Plant-feeding nematodes are an important problem for plants. These microscopic worms live in the soil and feed on roots, reducing the health of the plant. If you have seen galls on tomato roots, you have seen classic nematode feeding symptoms. However, not all nematodes feed on roots. A special group of nematodes called foliar nematodes (Aphelenchoides spp.) live in the leaves of ornamental plants. These nematodes swim up water films on plant stems to feed on leaves of herbaceous perennials. Pretty impressive for a little worm!
Once the nematodes reach a leaf, they enter through naturally occurring holes on the bottom of the leaf used for gas exchange. They feed on plant cells until they have depleted that area of the leaf. These nematodes cannot cross the thick veins in a plant leaf, so they must exit and reenter through another hole in a different part of the leaf. This feeding pattern sometimes results in angular browning in the leaf. If you see angular leaf lesions on an ornamental plant, it could be caused by foliar nematodes.
If you suspect nematodes are affecting your herbaceous perennials, contact the University of Florida Nematode Assay Lab. It can be challenging to manage foliar nematodes, but they can provide assistance diagnosing nematode problems. For more information on foliar nematodes, check out the University of Florida Department of Entomology and Nematology Featured Creature article on foliar nematodes.