Seeds: Diseases & Treatment

 Seeds can spread plant diseases from one farm to another, from one state to another, and from a distant country to the other. Some disease pests may survive for years, safely lodged on or in a seed or on bits of stem or leaf mixed with the seeds. Many seedborne diseases cannot be recognized when seeds are examined, and cannot be detected during incubation. Only by inspecting the growing crop can one be sure that the seeds are free of viruses, bacteria, and fungi. Most seedborne parasites do not affect germination immediately. They do not harm the seeds but multiply on emerging seedlings, which may then succumb to the disease. Some seed lots that show high germination in tests are nearly destroyed when they are planted under conditions that favor development of the organisms they carry.
Control of such diseases begins with the seed, it is easier and cheaper to eliminate a pathogen from a few pounds of seeds than to attempt to spray or dust entire fields of growing plants. Some pathogens can be eliminated or their range of occurrence can be reduced by treating the seed with suitable chemical compounds, hot water, or fumigants. Some seedborne diseases do not prevail in regions of low rainfall and relatively high temperature during the growing season. Seeds produced under such conditions usually are free of many of these destructive, disease-causing bacteria and fungi. The commercial production of seed of certain vegetable, ornamental, and forage crops therefore has been shifted from humid areas of the East and Midwest to irrigated, semiarid western areas.
Careful inspection and weeding out of diseased plants in fields destined for seed production greatly reduce the incidence of seedborne diseases. Although hundreds of pathogens are known to be seedborne, effective control measures have eliminated some and reduced the incidence of others to the point where they are troublesome only occasionally.
Some of the worst diseases of vegetable crops are seedborne. In most instances, no varieties resistant to seed-borne diseases have yet been developed. For some, no chemical seed treatment gives satisfactory control. Rain, hail, and high humidity following storms, which are responsible for the spread and development of the bacterial blight organisms, occur much less frequently during the growing season in parts of Idaho and California than in the other States. Consequently the production of seed of snap beans now centers in those sections.
Several fungi that cause seed decay and seedling diseases are seedborne. Phomopsis seed decay, frogeye leaf spot, anthracnose, purple seed stain, and downy mildew can cause seed rots, reduce emergence and prevent adequate stand establishment. These problems are usually more severe in cool wet soils. The best tactic for avoiding these diseases is the use of high quality disease-free seed. The most common of these seedborne diseases is phomopsis seed decay. The herbicides used on the field must be considered when a decision to replant is made.

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