Plant diseases leaf-spot

Leaves with brown spots. Cause Fungal diseases. Several fungi cause leaf spots that enlarge, run together, and form blotches. Don t overcrowd plants avoid working with phlox when leaves are wet remove and destroy infected plant parts and severely infected plants. If leaf spots are a regular problem, spray with sulfur or bordeaux mix. 

Practically all the coffee planted commercially comes from seed, except in the rather limited Robusta-growing region of Java where grafted plants are used. Coffee seeds are planted in seedbeds and are treated in about the same way all over the tropics. The mature and apparently healthy fruits are selected and the seeds are pressed out, washed and dried in the shade, and planted rather soon, because coffee seed viability is lost within a comparatively short while. Handled in this manner, the chances are lessened that coffee diseases will be carried by seeds. However, it has been proved experimentally that infected plants can be produced from seeds contaminated with both the coffee Colletotrichum and the coffee Cercospora from either field material or artificial inoculation. This contamination is probably not uncommon in plantation practice and thus far it is not of extreme importance. The Hemileia rust is probably not carried on the seed (93). The American leaf spot is not carried on seed (97). 

Higgins VJ. 1972. Role of the phytoalexin medicarpin in three leaf spot diseases of alfalfa. Physiol Plant Pathol 2 289-300. 

Alternaria has been knovm for centuries to cause various plant diseases such as early blight of potato and various leaf spots and fruit rot. Species of this fungus are widely distributed in soil and on aerial plant parts. Because Alternaria requires high moisture levels (28-34%) for growth, infection of seeds occurs when the seed moisture is high, either in early stages of development or after wetting of crops from rain. 

Many plant diseases cause similar symptoms in the host plants. Such things as leaf spots, wilts, galls on roots, or stunted growth may be caused by many... 

Consider plant color. Pale overall color indicates a need for nutrients, which is easy to correct. However, distinct yellow streaks or brown leaf spots indicate presence of disease. 

Fortunately, the same controls are effective against many leaf spot diseases. Remove and discard infected leaves. Thin plants and avoid crowding future plantings. Wash your tools and hands after handling infected plants.. Avoid overhead watering. Inspect bedding plants on purchase. Clean up plant debris to remove overwinterins sites. 

Fruit with small, dark, sunken spots or cracks on skin. Cause Bacterial leaf spot. This disease, common in the Southeast, is very difficult to control. Plant resistant cultivars, including Alfred , Curtis , Harcot , Hargrand , and Harlayne . For more information, see Fruit with small, dark, sunken spots or cracks on skin on page 166. 

Cause Cercospora leaf spot. Destroy spotted leaves. Spray plants with copper if this fungal disease is severe to prevent further spread, or before symptoms develop if it has been a problem in the past. To prevent problems, soak seed in 122°F water for 25 minutes before planting. (Be aware that this treatment can damage seed viability for complete instructions, see page 422.) Eliminate weeds that can harbor the disease. Plant cultivars, such as Big Red Hybrid and Red Ace , that are tolerant of this disease. 

Leaves with light-colored spots on upper leaf surfaces. Cause Downy mildew. Leaves infected with this fungal disease have spots covered with white fuzzy growth on the undersides. Spray plants with copper when symptoms first appear. 

Leaves spotted, yellow, and drop early. Causes Septoria leaf spot anthracnose. Since both of these fungal diseases overwinter on old leaf litter, rake up the leaves or bury them under a thick mulch in autumn. Copper sprays also control both diseases. If defoliation occurs late in the season, it does plants little harm. 

Leaves with circular brown spots. Cause Bacterial leaf spot. This bacteria can cause water-soaked spots on lower leaves. These spots turn brownish black and may spread to form large patches of dead tissue. To prevent the spread of this disease, avoid working around wet plants. Remove and destroy affected parts spray bordeaux mix on remaining plants. 

Leaves with yellow, hr tlii, or hlack spots. Cause Leaf spots. Irises may develop leaf spot, caused by several different species of fungi, especially in wet weather. Remove infected plant parts clean up debris in fall to remove disease spores. 

Leaves with dark or water-soaked spots. Cause Various bacterial or fungal leaf spot diseases. Destroy badly spotted plants or leaves. Thin plants to increase air movement, and a oid wetting leaves when watering. Prevent rroblems by keeping plants well-fed. 

Leaves with rotted patches or spots. Cause Fungal rots leaf spots. The moist soil conditions favored by lobelias encourage a variety of fungal rots and leaf spots that are best treated culturally. Remove infected plants and plant parts keep gardens free of plant debris and weeds where diseases can overwinter space plantings to permit good air circulation. 

Leaves with gray-brown spots. Cause Cercospora leaf spot. This fungal disease only occurs in very warm climates. Spc its develop a frog-eye appearance with ligm centers and dark edges. Spray plants with copper as soon as symptoms appear to prevent further syrrip-tom development. Presoak seed in a 10 percent bleach solution and plant resistant cultivars, such as California Wonder , to prevent problems. 

Leaves with small, round, brown spots. Cause Leaf spots. Fungal leaf spots rarely reduce yields. Destroy diseased leaves after harvest. Spray plants with sulfur if disease is severe. 

Leaves with water-soaked or brown spots. Causes Anthracnose other fungal leaf spots. Spots may enlarge rapidly, especially in wet weather. Destroy infected leaves or plants. Spray plants with sulfur to prevent disease from spreading, especially if weather is wet. Prevent problems by thinning plants to provide good air movement. 

Leaves mottled yellow between veins purple spots on leaf undersides. Cause Downy mildew. For an illustration of this disease, see the opposite page. As the disease progresses, spots enlarge, older leaves turn brown and die, and younger leaves become infected. Treat plants with a dilute solution of copper spray to reduce the spread of the disease. Prevent problems by planting tolerant cultivars such as Super Select and Zucchini Select . 

Leaves with spots. Causes Leaf spot leaf blight leaf scorch. Leaf spot causes small purple spots that develop tan centers on foliage. See page 218 for an illustration of leaf spot. Leaf blight is characterized by oval or V-shaped spots with purple centers and tan borders. Irregular, purplish blotches are the symptoms of leaf scorch. When severe, these diseases kill leaves, which weakens plants. Berries are... 

If the patches develop into circular, dark spots with light centers peppered with dark specks, suspect Septoria leaf spot, another fungal disease. Older leaves are affected first. Spray plants with copper to prevent further symptom development. Spraying transplants with an antitranspirant may help prevent Septoria. However, don t spray with antitranspirant when tomatoes are blooming heavily. 

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