Beans are a warm season vegetable that are the second most popular in the home vegetable garden following tomatoes, according to the University of Illinois Extension. Bush beans, also referred to as string beans, get their name from the shrub-like, bushy growth of the plants that do not require support or staking like pole beans. A number of viruses infecting the plants cause yellowing foliage.
Bush beans are susceptible to infection from the bean common mosaic virus or BCMV. The disease is transmitted to plants through pollen, aphids or mechanical means. Other likely diseases that can cause yellow leaves include curly top, also referred to as Ruga verrucosous, and golden mosaic virus. Curly top is transmitted from a variety of perennials and annuals and is common in the western regions of the United States. Golden mosaic virus is primarily transmitted by the whitefly.
Bean common mosaic virus is characterized by the appearance of yellow and dark green, mosaic-pattern on foliage followed by distortion, stunting and downward curling of leaves. Young plants are entirely yellow and smaller in size. Plants infected with curly top display an initial downward curling and puckering of leaves followed by yellowing and gradual death of plants. Foliage of bean plants infected with golden mosaic virus become yellow in color or develop a mosaic of gold and green. Plant growth is stunted and pods are deformed.
Warm temperatures ranging from 68 to 77 degrees F are most favorable for the development of bean common mosaic virus. Curly top is frequently a problem during the dry weather spells in winter and spring and with the presence of leafhoppers. Symptoms are worse in plants that are infected earlier in the season. Golden mosaic virus is common at temperatures of 75 to 86 degrees F with 80 degrees F being the optimal temperature and in areas with high population of whiteflies.
Use resistant varieties of bean plants to avoid bean common mosaic virus in plants. Obtain disease-free seed from reliable sources since infected seeds also look normal. Control aphids near the planting site because these insects are disease vectors. You can also help minimize chances of the curly top infection by using disease-free seed and resistant varieties. However, a number of resistant varieties tend to lose resistance when exposed to very high temperatures. Rotate crops to reduce the chance of golden mosaic, and plant beans away from major whitefly host plants such as tomatoes, tobacco, cotton and soybean. Plant as soon as soil is warm in spring to allow the plants to get established under cooler temperature and high moisture. Control whiteflies with the use of recommended insecticides.
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