University of Kentucky College of Agriculture Plant Pathology Extension

Cooperative Extension Service University of Kentucky College of Agriculture, Food and Environment

Plant Pathology Fact Sheet PPFS-VG-15 Tomato Wilt Problems Kenneth W. Seebold Extension Plant Pathologist

Fusarium & Verticillium Wilts Fusarium and Verticillium wilts are two fungal diseases that cause similar wilts in tomato. Fusarium wilt tends to be more common during warm weather, while Verticillium wilt is found more often when temperatures are cool. Both diseases share similar symptoms and can be hard to tell apart visually; laboratory tests are often needed for an accurate diagnosis.

Symptoms The first symptom of both diseases is a slight wilting of the plants, especially during the hottest part of the day.

Fusarium wilt symptoms also include drooping, yellowing, wilting, and dying of the lower leaves, often on one side of the plant (Figure 1). These symptoms may appear on successively younger Figure 1. Fusarium wilt symptoms include wilt, yellowing, leaves with one or more branches being affected and browning of foliage. Symptoms often occur only on one side of the plant. (Photo: Edward Sikora, Auburn and others remaining healthy. After a few weeks, University, Bugwood.org) browning of the vascular system (Figure 2) may be observed by slicing the stem open lengthwise symptoms on leaves may also include yellowing of with a knife. This brown discoloration inside the V-shaped areas between the veins or leaf margins stem can be found from the roots to the top of the (Figure 3). Frequently, leaves on all sides of the plant. Plant growth is stunted and, under warm plant show symptoms. Plants may wilt during the conditions, the plant may die. day and recover at night. Plants are stunted and may eventually die under relatively cool growing Verticillium wilt symptoms are very similar to conditions. Tannish-brown streaks of discolored those of Fusarium wilt, but they often occur more vascular tissue can be found inside the stem, as slowly and with much less yellowing of leaves. Early with Fusarium wilt, but mainly in the lower stem.

Agriculture & Natural Resources • Family & Consumer Sciences • 4-H/Youth Development • Community & Economic Development Figure 2 Figure 3A Figure 3B

Figure 2. Vascular discoloration due to Fusarium wilt. (Photo: Clemson University-USDA CES slide series, Bugwood.org) Figure 3. Verticillium wilt may result in V-shaped lesions between veins. Yellowed tissue (A) eventually turns brown (B). (Photos: Gerald Holmes, Valent USA Corp, Bugwood.org)

Cause and Disease Development so it is important to control nematodes if they are Both fungi (Fusarium oxysporum f. sp. lycopersici present or to use varieties labeled VFN. and Verticillium albo-atrum) are common inhabitants of Kentucky soils. These organisms • Sanitation – Greenhouse soils should be infect plants through roots and spread through fumigated or steam-sterilized. the water-conducting vessels (vascular tissue). The cells in the vascular tissue are plugged by fungal growth that stops water movement through this Southern Bacterial Wilt tissue, causing wilting. Fusarium and Verticillium may be introduced in several ways: pathogen- Bacterial wilt is not a serious problem in Kentucky, infested soil, old crop residues, contaminated seed but some damage occasionally does occur in and transplants, wind, water, or mulches. These scattered areas and during hot growing conditions. fungi become established readily in most soils and can remain there for many years, even in the absence of a host. Both diseases are much more serious when plants are also infected with root- knot nematode.

Disease Management • Resistant varieties – A number of tomato cultivars are resistant to one or both of these diseases. Resistant varieties are generally designated in seed catalogs with the letter “V” (for Verticillium) or “F” (for Fusarium). While there are three known races of the Fusarium wilt pathogen, with races 1 and 2 being most common, resistance may be to only one or two of these races; this information is also generally noted in the catalog. The letter “N” (as in VFN) signifies resistance to root-knot nematode As a rule, damage from Figure 4. Bacterial wilt typically results in rapid wilting, nematode feeding can reduce the effectiveness without the yellowing associated with the fungal wilt of resistance to Fusarium and Verticillium wilts, diseases. (Photo: Kenneth Seebold, UK) Symptoms transplants or through drainage water from The vascular tissue of affected plants turns adjacent infested land. The bacterial wilt pathogen black and plants rapidly wilt without yellowing can persist for many years after it is introduced (Figure 4). As the disease progresses, the pith into an area, and eradication is extremely difficult. decays, appearing dark and water-soaked; sunken, brown cankers may be visible on the lower stem. A Disease Management slimy bacterial slime oozes from the stem when it is • Disease-free transplants – Inspect plants prior pressed and the stem may become hollow. When to transplanting to be sure they are disease-free. the stem of an infected plant is placed in water, a milky flow (made up of the many bacterial cells • Crop rotation – Do not plant tomatoes in sites clogging vascular tissue) will emerge from the cut where the disease has been a problem in the past. end of the stem in a matter of minutes. Infected Practice long crop rotations. plants collapse and die in hot weather. • Sanitation – Remove and destroy infected Cause and Disease Development plants promptly. The bacterial wilt organism (Ralstonia solanacearum) survives in the soil and on weedy • Hydroponic production – Take care when hosts. The bacterium infects susceptible plants installing hydroponic production systems where through wounds in the roots or stem and initially this pathogen is known to exist. The bacterial wilt invades the water-conducting tissue of the vascular pathogen can spread easily in these systems if system. Bacterial cells released into the soil from contaminated soil or water is introduced. collapsed plants can survive even without a host. The pathogen can be carried into “clean” fields, greenhouses, high-tunnels, or gardens via infected Walnut Wilt Wilting of tomato plants may be associated A B with walnut trees, especially black walnut (Juglans nigra) (Figure 5), and butternut (Juglans cinerea) trees. Injury occurs when tomatoes are grown near these trees because walnut and butternut roots excrete large amounts of a toxic substance into the soil.

Symptoms C Affected plants can initially appear unthrifty. These plants may continue to survive the growing season, but be stunted, unhealthy, and low yielding. Severely affected plants, however, can turn yellow, suddenly wilt, and die. Wilted plants (Figure 6) often show a discoloration of the vascular system (Figure 7) similar to that caused by Fusarium and Verticillium wilt diseases.

Figure 5. Black walnut trees (A) produce a substance toxic to tomato plants that is present in tree bark, leaves (B), and fruit (C), as well as roots. (Photos courtesy of Bugwood. org (a) Vern Wilkins, Indiana University, (b) Jason Sharman, Vitalitree, and (c) Franklin Bonner, US Forest Service) Figure 7. Plants Management that have been Avoid planting tomatoes near affected by walnut wilt often show walnut or butternut trees, or in discoloration of the locations where these trees may vascular system, have grown previously. Juglone similar to the fungal can remain in the soil several wilts. (Photo: Cheryl Kaiser, UK) years after a tree has been cut down. Wood chips and other debris from walnut trees should not be used as mulch unless composted beforehand.

Additional Resources • Home Vegetable Gardening in Kentucky (ID-128) http://www.ca.uky.edu/agc/ pubs/id/id128/id128.pdf • IPM Scouting Guide for Common Pests of Solanaceous Crops in Kentucky (ID-172) http://www.ca.uky.edu/agc/ Figure 6. Symptoms of walnut wilt include wilting, yellowing, unthrifty plants, and low yields. Note the black pubs/id/id172/id172.pdf walnut tree in the background. (Photo: Cheryl Kaiser, UK) • Root-knot Nematode (PPFS-GEN-10) http://www2.ca.uky.edu/agcollege/ Cause and Disease Development plantpathology/ext_files/PPFShtml/PPFS-GEN-10. Black walnut and butternut trees produce a toxin pdf called juglone in leaves, stems, fruit hulls, inner • Vegetable Production Guide for Commercial bark, and roots. Other walnuts and related trees, Growers (ID-36) such as hickories and pecans, also produce juglone, http://www.ca.uky.edu/agc/pubs/id/id36/id36. but in much lower amounts. The toxin leaches htm into soil where roots of sensitive plants, such as tomato, may come into contact with it.

Tomato plants located beneath the canopy of Acknowledgements walnut trees are at greatest risk because juglone Thanks to Daniel Egel, Extension Plant Pathologist from roots and fallen leaves accumulates there. at Purdue University, and Anthony Keinath, Because walnut roots extend well beyond the drip Vegetable Plant Pathologist at Clemson University, line of the tree, injury to plantings may occur at a for their reviews of this publication. distance equal to the height of the tree. Juglone can be toxic in very low doses and plant roots can encounter this chemical by growing within a half- inch of a walnut root. The toxin can persist in tree roots even after the tree has been cut down and roots have begun to decompose. May 2014

Revised from the original fact sheet, Tomato Wilt Problems (PPA-19), written by W.C. Nesmith, J.R. Hartman, and C.A. Kaiser

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