A Detailed Guide to the Common Canna Disease: The Canna Leaf-roller
Canna
The canna leaf-roller is mainly distributed in southern regions and is a relatively serious disease. If it is not prevented and controlled, it will mean a great loss of wealth for growers. Therefore, understanding the characteristics of this disease and its patterns of occurrence will make it easier for growers to cultivate and control it.
I. Damage Characteristics
The larvae often roll leaves into tubes and feed on the leaves. When the infestation is severe, leaf tubes pile up one after another, causing the leaves to become scorched and incomplete, which affects the plant's photosynthesis.
II. Morphological Characteristics of the Canna Leaf-roller
The female adult is 28-31 mm long with a wingspan of 60-80 mm; the male adult is 24-27 mm long with a wingspan of 55-70 mm. The body is dark brown, and the head and thorax are densely covered with grayish-brown scales. The antennae are club-shaped and dark brown, with the area near the swelling appearing white. Both the forewings and hindwings are black, with white marginal hairs. The front margin of the forewing near the base is covered with grayish-yellow scales; in the center of the wing there are two large yellow square patches, and near the outer margin there is 1 small square patch.
The egg is red, shaped like a steamed bun, with a transverse diameter of 2 mm. The surface of the eggshell has radial white longitudinal stripes.
The mature larva is 50-64 mm long, and its body surface is covered with white wax powder. The head is triangular and black. Each body segment has transverse wrinkles and is densely covered with fine hairs.
The pupa is roughly barrel-shaped, 35-41 mm long, pale yellow-white, and covered with white powder. The proboscis reaches or exceeds the end of the abdomen, and the rear part of the proboscis does not separate from the pupal body. The tip of the abdominal cremaster has many hooked spines.
III. Patterns of Occurrence
In Fujian, it produces 4 generations per year. It overwinters as mature larvae inside leaf tubes, and adults appear in mid to late March of the following year. Adults of generations 1-3 emerge from mid to late June to early October, and the larvae enter the overwintering period in November. In summer and autumn, the egg stage lasts about 5 days. The larval stage lasts 25 days, and the pupal stage lasts 10 days. Adults prefer cool, shaded environments and are active in the morning and evening on sunny days, and throughout the day on cloudy days. They generally lay eggs singly on the host's leaves, tender stems, and petioles. After hatching, the larvae crawl to the leaf margins and bite the leaves into notches, then spin silk to glue the leaves together into a cylindrical tube. The larvae inside the tube extend their bodies out of the tube in the morning and evening to feed on nearby leaves. August to September is the peak period of damage.
IV. Control Methods
1. During the period when larvae occur, the leaf tubes can be removed manually and the larvae killed.
2. Protect and utilize natural enemies.
3. In late autumn and early winter, clean up diseased leaves and dead leaves to eliminate overwintering larvae.
Common Pests of Canna and Their Control Methods
Canna
Canna is a plant with low requirements for its living environment. It is easy to grow and easy to propagate, and has a long flowering period. It is a common landscaping and environmentally friendly plant along roadsides, and it is a plant used in many courtyards to beautify the environment. Generally speaking, as long as there is sufficient sunlight and sufficient water, it can survive anywhere. But no matter where canna grows, it cannot avoid disturbance by pests. So what are the common pests and diseases of canna?
I. Mosaic Disease
Symptoms
Mosaic or alternating yellow-green mottling appears on the leaves of infected plants, the petals become smaller and form mixed colors, and when the plant is more severely affected, the leaves become deformed and curled inward, with necrotic patches.
Control Methods
1. Since canna is propagated by division of roots, it is easy for the virus to be passed on year after year. Therefore, when propagating, virus-free mother plants should be selected as propagation material. Diseased plants found should be immediately pulled up and destroyed to reduce the source of infection.
2. This disease is transmitted by aphids. 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 insect body is relatively small and covered all over with white powdery waxy material, and it usually gathers in groups to damage plants. It is prone to occur when cultivation is poorly ventilated. It often damages the tender leaves and flower buds of canna. When damaging, it inserts its piercing-sucking mouthparts from the underside of the leaf and sucks the sap from the plant tissues, causing the leaves to turn yellow and wither, and it often excretes 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 9-10 generations per year in greenhouses and can form huge populations in a short time.
Control Methods
Because the adult whitefly has white waxy powdery material on its body, control is 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 5-6 days, and must be sprayed continuously 2-3 times. Natural enemies such as Encarsia formosa can also be used and have a certain effect.
III. Bud Rot
Symptoms
Before canna unfolds its leaves and flowers, the bud rot bacteria invade through the stomata of young leaves and flower buds. When the leaves unfold, many small spot lesions appear on the leaves and gradually expand, joining with each other along the leaf veins to form large patches, and sometimes the lesions form stripes. The lesions are initially 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 and 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 500-1000 times dilution for 30 minutes before planting, which can both prevent disease and promote the growth of buds and branches.
2. It is best to plant in areas with sufficient sunlight, fertile and moist soil, and good drainage, and avoid planting too densely.
3. In the early stage of plant 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 residues at any time and burn them.
Canna
IV. Canna Leaf-roller
The adult canna leaf-roller lays eggs on the leaves, tender stems, and petioles of canna. After the larvae hatch, they crawl to the leaf margins to bite the leaves, and spin silk to glue the leaves into rolled tubes. In the morning and evening they crawl out of the tubes to bite nearby leaves. When severe, the plant shows piles of leaf tubes and incomplete leaves, affecting growth and ornamental effect.
Control Methods
Remove the leaf tubes promptly and kill the larvae;
Before the larvae hatch and form leaf tubes, use 90% trichlorfon at 1000 times dilution to kill the larvae, or use chlorfluazuron at 1000 times dilution and spray to kill them in the morning or evening.
V. Black Cutworm
The black cutworm, also known as the soil silkworm, black soil silkworm, etc., is the larva of a moth. Its body is yellow-brown to dark brown, with a distinct dorsal line and rough skin, and it can reproduce 4-5 generations per year. Its adult is a medium-sized moth. The forewings are brown, with kidney-shaped markings and black wedge-shaped spots that are very obvious. When it causes damage, wormholes 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 poisoned bait can be used to trap and kill larvae. For example, mix 90% crystalline trichlorfon with wheat bran or soybean cake crumbs at 1:50 with an appropriate amount of water, and scatter it around the root zone in the evening to trap and kill them. You can also pour 50% phoxim, or 40% dimethoate, or 80% dichlorvos at 1000 times dilution around the root zone or on the seedling bed to poison and kill black cutworms.
Whether raising animals or plants, what growers worry about most is disease. Generally, ordinary diseases can be treated as long as the cause is found and the right medicine is found, but infectious diseases are not something growers can control, so prevention is crucial.
Control of Major Pests and Diseases of Canna indica
Canna indicaCommonpests and diseases include:
① Mosaic disease.When Canna indica is infected with mosaic virus, chlorosis and intermittent yellow stripes appear along the leaf veins to the leaf margins, and later spread to most of the leaf, or even the entire leaf shows yellowing, shrinking, and curling. When flowering, the petals show broken-color stripes.
Control methods:
a. When propagating, choose virus-free, robust rhizome material, and control the aphids that transmit this disease throughout the entire growth period;
b. Diseased plants found should be promptly pulled up and destroyed.
② Canna leaf-roller.The adult canna leaf-roller lays eggs on the leaves, tender stems, and petioles of Canna indica. After the larvae hatch, they crawl to the leaf margins to bite the leaves, and spin silk to glue the leaves into rolled tubes. In the morning and evening they crawl out of the tubes to bite nearby leaves. When severe, the plant shows piles of leaf tubes and incomplete leaves,affectinggrowth and ornamentaleffect。
Control methods:
a. Remove the leaf tubes promptly and kill the larvae;
b. Before the larvae hatch and form leaf tubes, use 90% trichlorfon at 1000 times dilution to kill the larvae, or use chlorfluazuron at 1000 times dilution and spray to kill them in the morning or evening.