ALS – Alternaria Leaf Spot
Scientific Name: Alternaria brassicicola, Alternaria cucumerina, Alternaria dauci
Type: Fungus
Alternaria Leaf Spot, also known Alternaria Leaf Blight, is a world-wide fungal disease that affects the growth of broccoli, Brussels sprouts, cabbage, cantaloupes & melons, carrots, cauliflower, cucumbers, kale, kohlrabi, pumpkins, radishes, rutabaga, squash, tomatoes, turnips, and watermelons. Symptoms may first develop on young plants where leaf spots develop, plants become stunted, and damping off may occur. Greenish-brown lesions appear on the leaves, and turn from dark brown to black spots. The disease may appear on the leaves at any stage and start off as concentric circles and mature to lesions with a bulls eye appearance. The leaves curl, turn yellow, wither, and eventually die off, and heavy infestations may cause complete defoliation. The infected plants should be removed to avoid further infestation. Increase space between the plants to maximize air flow and drying of the leaves. The disease is favorable when temperatures are 75-82 F and usually occur when moisture and humidity are very high. Plan on using a 3 year crop rotation and avoid planting in the same location, year after year, as the disease can survive in the soil for 8 years. Fungicides can help manage the disease. The best option is to use disease resistant varieties.
DM – Downy Mildew
Scientific Name: Peronospora farinosa, Peronospora parasitica, Pseudoperonospora cubensis
Type: Fungus
Downy mildew is a fungal disease that affects the growth of beets, broccoli, cantaloupes & melons, cauliflower, cucumbers, spinach, Swiss chard, and watermelons. Downy Mildew is most serious for cucumbers, which can drop dead in a week and stop producing any fruit to harvest. The disease affects both seedlings and mature plants.The infected leaves are retarded in growth, turn yellow then brown, and turn downward. A white to gray color mold appears on the underside of the leaves. The leaves will wilt and eventually die. The disease can spread rapidly under favorable conditions and infect the entire field. The infected plants should be removed and burned to avoid further infestation. The disease is favorable when temperatures are 58-72 F and usually occur in early spring and autumn in cooler weather when moisture and humidity are very high. Fungicides can help manage the disease. Good air circulation and increasing space between the plants can help control and prevent the disease, so use wide plant spacing to promote drying of the leaves. The best option is to use disease resistant varieties.
PM – Powdery Mildew
Scientific Name: Erysiphe betae
Type: Fungus
Powdery mildew is a fungal disease that affects the growth of beets, cantaloupes & melons, cucumbers, peas, squash, Swiss chard, and tomatoes. The fungal disease may cause poor growth of the fruits in cucumbers if the infection is severe. The leaves of the cucumber begin to wither and then fall off prematurely. The disease usually affects older leaves. The leaves tend to turn a light green or a yellow green when infected. A powdery white or light gray color mold appears on the underside of the leaves. An odor similar to that of a musty basement is noticeable in fields with severe powdery mildew. The disease can spread rapidly under favorable conditions and infect the entire leaves within a week. The disease is favorable with long periods of dry weather, warm days, and cool nights, and fluctuations of day/night temperatures. The most favorable temperatures are 54-81 F and usually occur in early spring and autumn when moisture and humidity are very high. The disease can spread rapidly and can infect a field within 5 days. Fungicides for powdery mildew can help manage the disease. Good air circulation and increasing space between the plants can help control and prevent the disease. The best option is to use disease resistant varieties.
PRSV – Papaya Ringspot Virus
Type: Virus - Potyvirus
Papaya Ringspot Virus is a virus disease that affects the growth of cantaloupes & melons, cucumbers, pumpkins, and squash. Papaya ringspot virus is primarily a problem in the southern and western regions of the United States. Symptoms include yellowing and vein-clearing of young leaves, yellow mottling of the leaves, distinctive ringspot patterns on the fruit, and fruit quality, particularly flavor, is adversely affected. The infected plants should be removed to avoid further infestation. It is only spread by aphids. There is no cure for papaya ringspot disease. Insecticides for aphids are of limited value to control the disease. The best option is to use disease resistant varieties.
S - Smut
Scientific Name: Urocystis cepulae or Urocystis colhici
Type: Fungus
Smut is a world-wide soil borne disease that affects the growth of cantaloupes & melons, leeks, onions, and shallots. Smut has not been found in chives and garlic. It is one of the most destructive disease in growing onions in northern parts of the United States. The disease infects plants only when they are seedlings, killing the plants early in the season. Symptoms of smut include black streaks, blisters, or lesions appearing on the young leaves near the bulbs. A black powdery spore mass will be released when the bulbs rupture. Cold damp weather in the spring can make the seedling acceptable to the disease. Once affected by the disease, most of the seedlings will die in 3 to 5 weeks after germination. Infected plants may survive in a weaken condition, but the plant growth will be stunted, and the plant will die slowly. The infected plants should be removed and burned on the spot to avoid further infestation. The disease is also favorable when temperatures are 61-72 F, and usually occur in the spring. If the soil temperature is above 84%, when the seedlings are susceptible to the disease, there is usually no infection. Plan on using a 3 year crop rotation and avoid planting onions in the same location, year after year, as the disease can survive in the soil for a long time, up to 15 years. The smut disease can be transmitted from one field to another by water, by wind, and by farm equipment. Once the soil is infected, only seeds treated with fungicide should be planted. The best option is to use disease resistant varieties.
WMV – Watermelon Mosaic Virus
Type: Virus - Potyvirus
Watermelon Mosaic Virus is a virus disease that affects the growth of cantaloupes & melons, cucumbers, gourds, pumpkins, squash, and watermelons. Watermelon mosaic virus is primarily a problem in the southern and western regions of the United States. Symptoms include stunted or dwarfed plants, yellow or light green mottling, blistering, marginal yellowing, leaf distortion, and reduced growth rate and yields. Losses of 50 percent or more in yield and fruit quality may occur. The fruit frequently show color breaking and warts. It is only spread by aphids. Symptoms usually begin to show in June. Plan on using a 3 year crop rotation and avoid planting in the same location, year after year. Plastic mulches have been shown to reduce losses. Insecticides for aphids are of limited value to control the disease. The best option is to use disease resistant varieties.