Growing Tomatoes How To

How to Read Tomato Disease Resistance Codes and Chart

When you are going to buy tomato seeds or plants you may find some special letters alphabet in the seed packet or plant level. These are the diseases resistant codes for that specific tomato variety.

You may also find these tomato disease-resistant codes when searching for different garden blogs or e-commerce sites.

If you are a beginner gardener you may often fall in confusion to identify which code indicates which disease. 

So, I suggest you get some primary knowledge about the disease resistance codes of tomatoes before buying tomato seeds or plants.

Tomato Diseases Resistance Codes

These codes are very useful information to choose which tomato varieties to buy for your growing region. Sometimes you may find various codes for the same disease. Besides, different seed companies present the same disease code in different ways.  So, it’s a little bit confusing.

These disease resistance codes are especially gardening lingo which represents the plant characteristics. 

For example-

If you find a tomato seed packet or a plant label with resistant code like VFFNSt after its name those meats it resistant to Verticillium wilt, Fusarium Wilt (Races 1 and 2), Root-knot Nematodes, Stemphylium Grey Spot Leaf.

Typically, every single letter stands for a specific disease but sometimes a group of letters stands for a particular disease or pest.

Besides, you may also notice HR or IR codes which stand for:

  • HR= High Resistance
  • IR= Intermediate Resistance

Here I decipher and introduce the most common disease resistance codes for tomatoes.

A – Anthracnose

Scientific Name: Colletotrichum lagenarium

Type: Fungus

Causes and Symptoms:

  • This disease mainly affected tomato fruits but also attack leaves, stems, and roots 
  • Lesions appear on leaves and gradually create a yellowish circular spot.
  • Black sunken water-soaked round spots appear on tomatoes.  
  • The disease flourishes in high moisture and humid weather condition when the temperature remains between 75-82° F.

Most Susceptible Regions:

Southern, mid-Atlantic, and mid-Western parts of the United States.

A / Aal / AS/ ASC – Alternaria Stem Canker

Scientific Name: Alternaria alternata f.sp. lycopersici

Type: Fungus

Causes and Symptoms:

  • Primarily small brown or dark spots appear on stems.
  • Gradually the cankers growing bigger to girdle the whole stem and kill the plants.
  • The diseases can attack the base of the plant or other parts of the tomato plants.
  • It can also attack tomato leaves and fruits.

Most Susceptible Regions:

All over the United States.

BS or (Pst/Pst: 0) – Bacterial Speck (Races 0)

Scientific Name: Pseudomonas syringae

Type: Bacterium

Causes and Symptoms:

  • Brown spots surrounded by yellow rings on the leaves.
  • Leaf curling.
  • Fruits may also affect in severe cases. 
  • The disease spread out by seeds, human movement, garden tools, wind, and water.

Most Susceptible Regions:

The disease favorable when the temperatures are 63-75° F with high moisture and humid weather condition all over the United States.

BW – Bacterial Wilt

Scientific Name: Erwinia tracheiphila

Type: Bacterium

Causes and Symptoms:

  • Stunt the growth of the tomato plants.
  • At the primary stage, particular leaves are wilting and drying.
  • Suddenly the entire stems become wilting and drying out.
  • Wilting occurs during the mid day and recovers at night.  
  • After that, wilting spread out all through the vines and ultimately kills the plants.
  • The disease spreads through cucumber beetles.

Most Susceptible Regions:

Tropical and sub-tropical regions with high humidity and temperatures.

CRRCorky Root Rot

Scientific Name: Pyrenochaeta lycopersici

Type: Fungus

Causes and Symptoms:

  • Early planting when the temperature down below 60° to 68°F is the main cause behind the diseases.
  • Cork shape brown lesions develop in bands with lengthwise cracking on the larger stems.
  • The tips of the damaged roots are pinched off.
  • Plants grow up slowly.
  • Reduces yields but doesn’t kill the plants.

Most Susceptible Regions:

All over the United States mostly northern or cooler parts.

EB/AB – Early Blight (Alternaria Blight)

Scientific Name: Alternaria solani

Type: Fungus

  • Causes and Symptoms:
  • Small dark spots appear on the lower leaves.
  • Circular brown spots can grow up on plant leaves.
  • Larger spots create concentric rings like brown to yellow.
  • Finally, the leaves drop off.
  • Brown, sunken spots girdle the plant stems just above the soil line.
  • Concentric leathery spots may appear on Fruits and finally drop off.
  • Sunscald or fruits crack may also occur.

Most Susceptible Regions:

Warm regions of the United States especially southern parts.

F/FF/FFF or (Fol: 1, 2, 3) – Fusarium Wilt (Races 1, 2 and 3)

Scientific Name: Fusarium oxysporum, Fusarium oxysporum f. sp. lycopersici

Type: Fungus

Causes and Symptoms:

  • Diseases start from the roots and climb up to the stems.
  • Lower leaves turn yellowing and browning.
  • Plants stop growing and wilting.
  • The plant produces little or no fruits.
  • ·         Finally, the entire plant becomes dry off.

Most Susceptible Regions:

F- Warm regions all over the United States.

FF – Arkansas, Florida, New Jersey, and Ohio in the United States.

FFF- California, Florida, North Carolina, and South Carolina in the United States.

FOR – Fusarium Crown and Root Rot

Scientific Name: Fusarium oxysporum f. sp. radicis–lycopersici

Type: Fungus

Causes and Symptoms:

  • Attacks mature plants.
  • Gradually reduces fruit production and growth.
  • Stunting, wilting, dry rot of the crowns.
  • Yellowing the edges of the older leaves.
  • Dry reddish-brown lesions may develop on stems above the soil line and the cortex of the taproot. 
  • Old plants may die.

Most Susceptible Regions:

All over California, especially greenhouses and cool soil temperatures.

LB – Late Blight

Scientific Name: Phytophthora infestans

Type: Oomycete, Water Mold, Fungus

Causes and Symptoms:

  • Dark brown blotches on leaves turned into dry brown foliage.
  • The lesions may also appear on tomato plant stems and fruits.
  • The entire field may turn into brown, wilted and create significant yield loss in a few days after first lesions appeared.

Most Susceptible Regions:

The disease performs better when the temperatures are 60-70° F with high moisture and humid weather condition all over the United States.

LM or (Ff: A-E) – Leaf Mold (Races A, B, C, D, and E)

Scientific Name: Passalora fulva, Cladosporium fulvum, Fulvia fulva,

Type: Fungus

Causes and Symptoms:

  • Greenish-yellow spots appear on the front sides of the leaves and turn brown.
  • Leaves start wilting and dry off.
  • Dark spots appear on blossoms and finally fall off.
  • Diseases spread by the garden tools, human movement, wind, and water.

Most Susceptible Regions:

The disease prefers when the temperatures are 71-75° F with high moisture and humid weather condition all over the United States.

N or (Ma/Mi/Mj) – Root-Knot Nematode

Scientific Name: Meloidogyne spp., Meloidogyne arenaria, M. incognita, M. javanica

Type: Parasites

Causes and Symptoms:

  • Leaves turn yellowing, wilting and stop growing.
  • Roots become galled and decayed.
  • Performs better in warm soil with high moisture while temperatures rise up 85 – 95° F.

Most Susceptible Regions:

Most warm regions with high soil moistures of the United States.

PM or (On) – Powdery Mildew

Scientific Name: Oidium neolycopersici, Oidium lycopersicum, Leveillula taurica, Oidium lucopersici

Type: Fungus

Causes and Symptoms:

  • White powdery patches appear underside of the lower leaves.
  • Upperside of the leaves appear yellow to brownish spots and shrinking.

Most Susceptible Regions:

Tropic and sub-tropics regions particularly North, South and Central America.

St or GLS – Stemphylium Gray Spot Leaf (Gray Leaf Spot)

Scientific Name: Stemphylium solani, S. lycopersici, S. floridanum, and S. botryosum

Type: Fungus

Causes and Symptoms:

  • Brown to black specks appears on tomato leaves.
  • Small round gray spots slowly develop on plant leaves surrounded by the yellow area.
  • Leaves turn yellow to brown and drop off.
  • Finally, the plants stop growing.

Most Susceptible Regions:

Warm regions, most commonly Southeastern parts of the United States.

T or TMV – Tobacco Mosaic Virus

Disease Name: Scientific Name: Tobacco mosaic virus, positive-sense single-stranded RNA virus (Tobamovirus)

Type: Virus – Potyvirus

Causes and Symptoms:

  • Damages flowers, leaves and tomatoes rather kill them.
  • Appear irregular yellow-green, light-green or dark-green spots on leaves.
  • Plants stop growing and produce fewer yields.
  • Sunken brown ring spots may appear on tomatoes.

Most Susceptible Regions:

Found worldwide and throughout the United States. The disease may spread out through infected plant debris, using garden tools after using Tobacco products or while smoking in the garden. 

ToMV or (ToMV:0-2) – Tomato Mosaic Virus (Races 0, 1, and 2)

Scientific Name: Tobamovirus

Type: Virus

Causes and Symptoms:

  • Leaves appear dark green to yellow spots, small in size and curled.
  • Yellow ring spots appear on tomato fruits and ripen unevenly.

Most Susceptible Regions:

Warm regions.

TSWV or SWV – Tomato spotted wilt virus

Scientific Name: Tomato spotted wilt virus (genus Tospovirus; family Bunyaviridae)

Type: Virus – Tospovirus

Causes and Symptoms:

Upper leaves change their color from yellow to brown ring spots

  • Plants stop growing and dark streaking appears on stems.
  • Produces irregular shapes of fruits.
  • Plants become wilted and finally die off.
  • The virus may transmit by Thrips.

Most Susceptible Regions:

Found throughout the United States.

TYLCV – Tomato Yellow Leaf Curl Virus

Scientific Name: Begomovirusa (Tomato yellow leaf curl virus)

Type: Virus

Causes and Symptoms:

  • Reducing leaf size, stunting, and yellowing.
  • Leaves curling upwards.
  • Infected plants don’t develop flowers.
  • Fruits fall off earlier. 

Most Susceptible Regions:

California and Florida.

V / Va / Vd – Verticillium Wilt (Races Va: 1 or Vd: 1)

Scientific Name: Verticillium dahlia, Verticillium albo–atrum

Type: Fungus

Causes and Symptoms:

  • Soil-borne/seed-borne tomato disease.
  • Spread through gardening tools, wind, and water.
  • Wilting, yellowing of leaves, defoliation.

Most Susceptible Regions:

Most regions of the United States.

John Michael
John Michael is a self-help writer and a hobby gardener. He has a bachelor's degree in Library Science. Michael’s passion in writing is to inspire the beginner gardeners to not just “hang in there” or “make it through” but to thrive. He does this through blogging at ofags.com. He began writing in 2017.

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