You walk out to your kale on a warm June morning and the leaves are peppered with holes, something sticky is coating the undersides, and a few plants near the end of the row have yellowing edges that were not there yesterday. Before you reach for a spray bottle — stop and identify. Most kale problems in Pennsylvania are caused by a short list of specific pests and diseases, and each one responds to a different treatment. Spraying the wrong product wastes money and can actually make things worse by killing the beneficial insects that were helping you.
PA’s climate creates a particular set of challenges for kale growers. Our humid summers breed fungal diseases that drier regions rarely see. The two distinct pest pressure peaks — one in late spring as overwintering insects emerge, and another in early fall when a second generation hatches — mean your kale faces threats across the entire growing season. And the mild winters in zones 6b and 7a allow pest populations to survive from year to year at higher densities than in colder states.
Below you will find every pest and disease you are likely to encounter growing kale in Pennsylvania zones 5a through 7a: exact identification details so you know what you are dealing with, the timing of each problem in our climate, organic and conventional control options ranked by effectiveness, a month-by-month prevention calendar, and the cultural practices that prevent most issues before they start. For the full growing guide including planting schedules and variety selection, see our kale growing hub.
▲
Kale Pest and Disease Pressure Calendar — Pennsylvania (Zones 5a-7a)
Early Season Pests
Moderate Pressure
Rising Pressure
Peak Pressure
Fall Transition
Quick Reference — Top Kale Threats in Pennsylvania
Common Kale Pests in Pennsylvania
Pennsylvania kale faces a predictable roster of insect pests. The good news is that the list is short — about six species cause the vast majority of damage. The better news is that every one of them can be controlled organically without expensive products. The key is identifying the pest correctly before you treat, because the controls for caterpillars are completely different from the controls for aphids, and using the wrong one wastes time while the real problem gets worse.
Imported Cabbageworm (Pieris rapae)
This is the number one kale pest in Pennsylvania and the reason more kale is lost in home gardens than any other single cause. The adult is a small white butterfly with black wing tips that you see fluttering around brassica plants from April through October. Each butterfly lays 200 to 300 eggs on the undersides of kale leaves over its 2 to 3 week lifespan. The eggs hatch in 5 to 7 days, and the pale green caterpillars begin feeding immediately.
Identification
| Stage | What to Look For | Where to Check |
|---|---|---|
| Adult butterfly | White wings, 1.5-2 inch wingspan, 1-2 black spots per wing; erratic fluttering flight around plants | Flying near and landing on kale plants, especially mid-morning on sunny days |
| Eggs | Tiny yellow-white bullet-shaped dots, about the size of a pinhead, laid singly (not in clusters) | Undersides of leaves, particularly on newer growth near the center of the plant |
| Caterpillar (larva) | Pale green, velvety body with a faint yellow stripe down the back; up to 1.25 inches long | Along leaf veins and ribs where the green color provides camouflage; frass (droppings) on leaves below |
| Damage pattern | Irregular, ragged holes in leaves (not round — that is flea beetles); large sections of leaf tissue eaten from edges inward | Start checking outer leaves first; caterpillars work from the outside of the plant inward |
Control Methods — Ranked by Effectiveness
| Method | Effectiveness | When to Apply | Notes for PA |
|---|---|---|---|
| Row cover (physical barrier) | 99-100% | Install at transplant time before first butterflies appear (mid-April in zone 7a, late April in 5a) | Best single investment for PA kale — blocks all flying pests including cabbageworms, loopers, and flea beetles simultaneously |
| Bt spray (Bacillus thuringiensis var. kurstaki) | 90-95% | Spray every 7-10 days when caterpillars are active; reapply after rain | Only kills caterpillars that eat treated leaves — safe for bees, ladybugs, and all beneficial insects; OMRI-listed organic |
| Hand picking | 70-85% | Check plants every 2-3 days; crush eggs and remove caterpillars by hand | Practical for small plantings (under 12 plants); time-consuming for larger gardens |
| Spinosad spray | 85-95% | Apply in evening (toxic to bees when wet — safe once dry); every 7-14 days | Derived from soil bacteria; OMRI-listed organic; broader spectrum than Bt — also kills thrips and beetles |
| Parasitic wasps (Trichogramma) | 50-70% | Release in spring when butterflies first appear; they parasitize eggs before caterpillars hatch | Best as a supplement to other methods; PA gardens with diverse plantings already host some naturally |
Two Generation Peaks in PA: Imported cabbageworms have two major population peaks in Pennsylvania — one in late May through June and a second, often larger one in September. Many gardeners relax their vigilance after the spring generation fades in July, only to be blindsided when the fall generation devastates their autumn kale. Keep row covers on or continue Bt sprays through the entire season, not just spring.
Aphids (Green Peach and Cabbage Aphid)
Aphids are the second most common kale pest in PA and the one that frustrates gardeners the most because they come back so quickly after treatment. A single female produces 50 to 80 offspring in her lifetime without mating, and those offspring start reproducing within a week. A small cluster on Monday can become a colony of hundreds by Friday if conditions are warm and humid — which they are in a PA summer from June through August.
Identification
Two aphid species attack kale in Pennsylvania. The green peach aphid (Myzus persicae) is pale yellowish-green and found on leaf undersides. The cabbage aphid (Brevicoryne brassicae) is gray-green with a waxy coating that makes it look dusty or powdered. Both cluster tightly on the undersides of leaves and at the base of new growth where the tissue is soft.
Look for these signs: sticky, shiny residue (honeydew) on leaf surfaces below the colony, curled or distorted new leaves, and a general yellowing or wilting of infested plants. In heavy infestations, black sooty mold grows on the honeydew, making leaves look dirty. Ants crawling up and down kale stems often indicate an aphid colony — ants farm aphids for the honeydew and will actually protect them from predators.
Control Methods
| Method | Effectiveness | When to Apply | Notes for PA |
|---|---|---|---|
| Strong water spray | 70-80% per application | As soon as you see the first cluster; repeat every 2-3 days until population crashes | Use a hose nozzle directed at undersides of leaves; dislodged aphids rarely climb back up; free and immediate |
| Insecticidal soap | 80-90% | Spray directly on aphids — must make contact to work; every 5-7 days | Works on contact only; no residual; safe for food crops; apply in early morning or evening to avoid leaf burn in PA summer heat |
| Neem oil spray | 75-85% | Spray undersides of leaves every 7-14 days; acts as repellent and disrupts feeding | Also has fungicidal properties — useful in PA where aphids and fungal diseases often coincide |
| Ladybug/lacewing release | 60-80% | Release in evening near infested plants; each ladybug eats 50+ aphids per day | PA gardens with mixed plantings and minimal spraying build natural predator populations over time |
| Reflective mulch | 50-70% reduction | Place aluminum foil or reflective plastic mulch around plants at planting time | Confuses flying aphids that use sky-reflection to find plants; best for preventing new colonies from starting |
This page contains affiliate links. We may earn a small commission at no extra cost to you.
Neem Oil Concentrate for Garden Pest Control
Cold-pressed neem oil works as an insecticide, miticide, and fungicide in one product — effective against aphids, whiteflies, spider mites, and the early stages of powdery mildew and downy mildew. Mix with water per label directions and spray every 7 to 14 days during active pest pressure. OMRI-listed for organic gardening.
Flea Beetles
Flea beetles are small (1/16 to 1/8 inch), dark, shiny beetles that jump like fleas when disturbed. They chew tiny round holes in kale leaves — the damage looks like someone hit the leaf with a miniature hole punch, producing dozens of perfectly circular holes scattered across the leaf surface. This pattern is unmistakable and instantly distinguishes flea beetle damage from the irregular, ragged holes caused by caterpillars.
Flea beetles are the first pest to appear each spring in PA, emerging from the soil in late March to mid-April as soil temperatures reach 50 degrees. They are most damaging to young seedlings and recent transplants because the small plants cannot tolerate the leaf area loss. A mature kale plant with 20 or more leaves can absorb moderate flea beetle feeding without any impact on production, but a seedling with 4 leaves can be killed.
Control Methods
| Method | Effectiveness | Notes for PA |
|---|---|---|
| Row cover at transplant time | 95-100% | Physical barrier prevents beetles from reaching plants; same cover that blocks cabbageworms also blocks flea beetles |
| Transplant larger seedlings | 70-80% (damage tolerance) | Wait until seedlings have 6+ true leaves before transplanting; larger plants outgrow the damage |
| Diatomaceous earth | 60-70% | Dust on dry leaves; must reapply after every rain — impractical in PA’s wet spring weeks |
| Kaolin clay spray (Surround WP) | 75-85% | Creates a white film on leaves that confuses and repels beetles; wash off at harvest |
| Spinosad spray | 80-90% | Apply in evening to protect bees; effective for 7-14 days; OMRI-listed |
| Yellow sticky traps | 30-40% (monitoring tool) | Good for detecting when beetles are active so you know when to cover plants; not effective as sole control |
Free PA Planting Calendar
Zone-specific · 4 pages · Instant download
Get the exact dates for your Pennsylvania zone — when to start seeds indoors, direct sow, transplant, and harvest. Built around your local frost window, not a generic national average.
- Wall chart with all key dates
- Seed-start schedule (50+ crops)
- First & last frost reference
- Soil temp cheat sheet
Cabbage Looper (Trichoplusia ni)
The cabbage looper is often confused with the imported cabbageworm, but it is a different species with different behavior. Loopers are bright green caterpillars that move with a distinctive inchworm motion — they hunch up in the middle with each step, forming a loop shape. They are slightly larger than cabbageworms (up to 1.5 inches) and tend to feed more aggressively, consuming three times as much leaf tissue as a cabbageworm of the same size.
The adult is a brownish-gray moth with a silver figure-8 mark on each forewing. Unlike the cabbageworm butterfly that flies during the day, looper moths are active at dusk and dawn, making them harder to spot. In PA, loopers typically have 2 to 3 generations per year, with populations building through summer and reaching peak numbers in August and September — exactly when your fall kale is getting established.
Control Methods
The same controls that work for cabbageworms work for loopers: row cover for prevention, Bt spray for active infestations, and hand picking for small gardens. Bt is equally effective against both species because both are Lepidoptera larvae. The one difference is timing — because loopers peak later in the season, you may need to continue Bt applications through September even if cabbageworm pressure dropped off in July. Caterpillar pests of brassicas respond consistently to Bt-based controls regardless of species because the mode of action targets the same gut physiology.
Harlequin Bug (Murgantia histrionica)
Harlequin bugs are shield-shaped stink bugs with dramatic orange and black markings that make them easy to identify. They feed by piercing leaf tissue and sucking plant fluids, leaving behind white or yellow stippled spots where the cells have been drained. Heavy feeding causes wilting, brown patches, and eventual plant death. These are among the most destructive kale pests in southern and central PA — they are less common in the northern tier counties (zones 5a-5b) where cold winters kill overwintering adults.
Identification and Control
| Stage | What to Look For | Control |
|---|---|---|
| Adults | 1/2 inch shield-shaped bugs; bold orange and black pattern; strong odor when crushed | Hand pick into a bucket of soapy water (they are too large for most sprays to kill effectively); check daily in morning when bugs are sluggish |
| Eggs | Tiny white barrel-shaped eggs arranged in neat double rows of 10-12 on leaf undersides | Crush eggs on sight; the distinctive double-row pattern makes them easy to identify |
| Nymphs | Round-bodied, wingless, green and orange; cluster near eggs after hatching | Insecticidal soap or neem oil spray while young and soft-bodied; harder to kill as they mature |
Trap Crop Strategy: Plant a few mustard or turnip green plants at the edges of your kale patch. Harlequin bugs prefer mustard-family plants with stronger oils over kale, and they will congregate on the trap crop where you can hand pick them in concentrated groups. Destroy the trap crop at the end of the season so it does not harbor overwintering bugs. This works especially well in zones 6b and 7a where harlequin bug populations are highest.
Other Kale Pests in Pennsylvania
Beyond the big four (cabbageworms, aphids, flea beetles, and loopers), PA kale growers occasionally deal with a few secondary pests. These cause less damage overall but can create problems under specific conditions.
| Pest | Damage | When Active in PA | Control |
|---|---|---|---|
| Slugs | Irregular holes with shiny slime trails; feed at night and during rainy periods | April-October; worst in wet spring weeks (our specialty in PA) | Iron phosphate bait (Sluggo); copper tape barriers around raised beds; remove mulch from immediate base of plants if severe |
| Whiteflies | Tiny white flying insects cloud up when plant is disturbed; yellowing leaves; sticky honeydew | June-September; worse in sheltered gardens with poor airflow | Yellow sticky traps; insecticidal soap; neem oil spray; improve air circulation by thinning |
| Diamondback moth | Small green caterpillars (3/8 inch) that wriggle violently when touched; feed on leaf undersides creating windowpane damage (eat tissue but leave upper skin intact) | May-September; usually minor in PA home gardens but can spike in dry years | Bt spray; row cover; most PA gardens see only light damage from this pest |
| Cabbage root maggot | Wilting plants despite adequate water; white maggots feeding on roots below soil line | May-June; adults (small gray flies) lay eggs at base of plants in spring | Cardboard collars around stems at soil line prevent egg-laying; row cover blocks adult flies |
| Deer | Entire plants eaten overnight; clean-cut browse lines; tracks and droppings nearby | Year-round; worst in winter when other food is scarce | Fencing (8 feet tall); netting over beds; deer repellent sprays (reapply after rain); row cover provides some deterrent |
| Groundhogs (woodchucks) | Plants stripped to stems; large amounts eaten in a single feeding; burrow entrances nearby | March-November; active during day | Hardware cloth buried 12 inches below and extending 12 inches outward around raised beds; live trapping and relocation |
Common Kale Diseases in Pennsylvania
Pennsylvania’s combination of humid summers, wet springs, and moderate temperatures creates ideal conditions for several kale diseases. Unlike pests, most kale diseases cannot be cured once the plant is infected — they can only be prevented or managed to slow spread. This makes prevention through cultural practices far more important than any spray program.
Disease Identification and Management
| Disease | Symptoms | Conditions That Trigger It | Management in PA |
|---|---|---|---|
| Black rot (Xanthomonas campestris) | V-shaped yellow lesions starting at leaf margins and expanding inward; leaf veins turn dark brown or black; lesions eventually dry to papery tan | Warm weather (77-86 F optimal); splashing rain or overhead irrigation; contaminated seed; wounds from insect feeding | Buy hot-water-treated or certified disease-free seed; water at base only with drip irrigation; remove and destroy infected plants immediately — black rot bacteria survive on debris for 2+ years; 3-year rotation away from all brassicas |
| Downy mildew (Hyaloperonospora parasitica) | Angular yellow patches on upper leaf surface bounded by veins; gray to purplish fuzzy growth on undersides; infected areas turn tan and papery | Cool temperatures (50-60 F); high humidity; wet leaf surfaces; poor air circulation — perfect description of PA in October | Space plants for airflow (18-inch minimum); avoid overhead watering; remove lower leaves that touch soil; copper-based fungicide sprays as preventive in fall; harvest outer leaves promptly to improve air movement around plant center |
| Alternaria leaf spot (Alternaria brassicae) | Small dark spots (1/4 to 1/2 inch) with concentric rings creating a target or bullseye pattern; older lower leaves affected first; spots enlarge and merge in wet weather | Warm, humid weather (75-85 F); prolonged leaf wetness; splashing rain carrying spores from soil to leaves | Mulch to prevent soil splash onto leaves; remove and destroy affected lower leaves; avoid working in garden when foliage is wet; copper fungicide as preventive; clean up all crop debris at end of season |
| Clubroot (Plasmodiophora brassicae) | Plants wilt on warm days but recover at night; stunted growth; roots swollen, distorted, and club-shaped when pulled up | Acidic soil (pH below 6.5); wet conditions; moves on contaminated soil (boots, tools, transplants) | Maintain raised bed soil pH above 7.0 with lime; clean tools between beds; buy certified transplants; once established in soil, the pathogen persists for 15-20 years — do not plant brassicas in infected ground; raised beds with imported soil are the best defense |
| Powdery mildew (Erysiphe cruciferarum) | White powdery coating on upper leaf surfaces; spreads across leaf as infection advances; leaves may yellow and drop | Moderate temperatures (60-80 F); dry conditions with humid air; crowded plantings with poor airflow — less common in PA than downy mildew but appears during dry stretches in August-September | Space plants for air circulation; prune lower leaves; neem oil or potassium bicarbonate sprays as preventive; usually a minor issue in PA because our humidity favors downy mildew instead |
| Black leg (Phoma lingam) | Gray-brown spots with dark borders on leaves and stems; cankers at stem base that girdle the plant; internal stem tissue turns dark | Cool wet weather; contaminated seed; crop debris from previous brassica plantings | Buy treated seed; 4-year rotation; remove all brassica crop debris at season end; do not compost infected plants — bag and discard |
When to Remove a Diseased Plant: If more than 50 percent of the leaves on a single kale plant show disease symptoms, pull the entire plant and bag it for trash — do not compost it. Leaving a heavily diseased plant in the bed serves as a constant source of spores and bacteria that infect your healthy plants. One early removal saves the rest of the bed. Selecting disease-resistant varieties reduces the number of plants lost to infections in regions with consistent disease pressure.
Month-by-Month Prevention Calendar for PA Kale
Preventing kale problems is easier and cheaper than treating them. This calendar gives you specific actions for each month of the PA growing season so you stay ahead of pests and diseases rather than reacting after damage is done.
| Month | Prevention Actions | What to Watch For |
|---|---|---|
| February-March | Order certified disease-free seed; clean and sterilize tools, pots, and row cover fabric from last season; test raised bed soil pH and lime if needed | Nothing active yet — this is prep time |
| April | Install row cover over transplants immediately at planting; apply cardboard collars around stems for root maggot prevention; set out yellow sticky traps to monitor flea beetle emergence | Flea beetles emerge from soil when temps reach 50 F; first cabbage white butterflies appear in zone 7a |
| May | Begin weekly inspection of leaf undersides for cabbageworm eggs; start Bt spray program if not using row cover; check for aphid clusters on new growth | Cabbageworm first generation reaches feeding size; aphid colonies start building; flea beetle damage peaks on young plants |
| June | Continue Bt sprays every 7-10 days; blast aphid colonies with water every 2-3 days; remove and destroy any leaves showing disease spots; mulch beds to prevent soil splash | Peak cabbageworm damage; aphid populations exploding; first signs of Alternaria leaf spot on lower leaves; harlequin bug adults appearing in zones 6b-7a |
| July | Switch to fall crop planning; start fall kale seeds indoors; clean up spring kale debris thoroughly; hand pick harlequin bugs and crush egg masses | Disease pressure highest as humidity peaks; black rot can appear after storms; cabbage looper numbers building; spring kale declining in quality |
| August | Transplant fall kale under row cover on day one; apply Bt immediately if cover not used; monitor for second-generation cabbageworms closely | Second generation of cabbageworms hatching; fall kale seedlings most vulnerable to flea beetles; Alternaria spreading in humid conditions |
| September | Continue Bt or row cover protection; second cabbageworm generation peaks; begin watching for downy mildew symptoms on cool wet mornings; increase spacing if plants are crowded | Peak fall caterpillar damage (both worms and loopers); downy mildew conditions developing as nights cool and dew increases |
| October | Preventive copper fungicide spray if downy mildew appeared in September; remove infected leaves immediately; apply fall mulch for winter protection; check for overwintering harlequin bugs under debris | Downy mildew peak; pest pressure declining as temps drop; aphids crashing as cold arrives |
| November-December | Clean up all crop debris from beds; destroy (do not compost) any diseased plant material; apply lime to beds that tested acidic; cover beds with mulch or winter cover crop | Most pests dormant; occasional aphid activity on warm days in zone 7a; focus is on cleaning up to reduce next year’s pest and disease carryover |
Organic Spray Guide for PA Kale
If you choose to spray, these are the organic products that work on PA kale pests and diseases. Each product has specific strengths and limitations — using the right one for the right pest makes the difference between success and wasted effort.
| Product | Target | Mode of Action | Application Rate | Reapply Interval | Preharvest Interval |
|---|---|---|---|---|---|
| Bt (Bacillus thuringiensis var. kurstaki) | Caterpillars only (cabbageworms, loopers, diamondback moth) | Stomach poison — caterpillar must eat treated leaf; stops feeding within hours, dies in 2-3 days | 1-2 tsp per gallon of water (follow label) | Every 7-10 days; reapply after rain | 0 days (safe to harvest same day) |
| Neem oil | Aphids, whiteflies, flea beetles, soft-bodied insects; also fungicidal | Contact killer; disrupts feeding and reproduction; repels insects; suppresses fungal spores | 2 tbsp per gallon of water with 1 tsp dish soap as emulsifier | Every 7-14 days | 0 days |
| Insecticidal soap | Aphids, whiteflies, spider mites, soft-bodied insects | Contact only — must spray directly on insect; dissolves waxy coating causing dehydration | 2.5 tbsp per gallon of water | Every 5-7 days | 0 days |
| Spinosad | Caterpillars, flea beetles, thrips | Stomach and contact poison; causes excitation of insect nervous system | Follow label (varies by brand) | Every 7-14 days | 1 day |
| Copper fungicide | Downy mildew, black rot, Alternaria, black leg | Preventive — kills fungal spores on leaf surface before they penetrate; does not cure existing infections | 1-3 tbsp per gallon (follow label for specific product) | Every 7-10 days in wet weather | 0-1 days |
| Potassium bicarbonate | Powdery mildew | Raises leaf surface pH to kill fungal mycelium on contact | 1 tbsp per gallon of water + 1 tsp dish soap | Every 7-14 days | 0 days |
Spray Timing Matters: Apply all sprays in early morning or late evening when temperatures are below 85 degrees and bees are not active. Spraying in midday PA summer heat causes leaf burn from oil-based products (neem) and kills pollinators visiting nearby flowers. Always spray undersides of leaves — that is where most pests and disease entry points are. A spray that only hits the top of the leaf misses the target entirely.
Cultural Practices That Prevent Most Kale Problems
The majority of kale pest and disease problems in PA can be prevented without spraying a single drop of anything. These cultural practices are the foundation of a healthy kale patch — sprays and treatments are only needed when prevention breaks down.
The Five Pillars of Kale IPM in Pennsylvania
| Practice | What It Prevents | How to Do It | Impact Level |
|---|---|---|---|
| Crop rotation (3-year minimum) | Clubroot, black rot, black leg, Alternaria, root maggots, and all soil-borne pathogens | Never plant kale or any brassica in the same bed more than once every 3 years; rotate with tomatoes, beans, squash, or root vegetables | Critical — single most important disease prevention practice |
| Row cover from day one | Cabbageworms, loopers, flea beetles, root maggots, cabbage moths, and all flying insect pests | Install lightweight row cover over wire hoops at transplant time; keep sealed edges; leave on all season (kale does not need pollination) | Critical — eliminates 95%+ of insect pest problems with zero spraying |
| Drip irrigation (no overhead water) | Black rot, downy mildew, Alternaria, and all diseases spread by water splashing from soil to leaves | Run drip tape or soaker hose at soil level; never use overhead sprinklers on kale; water in morning so foliage dries before evening | High — eliminates the primary disease transmission method in PA’s humid climate |
| Proper spacing (18 inches) | Downy mildew, powdery mildew, Alternaria, and all diseases favored by poor air circulation | Space full-size kale at 18 inches minimum; remove lower leaves that touch soil; thin overcrowded plantings | High — airflow between plants dries foliage faster after rain and dew |
| Fall cleanup | Overwintering pests and diseases that carry over to next season | Remove all brassica crop debris after final harvest; destroy (do not compost) any diseased material; clean and store row covers for next year | Moderate-High — breaks the cycle that builds pest and disease pressure year over year |
If you do only two things from this list, make them row cover and crop rotation. Together, these two practices prevent the vast majority of kale problems that PA gardeners face. Row cover stops the insects; rotation stops the soil-borne diseases. Everything else is refinement on top of that foundation. For the full growing guide including soil preparation and planting techniques, see our how to grow kale in PA guide.
Symptom Troubleshooting Table
Use this table when you see something wrong with your kale and need to figure out the cause quickly. Start with the symptom you see, match it to the most likely cause, and follow the recommended action.
| What You See | Most Likely Cause | Confirm By | Immediate Action |
|---|---|---|---|
| Irregular ragged holes in leaves | Cabbageworm or cabbage looper | Look for green caterpillars on leaf undersides; check for dark frass pellets | Hand pick caterpillars; spray Bt on all leaf surfaces; install row cover |
| Tiny round shot-holes (like hole punch) | Flea beetles | Disturb the plant — tiny dark beetles will jump away | Cover with row cover; apply kaolin clay; transplant larger seedlings next time |
| Clusters of small insects on leaf undersides; sticky residue | Aphids (green peach or cabbage) | Look for honeydew (sticky coating) on lower leaves; check for ants farming them | Blast with strong water spray daily for 3-5 days; follow up with insecticidal soap if persistent |
| V-shaped yellow lesions at leaf edges; dark veins | Black rot (bacterial) | Cut stem — internal tissue shows darkened vascular ring | Remove infected plant immediately; do not compost; water at base only; rotate out of brassicas for 3+ years |
| Yellow patches above; gray-purple fuzz underneath | Downy mildew | Check leaf undersides with a hand lens — fuzzy gray-purple spore growth confirms | Remove infected leaves; improve spacing and airflow; apply copper fungicide to remaining healthy plants |
| Dark target-shaped spots with concentric rings | Alternaria leaf spot | Distinctive bullseye pattern on older lower leaves; spots enlarge in wet weather | Remove affected lower leaves; mulch to stop soil splash; copper fungicide as preventive on healthy leaves |
| Plants wilting on warm days; recover overnight | Clubroot | Pull one plant and check roots — swollen, distorted, club-shaped roots confirm | Remove plant; do not plant brassicas in that soil for 15+ years; raise pH above 7.0 with lime; use clean soil in raised beds |
| White powdery coating on leaf tops | Powdery mildew | Rub finger across coating — white powder comes off (unlike downy mildew which is on underside) | Remove worst leaves; spray potassium bicarbonate or neem oil; improve air circulation |
| Entire plant eaten to stems overnight | Deer or groundhog | Deer leave clean-cut browse; groundhogs eat messily and leave droppings nearby | Fencing (8 ft for deer); hardware cloth around raised beds for groundhogs; repellent sprays as temporary measure |
| Windowpane damage (leaf skin intact but tissue eaten from below) | Diamondback moth caterpillar | Tiny green caterpillars (3/8 inch) that wriggle violently when poked | Bt spray; usually minor in PA — treatment only needed if damage is widespread |
| Orange and black bugs; white stippled spots on leaves | Harlequin bugs | Shield-shaped bugs with bright warning coloration; strong smell when crushed | Hand pick into soapy water daily; crush egg masses (neat double rows on leaf undersides); plant mustard trap crop |
| Yellowing lower leaves; rest of plant looks healthy | Nitrogen deficiency (not a pest or disease) | No insects present; no lesions or spots; just uniform yellowing of oldest leaves | Side-dress with fish emulsion or blood meal; increase feeding frequency |
If you are growing kale in containers and experiencing pest problems, the controls are the same but easier to apply at a small scale — see our container kale guide for container-specific pest management tips. For raised bed growers, our raised bed kale guide covers how bed height and construction affect pest pressure.
For a comprehensive overview of garden pests across all crops, see our complete Pennsylvania garden pest identification guide.
Plan your full season: See our monthly planting guide for a month-by-month schedule, or browse all crops in our Pennsylvania vegetables hub. For frost timing, check our PA frost dates by region.
Frequently Asked Questions About Kale Pests and Diseases in Pennsylvania
1. What is eating holes in my kale leaves in Pennsylvania?
The two most likely culprits are imported cabbageworms and flea beetles. Cabbageworms create large, irregular, ragged holes and leave dark frass pellets on leaves — look for pale green caterpillars on undersides. Flea beetles create tiny, perfectly round holes that look like a hole punch. Cabbageworms are controlled with Bt spray or row cover. Flea beetles are controlled with row cover or by transplanting larger seedlings that can tolerate the damage.
2. Is neem oil safe to use on kale I am going to eat?
Yes. Neem oil is OMRI-listed for organic production and has a zero-day preharvest interval, meaning you can harvest and eat kale the same day you spray. Wash leaves thoroughly before eating, as with any produce. Apply neem oil in early morning or evening — never in direct midday sun, which causes leaf burn. Mix with water and a few drops of dish soap as an emulsifier per label directions.
3. How do I prevent downy mildew on kale in Pennsylvania’s fall?
Downy mildew thrives in the cool, wet conditions that PA delivers every October. Prevent it by spacing plants at least 18 inches apart for air circulation, watering only at the base with drip irrigation (never overhead), removing lower leaves that touch the soil, and harvesting outer leaves promptly so the plant center stays open and airy. If downy mildew has been a problem in previous seasons, apply a copper-based fungicide preventively every 7 to 10 days starting in late September before symptoms appear.
4. Should I pull out kale plants that have black rot?
Yes — immediately. Black rot is bacterial and cannot be cured once a plant is infected. Every day an infected plant stays in the garden, rain splashes bacteria onto neighboring healthy plants. Pull the entire plant including roots, bag it, and put it in the trash. Do not compost black rot material. The bacteria survive in soil and plant debris for 2 or more years, so avoid planting any brassica in that spot for at least 3 years.
5. Do I need to spray my kale if I use row cover?
In most cases, no. A properly installed row cover blocks all flying insect pests — cabbageworms, loopers, flea beetles, root maggots, and harlequin bugs. If the cover is sealed at the edges and was installed before the first pests appeared, you should not need any insecticide sprays. The only situations where you might still need to spray under row cover are soil-borne pests already present when the cover was installed, or if you lift the cover frequently and pests get underneath.
6. When should I start spraying Bt for cabbageworms in PA?
Begin Bt applications when you first see white cabbage butterflies flying in your garden — typically mid-April in zone 7a, late April in zones 6a-6b, and early May in zones 5a-5b. Spray every 7 to 10 days as long as butterflies are active, and reapply after any rain because Bt washes off. Do not stop spraying after the spring generation fades in July — the second generation in September is often worse. Continue through the end of October or until hard frost ends butterfly activity.
Continue Reading: Kale Growing Guides for Pennsylvania
- Growing Kale in Pennsylvania — complete hub guide with varieties, zones, and overview
- How to Grow Kale in Pennsylvania — step-by-step planting, care, and harvest techniques
- When to Plant Kale in Pennsylvania — zone-by-zone planting calendars for spring and fall
- Growing Kale in Containers in Pennsylvania — pot selection, soil, and care for small spaces
- Growing Kale in Raised Beds in Pennsylvania — bed setup, soil recipes, and planting layouts
- Best Vegetables to Grow in Pennsylvania — our full guide to the top crops for PA gardens
