Tomatoes (Lycopersicon lycopersicum) are a favorite crops of the home gardener. Store-bought varieties rarely compare to the flavor of a fresh, ripe tomato straight from the vine. Today, many varieties of tomato are resistant to particular diseases, but there are several disorders to be aware of when growing a tomato garden.
Types of Disease
Diseases that afflict tomato plants are bacterial, fungal or viral in origin. Two of the most common are fusarium and verticillium wilts, which are fungal diseases, as are molds and mildews. Tomato leaf spot, canker, and stem rot are a few bacterial diseases. Viral disease of tomato plants affecting leaves include, among others, tobacco (tomato) mosaic, tomato yellow leaf curl, and tomato spotted wilt.
Lack of water is not the only factor to cause a tomato plant to wilt. An unhealthy plant will have visible symptoms such as drooping branches and curled leaves or loss of leaves. Diseased tomato leaves may exhibit dark spots, or yellowing followed by leaf necrosis (death) and wilting, brown coloring inside the stem when cut open and hollowness of the stems. Stunted, fern-like leaves may be infected with tobacco (tomato) mosaic virus. Paying close attention to the growing tomato plant and studying its leaves is key to discovering disease before it has a chance to spread.
Viruses are often spread by insects such as aphids and white flies. Control of these pests will help control the spread of disease. Commercial and organic pest control sprays may be useful. Also, refraining from planting tomatoes and other Solanaceous plants like peppers and potatoes in the same location can help guard against the spread of fusarium and verticillium wilt diseases, which are incurable.
Eliminating weeds and infected plants from the garden will also help lessen the spread of disease. Fungicides can help treat tomato leaf diseases, but since some fungal diseases can survive from year to year, removal of old plant matter and weeds is very important.
One of the best measures to avoid certain plant leaf diseases is to grow wilt-resistant varieties. Heirloom (old) varieties are often more flavorful, but do not have the ability to combat wilt disease. Planting commercial, resistant varieties that have been designated as wilt-resistant, nematode- and mosaic virus-resistant will be labeled as such. Weed control helps eliminate the source of some disease, and also allows the tomato plant to be more vigorous and healthy, which results in plants that can more effectively resist disease. Using clean garden tools also helps reduce the spread of disease. Although many diseases are caused by viruses, bacterias and fungi, nutritional deficiencies can also be to blame for an unhealthy tomato plant -- and an unhealthy plant invites disease. Follow the recommended cultural practices for a particular variety to receive the best fruit at harvest.
Local county extension agencies and university agricultural extension departments are a recommended source of information regarding details about diseases that are particularly relevant in some locations. Often, a home gardener can provide a plant sample to be tested to determine the exact disease and receive recommendations for remedy. Photo galleries, clearly showing symptoms and characteristics of diseases affecting tomato leaves, are readily available online, through university extension departments.