What are the common disease prevention and control methods for primroses?

Primrose

From the moment primroses are sown, not only must you do a good job with care and management, but pest and disease prevention is also one of the keys to growing primroses well. Once a small problem arises at any step, primroses will throw their little tantrums and leave you scrambling with no idea where to start. So what are the common pests and diseases primroses encounter during cultivation?

I. Mosaic disease

Symptoms: A whole-plant disease caused by Cucumber mosaic virus (CMV). Symptoms include smaller, deformed leaves with dark green mottling or yellowing. Infected plants do not flower, or if they do, the flowers are stunted and deformed with mottling. The main transmission route is virus transmission by green peach aphids and cotton aphids. The main source of infection is infected weed plants nearby.

Prevention and control methods: First, promptly remove weeds to reduce sources of infection. Second, control aphids early to eliminate the virus-transmitting vectors.

II. Brown spot disease

Symptoms: Mostly occurs on fairy primrose (Primula malacoides). Caused by Alternaria fungi of the Deuteromycetes (Fungi Imperfecti). Infected plants have brown spots on the leaves. The transmission route is conidia spread by wind and rain.

Prevention and control methods: In the early stages of disease, spray 70% chlorothalonil wettable powder at 1000 times dilution or other fungicides.

III. Gray mold disease

Symptoms: One of the common diseases of primroses, occurring throughout the country. After infection, the entire plant yellows and dies. The disease mainly infects leaves, tender stems, flowers and other parts. It mostly occurs at leaf tips and leaf margins. In the early stages, water-soaked spots appear on the leaves, which gradually expand, turn brown and rot. Later, a grayish-yellow mold layer forms on the surface of the lesions. After the stem is infected, the lesions turn brown and gradually rot. After the flowers are infected, they also turn brown, rot and drop off. Under humid conditions, a gray mold layer appears on the diseased parts, which is a major characteristic of this disease. The disease overwinters as sclerotia in diseased plant debris and soil. It is prone to occur when the temperature is around 20°C and air humidity is high. It spreads through wind and rain, tools and irrigation water. In greenhouses, it is most severe in late winter and early spring.

Prevention and control methods: Planting density should be reasonable. Pay attention to ventilation and reduce air humidity. Promptly remove diseased leaves and plants to reduce sources of infection. In the early stages of disease, spray 50% procymidone or 50% iprodione wettable powder at 1500 times dilution. It is best to alternate with 65% dimethachlon wettable powder at 500 times dilution to prevent the development of fungicide resistance.

Primrose

IV. Leaf spot disease

Symptoms: Mainly affects the leaves of the plant. The disease spreads from the lower part of the plant upward. Lesions are usually 3 to 4 mm in diameter, brown, and in severe cases, diseased leaves wither and die, causing defoliation. The disease is caused by Ramularia primulae. The pathogen overwinters as mycelium or conidiomata on diseased plant debris, and seeds can also carry the pathogen, becoming the primary infection source for the following year. The disease mainly spreads through conidia carried by air and rainwater. Reinfection is frequent during the growing season. Plants are prone to the disease in warm, humid weather and when excessive nitrogen fertilizer is applied. It generally begins in July and becomes epidemic from August to October.

Prevention and control methods: Breed disease-resistant varieties, strengthen fertilizer and water management, apply more organic fertilizer and phosphorus-potassium fertilizer, and avoid excessive nitrogen fertilizer. In the early stages of disease, spray 70% thiophanate-methyl at 1000 times dilution plus 75% chlorothalonil wettable powder at 1000 times dilution, or 1:1:100 Bordeaux mixture.

V. Bacterial leaf spot disease

Symptoms: Mostly occurs on leaves and receptacles. In the early stages, water-soaked irregular lesions appear along the leaf veins, which later yellow and turn brown, the lesions expand, and leaf margins dry up. In severe cases, the lower leaves wither and die.

Prevention and control methods: Strengthen cultivation management, cultivate disease-free seedlings, and sterilize seedbed soil; ventilate greenhouses promptly to reduce air humidity. Promptly remove diseased plant debris. After disease onset, spray 50% copper succinate wettable powder at 500 times dilution, or 72% agricultural streptomycin wettable powder at 4000 times dilution.

VI. Iron deficiency chlorosis

Symptoms: The young leaves at the top of the plant lose their green color first, while the old leaves remain normal. In chlorotic leaves, the mesophyll turns yellow while the veins remain green. In severe cases, brown spots appear at leaf tips, and leaves may even drop off.

Prevention and control methods: Use loamy soil rich in iron for potting. Mix ferrous sulfate and zinc sulfate into organic fertilizer to promote root development and increase iron absorption capacity. When iron deficiency symptoms appear, spray 0.2 to 0.5% ferrous sulfate solution, which is more effective than directly applying it to the soil.

Perhaps many flower enthusiasts have never encountered the above problems when growing primroses, which is fortunate, but I suggest learning about them first, because the road of growing flowers is full of surprises. Perhaps today the leaves suddenly turn yellow and withered, or tomorrow the flowers fade. So knowing about these problems in advance will help us on our future flower-growing journey.

Common diseases of primroses and their prevention and control

Primrose is a perennial herbaceous plant of the genus Primula in the family Primulaceae. This genus includes many species that bloom in winter and spring. The plants can produce large numbers of beautiful flowers, clustered in the center of the leaf rosette, with a very rich range of flower colors. The author now introduces the common diseases of primroses as follows.

Primrose mosaic disease

Symptoms: A whole-plant disease caused by Cucumber mosaic virus (CMV). Symptoms include smaller, deformed leaves with dark green mottling or yellowing. Infected plants do not flower, or if they do, the flowers are stunted and deformed with mottling (see figure). The main transmission route is virus transmission by green peach aphids and cotton aphids. The main source of infection is infected weed plants nearby.

Prevention and control methods: First, promptly remove weeds to reduce sources of infection. Second, control aphids early to eliminate the virus-transmitting vectors.

Primrose brown spot

disease symptoms: Mostly occurs on fairy primrose (Primula malacoides). Caused by Alternaria fungi of the Deuteromycetes (Fungi Imperfecti). Infected plants have brown spots on the leaves. The transmission route is conidia spread by wind and rain.

Prevention and control methods: In the early stages of disease, spray 70% chlorothalonil wettable powder at 1000 times dilution or other fungicides. Primrose gray mold disease

Symptoms: One of the common diseases of primroses, occurring throughout the country. After infection, the entire plant yellows and dies. The disease mainly infects leaves, tender stems, flowers and other parts. It mostly occurs at leaf tips and leaf margins. In the early stages, water-soaked spots appear on the leaves, which gradually expand, turn brown and rot. Later, a grayish-yellow mold layer forms on the surface of the lesions. After the stem is infected, the lesions turn brown and gradually rot. After the flowers are infected, they also turn brown, rot and drop off. Under humid conditions, a gray mold layer appears on the diseased parts, which is a major characteristic of this disease. The disease overwinters as sclerotia in diseased plant debris and soil. It is prone to occur when the temperature is around 20°C and air humidity is high. It spreads through wind and rain, tools and irrigation water. In greenhouses, it is most severe in late winter and early spring.

Prevention and control methods: Planting density should be reasonable. Pay attention to ventilation and reduce air humidity. Promptly remove diseased leaves and plants to reduce sources of infection. In the early stages of disease, spray 50% procymidone or 50% iprodione wettable powder at 1500 times dilution. It is best to alternate with 65% dimethachlon wettable powder at 500 times dilution to prevent the development of fungicide resistance.

Primrose leaf spot disease

Symptoms: Mainly affects the leaves of the plant. The disease spreads from the lower part of the plant upward. Lesions are usually 3 to 4 mm in diameter, brown, and in severe cases, diseased leaves wither and die, causing defoliation. The disease is caused by Ramularia primulae. The pathogen overwinters as mycelium or conidiomata on diseased plant debris, and seeds can also carry the pathogen, becoming the primary infection source for the following year. The disease mainly spreads through conidia carried by air and rainwater. Reinfection is frequent during the growing season. Plants are prone to the disease in warm, humid weather and when excessive nitrogen fertilizer is applied. It generally begins in July and becomes epidemic from August to October.

Prevention and control methods: Breed disease-resistant varieties, strengthen fertilizer and water management, apply more organic fertilizer and phosphorus-potassium fertilizer, and avoid excessive nitrogen fertilizer. In the early stages of disease, spray 70% thiophanate-methyl at 1000 times dilution plus 75% chlorothalonil wettable powder at 1000 times dilution, or 1:1:100 Bordeaux mixture.

Primrose bacterial leaf spot disease

Symptoms: Mostly occurs on leaves and receptacles. In the early stages, water-soaked irregular lesions appear along the leaf veins, which later yellow and turn brown, the lesions expand, and leaf margins dry up. In severe cases, the lower leaves wither and die.

Prevention and control methods: Strengthen cultivation management, cultivate disease-free seedlings, and sterilize seedbed soil; ventilate greenhouses promptly to reduce air humidity. Promptly remove diseased plant debris. After disease onset, spray 50% copper succinate wettable powder at 500 times dilution, or 72% agricultural streptomycin wettable powder at 4000 times dilution.

Primrose iron deficiency chlorosis

Symptoms: The young leaves at the top of the plant lose their green color first, while the old leaves remain normal. In chlorotic leaves, the mesophyll turns yellow while the veins remain green. In severe cases, brown spots appear at leaf tips, and leaves may even drop off.

Prevention and control methods: Use loamy soil rich in iron for potting. Mix ferrous sulfate and zinc sulfate into organic fertilizer to promote root development and increase iron absorption capacity. When iron deficiency symptoms appear, spray 0.2 to 0.5% ferrous sulfate solution, which is more effective than directly applying it to the soil.

Common diseases of primroses and their prevention and control with pictures