Potatoes (Solanum tuberosum L.) are host to many pathogenic organisms that can affect any plant part during the growing and storage seasons. Historically, certain diseases of potato have had significant socio-economical impact, like the Irish potato famine of the 1840s caused, in part, by Phytophthora infestans (late blight).

Most of onion diseases are caused by fungi that can contribute to severe losses and reduce yield, quality and marketability of the product. Diseases such as downy mildew and numerous problems caused by Botrytis spp. can cause extensive damage to the onion production worldwide. Other diseases can be equally important but are confined to certain geographical areas. To use best management practices, understanding and properly identifying these diseases is crucial.

Cauliflower (Brassica oleracea) and other cruciferous crops including cabbage, brussels sprouts and broccoli are susceptible to many diseases. Alternaria leaf spot and downy mildew are common in crucifer production and can reduce plant yield and market value. Alternaria leaf spot, in contrast to downy mildew, is favored by warm, moist weather.

The most common diseases of broccoli (Brassica oleracea L.) include black leg, black rot, downy mildew and soft rot. Black leg is mainly associated with the early stages of the plant development, while black rot and downy mildew are common when the plant matures. Both black leg and black rot are usually transmitted through seed or diseased transplants. Because of that, it is imperative that a grower plants disease-free, certified transplants or certified seeds.

Because of prolonged periods of heat and drought, growing and maintaining a healthy lawn in the South are more challenging and require homeowners to consider many factors. There are numerous diseases associated with turf In Louisiana, the most common problems include, but are not limited to, brown patch, melting out, Bermudagrass decline (take-all root rot), dollar spot and St. Augustine decline (SAD).

There are nearly 75 known lettuce diseases with diverse causes that can be limiingt factors to lettuce production when resistant or tolerant cultivars are not available.

Bacterial speck is favored by cool temperatures and high-moisture conditions. Severe fruit spotting can decrease yield potential by reducing its marketability.

Bacterial wilt is a soil-borne disease found in warm, temperate, subtropical and tropical areas. Ralstonia solanacearum (previously called Pseudomonas solanacearum) enters its host through roots and colonizes the xylem elements in the vascular tissue. Ralstonia has an extremely wide host range with well over 200 hosts reported.

Bacterial spot is present wherever tomatoes or peppers are grown. Crop losses result from both defoliation and spotting on the fruit, reducing yield potential and fruit marketability.

Plant diseases can become the limiting factor ito tomato production worldwide. There are nearly 200 known tomato diseases of diverse causes and etiologies. Control of these diseases involves host resistance, exclusion, eradication and most importantly, use of best management practices.

A localized calcium (Ca) deficiency in the distal end of the fruit results in blossom-end rot. Fruit and undeveloped leaves have low transpiration rates and, therefore, are subject to this physiological disorder. Because calcium is not a highly mobile element, deficiency can occur with water supply fluctuations, high salt levels, the use of ammonium nitrogen and moisture extremes. Both blossom-end rot and sunscald are physiological disorders that cannot spread from plant to plant.

Southern blight (or southern wilt) is a disease of hundreds of plant species, including tomatoes. It is favored by moist conditions and high temperatures. The fungus can survive for years in soil and plant debris.

Fusarium wilt is a warm-weather disease, and infection occurs through wounds in the roots. Disease symptoms include seedling stunting, drooping and downward curling of older leaves and discoloration of the vascular tissue. This is usually noticeable during the period from blossoming to fruit maturation. This pathogen is soilborne and can remain in infested soils for several years.

Image gallery of strawberry diseases - bacterial and fungal pathogens affecting appearance as well as marketability of strawberries.

Early blight is one of the most common tomato diseases and is distributed world-wide. Early blight is generally found in humid or semiarid climates where frequent dews provide significant moisture for disease development. This disease can result in severe crop losses due to defoliation and reduction in fruit size and quality.

Beans and peas are commonly affected by many diseases. If proper cultural practices, such as seed certification, use of resistant varieties, proper planting and crop rotation are followed, many of these problems can be avoided.

Alternate freezing and thawing of plant tissues can destroy plant cell walls, often killing tender plants. In hardier plants, flowers, buds or leaves may blacken or become distorted. In woody plants bark can split if damage is severe.

Solanum melongena L. (eggplant) is a member of Solanaceae family. This is frost-tender herbaceous perennial, usually grown as an annual plant. Diseases such as Verticillium wilt, Southern blight, Phomopsis blight, Anthracnose fruit rot and Altenaria blight are commonly associated with eggplant and can reduce its harvestable yield significantly.

Cabbage, broccoli, cauliflower, brussels sprouts and kale are some of the members of the crucifer family often referred to as cole crops. Several diseases are associated with these plants, including root and stem rots of young plants, black rot, downy mildew and viruses.

Cucumber (Cucumis spp.), like other cucurbits (melons, squash, pumpkins, etc.), are attacked by several pathogens that can result in severe crop losses. Most damage is observed on cucumber leaves and stems. Fruits can also be severely affected, resulting in overall poor quality and yield, especially if disease has already weakened the plant.

The pepper (Capsicum spp) originated in Mexico and surrounding areas of Central America. It is an excellent source of vitamin A, vitamin C and calcium. An important crop in commercial vegetable production, peppers have disease problems with which growers must be concerned.

Mustard (Brassica juncea ) is vulnerable to several diseases. The most serious ones include downy mildew, white rust, sclerotinia stalk rot (white mold), leaf spots and virus mosaic.

Pumpkin (Cucurbita pepo) is a warm-season vegetable that can be grown throughout much of the United States. Together with winter squash, pumpkins are among the most-resistant of the cucurbits to certain diseases and insect damage. However, diseases such as Phytophthora fruit rot, Microdochium blight, Zucchini yellow mosaic, Fusarium rot and gummy stem blight are several common diseases that can severely affect pumpkin production.

Like any other crop, squash is susceptible to a variety of diseases that attack below- and above-ground parts of the plant. Major squash diseases include gummy stem blight/black rot, scab, powdery mildew, nematodes and several viral diseases. Because many of the fungal, bacterial and nematode pathogens survive in soil and/or crop debris, crop rotation with non-cucurbit crops for at least three years is highly recommended.

There are many fungal, bacterial, viral and abiotic diseases associated with ornamental plants. New diseases and disorders are being discovered all of the time. Therefore, proper identification and management are needed to prevent further damage and avoid future outbreaks.

Herbs, whether annuals, biennials or perennials, are widely grown for their culinary, aromatic, medicinal and ornamental properties. The diversity of herbs grown is reflected by the diversity of diseases that occur on them.

The use of annuals in the landscape provides color and allows for seasonal changes in the landscape. Because their growth is more intensely managed than trees and shrubs, conditions are often quite suitable for the development and spread of diseases and other pests.

Trees and shrubs are important components of the landscape, providing structure, texture and color. A variety of plant health problems caused by biotic and abiotic agents greatly affect the quality of these plants. The use of best management practices is essential for the establishment and care of landscape trees and shrubs and the prevention of disease.

Because of generally low maintenance and reduced problems associated with this group of plants, use of perennials in the landscape has increased over the years. By following best management practices many of disease problems could be eliminated.

Sun scald is a non-pathogenic disease found on a number of plants, including ornamentals, vegetables and fruits. This type of damage occurs when plants are exposed to too much direct sunlight. The injuries are more severe on stressed, weakened or recently transplanted plants.

During prolonged days of high temperatures and increased stress, plants try to maintain their water balance by reducing water loss through stomatal closure, which may result in foliage wilting, abnormal growth and, in severe cases, plant death.