Pacific Northwest Plant Disease Management Handbook

Lawn and Turf-Net Blotch

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Latest revision: 
March 2024
PNW Plant Disease Image

Small, reddish brown spots girdle leaves, causing dieback from the tip.

Alec Kowalewski.

PNW Plant Disease Image

Small, reddish brown spots girdle leaves, causing dieback from the tip.

Alec Kowalewski.

PNW Plant Disease Image

Heavily infected stands turn yellow, then brown.

Alec Kowalewski.

PNW Plant Disease Image

Small, reddish brown spots on leaves.

Alec Kowalewski.

See:

Grass for Seed - Drechslera Leaf Blights (Helminthosporium Net Blotch)

Cause Pyrenophora dictyoides (formerly Drechslera dictyoides) causes foliar disease on tall and fine fescues and perennial and annual ryegrasses. This fungal disease is most severe on young stands in wet, shady areas. The fungus survives unfavorable conditions in plant debris or in infected plants. Leaf infections are most common in cooler months. Conidia spread by wind, splashing rain, grass clippings, or by equipment.

Symptoms Fine fescue-small, reddish brown spots girdle leaves, causing dieback from the tip. Small brown patches of dead foliage may be found over large areas of fine fescue if the disease is severe.

Tall fescue and perennial ryegrass-short brown streaks run parallel and perpendicular to the leaf axis, producing a net-like symptom on leaves. Heavily infected stands turn yellow, then brown.

Cultural control

  • Plant resistant cultivars: Ranger perennial ryegrass reportedly has high resistance to net blotch, Gator has good resistance, and Manhattan II has some resistance.
  • Fertilize lightly.
  • Mow 2 to 2.5 inches tall and remove clippings.
  • Avoid light, frequent waterings. Use enough water, based on local growing conditions. Water in morning so turf will dry before night.
  • Remove excess thatch in early spring and aerify if needed to provide good aeration and drainage.
  • Remove turf in heavily-shaded areas.

Chemical control Needed only in areas that favor disease development. Note: Avoid using fungicides containing Group 1 fungicides (such as Cleary's 3336 or OHP 6672) on affected lawns because they can increase the severity of the disease. To prevent developing resistant fungi, alternate or tank-mix materials from different groups with different modes of action. Limit the use of any one group during crop production.

  • Chipco 26019 FLO at 3 to 4 fl oz/1,000 sq ft. Group 2 fungicide. 12-hr reentry.
  • Compass 50 WDG at 0.1 to 0.25 oz/1,000 sq ft. Do not use organosilicate additive. Group 11 fungicide. 12-hr reentry.
  • Daconil Weather Stik at 2 to 5.5 fl oz/1,000 sq ft depending on whether the application is preventive or curative. Group M5 fungicide. 12-hr reentry.
  • Eagle 20 EW at 1.2 fl oz/1,000 sq ft. May produce a growth regulation effect on Kentucky bluegrass. Group 3 fungicide. 24-hr reentry.
  • Fame SC at 0.2 to 0.4 fl oz/1,000 sq ft. Group 11 fungicide. 12-hr reentry.
  • Heritage at 0.2 to 0.4 oz/1,000 sq ft. Group 11 fungicide. 4-hr reentry.
  • Insignia SC at 0.4 to 0.7 fl oz/1,000 sq ft. Do not use with organosilicate adjuvants. Group 11 fungicide. 12-hr reentry.
  • Mancozeb 80% (Fore, Manzate, and Protect DF) at 4 oz/1,000 sq ft. Group M3 fungicide. 24-hr reentry.
  • Medallion SC at 1 to 2 fl oz/1,000 sq ft. Apply after mowing. Using with oils or adjuvants may damage plant. Group 12 fungicide. 12-hr reentry.
  • Previa at 2 to 5.5 fl oz/1,000 sq ft. Group M5 fungicide. 12-hr reentry.
  • Propiconazole-based products. Group 3 fungicides.
    • Banner MAXX at 1 to 2 fl oz/1,000 sq ft. 12-hr reentry.
    • PropiMax EC at 0.37 to 0.73 fl oz/1,000 sq ft. 12-hr reentry.
  • Secure at 0.5 fl oz/1,000 sq ft. Group 29 fungicide. Reentry when sprays have dried.
  • Trinity at 0.5 to 2 fl oz/1,000 sq ft. Do not mix with growth regulators during hot weather as injury may develop. Group 3 fungicide. 12-hr reentry.
  • Velista at 0.3 to 0.5 oz/1,000 sq ft. Group 7 fungicide. 12-hr reentry.

Combination Fungicides

  • Encartis at 3 to 4 fl oz/1,000 sq ft. Do not use with oil-based pesticides. Group 7 + M5 fungicide. Reentry when sprays have dried.
  • Headway at 1.5 to 3 fl oz/1,000 sq ft. Do not use with silicone-based surfactants or EC formulations. Group 3 + 11 fungicide. 12-hr reentry.
  • Heritage Action at 0.2 to 0.4 oz/1,000 sq ft. Group 11 + P1 fungicide. 12-hr reentry.
  • Honor at 0.55 to 1.1 oz/1,000 sq ft. Do not use with organosilicone-based adjuvants. Group 7 + 11 fungicide. Golf course turf only.
  • Interface at 3 to 5 fl oz/1,000 sq ft. Maintain agitation while spraying. Do not mix with adjuvants. Group 2 + 11 fungicide. 24-hr reentry.
  • Navicon at 0.7 to 0.85 fl oz/1,000 sq ft. Group 3 + 11 fungicide. 12-hr reentry.
  • Pillar G at 3 lb/1,000 sq ft. Group 3 + 11 fungicide. 12-hr reentry.
  • Renown at 2.5 to 4.5 fl oz/1,000 sq ft. Group M5 + 11 fungicide. 12-hr reentry.
  • Tartan at 1 to 2 fl oz/1,000 sq ft. Group 3 + 11 fungicide. 12-hr reentry.

Reference Smiley, R.W., Dernoeden, P.H., and Clarke, B.B. 2005. Compendium of Turfgrass Diseases. 3rd edition. St. Paul, MN: APS Press.

Pscheidt, J.W., and Ocamb, C.M. (Senior Eds.). 2024 Pacific Northwest Plant Disease Management Handbook.
© Oregon State University.

Use pesticides safely!

  • Wear protective clothing and safety devices as recommended on the label. Bathe or shower after each use.
  • Read the pesticide label—even if you’ve used the pesticide before. Follow closely the instructions on the label (and any other directions you have).
  • Be cautious when you apply pesticides. Know your legal responsibility as a pesticide applicator. You may be liable for injury or damage resulting from pesticide use.

Trade-name products and services are mentioned as illustrations only. This does not mean that the participating Extension Services endorse these products and services or that they intend to discriminate against products and services not mentioned.

H - Home garden packaging commonly available.     O - Acceptable in organic production.