bag, after which the longhorn beetle eggs will lose water and die.

4. Chemical control
b. During the peak activity period of older larvae (late March to mid-April), use 30 times dilution of bifenthrin or dichlorvos or fenvalerate or monocrotophos, inject it into the frass holes or breathing holes with a syringe, then seal the holes tightly with yellow mud.
c. From mid-June to mid-July each year, during the peak activity period of adults, spray the host tree canopy with 2000 times dilution of fenpropathrin once every 15 days, continuously spraying twice, which can achieve good results.
d. Before overwintering (November and December), use 10 kg lime + 1 kg sulfur + 10 g salt + 20 kg to 40 kg water to make a whitewash and brush the trunk to prevent egg laying. (Source: China Lawn Network, compiled by Yang Yanwei and Xie Xiaomin)