What to do now
Mildest step first.
- Note whether the curl is on new growth at the top or on older leaves, and check undersides with a hand lens.
- In hot, dry weather, water deeply and mulch; curl from heat alone usually eases when it cools.
- Hose aphids off the leaf undersides; for mites or thrips, read the pest pages before you spray.
- Pull up stunted plants with mottled or shoestring-thin leaves; viruses can't be cured.
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Where is the curl?
Pepper leaves curl for several reasons, and where the curl shows up is the quickest clue. Texas A&M AgriLife Extension notes that sometimes every leaf on a plant is twisted or curled, and sometimes only the new growth is, while older leaves look normal. Curl on the older leaves of an otherwise healthy plant during hot, dry weather is usually stress. Curl limited to the newest leaves at the top points to something that attacks growing tips: tiny mites, thrips, aphids or herbicide. Turn several leaves over and look with a hand lens before treating anything, because these causes can look alike and the fixes are different.
Heat and dry soil
Texas A&M describes physiological leaf roll as a self-defense response to hot, dry weather: the leaves curl slightly to cut water loss. Heat, wind and low moisture can also make leaf edges die back and then twist. Mild leaf roll generally doesn't lower yields, though Texas A&M says severe symptoms can make flowers drop and fewer fruit set. Water deeply so the whole root zone is wet, mulch to keep moisture even, and watch the new leaves. If they come in flat once the weather cools, there's nothing more to fix. Wind damage, which can be mistaken for herbicide injury, also clears up once conditions improve.
Mites, thrips and aphids
Broad mites are a common cause of badly curled pepper tops, and they are too small to see without strong magnification. University of Connecticut Extension lists peppers among the vegetables they infest: leaves become twisted, hardened and distorted with bronzed undersides, leaf edges turn down, and growing tips can die. UConn notes the injury can resemble herbicide damage or calcium or boron deficiency, often appears suddenly in patches, and can last after the mites are gone. Thrips also distort young leaves, usually with silvery streaks and tiny black specks. Aphids cluster under curled leaves and leave sticky ; Clemson Extension lists aphids and thrips among the insects that trouble peppers. Spider mites leave fine pale stippling and webbing, mostly in hot, dry spells. Hose off aphids and spider mites first. Texas A&M suggests pulling plants with severe broad mite damage; horticultural oils, insecticidal soaps and predatory mites are options for lighter cases.
Herbicide drift
Peppers and tomatoes are very sensitive to growth-regulator weed killers such as 2,4-D and dicamba, which Texas A&M notes are common in lawn products, and it adds that wind as light as 5 mph can carry farm herbicides up to a mile. South Dakota State University Extension explains that because these herbicides affect the growing points, only leaves that grow after the exposure show damage: small, misshapen, tightly curled or cupped leaves that may feel thick or rubbery. Damage can also come from mulch or compost made with hay, straw or manure from fields treated with aminopyralid. There is no remedy for leaves already injured. SDSU says a lightly exposed plant may outgrow the damage, though yields will likely drop. Texas A&M says that if at least 4 to 6 weeks remain in the season, plants may outgrow it, with normal new buds and leaves within about a week; if not, pull and replant.
Viruses
If a plant is stunted while its neighbors look fine, and its leaves are mottled yellow and light green, curled, or long and like a shoestring, suspect a virus. University of Minnesota Extension lists cucumber mosaic virus, potato virus Y and tomato spotted wilt virus among the causes, and notes the fruit may show yellow blotches, mottling or brown rings. The Pacific Northwest disease handbook says pepper can be infected by at least 70 viruses, many spread by aphids or thrips and carried over in weeds and in perennial legumes such as alfalfa and clover. There's no cure. Pull infected plants so insects don't carry the virus to the rest, keep weeds down, and control aphids and thrips, though the handbook cautions that insect control helps but won't fully stop the viruses they spread.
Read the whole label first: it must list your crop, and its directions (amount, timing, gear, bees, days before harvest) are the law. If this page and the label differ, follow the label.
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- ThripsSilver-streaked or stippled leaves with distorted growth; tiny slender insects visible on flowers and undersides.
- AphidSoft, clustered insects on new growth causing curled leaves and sticky honeydew.
- Spider MiteStippled, bronzed leaves with fine webbing on undersides; damage intensifies in hot, dry weather.
- Blossom DropFlowers fall before setting fruit, often during temperature extremes or after weather stress.
- Fruit CrackingTomatoes crack at the stem end or shoulder, cabbage heads split, and carrots split lengthwise — usually after heavy rain follows dry weather.
- Why are my tomato leaves curling?Tomato leaf curl has three main causes — heat stress, herbicide damage (from drift or from contaminated manure, compost or straw), or a virus — and the curl pattern and which leaves are affected help narrow down which one you're dealing with.
- I have aphids on multiple plants — do I need to spray everything?Aphid outbreaks often crash on their own once lady beetles, parasitic wasps, and other natural enemies find them — water sprays and patience are often more effective than pesticides.
- Why are my pepper plant leaves turning yellow?Peppers yellow their lower leaves most often from cold stress or nitrogen deficiency — they grow slowly in cool soil and do best with nights of 60–70°F.