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Defying Tomato Disorders & Diseases - Solution Guide

Disorders vs Diseases - Important Distinctions

Disorders

Physiological issues caused by abiotic factors like temperature, water, sunlight, etc.
Rarely fatal but affect fruit production and physical growth.
Preventable with proper cultural care and adjustments.

Diseases

Caused by pathogens and biotic factors in combination with environmental conditions.
Can lead to adverse growth symptoms or plant death.
Prevention is crucial to limit disease infections.

Disease management = Proactive steps to avoid or reduce disease potential. (i.e. Prevention)
Disease control = Reactive steps to mitigate symptoms or limit disease progression. (i.e. Treatments)

Common Disorders (Not diseases)

Leaf roll, Blossom end rot, Cracking/Splitting, Yellow shoulder, Cat facing, Hard center cores, Poor fruit set.

Leaf roll/curl

Causes:

Plant stress, heat, drought, nutritional imbalances, temperature fluctuations, herbicide damage or plants pruned during dry soil conditions, excess moisture during hot/humid growing conditions.

NOTE: Viral infections can produce leaf curling but with additional symptoms (TMV, ToMV, TYLCV).

Symptoms:

Leaf curling or rolling. The type, season, and direction of leaf curling help narrow down the leading cause.
Physical plant stress typically affects older leaves first, but not always, moving from low to higher on the plant or from the bottom up, which is how many diseases infect tomato plants, but no leaf spots, yellowing, or necrotic tissue symptoms.
Stress-induced curling is typically lengthwise from the margins inward toward the center vein and commonly upward cupping of leaves.
Due to abiotic causes, the leaves develop a thick, leathery texture and can become brittle, but they retain their normal green color.
Herbicide damage looks freakishly distorted, curled, clubbed, or balled with proliferation, mainly on the new growth or near the ends of stems. On tomatoes, the leaf color typically remains usually green or slightly silvery-green.
Viral infections (vectored by insects or tools) can stunt and curl leaves, but discolored or mottle-patterned foliage usually results.

Management: Prevention via proper cultural care.

Maintain proper and stable cultural conditions to avoid plant stress.
Plant tomatoes in well-drained, healthy soil with a pH of 6.0-6.5.
Maintain consistent watering, apply mulch around plants, limit nitrogen fertilizer applications, and avoid pruning indeterminate types during high temperatures.

Choose determinate tomato varieties with viral disease resistance.
Follow proper Integrated Pest Management (IPM) methods to prevent insects, and only use clean, sterile tools.
Avoid garden products with 2,4-D, glyphosate, dicamba, or other chemicals near vegetable gardens.

Cracking & Blossom End Rot (BER)

Causes:

Inconsistent watering or rapid changes in soil moisture, which a lack of available calcium can exacerbate.

Symptoms:

Splitting & Cracking = Linear cracks typically from the tops down or latitudinally partially around the fruits, usually near the top (stem end).
Blossom end rot = A brown, rotten circle patch at the bottom (flower end) of the fruits.

Management Steps: Prevention via proper varietal choice and cultural care are the best avoidance measures.

Choose crack-resistant varieties. (Determinate varieties are less susceptible than Indeterminate types)
Water consistently and keep soil evenly moist, especially early in the season, while fruits transition from green to ripe.
Water before forecasted rain events, especially if dry conditions lead up to rainy conditions. (T-storms)
Fertilize consistently with tomato-specific food with added calcium.
Avoid over-fertilization & read product ingredients. What are you applying for & why? Who uses Epsom salts?
Maintain a proper soil pH range of 6.0 to 6.5.
If cracks or splits develop, fruits should be harvested as soon as possible since fissures quickly lead to secondary fungal infections. With BER, rotted portions can be cut out, and the healthy parts can be used.

Yellow/Green Shoulder

Cause:

The main factors leading to yellow/green shoulder disorder are low potassium, sun exposure, high temperatures, and elevated pH or alkaline soil.

Note: This is not a simple lack of ripening. This is a physiological disorder with specific symptoms and causes.

Symptoms:

Yellow, green to orange areas primarily at the top (stem end) of fruits that fail to ripen. No foliage distress.

Management Steps: Prevention via a variety of choices and provide proper cultural care or adjustments.

Plant less susceptible cultivars. While any tomato variety can suffer from this disorder, heirloom types and varieties with sparse foliage tend to be more prone to this disorder.
In general, hybrid varieties listed as "good for canning" or with higher acid are typically less susceptible.
Avoid re-planting varieties that have experienced yellow shoulder for at least 1-2 years.
Amend soil with organic matter to boost beneficial microbes, test for & maintain proper pH.
Fertilize with a complete, tomato-specific food including adequate potassium (K). Have a soil test once every 3-5 years, but also when disorders keep occurring, even though all other prevention measures are followed, and abiotic factors have been successfully mitigated.

Other Tomato Disorders

Includes Catfacing, Hard center cores, Poor fruit set, small fruits, etc.

All of these disorders occur due to abiotic issues - weather conditions, heat, drought, excess moisture, etc., nutrient imbalances, pollination issues, variety, and planting time, which means all can be prevented or avoided.

Understanding Diseases

Plant disease triangle

Plant host X Conducive conditions X Pathogen = Plant Disease.
Best management & control measures include exclusion, prevention, and resistance.

Soil-borne diseases

Fusarium wilt, Verticillium wilt, Pythium, Nematodes, etc.
There are no current effective cures or treatment options for S-B diseases. Chemical fumigations or solarization are frustratingly ineffective, especially in N climates, and they are significantly cost-prohibitive. Planting-resistant varieties, sanitation, and proper spacing are the best preventative protections to adhere to.

Air-borne & direct contact diseases

Alternaria solani (EB), Septoria lycopersici leaf spot (SLS), Stemphylium sp. - gray leaf spot (GLS), Phytophthora infestans (LB), Botrytis cinerea - gray mold, Oidium neolycopersici - powdery mildew, etc.

Types of Diseases

Bacterial

Most often vectored by insects, wind, rain, or mechanical transmission is possible through natural openings or wounds on plants.
Microscopic bacteria overwinter on plant debris or inside insects.
Little to no controls once infection occurs.
Once positively identified via pathology testing, remove and destroy infected plants.
Preventing insect feeding and buying from certified sources are the best control measures.

Fungal

The most destructive tomato/vegetable diseases are fungal or fungal-like.

Most often spread by wind, rain, direct contact, or insects. (Some are soil-borne)
Effective controls include exclusion, prevention, and resistance, such as proper sanitation, ideal cultural practices, and crop rotations.
Planting resistant varieties is a critical step.
Applying the proper fungicide at the right time and in the right amounts is beneficial.

Viruses/Viroid

Least common diseases in home gardens, although they get a lot of attention.
Viruses are intracellular nucleic acids restricted to a particular host plant.
On tomatoes, primarily vectored by insects (aphids, leafhoppers, mites, whitefly, nematodes).
Once positively identified, remove & destroy infected plants.
Plant resistant varieties (know the codes) and prevent insect feeding.
Practice proper sanitation - clean & sanitize pruners & cutting tools.

Know the Codes

Tomato breeders utilize a logical, universal coding system for quick gardener reference for high disease resistance. Extension service professionals can help you determine common diseases in your area. Then, research varieties with the corresponding disease resistance codes. (IPPC codes use pathogen genus & species for codes)

V = Verticillium wilt
F = Fusarium wilt (The number of Fs indicates races 1, 2, or 3 resistance F, FF, or FFF)
N = Nematodes
T = Tobacco mosaic virus (TMV)
ToMV = Tomato mosaic virus
A = Alternaria stem canker
GLS = Gray leaf spot. (Sometimes listed as (St) for Stemphylium sp., the genus of the causing pathogen)
TSWV = Tomato spotted wilt virus
BS = Bacterial speck
EB = Early blight
LB = Late blight
YLCV = Yellow leaf curl virus

NOTE: Not all are represented here, but these are the 12 most common.

HR = High resistance. Only those plants that prove high resistance are assigned corresponding disease codes.
IR/ir = Intermediate resistance. Intermediate resistances are mentioned in the variety descriptions or as (ir:) w/code.

NOTE: High resistance does not mean plants are immune to disease; they only show better protection from existing threats of disease-causing pathogens when exposure and conditions are conducive to that disease.

Too many environmental and cultural variables exist to protect plants 100% from disease pathogens. Management and control measures still need to be employed to help prevent diseases.

Fungal Disease Symptoms

Fungal disease symptoms can be numerous, but most have similar infection habits. Therefore, prevention & treatments are identical, so an exact disease diagnosis is not critically important for taking management steps.

A common symptom is leaf spotting. Spots can be purple, brown, tan, or tan with white centers that drop out.
Leaves turn yellow and then develop necrotic tissue, with spots gaining in size, often leaving behind concentric rings and having a visible yellow halo between green, healthy tissue and showing dying necrotic tissue.
Spots often congeal to form larger leaf lesions & destroy the entire leaves.
Most fungal infections start low on the plants and move upward as they progress.

An exception is Late blight (LB), which starts low and then quickly jumps to the upper parts of the plant. LB infections form water-soaked spots that morph quickly to tan or brown with no yellow halo between green and necrotic tissue. With LB, plants succumb to the disease seemingly overnight, which is extreme compared to other fungal infections. (Most are symbiotic parasites that do not want to kill their host)

However, LB is highly weather-dependent. Infections are rarely severe every year. Misdiagnosis is common. Late blight is of little to no concern during many growing seasons because of its dependence on conducive weather conditions. LB infections start in southern states and migrate north with the warming weather. (Visit USABlight hosted by NC State)

Preventing Diseases on Tomato Plants = 6 Easy Steps

Choose varieties with HR to local potential diseases.
- Even varieties with IR are usually enough to prevent major seasonal disasters.
Rotate where tomato plants are grown every season.
- Most fungi & FLO are cumulative. This is why rotation is so helpful in preventing fungi population buildups.
Practice proper plant spacing.
- Plant fewer plants, leaving enough room to walk between them without brushing foliage.
- Prune indeterminate plants correctly to remove vigorous, unproductive, crowded growth. Do it early.
Sanitation, sanitation, sanitation.
- Pick infected leaves off ASAP. Then wash your hands or change gloves.
- Pick up fallen leaves and debris. Then wash your hands and change gloves.
- Clean and disinfect tools after every use.
- Lift low-hanging foliage. Keep 12 inches between the ground and the lowest leaves.
- Apply & maintain ample clean mulch material under plants.
- Avoid using dirty, used soil, and never transfer soil from one spot to another.
- Keep adjacent areas free from weeds and debris unless trapping crops are used.
- If/when plants become increasingly infected, remove them entirely and clean up thoroughly after them.
Keep plants healthy.
- Do proper fertilization.
- Apply water consistently and use proper spacing & caging.
- The healthier the plants are, the more natural disease defenses they have.
Follow 3-Rs for fungicide use.
- Apply the proper fungicide at the right time in the right amounts.

Fungicides 101

The efficacy of any fungicide increases when combined with proper sanitation, appropriate plant spacing, proper care, watering, and recommended pruning with caging.

Topical fungicides are preventative, not curative.
Once an infection occurs, managing the symptoms & reducing potential adverse effects is the goal.
Most seasons, some disease infection is inevitable. Some infections are tolerable but do continual scouting and take the proper steps to slow or limit disease spread.
Utilize mineral-based (sulfur or copper) or bio-fungicides early in the season, then switch to a broad-spectrum synthetic product later in the season as pressures increase due to summer moisture, humidity, heat, and insect populations.

IMPORTANT: Fungi cannot develop resistance to mineral-based or bio-fungicides like they can with synthetic fungicides. Fungi are most elastic in spring. When synthetic fungicides are applied, fungi can mutate and become more resistant to synthetic chemicals.

Rotating products may be necessary year to year depending on the environment, weather, and amount or level of past disease pressures.

NOTE: Neem oil provides low efficacy against most fungal diseases like Early or Late blight. It can help prevent the spread of PM if applied just before the outbreak, but that's it.

Tomato varieties with good disease resistance

Item #	Var. Name	No. days	Habit	Class	Disease Resistance Code
033	Amelia VR Hyb.	75	Det.	slicer	V, F1-3, N, GLS, TSWV
066	Bella Rosa Hyb.	75	Det.	slicer	V, F1-2, A, GLS (ir: TSWV)
070	Bellatrix Hyb.	70	Det.	sm. Slicer	F1-2, TMV, LB, ToMV
076	Bellerose Hyb.	75	Ind.	bfstk	V, F1-2, N, TSWV, TYLCV
071	Bendida Hyb.	80	Semi-det.	Med. slicer	V, F1-2, A, ToMV (ir: EB)
074	Bet. Boy Plus Hy	75	Ind.	slicer	V, F, A, FOR, GLS, ToMV (ir: TSWV, N)
080	Big Bf Plus Hyb.	75	Ind.	Slicer	V, F1-2, FOR, GLS, ToMV, ToTV (ir: TSWV, N)
195	Celeb. Plus Hyb.	70	Semi-det.	slicer	V, F1-2, A, GLS, ToMV (ir: TSWV, N)
210	Crokini Hyb.	65	Ind.	cherry	F, LM, ToMV (ir: LB, N, TYLCV)
213	Defiant PhR Hyb.	70	Det.	slicer	V, F1-2, LB (ir: EB)
221	Dixie Red Hyb.	90	Det.	Slicer	V, F1-3, A, GLS, (ir: N, TSWV)
242	Early G. Plus Hyb.	70	Ind.	slicer	V, F1-2, A, GLS, TSWV
243	Early Resil. Hyb.	70	Det.	sm slice	V, F1-2, A, GLS, LB (ir: BC, BS)
284	Galahad Hyb.	7	Det.	slicer	V, F1-3, N, GLS, TSWV, LB
003	Gol.™ Early Hyb.	60	Ind.	slicer	V, F1-2, N, TMV, TSWV, TYLCV
001	Gol.™ Orig. Hyb.	65	Ind.	slicer	V, F1-2, TMV, A, GLS, ToMV (ir: N)
376	Invincible Hyb.	70	Det.	Campari	V, F1-2, ToMV (ir: TYLCV, GLS, LB, BW)
385	Jasper Hyb.	60	Ind.	currant	LB (ir: EB)
430	LM Boy Plus Hyb	75	Ind.	slicer	V, F1-3, A, GLS, FOR, LM, ToMV, ToTV (ir: N)
490	Mtn. Fresh Hyb.	79	Det.	slicer	V, F1-2, N (ir: EB)
495	Mt. Magic Hyb.	75	Ind.	saladette	V, F1-2, GLS (ir: LB)
497	Mt. Merit Hyb.	75	Det.	slicer	V, F-1-3, N, GLS (ir: EB, LB, TSWV)
498	Mt. Rouge Hyb	73	Inf.	bfstk	V, F, N (ir: LB)
573	Plum Regal Hyb.	8	Det.	Roma	V, F1-2, GLS (ir: TSWV, LB)
632	Red Racer Hyb.	57	Det.	saladette	V, F1-2, N, GLS (ir: ToMV)
629	RuBee G. Hyb.	65	Ind.	slicer	V, F1-2, FOR, LM, ToMV (ir: LB)
849	Zenzei Hyb.	80	Ind.	bfstk	ToMV, TSWV, FF, V (ir:PM, N)

All home gardeners can have disease & disorder free tomato plants. It just takes planning, proper cultural practices, and mindful variety selection.