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Clover (Trifolium spp.) - Leaf Spots
Cause Pseudopeziza trifolii, a fungus. It attacks red clover primarily, but also can infect white and crimson clover species. Leaf spot occurs throughout the growing season but is most severe in fall. Long-term infections may reduce plant vigor and contribute to winter injury. The fungus survives in plant residue and on diseased leaves. No resistant varieties are known; tetraploid varieties are more susceptible than diploids.
Symptoms Leaf spots are small, dark brown to black circular areas with irregular or fringed edges. Spots can occur on both leaf surfaces. Fruiting structures (small, light colored raised disks comprised of apothecia) appear on the upper surface and ooze an amber liquid under moist conditions. Spots on petioles and stems are rare.
Cultural control
- Cut early to minimize leaf loss and to reduce inoculum.
Chemical control Foliar fungicides effectively reduce disease severity and may be considered for clover seed crops.
- Azoxystrobin formulations (Group 11) including Azoxyzone, A-Zox 25SC, Quadris Flowable, Tetraban, and Trevo at 6 to 15.5 fl oz/A or Azteroid FC 3.3 at 3.9 to 9.7 fl oz/A; Azoxystar, Cadera, Satori, and Tigris Azoxy 2 SC are labeled for other diseases in clover and can be used for common leaf spot on clover in Oregon only. Do not apply more than two sequential applications of Group 11 fungicides before alternating with a fungicide that is not in Group 11. Preharvest interval is 14 days for grazing or harvest for forage and hay. 4-hr reentry.
- Badge SC (Group M1) at 0.5 to 1.8 pints/A on 7- to 14-day intervals is labeled for other leaf spot diseases in clover and can be used for common leaf spot on clover in Oregon only. Preharvest interval is 0 days. 48-hr reentry.
- Regalia (Group P5) is registered for use on clover for other pathogens and can be used for common leaf spot on clover in Oregon. Apply at 1 to 4 quart/A on 7- to 10-day intervals starting prior to infection. Under high-disease pressure, use in combination with another fungicide. Does not benefit from the addition of an adjuvant. 4-hr reentry. O