HPIPM:Cercospora Leaf Spot Spinach

Author: Howard F. Schwartz and David H. Gent

Identification and Life Cycle

Cercospora leaf spot is caused by the fungua Cercospora beticola. The disease cycle is initiated by conidia disseminated by wind and splashing rain and irrigation water. Conidia germinate when humidity is high or free moisture is available under high (77 to 95ºF) temperatures. The fungus sporulates optimally between 68 to 79°F and 90 to 100% relative humidity. The disease is highly influenced by weather conditions; plantings that mature in cool weather often escape severe infection. The fungus overwinters in infested seed and crop residues.

Plant Response and Damage

Cercospora leaf spot symptoms begin as small (0.1 to 0.2 inches in diameter), circular to angular, brown to dark green spots with a reddish brown margin form on older leaves. During periods of warm temperatures and high humidity or leaf wetness, tan necrotic spots on lower leaves will turn gray and lower quality or make the leaves unmarketable. The disease reduces spinach yield, quality, and marketability.

Biological Control

No biological control practices have been developed for Cercospora leaf spot.

Cultural Control

Plant high quality spinach seed free from C. beticola. Practice a three-year or longer rotation to nonhosts, such as small grains or corn. Avoid overhead irrigation, especially during humid, cloudy weather. Deeply bury crop residues soon after harvest to reduce pathogen survival and overwintering. Eliminate volunteer spinach, alternate hosts (mangel, red beet, Swiss chard, sugarbeet), and weeds (common lambsquarter, redroot pigweed, mallow, and bindweed) that can serve as Cercospora leaf spot inoculum sources. Reduce periods of leaf wetness by decreasing planting densities, orientating rows parallel to the prevailing wind direction, and avoiding overhead irrigation.

Chemical Control

Chemical controls are most effective when integrated with sound cultural control practices. Copper-based fungicides may leave unattractive residues on leaves and make them unmarketable.

Due to constantly changing labels, laws and regulations, the sponsors of this web site assume no liability for the suggested use of any chemicals noted in the management section. Contact your local pest management personnel for current information on labeled pesticides that can be used for the intended plant disease, insect pest or weed.