Plant Disease Guide

🔍 Symptoms

• ▸White or gray powdery coating on leaf surfaces
• ▸Leaves may curl, yellow, or drop prematurely
• ▸Most visible on upper leaf surface but can appear underneath
• ▸Affected tissue may turn brown and die in severe cases

⚡ Causes

Caused by fungal spores spread by wind. Favored by warm days, cool nights, and high humidity — though dry conditions can also allow spread since spores do not need free water to germinate.

💊 Treatment

1. 1.Remove and dispose of heavily infected leaves immediately
2. 2.Apply potassium bicarbonate or neem oil spray to affected plants
3. 3.Use a diluted baking soda solution (1 tsp per quart of water) as a home remedy
4. 4.Apply sulfur-based fungicide for more severe infections

🛡️ Prevention

• ✓Space plants to allow good air circulation
• ✓Avoid overhead watering — water at the base
• ✓Choose resistant varieties when available
• ✓Apply preventive neem oil sprays at the start of the season

🔍 Symptoms

• ▸Yellow or pale green patches on the upper leaf surface
• ▸Gray, purple, or white fuzzy growth on the underside of leaves
• ▸Affected leaves eventually turn brown and die
• ▸Stunted growth in seedlings

⚡ Causes

Caused by water molds (oomycetes). Requires moisture and cool temperatures (50–70°F) to spread. Spores are spread by wind and splashing water.

💊 Treatment

1. 1.Remove infected plant material immediately and bag it — do not compost
2. 2.Apply copper-based fungicide or phosphonate products
3. 3.Improve air circulation by thinning plants
4. 4.Avoid wetting foliage, especially in cool weather

🛡️ Prevention

• ✓Use drip irrigation instead of overhead watering
• ✓Plant in well-drained, sunny locations
• ✓Rotate crops annually
• ✓Select downy mildew-resistant varieties

🔍 Symptoms

• ▸Gray, fuzzy mold covering affected tissue
• ▸Water-soaked, brown lesions on stems, leaves, and fruit
• ▸Flower petals develop brown spots and collapse
• ▸Infected stems may develop a grayish tan canker

⚡ Causes

Botrytis cinerea fungus thrives in cool (60–75°F), humid conditions. Spores spread easily through air, water, and physical contact. Dead or dying tissue is the most common entry point.

💊 Treatment

1. 1.Remove and destroy all infected plant parts immediately
2. 2.Apply fungicides containing fenhexamid, iprodione, or captan
3. 3.Reduce humidity around plants by improving airflow
4. 4.Avoid wetting foliage during watering

🛡️ Prevention

• ✓Space plants adequately for airflow
• ✓Remove dead flowers and debris promptly
• ✓Water in the morning so foliage dries before nightfall
• ✓Avoid over-fertilizing with nitrogen, which creates soft, susceptible growth

🔍 Symptoms

• ▸Dark brown spots with concentric rings (target-like appearance)
• ▸Yellow halo surrounding each lesion
• ▸Begins on lower, older leaves and progresses upward
• ▸Stems may develop dark lesions near the soil line

⚡ Causes

Caused by Alternaria solani fungus. Spreads via water splash and wind. Favored by warm temperatures (75–85°F), high humidity, and wet foliage. Overwinters in infected plant debris in the soil.

💊 Treatment

1. 1.Remove infected leaves at first sign, starting from the bottom
2. 2.Apply chlorothalonil, copper, or mancozeb fungicide every 7–10 days
3. 3.Mulch around the base of plants to prevent soil splash
4. 4.Stake or cage plants to keep foliage off the ground

🛡️ Prevention

• ✓Rotate nightshade crops (tomato, potato, pepper) on a 3-year cycle
• ✓Remove all plant debris at end of season
• ✓Choose resistant varieties
• ✓Avoid overhead watering

🔍 Symptoms

• ▸Water-soaked, pale green to dark brown lesions on leaves
• ▸White, cottony mold on the underside of leaves in humid conditions
• ▸Dark brown, greasy-looking patches on stems
• ▸Fruit develops firm, brown, irregular rot

⚡ Causes

Caused by Phytophthora infestans — the same pathogen responsible for the Irish Potato Famine. Spreads rapidly in cool (60–70°F), wet weather. Spores spread by wind and rain.

💊 Treatment

1. 1.Remove and destroy infected plants immediately — do not compost
2. 2.Apply copper-based fungicide or chlorothalonil at first sign
3. 3.Repeat applications every 5–7 days during wet weather
4. 4.Avoid any overhead watering once infection is detected

🛡️ Prevention

• ✓Plant certified disease-free seed potatoes
• ✓Choose blight-resistant tomato varieties (e.g., Mountain Merit, Defiant)
• ✓Ensure excellent air circulation
• ✓Monitor plants closely during cool, wet periods

🔍 Symptoms

• ▸Yellowing and wilting of lower leaves, often on one side of the plant first
• ▸Brown discoloration inside the stem when cut — a key diagnostic sign
• ▸Wilting even when soil moisture is adequate
• ▸Plant death can occur rapidly in hot weather

⚡ Causes

Caused by Fusarium oxysporum fungus that lives in soil. Enters through roots and blocks water-conducting vessels. Favored by warm soil (75–90°F) and acidic conditions. Persists in soil for years.

💊 Treatment

1. 1.No effective chemical cure once a plant is infected
2. 2.Remove and destroy infected plants to prevent spread
3. 3.Solarize soil in summer to reduce fungal load
4. 4.Drench surrounding soil with beneficial Trichoderma products

🛡️ Prevention

• ✓Use resistant varieties (look for "F" designation on tomato labels)
• ✓Rotate crops on a 4-year cycle
• ✓Avoid over-watering and improve drainage
• ✓Maintain slightly alkaline soil pH (6.5–7.0)

🔍 Symptoms

• ▸V-shaped yellow lesions on leaf margins
• ▸Older leaves yellow and drop first
• ▸Brown streaking inside lower stem when cut
• ▸Slow decline over the season, unlike the rapid collapse of Fusarium

⚡ Causes

Caused by Verticillium dahliae or V. albo-atrum fungi that infect roots and move into the vascular system. Survives in soil for many years. Favored by cool soil (65–75°F).

💊 Treatment

1. 1.Remove and destroy infected plants
2. 2.No effective in-season chemical treatment
3. 3.Soil solarization can reduce pathogen levels

🛡️ Prevention

• ✓Plant resistant varieties where available
• ✓Practice long crop rotations (minimum 4 years)
• ✓Avoid planting susceptible crops after strawberries or potatoes
• ✓Improve soil drainage

🔍 Symptoms

• ▸Circular black spots with fringed margins on upper leaf surfaces
• ▸Yellow halos surrounding spots
• ▸Leaves drop prematurely, weakening the plant
• ▸Dark purple-red spots may appear on young canes

⚡ Causes

Caused by Diplocarpon rosae fungus. Requires water on leaf surface for at least 7 hours to infect. Spreads via rain splash and overhead watering. Overwinters on infected canes and fallen leaves.

💊 Treatment

1. 1.Remove and dispose of all infected leaves — never compost them
2. 2.Apply fungicides containing myclobutanil, tebuconazole, or copper
3. 3.Begin treatment at bud break and repeat every 7–14 days
4. 4.Neem oil is an effective organic option

🛡️ Prevention

• ✓Choose disease-resistant rose varieties
• ✓Water at the base — avoid wetting foliage
• ✓Rake and remove fallen leaves promptly
• ✓Prune to open up the center of the plant for airflow

🔍 Symptoms

• ▸Orange, yellow, or rust-brown powdery pustules on the underside of leaves
• ▸Yellow or pale spots on the upper leaf surface above the pustules
• ▸Severely infected leaves may drop early
• ▸Rust-colored spore masses may also appear on stems

⚡ Causes

Caused by obligate parasitic fungi in the order Pucciniales. Each rust species infects specific plants. Spores spread by wind and require leaf moisture to germinate. Thrives in moderate temperatures (60–75°F).

💊 Treatment

1. 1.Remove infected leaves immediately
2. 2.Apply sulfur-based fungicide or neem oil at first sign
3. 3.For severe infections, use systemic fungicides (triazoles)
4. 4.Improve airflow around plants

🛡️ Prevention

• ✓Plant resistant varieties
• ✓Avoid overhead watering
• ✓Remove and destroy plant debris at end of season
• ✓Ensure wide plant spacing

🔍 Symptoms

• ▸Small, dark, water-soaked circular lesions on fruit that enlarge and sink inward
• ▸Orange or pink spore masses visible in the center of lesions in humid conditions
• ▸Dark brown to black lesions on leaves with irregular margins
• ▸Cankers on stems, particularly near the soil line

⚡ Causes

Caused by Colletotrichum species fungi. Spreads rapidly in warm (75–85°F), wet conditions. Spores are spread by rain splash, insects, and contaminated tools.

💊 Treatment

1. 1.Remove infected fruit and plant tissue immediately
2. 2.Apply copper-based or chlorothalonil fungicide
3. 3.Avoid working with plants when wet
4. 4.Clean and sanitize tools between plants

🛡️ Prevention

• ✓Use disease-free seed and transplants
• ✓Mulch to prevent soil splash
• ✓Rotate crops on a 2–3 year schedule
• ✓Avoid overhead irrigation

🔍 Symptoms

• ▸Seedlings collapse suddenly at or near the soil line
• ▸Stem appears water-soaked and pinched at the base
• ▸Seeds may fail to germinate entirely
• ▸White, cottony mold may be visible on the soil surface

⚡ Causes

Caused by various soil-borne pathogens including Pythium, Rhizoctonia, and Fusarium. Triggered by consistently wet, cold soil with poor drainage and poor air circulation.

💊 Treatment

1. 1.Remove affected seedlings immediately to prevent spread
2. 2.Allow soil surface to dry between waterings
3. 3.Improve air circulation with a small fan
4. 4.Drench soil with a diluted hydrogen peroxide solution (3%) for mild cases

🛡️ Prevention

• ✓Use sterile, well-draining seed-starting mix — never garden soil
• ✓Avoid overwatering; water from the bottom when possible
• ✓Provide good airflow around seedlings
• ✓Sow seeds at the correct depth and avoid overcrowding

🔍 Symptoms

• ▸Swollen, distorted, club-shaped roots
• ▸Plants wilt during the heat of the day and recover overnight
• ▸Stunted growth and yellowing of leaves
• ▸Premature death in severe cases

⚡ Causes

Caused by Plasmodiophora brassicae, a soil-borne pathogen that can persist in soil for 20+ years. Favored by acidic soil (pH below 6.5) and wet conditions.

💊 Treatment

1. 1.Remove and destroy infected plants — do not compost
2. 2.Apply lime to raise soil pH to 7.0–7.2, which suppresses the pathogen
3. 3.No effective fungicide treatment once infected

🛡️ Prevention

• ✓Raise soil pH above 7.0 with lime before planting brassicas
• ✓Rotate brassica crops on a minimum 7-year cycle
• ✓Use certified disease-free transplants
• ✓Improve drainage in the planting area

🔍 Symptoms

• ▸Sudden wilting of individual vines during the day, even with adequate water
• ▸Wilt spreads to entire plant within days
• ▸Cut stem near soil line and press the two cut ends together — bacterial ooze creates sticky threads
• ▸No recovery overnight distinguishes this from heat stress

⚡ Causes

Caused by Erwinia tracheiphila bacteria, spread exclusively by cucumber beetles feeding on infected plants. Overwinters in beetle digestive tracts — the beetles are the vector, not the soil.

💊 Treatment

1. 1.No cure once a plant is infected — remove and destroy it immediately
2. 2.Control cucumber beetle populations with insecticides or row covers
3. 3.Apply kaolin clay to deter beetle feeding

🛡️ Prevention

• ✓Cover transplants with row covers until flowering begins
• ✓Use yellow sticky traps to monitor and catch cucumber beetles
• ✓Plant resistant varieties where available
• ✓Remove and destroy infected plants quickly to limit beetle feeding

🔍 Symptoms

• ▸Shoot tips die and bend into a characteristic "shepherd's crook" shape
• ▸Blossoms turn water-soaked then brown and remain attached to the tree
• ▸Bark develops water-soaked, then sunken, reddish-brown cankers
• ▸Bacterial ooze may be visible on cankers during wet weather

⚡ Causes

Caused by Erwinia amylovora bacteria. Spreads through open flowers, wounds, and insect activity during warm (75–85°F), humid spring weather. Bees and rain spread the bacteria during bloom.

💊 Treatment

1. 1.Prune infected branches 12 inches below visible infection — cut into healthy wood
2. 2.Sterilize pruning tools between every cut with 70% isopropyl alcohol
3. 3.Apply copper bactericide during bloom at 4–5 day intervals
4. 4.Remove and destroy all pruned material

🛡️ Prevention

• ✓Choose fire blight-resistant varieties
• ✓Avoid excessive nitrogen fertilization, which promotes succulent growth
• ✓Prune during dry weather when bacteria are less active
• ✓Apply copper spray at pink bud stage before bloom

🔍 Symptoms

• ▸Small, water-soaked spots on leaves that enlarge and turn brown with yellow halos
• ▸Spots have an angular shape constrained by leaf veins
• ▸Lesions may drop out, leaving a shot-hole appearance
• ▸Fruit may develop raised, rough, or scabby spots

⚡ Causes

Caused by Xanthomonas or Pseudomonas bacteria. Spreads through rain splash, wind, and contaminated tools. Enters through stomata and wounds. Thrives in warm (75–85°F), wet weather.

💊 Treatment

1. 1.Apply copper-based bactericide at first sign of symptoms
2. 2.Remove heavily infected leaves
3. 3.Avoid working with plants when wet
4. 4.Repeat copper applications every 7–10 days during wet weather

🛡️ Prevention

• ✓Use certified disease-free seed — treat seed with hot water (122°F for 25 min)
• ✓Rotate crops for at least 2 years
• ✓Use drip irrigation
• ✓Sanitize tools with bleach solution (1 part bleach to 9 parts water)

🔍 Symptoms

• ▸Mottled pattern of light green and dark green (mosaic) on leaves
• ▸Leaves may be distorted, blistered, or curled
• ▸Stunted plant growth and reduced yields
• ▸Fruit may show mottled coloring or deformation

⚡ Causes

Caused by various mosaic viruses (TMV, CMV, ZYMV, etc.) transmitted primarily by aphids, and in some cases through infected seed or mechanical contact. Tobacco mosaic virus can spread via hands after handling tobacco products.

💊 Treatment

1. 1.No cure — remove and destroy infected plants to prevent spread
2. 2.Control aphid populations with insecticidal soap or neem oil
3. 3.Wash hands thoroughly before handling plants
4. 4.Remove weeds that serve as virus reservoirs

🛡️ Prevention

• ✓Use virus-resistant varieties (look for "TMV" or "CMV" resistance on labels)
• ✓Control aphids with reflective mulch or row covers
• ✓Avoid using tobacco products near the garden
• ✓Purchase certified virus-free seed

🔍 Symptoms

• ▸Bronze or purplish discoloration of young leaves
• ▸Concentric ring patterns (target spots) on fruit and foliage
• ▸Growing tips may die back
• ▸Stunted, distorted growth; one-sided wilting

⚡ Causes

Spread exclusively by thrips (tiny insects). Western flower thrips is the primary vector. The virus is acquired by thrips larvae feeding on infected plants and transmitted as adults.

💊 Treatment

1. 1.No cure — remove infected plants immediately
2. 2.Control thrips populations with spinosad, neem oil, or insecticidal soap
3. 3.Use blue or yellow sticky traps to monitor thrips levels
4. 4.Remove weeds and volunteer plants nearby that harbor thrips

🛡️ Prevention

• ✓Use TSWV-resistant tomato and pepper varieties
• ✓Install reflective silver mulch to deter thrips
• ✓Cover transplants with floating row covers
• ✓Avoid planting next to ornamental beds where thrips are common

🔍 Symptoms

• ▸Dark, sunken, leathery spot on the blossom end (bottom) of the fruit
• ▸Affected area starts light brown, turns dark brown or black
• ▸First fruits of the season are most commonly affected
• ▸Interior flesh beneath the lesion may be dry and firm

⚡ Causes

A physiological disorder caused by calcium deficiency in developing fruit tissue. The root cause is usually inconsistent soil moisture, which disrupts calcium uptake — not a lack of calcium in the soil.

💊 Treatment

1. 1.Remove affected fruit so the plant directs energy to healthy fruit
2. 2.Apply calcium chloride foliar spray as a short-term fix
3. 3.Mulch heavily to stabilize soil moisture
4. 4.Water consistently and deeply — avoid letting soil dry out between waterings

🛡️ Prevention

• ✓Maintain consistent, even watering — drip irrigation is ideal
• ✓Mulch plants to retain soil moisture
• ✓Avoid over-fertilizing with nitrogen, which competes with calcium uptake
• ✓Maintain soil pH between 6.0–6.8 for optimal calcium availability

🔍 Symptoms

• ▸Pale yellow-green color starting with the oldest (lower) leaves first
• ▸Yellowing progresses uniformly from leaf tip inward
• ▸Stunted growth and reduced leaf size
• ▸Stems may be thin and weak; plants may be spindly

⚡ Causes

Insufficient available nitrogen in the soil. Can result from sandy or poor soil, overwatering that leaches nutrients, high carbon soil amendments (fresh wood chips), or depleted soil after heavy cropping.

💊 Treatment

1. 1.Apply balanced liquid fertilizer or fish emulsion for quick results
2. 2.Side-dress with compost or blood meal for a slower release
3. 3.Foliar spray with diluted fish emulsion provides the fastest uptake

🛡️ Prevention

• ✓Incorporate compost into beds before each season
• ✓Use a balanced vegetable fertilizer throughout the growing season
• ✓Follow crop rotations that include nitrogen-fixing legumes
• ✓Test soil annually to monitor nutrient levels

🔍 Symptoms

• ▸Yellowing between the veins of young, new leaves — veins remain green (interveinal chlorosis)
• ▸Distinct green network pattern on yellow background
• ▸Older leaves may remain green initially
• ▸Severe cases result in brown leaf margins and dieback

⚡ Causes

Usually not from a true lack of iron, but from high soil pH (above 7.0) that locks iron into unavailable forms. Poor drainage, compacted soil, and overwatering also restrict iron uptake.

💊 Treatment

1. 1.Apply chelated iron (EDTA or EDDHA) as a foliar spray or soil drench for fast results
2. 2.Lower soil pH with elemental sulfur, acidifying fertilizers, or sphagnum peat
3. 3.For acid-loving plants, use acidic fertilizers (ammonium sulfate)

🛡️ Prevention

• ✓Test soil pH and maintain it at the appropriate range for your crops
• ✓Avoid overwatering which creates anaerobic conditions that impair iron uptake
• ✓Amend soil pH before planting acid-loving plants
• ✓Use acidifying mulches (pine needles, oak leaves) around susceptible plants

🔍 Symptoms

• ▸Tip burn: brown, scorched edges on young leaves at growing tips
• ▸In cabbage and lettuce, inner leaves may turn brown (internal tip burn)
• ▸Blossom end rot in fruiting vegetables
• ▸Distorted, cupped, or crinkled new growth

⚡ Causes

Calcium moves slowly in plants and deficiency appears in actively growing tissue. Usually caused by irregular watering, excessive potassium or magnesium fertilization, or low soil calcium.

💊 Treatment

1. 1.Apply calcium chloride foliar spray to affected plants
2. 2.Add gypsum (calcium sulfate) to the soil without altering pH
3. 3.Maintain consistent watering to aid calcium transport

🛡️ Prevention

• ✓Lime acidic soils to raise pH and add calcium simultaneously
• ✓Water consistently — calcium transport requires steady transpiration
• ✓Avoid excess potassium and magnesium fertilizers
• ✓Incorporate oyster shell or bone meal into beds

🔍 Symptoms

• ▸Bleached, white, or yellowish papery patches on the sun-exposed side of fruit
• ▸Affected tissue may collapse or become papery and dry
• ▸Secondary mold may colonize damaged areas
• ▸Most common on fruit that was recently exposed by pruning or leaf loss

⚡ Causes

Direct exposure of fruit to intense sunlight, especially when foliage cover is suddenly removed through pruning, disease defoliation, or strong winds. Temperatures inside the fruit can exceed 100°F.

💊 Treatment

1. 1.No treatment reverses damage — harvest affected fruit early if edible
2. 2.Cover exposed fruit with shade cloth or row cover fabric temporarily
3. 3.Restore foliage cover where possible

🛡️ Prevention

• ✓Avoid heavy pruning that suddenly exposes previously shaded fruit
• ✓Maintain good leaf canopy over developing fruit
• ✓Use shade cloth (30–40%) during heatwaves
• ✓Plant heat-tolerant varieties in very hot climates

🔍 Symptoms

• ▸Brown, necrotic edges on the tips and margins of inner or outer leaves
• ▸Tissue appears burned or dried out despite adequate soil moisture
• ▸Outer leaf tip burn is caused by heat and drying
• ▸Inner leaf tip burn is caused by calcium deficiency in rapidly growing tissue

⚡ Causes

Two forms: (1) Outer tip burn from heat, low humidity, and rapid transpiration exceeding water uptake. (2) Inner tip burn from insufficient calcium reaching the innermost leaves during rapid growth.

💊 Treatment

1. 1.Harvest immediately if inner leaves are affected — it does not spread
2. 2.Increase watering frequency during heat spikes
3. 3.Apply calcium foliar spray for inner tip burn
4. 4.Provide shade during extreme heat

🛡️ Prevention

• ✓Choose heat-tolerant lettuce varieties for summer growing
• ✓Provide afternoon shade with row covers or shade cloth
• ✓Water consistently and avoid allowing plants to dry out
• ✓Avoid harvesting during the hottest part of the day