Wheat Stripe Rust and Bacterial Streak
More fields were treated with fungicide this week for stripe rust. The disease really took off this week and is working over some wheat. These fungicide treatments should do the trick though.
I am also seeing a lot of bacterial streak. Bacterial streak (black chaff), caused by the bacterium Xanthomonas translucens, is a sporadic disease that attacks all aboveground parts of the plant. Initial infections originate from infected seeds. Research in Arkansas has shown that cells of the bacterium on or within seed can be transferred to the first leaf where they multiply to high populations. Splashing rain disperses the bacteria to new leaves and provides favorable conditions for bacterial multiplication and disease development. The bacterium can multiply to high populations on the surface of leaves before the first symptoms appear. Bacterial cells enter the plant through stomata, hydathodes (pores at the tips of leaves that discharge drops of water), and wounds and then multiply inside the plant. Symptoms first appear on leaves as small watersoaked brown spots at the edge of leaves or between the veins that elongate quickly. These elongated lesions are the basis for the name “bacterial streak.” Under Arkansas conditions, symptoms are most conspicuous shortly after flowering when a flush of symptoms appears quickly on upper leaves with little evidence of an upward progression of symptoms. Lesions may grow together to kill large areas of a leaf and soon turn dry and brown. Dried bacterial exudate, usually in the form of thin transparent scales, may be associated with some of the lesions. Under hot, dry conditions the streaks will dry and turn brown in a few days. Saprophytic fungi may sporulate in the old lesions to mask the bacterial streak symptoms. It is important to distinguish bacterial streak from fungal diseases because foliar fungicides will not control bacterial streak.