Yellows
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Yellows 
Yellows are commonly transmitted by leafhoppers as they feed, these diseases are caused by mycoplasmalike organisms. There is no cure for infected plants
The aster yellows phytoplasma (formerly known as mycoplasmalike organisms) overwinters in the body of adult leafhoppers and in perennial or biennial host plants, including native plants, ornamentals, and weeds such as Russian thistle (Salsola tragus), sowthistle , prickly lettuce, dandelion , and many others. The principal vector is the aster leafhopper, although the phytoplasma can be transmitted by many other species of leafhoppers. Leafhoppers can remain inoculative for at least 100 days. In some areas, the occurrence of aster yellows may follow the pattern of leafhopper migration. Susceptible Plants- A wide range of woody and herbaceous plants are affected by yellows. Aster yellow affects many plants including carrots, asteraceae family., tomatoes, China asters, and gladiolus. Elm yellows also know as elm phloem attacks several species of elms.
Symptoms- The disease produces a gradual yellowing of the leaves. Plants often appear dwarfed. Plant parts including roots and leaves may become deformed. On trees leaves turn yellow then brown and may drop early. Symptoms appear over the whole crown of the tree. Plants may die in a single growing season.
In vegetable crops such as cabbage, an celery invasion by secondary rot organisms results in soft rots and hollowed cavities in the plant crowns. Aster yellows also cause similar yellowing and stunting. However, aster yellows usually causes severe petiole twisting and lacks the vascular discoloration caused by Fusarium yellows Prevention and Control- Controlling leafhopper will reduce the chances of this disease. Removing weeds that provide overwintering sites for the pathogen including thistles, Queen Anne lac, dandelions and wild chicory. Remove and destroy infected plants. Do not compost plants infected with yellows. Use resistant or tolerant cultivars when available. Avoid contaminating uninfested fields or beds by preventing introduction of soil/crop residue. Leaf Hopper Control- More times than not if your plants or trees have yellows, leafhoppers are the cause. Biological Controls of these pests include Green Lacewing
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