Initial signs of fusarium wilt are yellowing leaves and wilting along one side of the plant, a leaf, branch, or several branches. As the fungus spreads, more yellowing and wilting occurs with leaves dropping off prematurely (image: ag.purdue.edu).
By John Green, Texas Certified Expert Gardener, Orange, TX
Gardeners, many of you have grown tomatoes at home and will understand my description of how homegrown tomato tastes. Homegrown tomato flavor is intensely rich and tangy, having a pleasant balance of sweetness to acidity, and where the fruit is juicy. It is my opinion the homegrown tomato flavor exceeds the ‘ho-hum’, bland tasting supermarket tomato which has a mealy (grainy) texture. Of course, there are exceptions, for consumers who are willing to pay a premium price for more flavorful tomatoes…this gardener is not! Tomatoes are easy to grow but do require specific nurturing, and observant gardeners to spearhead issues immediately.
Tomatoes require a significant amount of water, otherwise growth will slow dramatically, and the plant will wilt. Tomatoes typically wilt in the heat of the day (unless protected) though recover during the cooler evening temperatures. Tomatoes thrive when they receive 1 to 3-inches of water weekly. Plants growing in structured, fast-draining soil produce best when they receive 3-inches of water a week. Tomatoes planted in well-drained loam or slow draining clay, grow best with about 1 inch of water.
Water tomatoes slowly over an extended period, as this allows water to percolate deeply into the soil, encouraging development of deep root systems. Deliver water to the base of the plant, avoid splashing water from the soil onto the lower foliage, and avoid wetting upper leaves. During periods of excessive heat (greater than 90°F), additional watering may be necessary. Fertilize plants frequently (tomatoes are heavy feeders) to provide them with the needed nutrients to maintain healthy growth.
Unfortunately, gardening enthusiasts who enjoy cultivating ‘specific’ tomato varieties know that tomatoes are ‘favored’ by a multitude of pests. Topping the list of tomato pests in SETX are tomato fruit worms, potato aphids, stink & leaf-footed bugs, tobacco & tomato horn worms, two-spotted spider mites, cut worms, thrips, silver-leaf white flies, flea beetles, nematodes, slugs, and snails. Additionally, tomatoes are prone to several fungal, bacterial, and viral diseases. Fungal diseases include early blight, late blight, septoria leaf spot, fusarium wilt, verticillium wilt, anthracnose, and buck-eye rot. Bacterial diseases include bacterial spot, bacterial canker, and bacterial wilt. Lastly viral diseases include tomato spotted wilt virus (TSWV), tomato mosaic virus (TMV), and tomato leaf curl virus (TLCV).
Today, we are focusing on three of the most common types of tomato blight and wilt, beginning with blight: Early Blight, Late Blight and Septoria.
Early Blight (Alternaria solan)– a fungus which presents as dark, concentric spots ¼ – ½ inch on lower leaves, spots on the fruit near stems and the lower leaves yellow and drop. It affects the leaves, stem and fruit. It shows up in early to mid-season, usually during wet weather.
Late Blight (Phytophthora infetans)- a fungus presenting as blue-gray spots on leaves, before turning brown, and dropping away. Irregular brown ‘greasy’ spots appear on the fruit with white ‘mold’ rings around the spots. The fungus affects leaves, stem, and fruit developing in mid to late season, often during wet weather.
Septoria (Septoria lycopersici)– a fungus with indications of small black-brown spots on the lower leaves, where the leaves yellow and then drop away. It affects the plant leaves and stems but not the fruit appearing in early to mid-season during wet weather.
All can be treated/ controlled with fungicides. Remove and destroy infected leaves into a waste receptacle (never compost tomato or pepper debris), then wash hands to minimize cross infection of other crops.
Additionally, there are three types of tomato wilt which reside in the soil: Bacteria Wilt (known as Southern Bacterial Wilt), Verticillium Wilt, and Fusarium Wilt.
Bacterial Wilt (Pseuclomonas solanacerarum)– a bacterium which when a plant is under attack the plant wilts, quickly dying. The bacteria block the vascular system to where nutrients are unable to reach branches & leaves starving the plant. The plant will remain green until the main stem splits, where it is dark green and water-soaked, an effect of the blockage and the stem becomes hollow during the late stages.
Verticillium Wilt (Verticillium albo-atrum)- a fungus whose symptoms are mimic fusarium wilt, bacterial canker or early blight. Yellow spots appear on lower leaves, followed by brown veins. Leaves then turn brown and drop away. A ‘V-shaped’ infection pattern forms progressing upwards on the stem. Plants will wilt during the day and recover at night. If the interior stem is split, it will have discolored streaks about 10-12 inches above the soil line, which is the result of tissue being blocked. Use fertilizers low in nitrogen to slow the disease and higher in potassium.
Fusarium Wilt (Fusarium oxysporum f. sp Lycopersici)- a fungus which blocks water conducting tissues, preventing water and nutrients from reaching all parts of the plant, ending in death. Initial signs are yellowing leaves and wilting along one side of the plant, a leaf, single shoot, branch or several branches. As the fungus spreads, more yellowing and wilting will appear with leaves dropping off prematurely. If the plant does not die, it will produce weak and inferior fruit. Fusarium wilt can appear at any time during the plant’s growth cycle, usually appearing after the blooms start appearing, favoring 70°to 90°F temperature range and wet weather. The fungus multiplies rapidly in poor draining soil, quickly moving up the vascular system. Slow the disease by keeping soil pH range between 6.5 – 7.0 and using a nitrate-based nitrogen fertilizer, instead of a nitrogen based fertilizer. Root-knot nematodes assist the fungus become more prevalent as they allow the fungus ‘easy’ access into the plant system. Use disease-resistant tomato varieties with and “F” listed after the variety name on its label, indicating resistance to one or more strains for the fungus.
There are also non-pest related causes of tomato leaf yellowing which are often nutrient deficiencies. These are the more common nutritional deficiencies associated with yellowing leaves. Gardeners need to focus on the plants’ overall health, scrutinizing plants daily, and fertilize regularly. When using a lot of fertilizer, the tomato plant will require more water. Yellowing leaves can be the result of nutritional imbalances of nitrogen, iron, and magnesium.
Nitrogen is the most common cause, since people don’t often realize tomatoes are ‘heavy’ feeders requiring nitrogen based fertilizer. Tomatoes require twice the amount of fertilizer as a cucumber, and four times the amount as beans. Often, older leaves will begin turning yellow and then drop away. This is a defense mechanism where the plant provides nitrogen to the younger leaves, enabling them to survive.
An iron deficiency causes yellowing of leaves in the plant but is typically found on the youngest leaves only.
A magnesium deficiency produces yellow leaves which appear more like spots on the older leaves.
Growing Strategies:
Healthy tomato plants produce several pounds of flavorful, juicy fruit. Use these strategies for a better harvest:
- Planting- tomatoes require full sun, and the planting location must receive at minimum 8 hours direct sunlight.
- Friable soil- is easily crumbled when dry and clumps together slightly when wet.
- Moisture- two to three inches of water weekly, delivering water to the base of the plant.
- Nutrition- fertilize by amending planting area with aged compost at planting or applying a commercial organic fertilizer (my choice is to use seaweed and fish emulsion).
- Support- provide a cage or other support structure to maintain tomato plants’ and keep plant from sprawling on the soil surface.
Many of the diseases can be avoided by rotating planting areas yearly, using a four-year rotational cycle. Avoid planting peppers, eggplant, potatoes, sunflowers and cosmos all of which are susceptible to the same diseases if planted in the same spot.
Plant disease-resistant hybrids, plant in raised beds, allow plenty of space between plants, water the soil, not the plants, mulch and keep lower leaves from touching the ground to keep the fungus from spreading to them, stake your plants for better air circulation and most of all remove and destroy affected plants at the end of the season.
So long for now fellow gardeners, let’s go out and grow ourselves a greener, more sustainable world, one ‘tomato’ at a time! For answers to your gardening questions, send me an email: jongreene57@gmail.com.
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