Vegetable Diseases—Detect Them Early

Vegetable diseases can be a real heartbreak. You've been working hard in your garden and you're looking forward to harvesting.

Suddenly, your vegetables are rotting in the field. Or they're moldy.

Or perhaps they're die off as seedlings, before you can even plant them in your gardens.

Yes, it can be disheartening. The good news is that most diseases don't happen all of a sudden.

If you know the signs, you can detect vegetable diseases before they become an outbreak.

Use these links to jump directly to a particular vegetable type:

Tomatoes and Potatoes | Cucumbers, Melons, Squash, Pumpkin, Zucchini
Onions | Beans | Peas | Lettuce

Tomatoes

There are several tomato diseases.

Tomato Septoria Leaf Spot

This disease is one of the worst.

Symptoms

  • Tiny brown spots show up underneath the leaves first.
  • The leaves slowly become yellow and drop as the disease makes its way up the plant.

Gray Mold

Symptoms

  • Starts in a cool climate but, unlike many other diseases, it doesn't require high humidity to prosper.
  • Soil with a low pH (acid soil) promotes more serious gray mold infection.
  • The characteristic clue of gray mold is its fuzzy, felt-like appearance.

Blossom-End Rot

A condition caused by a lack of calcium in the soil.

Symptoms

  • Recessed brown patches on the underside of tomatoes, peppers, melons and cucumbers.
  • It usually happens after fast growth and then an extended dry spell or extended times of heavy rain that leach calcium from the soil.

Tomato Anthracnose

Symptoms

  • Shows up on mature fruit, creating small, round, recessed spots.
  • The spots get larger, and soon the whole fruit is affected and acquires a water rot.

Late Blight

Symptoms

  • Ruins fruits, stems and leaves when there are long periods of humid weather with cool nights and fairly warm days.
  • Damaged plants appear as if they were wiped out by frost.
  • Both immature and mature fruits turn corky brown on their tops and their skin starts to look like an orange peel.
  • Decayed areas stay firm but the fruit is inedible.

Pythium Rot (Damping-Off, Stem Rot)

Symptoms

  • Diseased condition of seedlings in excessive moisture occurs at or before sprouting, causing death of seeds or young seedlings.
  • Serious drooping and black stem, starting at ground level, resulting in stunting or death of plants.

Suggestions

  • If fertilizing, apply a slow-release organic source of nitrogen.
  • Stay away from planting in poorly drained regions.
  • Keeping soil pH at 6.5-7.0 helps.

Fusarium Root and Crown Rot

Symptoms

  • The whole root system is affected.
  • Brown discoloration is apparent at the pedestal of the stem.
  • Disease advances slowly from bottom to top, often causing drooping.

Suggestion

  • Keeping the soil pH at 6.5 to 7.0 helps.

Powdery Mildew

Symptoms

  • A white growth sometimes with a yellow border on the surface of leaves and stems.
  • Leaves finally become brown, die and drop off the plant.
  • Usually seen on the plant's lower leaves, traveling along upward.
  • Wounds do not appear on fruit, but fruit may hurt from sun scald due to defoliation in extreme cases.
  • Warm, wet weather favors growth of the disease.
  • Spores are transported by the wind, and all plantings may be rapidly infected.

Tomatoes and Potatoes

Early Blight

Symptoms

  • First atypical brown spots show up on lower leaves.
  • The lower leaves drop off, exposing tomatoes to sun, allowing them to suffer from sun scald.
  • With old plants, it often makes black sunken spots by the stem end of the fruit.

Cucumbers, Melons, Squash, Pumpkin and Zucchini

Angular Leaf Spot

Symptoms

  • Irregular or angular water-drenched spots form on the leaves.
  • If leaves are damp, a tiny drop of bacterial exudate from the bottom of lesions removes the moisture, leaving a white residue.
  • The lesions afterwards become gray to brown. They dry and pull away, leaving behind large holes.
  • Circulated by rain and by equipment, hands and clothing.
  • The bacterium winters in diseased plant scraps and on the seed cover.

Suggestions

  • Avoid doing work around cucurbits when leaves are wet.
  • Work soil only if it's dry.
  • Don't water with overhead sprinklers.
  • Remove all diseased plant parts from the infected area.

Cucumber Bacterial Wilt

Symptoms

  • Big vines slowly droop and die. Young plants die quickly.
  • Bacterial wilt is dispersed by cucumber beetles.

Suggestion

  • Remove and destroy wilted plants.

Downy Mildew

Symptoms

  • A period of at least 6 hours at 100% humidity on the leaf surface is needed for infection.
  • Its symptoms deviate substantially, plant to plant.
  • Lesions first appear on the oldest leaves and spread to the younger leaves.

Suggestions

  • Space plants to give them air movement.
  • Don't water from overhead, to avoid leaf wetness.

Fusarium Wilt

Symptoms

  • With young melon, cucumber and watermelon plants: damping-off, stem break down and death may happen.
  • With aged plants: yellowing, stunting, drooping and death.

Suggestion

  • Don't permit soil to completely dry out.

Anthracnose

Symptoms

  • Assaults most cucurbits in warm, wet climate.
  • Tainted fruit makes ring-shaped brown to black dark regions, up to 1 inch (2.5 cm) across.
  • Spores winter in and on the seed.
  • Cucumber beetles and spattering water will spread spores.

Scab

Symptoms

  • Seed-borne and it endures in the soil.
  • It normally develops in warm weather after the midseason, when wet weather conditions occur.
  • Spores can broadcast over long distances when the air is damp.

Suggestions

  • Like many diseases, it helps to plant cucurbits where others have not been planted for 2-3 years.
  • Set in exposed areas with lots of breezes and sunshine, to allow leaf surfaces to dry more rapidly, cutting back infection.

Alternaria Leaf Blight

Symptoms

  • Shows in midseason on the oldest leaves and spreads to newer leaves.
  • Expanding, circular brown spots form on the upper leaf surface and are later covered over by black, moldy growth.
  • Leaves dropping off may end in sun scalding of fruit.
  • The fungus is seed-borne and winters in harvest debris and weeds.

Suggestions

  • Do not plant cucurbits where they have been produced within the last 2 to 3 years.
  • Avoid sprinkler watering.
  • Remove all plant debris from the garden in autumn.

Squash Mosaic Virus

Symptoms

  • Yellow and green curled leaves.
  • Fruits are distorted and spotted, with wartlike growths.
  • Aphids spread this virus to squash plants.

Onions

Neck Rot

Symptoms

The disease attacks existing plants, often after they're in storage.

  • Recessed, dried regions appear at the neck of the bulb and bit by bit move down the bulb.
  • The symptoms commonly arise after the bulbs have been in storage for a month or more.
  • The fungus perforates leaf tissue and only affects the bulb.
  • When necks are lush at harvest time, they allow an entering point for the fungus.
  • The fungus can not attack a well-dried neck.

Suggestion

  • Space plants to allow good air penetration around each plant.

Soft Rot

Symptoms

Soft rot can cause major losses in stored onions.

  • Spread by spattering rain and by mechanical or insect damage.
  • The bulb is infected by the neck tissue of aging plants.

Suggestions

  • Allow onions tops to dry before storing them.
  • Avoid injuring bulbs.
  • Store onions only after they're well dried.

Downy Mildew

Symptoms

  • Spots on the leaves get covered with a lavender or purplish fungus.
  • Needs cool temperatures and rain or high humidity.
  • With these conditions, onion leaves flex, ending in smaller yields and lower bulb grade.

Suggestions

  • Grow onions in well-drained soil to prevent the roots from becoming soggy.
  • Prevent the spread of disease by washing tools and shoes after you work in the vegetable garden.
  • Get rid of weeds and garden debris, which protect insects that transfer diseases.
  • Observe plants every couple days for signs of damage and do away with infected plants immediately.

Fusarium Basal Rot

Symptoms

  • Curving, discoloring of leaf tips, gradually moving down the leaf.

Suggestion

  • Don't raise grain cover crops in rotation with onions and garlic.

Beans

Pythium Root Rot

Symptoms

  • Discoloring, poor growth, abrupt seedling wilting (damping-off) and death.
  • May also kill seedlings before emergence.

Gray Mold

Symptoms

  • Most common when blooming happens when it's cool with high humidity.
  • Infection starts in the flower and goes to the pod.
  • Crowded plants with a compact cover of leaves promote gray mold.

Suggestions

  • Space seedlings so that the air can dry leaves.
  • Don't overwater and don't overfertilize with nitrogen.

Bacterial Brown Spot

Symptoms

  • Infection usually happens with temperatures in the 80-90 degree F (27-33 degree C) range, and moist weather.
  • Yellow specks appear on the leaves, which afterwards become dark brown.
  • Single spots are normally atypical in shape and stay moderately small, encircled by a slim yellow edge.

Suggestions

  • Set disease-free seed, rotate crops, destroy infected plant tissues, and wash dirty equipment.
  • Avoid cultivating plants when they're wet, as water carries the bacteria.

Common Bacterial Blight

Symptom

  • Particularly damaging to pods during times of warm, humid weather.

Suggestions

  • After harvesting, clean up all crop residues (fallen beans, plant branches, etc.).
  • Rotate crops.

Anthracnose

Symptoms

  • Fungi exist on infected bean seed and in scraps on top of garden soil.
  • Moderate and frequent rainfalls, especially if accompanied by winds, give perfect conditions for the spread of anthracnose.

Suggestions

  • Put beans in a different area each year and obtain disease-free seed each year.
  • Don't handle or work around plants when the leaves are wet to avoid spreading the disease manually.

Fusarium Root Rot

Symptoms

  • Sluggish growth and the appearance of red spots or stripes on lower stem and roots.
  • The true leaves yellow and fall off early.
  • Diseased plants often remain alive by making new roots near the soil surface, but output is seriously reduced.

Suggestion

  • Don't compact the soil your beans grow in.

Rhizoctonia Root Rot

Symptoms

  • Mainly attacks seedlings and immature plants.
  • Reddish-brown spots show up on lower stems.
  • Many infected plants die as seedlings.

Suggestion

  • Shallow seeding depth and planting in good warm soil help.

Peas

Pythium Root Rot

Symptoms

  • Watery rot is usual.
  • Plants are frequently stunted and light green as a result of poor root development.

Suggestions

  • Plant as soon in the season as conceivable.
  • Peas are a cool time of year crop, while the pythium disease is most serious at temperatures from 64-75 degrees F (18-24 degrees C), which is higher than favored for pea germination. Plant in cooler seasons.

Fusarium Root Rot

Symptom

  • Blackening of the stem at soil level, root decline, and as disease progresses, general loss of energy, stunting of the plant and death of leaves.

Suggestion

  • Don't compact the soil you grow your peas in.

Lettuce

Damping-Off

Symptoms

  • Seed rot, abrupt wilting of seedlings, loss of energy.
  • Prefers high moisture level and poorly drained soils.

Suggestions

  • Don't compact the soil, and set plants in well-drained soil.
  • Rotating vegetables with cover crops aids general soil fertility and reduces soil compaction.

Pythium Wilt

Symptoms

  • Dark yellow-brown roots, stunting and discoloring of outer leaves.
  • Decreased root system.

Suggestion

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