Fusarium & Verticillium WiltsFusarium 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.

SymptomsThe 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 leaves with one or more branches being affected and others remaining healthy. After a few weeks, browning of the vascular system (Figure 2) may be observed by slicing the stem open lengthwise with a knife. This brown discoloration inside the stem can be found from the roots to the top of the plant. Plant growth is stunted and, under warm conditions, the plant may die.

Verticillium wilt symptoms are very similar to those of Fusarium wilt, but they often occur more slowly and with much less yellowing of leaves. Early

symptoms on leaves may also include yellowing of V-shaped areas between the veins or leaf margins (Figure 3). Frequently, leaves on all sides of the plant show symptoms. Plants may wilt during the day and recover at night. Plants are stunted and may eventually die under relatively cool growing conditions. Tannish-brown streaks of discolored vascular tissue can be found inside the stem, as with Fusarium wilt, but mainly in the lower stem.

Plant Pathology Fact Sheet

Tomato Wilt ProblemsKenneth W. Seebold

Extension Plant Pathologist

Figure 1. Fusarium wilt symptoms include wilt, yellowing, and browning oF Foliage. symptoms oFten occur only on one side oF the plant. (photo: edward sikora, auburn university, bugwood.org)

University of Kentucky College of Agriculture Plant Pathology Extension

PPFS-VG-15

CooPeraTiVe exTenSion SerViCeUniVerSiTy oF KenTUCKy College oF agriCUlTUre, Food and enVironmenT

agriculture & natural resources • Family & Consumer Sciences • 4-H/youth development • Community & economic development

Cause and disease developmentBoth fungi (Fusarium oxysporum f. sp. lycopersici and Verticillium albo-atrum) are common inhabitants of Kentucky soils. These organisms infect plants through roots and spread through the water-conducting vessels (vascular tissue). The cells in the vascular tissue are plugged by fungal growth that stops water movement through this tissue, causing wilting. Fusarium and Verticillium may be introduced in several ways: pathogen-infested soil, old crop residues, contaminated seed and transplants, wind, water, or mulches. These 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 nematode feeding can reduce the effectiveness of resistance to Fusarium and Verticillium wilts,

so it is important to control nematodes if they are present or to use varieties labeled VFN.

•   Sanitation – Greenhouse soils should be fumigated or steam-sterilized.

Southern Bacterial WiltBacterial wilt is not a serious problem in Kentucky, but some damage occasionally does occur in scattered areas and during hot growing conditions.

Figure 4. bacterial wilt typically results in rapid wilting, without the yellowing associated with the Fungal wilt diseases. (photo: kenneth seebold, uk)

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)

Figure 2 Figure 3A Figure 3B

SymptomsThe vascular tissue of affected plants turns black and plants rapidly wilt without yellowing (Figure 4). As the disease progresses, the pith decays, appearing dark and water-soaked; sunken, brown cankers may be visible on the lower stem. A slimy bacterial slime oozes from the stem when it is pressed and the stem may become hollow. When the stem of an infected plant is placed in water, a milky flow (made up of the many bacterial cells clogging vascular tissue) will emerge from the cut end of the stem in a matter of minutes. Infected plants collapse and die in hot weather.

Cause and disease developmentThe bacterial wilt organism (Ralstonia solanacearum) survives in the soil and on weedy hosts. The bacterium infects susceptible plants through wounds in the roots or stem and initially invades the water-conducting tissue of the vascular system. Bacterial cells released into the soil from collapsed plants can survive even without a host. The pathogen can be carried into “clean” fields, greenhouses, high-tunnels, or gardens via infected

transplants or through drainage water from adjacent infested land. The bacterial wilt pathogen can persist for many years after it is introduced into an area, and eradication is extremely difficult.

disease management•   disease-free transplants – Inspect plants prior to transplanting to be sure they are disease-free.

•   Crop rotation – Do not plant tomatoes in sites where the disease has been a problem in the past. Practice long crop rotations.

•   Sanitation – Remove and destroy infected plants promptly.

•   Hydroponic production – Take care when installing hydroponic production systems where this pathogen is known to exist. The bacterial wilt pathogen can spread easily in these systems if contaminated soil or water is introduced.

Walnut WiltWilting of tomato plants may be associated 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.

SymptomsAffected 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)

A B

C

Cause and disease developmentBlack walnut and butternut trees produce a toxin called juglone in leaves, stems, fruit hulls, inner bark, and roots. Other walnuts and related trees, such as hickories and pecans, also produce juglone, but in much lower amounts. The toxin leaches into soil where roots of sensitive plants, such as tomato, may come into contact with it.

Tomato plants located beneath the canopy of walnut trees are at greatest risk because juglone from roots and fallen leaves accumulates there. Because walnut roots extend well beyond the drip line of the tree, injury to plantings may occur at a 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.

managementAvoid planting tomatoes near walnut or butternut trees, or in locations where these trees may have grown previously. Juglone can remain in the soil several 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/pubs/id/id172/id172.pdf

•   Root-knot Nematode (PPFS-GEN-10)http://www2.ca.uky.edu/agcollege/plantpathology/ext_files/PPFShtml/PPFS-GEN-10.pdf•   Vegetable Production Guide for Commercial Growers (ID-36)http://www.ca.uky.edu/agc/pubs/id/id36/id36.htm

acknowledgementsThanks to Daniel Egel, Extension Plant Pathologist at Purdue University, and Anthony Keinath, Vegetable Plant Pathologist at Clemson University, for their reviews of this publication.

Educational programs of the Kentucky Cooperative Extension Service serve all people regardless of race, color, age, sex, religion, disability, or national origin.

May 2014

Figure 6. symptoms oF walnut wilt include wilting, yellowing, unthriFty plants, and low yields. note the black walnut tree in the background. (photo: cheryl kaiser, uk)

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

Figure 7. plants that have been aFFected by walnut wilt oFten show discoloration oF the vascular system, similar to the Fungal wilts. (photo: cheryl kaiser, uk)