LMV – Lettuce Mosaic Virus
Type: Virus - Potyvirus
Lettuce Mosaic Virus is a world-wide seed-borne disease that affects the growth of endive, lettuce, and spinach. Symptoms include stunted or dwarfed plants, show a mosaic or mottling pattern on leaves, and plants rarely grow to full size. Head lettuce may fail to form heads and the wrapper leaves often will curve back away from the head. Outer leaves will be yellow, twisted, and deformed. Yellow or brown blotches may appear on the leaves. Severe infection can lead to the death of the plant. The disease can cause substantial yield loss and total crop loss. It is a seed-borne disease and is spread by aphids. The virus can live in weeds, so use weed management techniques. Plan on using a 3 year crop rotation and avoid planting in the same location, year after year. Keep the fields weed free. Proper tillage practices may be helpful in managing the disease. Insecticides for aphids are of limited value to control the disease. The best option is to use virus-free seeds and 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.