Even though symptoms may notappear until after harvest,many of the disease-causing

organisms that cause fruit rot infectthe fruit before it ripens. Once fruitis infected, little can be done duringharvest or storage to reduce thedamage. Most fruit rot fungi andbacteria also cause foliar diseases,so management throughout theseason is critical not only toproduce a healthy plant and highyield, but also to provide high-quality fruit. Not all fruit damage is caused bydiseases. Environmental factorssuch as calcium deficiency or poorfertilization may also blemish fruit.For a description of some of themost common problems, seeExtension publication TomatoDisorder: Physiological Fruit Problems(A3798).

Alternaria (fungus Alternaria alternata f.sp.lycopersici)What to look for: On green fruit,the disease is called “freckle” andappears as small, slightly sunkenspecks surrounded by a yellowhalo. The lesions enlarge to about3⁄4 inch across and are often darkwith concentric lighter rings. Oncethe fruit ripens, the lesions stopexpanding. Fruit spots are notalways obvious at harvest, butdevelop 3–5 days after harvest.On fruit that’s infected while ripe,the disease is called “black mold.”Such fruit develops large, sunken,black lesions that may affect up to athird of the fruit. Symptoms often appear on the sideof the fruit that is exposed to thesun.Severity: Alternaria is rarelysevere.How it spreads: The disease over-winters on decaying plant debrisand is spread by wind andsplashing rain.What you can do: Plant resistantcultivars.

Tomato disorder:Post-harvest fruit diseases

A3799

K A R E N D E L A H A U T a n d W A L T S T E V E N S O N

To

ma

to

Alternaria

Anthracnose (commonly caused by the fungusColletotrichum coccodes)What to look for: Infections occurwhile fruit is young, althoughsymptoms don’t appear until afterfruit begins to ripen. Lesions are cir-cular, 1⁄2 inch in diameter, andslightly sunken. The tissue beneaththe lesions is grainy and lighter incolor than the surrounding healthytissue. The center of the lesion oftencontains small black specks.Secondary infections by yeast andsoft rot are common.

Severity: Anthracnose can causeserious fruit losses if not controlled.How it spreads: The fungus isseedborne, but may also overwinterin the field on infected debris.Overhead irrigation and wetweather worsens the disease.What you can do: Discard infectedtomatoes promptly. It is importantto use clean seed and practice croprotation out of solanaceous crops for2–3 years. Improve air circulation bystaking or caging plants, and allowadequate plant spacing. Fungicidesapplied to prevent Septoria leaf spotwill also protect fruit from anthrac-nose. Begin treatments when plantsstart to bloom and continue every7–10 days until harvest.

Bacterial speck (Pseudomonas syringae pv. tomato)What to look for: Tiny, slightlyraised, superficial black specks thatare less then 1⁄16 inch in diameter. Adarker green ring often surroundsthe lesions. Severity: Bacterial speck reducesyield through cosmetic injury. Ifleaves are also infected, yield lossesincrease to 25%.How it spreads: This is a cool-weather disease that occurs whentemperatures remain between55–77ºF with high humidity, heavydew, or frequent rainfall. Thepathogen overwinters in the field oninfected plant debris. It may also betransmitted on infected seed.What you can do: Use clean seed.Irrigate early in the day to promoterapid drying. Practice crop rotationand sanitation to reduce exposure ofthe current season’s fruit to lastseason’s inoculum. Fixed copperfungicides that are used to controlfoliar symptoms of this disease willalso help to protect the fruit. Formore details, see Extension publica-tion Tomato and Pepper Disorders:Bacterial Spot and Speck (A2604).

T O M A T O D I S O R D E R : P O S T - H A R V E S T F R U I T D I S E A S E S

Anthracnose

Bacterial speck

Bacterial spot (Xanthomonas campestris pv. vesicatoria)What to look for: Small lesions(about 3 mm in diameter) areslightly raised and scabby. Whenlesions are first forming, symptomsare similar to bacterial speck. Formore details about both diseases,see Extension publication Tomatoand Pepper Disorders: Bacterial Spotand Speck (A2604).Severity: Bacterial spot is rarely aserious disease on fruit.How it spreads: Infection occursduring warm, wet weather. Thepathogen overwinters on infectedplant debris or on seed.What you can do: Use clean ortreated seed and rotate out of toma-toes for at least 2 years. Protectantcopper sprays will reduce likeli-hood of bacterial spot.

Botrytis gray mold (fungus Botrytis cinerea)What to look for: Gray, velvetycoating on flowers, fruit, and leaves.Dying flowers are particularly sus-ceptible. Infection spreads to thefruit when infected flowers come incontact with them. Infected greenfruit develop circular, whitenedareas with distinct rings calledghost spots. During warm, sunnyweather, disease developmentstops, with only the ghost spotsremaining.Severity: Botrytis gray mold causesmoderate damage on tomatoes.How it spreads: The fungus iseverywhere and affects manyspecies of plants. It overwinters assclerotia (spores) in the soil or onany of the many perennial hosts innature. Cool, wet weather worsensdisease symptoms. What you can do: Improve air cir-culation and speed drying throughproper spacing and by staking orcaging plants. Fungicides can be usedto prevent the spread of infection.

Buckeye rot (fungus Phytophthora parasitica)What to look for: Fruit symptomsbegin as gray-green or brown,water-soaked lesions. The spotsdevelop concentric rings as theyenlarge, eventually covering asmuch as half of the fruit. Lesions areoften leathery in texture. Tomatoesinfected before they mature oftenremain firm and green. Infectionsthat occur later result in unevenfruit ripening. Severity: Buckeye rot is rarely aserious problem in Wisconsin.How it spreads: Fruit that comesinto contact with the soil is mostlikely to become infected. Splashingrain can also spread the pathogen.The fungus overwinters in infectedplant debris. What you can do: Plastic mulchwill prevent the fruit from touchingthe soil, reducing the likelihood ofinfection. Likewise, staking orcaging plants keeps the fruit off thesoil surface and reduces losses tothis disease. To reduce the buildupof fungi, rotate out of solanaceouscrops (tomatoes, peppers, egg-plants) for at least 3 years.

Bacterial spot

Buckeye rot

Early blight (fungus Alternaria solani)What to look for: Early blight com-monly affects both fruit and foliage.Initially, lesions on fruit are black orbrown and firm. Although thefungus enters through the stem end,lesions can occur anywhere on thefruit and can become quite sizeableand leathery.Severity: The disease may destroyup to half the crop.

How it spreads: Early blightdevelops best during cool, humidperiods. The fungus overwinters inthe soil on infected plant residueand can remain viable for at leastone year. What you can do: Plant disease-free seed and practice a 2–3 yearrotational sequence. Fungicides areavailable to commercial growers forcontrol of both foliar and fruit infec-tions. Extension publicationCommercial Vegetable Production inWisconsin (A3422) lists current rec-ommendations.

Late blight (fungus Phytophthora infestans)What to look for: Greasy, greenish-brown fruit lesions are characteristicof this disease. Fruit infectionsusually begin on the shoulders asthe spores are washed from thefoliage above. The spots may enlargeuntil the entire fruit is covered. Thefruit may remain firm or may softenas the disease spreads into the fruit.Severity: This disease occurs spo-radically in Wisconsin, but can beserious when present.How it spreads: Late blight ismore severe in cool, wet years. Thefungus is spread by wind and over-winters on infected plant debris orcull piles of tomatoes or potatoes. What you can do: Practice a 2–3year rotation out of solanaceouscrops. Destroy infected plantsimmediately, including any potatotubers. Copper fungicides may beused as a protectant if conditionsfavor disease development.

T O M A T O D I S O R D E R : P O S T - H A R V E S T F R U I T D I S E A S E S

Copyright © 2004 by the Board of Regents of the University of Wisconsin System doing business as the division ofCooperative Extension of the University of Wisconsin-Extension. All rights reserved. Send copyright inquiries to: Manager,Cooperative Extension Publishing, 432 N. Lake St., Rm. 103, Madison, WI 53706.Authors: Karen Delahaut is senior outreach specialist with the fresh market vegetable program, Walt Stevenson is professorof plant pathology, College of Agricultural and Life Sciences, University of Wisconsin-Madison and University of Wisconsin-Extension, Cooperative Extension. Produced by Cooperative Extension Publications, University of Wisconsin-Extension.University of Wisconsin-Extension, Cooperative Extension, an EEO/AA employer, provides equal opportunities inemployment and programming, including Title IX and American with Disabilities (ADA) requirements. This publication is available from your Wisconsin county Extension office or from Cooperative Extension Publishing. Toorder, call toll-free: 1-877-947-7827 (WIS-PUBS ) or visit our web site: cecommerce.uwex.edu. A3799 Tomato Disorder: Post-Harvest Fruit Diseases I-05-04

Early blight

Late blight