Spot on Fern Leaves

Reproduction

• The fern plants’ bladed leaves are naturally covered with small specks, which are part of the plant's reproductive process during part of the year. Each speck, called a sporangia, houses a collection of spores that can grow into mature plants without pollination. According to the University of Florida, the pattern and number of sporangia on fern leaves depends on the species. Fern spores can be many different colors, including black, red and yellow.

Bacterial Disease

• Bacterial infections create unsightly, necrotic spots on fern fronds' surfaces. According to the University of Florida, the bird's nest fern (Asplenium nidus) is vulnerable to a blight disease caused by the Pseudomonas cichorii bacteria. Symptoms include wet spots on leaves that gradually expand and turn to a darker shade of brown or red. There are few practical methods for treating a bacterial disease. Remove plants with severe infections should be removed. Pruning plants with localized infections prevents the spread of the disease.

Fungal Disease

• Several groups of fungal pathogens, including several common genera that affect a large number of plant species, attack ferns in North America. General leaf spot fungi, including species in the Cercospora and Pythium genera, damage fern plants’ leaves. According to the University of Hawaii, the Calonectria theae and Cylindrocladium pteridis fungi can harm the leaves and roots of ferns. Fungal leaf infections often begin as a series of small spots that eventually cause curling, discoloration and death of foliage. Discolorations begin as yellow or brown rings, but the tissue often darkens to a black or dark brown as it decays. Some leaf diseases wilt the entire plant.

Nematodes

• Foliar nematodes (Aphelenchoides spp.) are among the most insidious fern pests. Nematodes are exceptionally small wormlike organisms generally less than 1 mm long. They puncture the surface of fern leaves and feed on the soft tissue beneath the skin. According to the University of Florida, leaf tissue damaged by nematodes fades at first, and then turns to a darker shade of brown or black. Spots caused by nematodes may be bound by the leaf's veins, because the pest is too small to penetrate stronger structural tissues.