PRESENCE AND EFFECTS OF SEED-BORNE AND SOIL-BORNE DRECHSLERA-SOROKINIANA ON BARLEY IN NEW-ZEALAND .3. EFFECT ON GRAIN-YIELD

The effect of seed-borne Drechslera sorokiniana on barley yield was investigated in a field trial in Manawatu in the 1975–76 season. Captan and carboxin + thiram seed treatments, and mancozeb as a foliar spray, were used to establish various disease levels within plots. Lesions on subcrown internodes were found in all plots at growth stage (G.S.) 2, although carboxin + thiram as a seed treatment had provided some control. These lesions increased slightly in intensity through the growing season, but the low disease score meant that they had little effect on grain yield. Foliar lesions caused by D. sorokiniana were present at G.S. 2–3 on the bottom green leaf, but were not detected again until G.S. 11.1, when they appeared on the stem, flag leaf, and leaf 2, and accounted for over 60% of the total lesions recorded. Foliar lesions caused by Drechslera teres, the cause of net blotch, appeared in the plots at G.S. 5 and were present for the rest of the growing season. Because two foliar pathogens were present at the top of the plant, loss in yield attributable to either one could not be determined. However, spraying with mancozeb at G.S. 4, 7, and 10 significantly reduced the amount of infected tissue on the top two leaves at G.S. 11.2 and significant yield increases (17–20%) were recorded, mainly through a significant increase in 1000-grain weight. No other yield parameters were affected. Leaf lesions caused by D. sorokiniana were not detected in field surveys in 1976–77 and 1977–78, although slight substem internode lesions were sometimes found. These were not severe enough to affect yield. © 1979 Taylor & Francis Group, LLC.