Sep 12, 2011
I visited a field a few weeks ago in the Woodland area. Older leaves showed discolored tips and margins, and necrotic spots. Leaf tips eventually turned brown and die.
The grower was worried it might have been blast, because of some of the lesions were elliptical and resembled blast lesions.
A leaf tissue analysis showed that boron levels were very high. Most likely the symptoms were caused by boron toxicity. Boron toxicity can be caused by use of water with high boron concentration or by excessive boron levels in the soil.
The UC manual "Rice Nutrient Management in California" mentions that boron toxicity in California is rare and usually occurs due to use of irrigation water with high contents of boron. To reduce the level of boron in the soil solution, use irrigation water with low boron content to leach boron form the root zone.