This onion diseases and symptoms article will help you identify diseases before they affect your onion venture.
1. Pink Root Disease
Pink root is a soil-borne disease caused by a fungus called Pyrenochaeta Terrestris. The disease can cause significant losses to onion crops, and it is essential to identify and control it early. Identifying pink root in onions is relatively easy as the first visible symptom is a pinkish-red discoloration of the onion roots.
The infected roots will often be shorter and thicker than healthy roots. As the disease progresses, the roots will become more and more discolored, eventually turning a deep reddish-brown. The infected onion plants will also show signs of stunted growth, wilting, and yellowing of the leaves.
To control pink root in onions, various control measures can be employed. The first step is to use clean seed when planting onions. This ensures that you plant onion seeds that are free from the pink root fungus, preventing the disease from spreading.
Crop rotation is another critical control measure. Regularly rotate crops to prevent the buildup of the fungus in the soil. Avoid planting onions in the same field year after year.
Soil solarization is another effective control measure. This technique involves covering the soil with plastic for six to eight weeks to heat it up and kill the fungus.
Fungicides can also be used to control pink roots. Fungicides containing active ingredients like thiophanate-methyl, mancozeb, or captan can be applied according to the manufacturer’s instructions.
Finally, it is essential to improve soil drainage as pink root fungus thrives in moist soil.
Ensuring that the soil is well-drained and that irrigation is done appropriately can help prevent the disease from spreading.
2. Fusarium Basal Rot
The disease is caused by a fungus called Fusarium oxysporum f. sp. cepae and can survive in the soil for many years. The fungus infects the roots and basal plate of the onion plant, causing rotting and yellowing of the leaves. The infected plants eventually wilt and die, leading to significant yield losses.
To identify Fusarium Basal Rot in onions, look out for yellowing and wilting of the leaves and rotting of the basal plate. The disease often begins in the root zone and progresses upward toward the foliage. Early detection is crucial for effective control of the disease.
To control Fusarium Basal Rot in onions, farmers can employ various measures. Crop rotation is a useful control measure as it helps to break the disease cycle by preventing the fungus from building up in the soil. Farmers should avoid planting onions in the same field for more than two years in a row.
Another effective control measure is the use of fungicides. Fungicides containing active ingredients like thiophanate-methyl can be applied to the soil before planting to control the disease. The application of fungicides should be done according to the manufacturer’s instructions.
It is also essential to use disease-free onion seed to prevent the spread of the disease. Farmers can use seed treatment with hot water or fungicides to kill any fungus on the seed before planting.
3. Botrytis Neck Rot
Botrytis Neck Rot is a fungal disease caused by the fungus Botrytis allii and is prevalent in areas with high humidity and moisture. The disease affects the neck of the onion, causing it to rot and become soft. As the disease progresses, it can spread to the bulb, causing significant yield losses.
To identify Botrytis Neck Rot in onions, look out for soft, water-soaked lesions on the neck of the onion. The lesions will eventually turn brown or black and become dry and sunken. The affected onion leaves may also turn yellow and wilt.
To control Botrytis Neck Rot in onions, farmers should employ cultural practices such as good sanitation and proper irrigation to prevent the disease from spreading. Farmers should remove infected plants and debris from the field to prevent the fungus from surviving in the soil.
Fungicides containing active ingredients like cyprodinil or fludioxonil can be applied to the onion plants as a preventative measure. Application of fungicides should be done according to the manufacturer’s instructions.
Planting resistant onion varieties can also help prevent the spread of Botrytis Neck Rot. Farmers can select onion varieties that are resistant to the disease, making them less susceptible to infection.
4. Onion Smudge
Onion Smudge is caused by the bacterium, Pantoea ananatis. The disease is prevalent in areas with high humidity and warm temperatures such as the coastal parts of Kenya. Onion Smudge disease can cause significant yield losses, and it is essential to identify and control it early.
To identify Onion Smudge disease in onions, look for water-soaked, yellowish-green patches on the leaves. As the disease progresses, the patches will turn black, and the affected onion leaves will wilt and die. The disease can also affect the bulbs, causing soft rot.
To control Onion Smudge disease, farmers can employ various measures. Good sanitation practices are crucial in preventing the spread of the disease. Farmers should remove infected plants and debris from the field and practice crop rotation to prevent the buildup of the bacterium in the soil.
Copper-based fungicides can also be used to control the disease. Farmers can apply copper fungicides to the onion plants as a preventative measure. Application of fungicides should be done according to the manufacturer’s instructions.
Planting resistant onion varieties can also help prevent the spread of Onion Smudge disease. Farmers can select onion varieties that are resistant to the disease, making them less susceptible to infection.
Proper irrigation and soil drainage can also help prevent the disease from spreading. Over-watering should be avoided, and irrigation should be done early in the day to allow time for the leaves to dry before nightfall.
5. White Rot Disease
White Rot is a fungal disease that affects onions and other Allium crops such as garlic and shallots. It is caused by the fungus Sclerotium cepivorum and can survive in the soil for several years. White Rot can cause significant yield losses and is a major concern for onion farmers in Kenya.
To identify White Rot disease in onions, look out for yellowing and wilting of the leaves and soft rotting of the onion bulb. The infected bulbs will appear water-soaked and become soft, eventually disintegrating.
The fungus produces small, white, hard, and irregularly shaped sclerotia (tiny black balls) on or within the plant tissues.
To control White Rot disease, farmers can employ various measures. Good sanitation practices are crucial in preventing the spread of the disease.
Farmers should remove infected plants and debris from the field and practice crop rotation to prevent the buildup of the fungus in the soil. Avoiding the use of infected onion debris as mulch or compost can help prevent the spread of the disease.
Farmers can also use fungicides to control White Rot. Fungicides containing active ingredients like propiconazole or tebuconazole can be applied to the soil or as a foliar spray to control the disease. The application of fungicides should be done according to the manufacturer’s instructions.
Planting resistant onion varieties can also help prevent the spread of White Rot. Farmers can select onion varieties that are resistant to the disease, making them less susceptible to infection.
6. Onion Maggots
Onion Maggots are the larvae of the onion fly (Delia antiqua), a small grayish-brown fly that lays its eggs in the soil near the base of onion plants. The maggots hatch and feed on the roots and bulbs of the onion plants, causing significant damage and yield losses. Onion Maggots are a major problem for onion farmers in Kenya, and controlling them is crucial to a successful harvest.
To identify Onion Maggot infestation in onions, look out for stunted growth, yellowing, wilting, and eventual death of onion plants. Infested bulbs may also show signs of tunneling or rotting, and maggots may be visible inside the bulbs or in the soil surrounding the plants.
To control Onion Maggot infestation, farmers can employ various measures. Good sanitation practices are crucial in preventing the spread of the flies. Farmers should remove any infested onion plants and debris from the field and practice crop rotation to prevent the buildup of the flies in the soil.
Farmers can also use physical barriers like row covers to prevent adult flies from laying eggs on onion plants. Row covers should be applied early in the growing season and removed after the flies have finished laying eggs.
The use of insecticides can also be effective in controlling Onion Maggot infestation. Farmers can apply insecticides containing active ingredients like spinosad, chlorpyrifos, or permethrin to the soil or as a foliar spray to control the flies. The application of insecticides should be done according to the manufacturer’s instructions.
Planting onion varieties that are less attractive to the flies can also help prevent infestation. Farmers can select onion varieties that mature early or late in the season, as these are less attractive to the flies.
Additionally, intercropping onions with plants that are unattractive to the flies, such as garlic or marigolds, can help repel the flies and reduce infestation.
7.Alternaria Leaf Blight
Alternaria Leaf Blight is a fungal disease that affects also affects Allium crops such as garlic. It is caused by the fungus Alternaria porri and is prevalent in warm, humid environments. The disease can cause significant yield losses if not controlled, making it a major concern for onion farmers in Kenya.
To identify Alternaria Leaf Blight in onions, look out for brown or black spots on the leaves, which may also appear water-soaked or oily. The spots may coalesce to form large patches, and the leaves may become dry and brittle. In severe cases, the disease can spread to the neck and bulbs of the onion, causing rotting and spoilage.
To control Alternaria Leaf Blight, farmers can employ various measures. Good sanitation practices are crucial in preventing the spread of the disease. Farmers should remove infected plant debris from the field and practice crop rotation to prevent the buildup of the fungus in the soil.
Farmers can also use fungicides to control Alternaria Leaf Blight. Fungicides containing active ingredients like azoxystrobin or chlorothalonil can be applied as a foliar spray to control the disease.
8. Iris Yellow Spot Disease
Iris Yellow Spot Virus (IYSV) is a viral disease transmitted by onion thrips (Thrips tabaci) and is prevalent in warm, dry environments. To identify Iris Yellow Spot Virus in onions, look out for yellow or necrotic streaks or spots on the leaves, which may be accompanied by stunting or distortion of the plant. In severe cases, the disease can cause plant tissue necrosis, leading to reduced yield and quality of onion bulbs.
To control Iris Yellow Spot Virus, farmers can employ various measures. Good sanitation practices are crucial in preventing the spread of the virus. Farmers should remove infected plant debris from the field and practice crop rotation to prevent the buildup of the virus in the soil.
Farmers can also use insecticides to control onion thrips, which transmit the virus. Insecticides containing active ingredients like spinosad, acetamiprid, or chlorpyrifos can be applied as a foliar spray to control thrips.
9. Bacterial Wilt
Bacterial Soft Rot is a disease caused by bacteria from the genus Pectobacterium or Erwinia, family. The bacteria can survive in soil or on infected plant debris and can be spread by contaminated equipment or water.
To identify Bacterial Soft Rot in onions, look out for water-soaked spots on the leaves, bulbs, or roots, which may become soft and slimy, and emit a foul odor. The infected tissue may also turn brown or black and decay, eventually leading to plant death.
To control Bacterial Soft Rot, farmers can employ various measures. Good sanitation practices are crucial in preventing the spread of the bacteria. Farmers should remove infected plant debris from the field, and avoid injuring the plant during cultivation or harvest, as this can create entry points for the bacteria.
10. Thrips Infestation
Thrips are tiny insects that can cause significant damage to onion crops in Kenya. They feed on the plant sap, causing stunted growth and distortion of the leaves and bulbs. Thrips can also transmit viral diseases like Iris Yellow Spot Virus, which can cause severe yield losses.
To control thrips infestation in onions, farmers can employ various measures. Good sanitation practices are crucial in preventing the buildup of thrips populations. Farmers should remove weeds, plant debris, and other crop residues from the field, as they can serve as breeding grounds for thrips.
Farmers can also use insecticides to control thrips. Insecticides containing active ingredients like spinosad, acetamiprid, or chlorpyrifos can be applied as a foliar spray to control thrips. The application of insecticides should be done according to the manufacturer’s instructions.
Planting resistant onion varieties can also help prevent thrips infestation. Farmers can select onion varieties that are less attractive to thrips, making them less susceptible to infestation.
In conclusion, onion farmers in Kenya face several challenges, including diseases and pests that can significantly impact crop yield and quality. By following good agricultural practices and employing appropriate disease and pest control measures, farmers can minimize the impact of these challenges and ensure a successful onion harvest.
