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.
LD – Lettuce Drop
Scientific Name: Sclerotinia sclerotiorum and Sclerotinia minor
Type: Fungus
Lettuce Drop is a world-wide fungal disease that affects the growth of lettuce. The stems and leaves come in contact with the infected soil. Symptoms include wilting of the lower leaves and then leaves drop to the soil. The crown will develop a brown, soft, watery decay followed by the development of a snowy-white mycelium that eventually destroys the tissue. The entire plant will wilt and then collapse, making it unharvestable. The infected plants should be removed and burned 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 cool, conditions are moist, and soil is wet. 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 2 to 3 years. Deep tilling may be helpful in managing the disease. Drip irrigation below the soil surface. Assure good drainage with beds as high as possible. Fungicides can help manage the disease. The best option is to use disease resistant varieties.
TB - Tip Burn
Type: Physiological Disorder
Tip Burn is caused by inadequate transport of calcium to rapidly growing tissues. It has caused severe loses to growers in the United States and Europe. It affects Brussels sprouts, cabbage, cauliflower, kohlrabi, and lettuce. Uneven rainfall and watering, high temperatures, high humidity, windy conditions, dry soil conditions, and rapid growth are all factors. Tip burn consists of a breakdown of the plant tissue near the center of the head and develops as
the crop approaches maturity. The inner leaves of heads of cabbage are affected, often without external symptoms. The inner leaves turn dark brown, then to a black color. Symptoms can extend from a few small brown spots on interior leaf edges, to large areas of the leaf turning brown and eventually decaying. Secondary rot caused by bacteria can follow tip burn and heads of cauliflower can be severely affected. No completely effective controls are known, but excessive soil moisture and insufficient soil moisture have both been suspected as contributing to a calcium deficiency. Managing irrigation can regulate and control plant growth and calcium deficiency. The best option is to use varieties resistant to tip burn.