Leaf Cupping

Like leaf rolling, leaf cupping is an easy-to-see warning that calls for closer inspection.

Cupped leaf (Enid Martindale) CC BY 2.0

Cupped leaves tend to be thicker than healthy leaves. They may cup upwards or downwards. In some cases, they’ll do both. Sometimes, the conditions that cause cupping are temporary, and the leaves return to normal unaided. In other cases, the new shape is permanent, interfering with photosynthesis and creating safe havens for pests.

Leaf cupping may indicate diseases, insect feeding, or physiological factors.

Diseases that cause leaf cupping

When fungal diseases take hold, they often block the flow of water and nutrients through the vascular bundle. Armillaria root rot causes leaves to cup downward. Eutypa dieback also causes cupping. 

Tomato yellow leaf curl virus (Florida Division of Plant Industry, FDACS, Bugwood.org) CC BY 3.0 US

Several viral diseases can also exhibit leaf cupping:

• Bean common mosaic (downward)
• Bean yellow mosaic (downward)
• Cucumber mosaic
• Curly top
• Pea seed-borne mosaic (downward)
• Strawberry mild yellow edge virus
• Tomato bushy stunt
• Tomato mosaic virus
• Tomato spotted wilt
• Tomato yellow leaf curl (upward)

Leaf cupping and insects

Aphid and thrips feeding can result in leaf cupping. Regularly checking on the underside of leaves can help nip these problems in the proverbial bud.

Black aphids on bolting spinach caused severe cupping (Kate Russell)

Leaf cupping of coffee plant by thrips feeding (Smartse) CC BY-SA 3.0

Counter to popular myth, dish soap should never be used to eliminate pests. Dish soap damages plants. Horticultural oils and castile soap are better options.

Physiological causes of leaf cupping

Extreme weather, nutrient deficiencies and toxicities, and chemical overspray can cause leaf cupping. Chemical overspray occurs when herbicides are applied when a breeze is present (or a car drives by). The chemicals end up in places you don’t want them, causing phytotoxicity.

Tomato leaf cupping due to chemical overspray (Les Rosenthal)

Plants may cup their leaves on hot, windy days, especially when water is in short supply. They may also respond to heavy pruning and digging in this way. I suppose it’s something of a panic response. Most of us tend to withdraw when attacked, so it’s no surprise that plants do something similar.

Deficiencies of boron, calcium, manganese, and molybdenum can result in cupping. Cupping may also indicate over-fertilization. Again, lab-based soil tests are invaluable. Luckily, they are inexpensive, too.

Plants may not speak in ways that we can hear, but we can certainly watch for things like leaf cupping as clues to what’s going on in the garden.