NC State Extension Publications

Pathogen

Septoria leaf spot is caused by the fungus Septoria lycopersici Speg. The disease is particularly destructive in seasons of moderate temperature and abundant rainfall, with the ability to reduce tomato yields dramatically.

Septoria leaf spot on tomato.

Septoria leaf spot on tomato.

M. Bloomquist

Septoria leaf spot on tomato.

Septoria leaf spot on tomato.

M. Bloomquist

Septoria spore production on underside of tomato leaf

Septoria spore production on underside of tomato leaf.

I. Meadows

Host Crops and Plants

This disease primarily affects tomato, although some solanaceous weeds like horsenettle (Solanum carolinense L.) are known to be hosts.

Host Parts Affected

Symptoms generally develop on the lower leaves first, although the stems, petioles, and calyx also can become infected.

Identification

Circular, tan to gray, lesions develop on the leaves and stems of the plant. The lesions generally have a dark-brown perimeter and a yellow halo may develop around the leaf lesions. Small dark spots may appear in the center of the lesion – these are pycnidia, the fruiting body of the fungus where spores are produced. On the underside of the leaves, spots may appear as a darker green color or “water-soaked.” As the disease progresses, traveling from older growth to younger growth, spots may coalesce and the leaves may become entirely brown and wither. The fruit is rarely infected by this fungus.

Favorable Environmental Conditions for Disease

Areas with high humidity and warm temperatures are most susceptible to this disease. The fungus is known to overwinter on infected tomato debris and solanaceous weed hosts (such as horsenettle). Once an area has become infected, spores are generally spread by rain splash. Water is needed to spread the spores and even workers, equipment, or insects travelling through wet foliage infected with Septoria leaf spot can aid in the spreading of the disease.

General Disease Management

  • Rotate away from tomato for at least 1 year
  • Control presence of horsenettle
  • Remove crop debris from planting areas (particularly tomato crop debris)
  • Reduce the amount of time plants are wet when possible
  • Stake plants to improve air circulation and drying of leaves
  • Use mulches or plastic to reduce contact between leaves and soil
  • Avoid fields when leaves are wet
  • Scout plants often and remove infected plants
  • Clean tools and equipment after leaving a field
  • Use fungicides listed as effective against Septoria leaf spot

Disease Control for Conventional Growers

In addition to the cultural practices listed above, there are several products that are effective at controlling the disease. For the latest fungicide recommendations for Septoria leaf spot, consult the Southeastern US Vegetable Crop Handbook.


Example products for control of Septoria leaf spot in tomato.

Active Ingredient Example Product PHI (days) FRAC Group
azoxystrobin Quadris 0 11
chlorothalonil Bravo 0 M
chlorothalonil + cymoxanil Ariston 3 M + 27
difenoconazole +cyprodinil Inspire Super 0 3 + 9
penthiopyrad Fontelis 0 7
famoxadone + cymoxanil Tanos 3 11 + 27
fluopyram + trifloxystrobin Luna Sensation 3 7 + 11
fluxapyroxad + pyraclostrobin Priaxor 7 7 + 11
fixed copper Kocide 0 M
mancozeb Penncozeb 5 M
mancozeb + fixed copper ManKocide 7 M + M
mancozeb + zoxamide Gavel 5 M + 22
mandipropamid + difenoconazole Revus Top 1 40 + 3
penthiopyrad Fontelis 0 7
zinc dimethyldithiocarbamate Ziram 7 M

Disease Control for Organic Growers

Organic growers should implement the cultural management practices outlined above. Some formulations of copper are certified for organic use and may provide adequate control. Be sure to follow directions on the product label.

Disease Control for Home Gardeners

Home gardeners should first implement the cultural management practices outlined above.

Additional Resources

Authors:

Extension Associate
Entomology & Plant Pathology
Laboratory Technician
Entomology & Plant Pathology

Publication date: Dec. 19, 2016

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Recommendations for the use of agricultural chemicals are included in this publication as a convenience to the reader. The use of brand names and any mention or listing of commercial products or services in this publication does not imply endorsement by NC State University or N.C. A&T State University nor discrimination against similar products or services not mentioned. Individuals who use agricultural chemicals are responsible for ensuring that the intended use complies with current regulations and conforms to the product label. Be sure to obtain current information about usage regulations and examine a current product label before applying any chemical. For assistance, contact your local N.C. Cooperative Extension county center.

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