This will likely be the last of the biweekly report as nearly all of the spring wheat acres is past anthesis and started the grainfill period. The risk models for bot tan spot and leaf rust continue to indicate that weather conditions are favorable for initial infections to occur. Nevertheless. I'll reiterate what I wrote earlier this week.
I doubt the severities of any of these fungal diseases will get high enough to cause economic losses on susceptible varieties, even if some initial infections are now starting to develop. Although the higher dew points and resulting dews now favor initial infections, the forecast remains hot, slowing progression and disrupting additional infection events.
I'll be checking fields and trials in the next two weeks for not just any of the foliar diseases, root rots, and Fusarium head blight and report to you what I find as we start preparing for what looks like a very early grain harvest.
I will also start be looking for wheat stem sawfly (Cephus cinctus) damage. To date, our traps in our screening trial on the Northwest Research and Outreach Center have been almost curiously void of any adult WSS. We think of wheat stem sawfly as a western North Dakota and Montana problem that is worse in dry conditions.
The lack of emergence made me wonder if extremely hot and/or dry conditions could trigger an extended diapause and delay the emergence of the adult WSS till next year. Kirk Anderson at NDSU answered my question with a 1947 paper by R.W. Salt. He wrote that "the insect can be returned to diapause by either high temperatures or a lack of adequate moisture or a combination of these. This sometimes occurs in nature, resulting in a two-year life cycle". My crew does not know it yet but after the 4th of July break, they'll be digging for WSS larvae that hunkered down and waiting out this hot and dry summer.
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