Scab Epidemic Risk Model
Legend:
Plant Pathologist Commentary: 07/30/2012
This year proved to be an interesting in more ways than one for the cereal crops in Minnesota. The mild winter and spring saw many growers planting their crops very early. However these same conditions conspired to give us early influxes of aphids carrying Barley yellow dwarf virus (BYDV). While this disease can always be found in low levels in wheat, barley and oats (characterized by yellowing and eventually drying of leaf edges originating for the leaf tip and progressing down towards the stem in wheat and barley and red to purple discoloration in oats), symptom severity this year was far more extreme in a lot of cases due to plants being infected at very early growth stages. This resulted in severe dwarfing and excessive tillering, something rarely, if ever, seen before in Minnesota.
By the same token, parts of Minnesota also experienced large populations of Aster leaf hopper early in the year which have the potential to transmit Aster Yellows (AY) to the crop. This disease can cause symptoms very similar to BYDV, and without lab testing it can be very difficult to distinguish between these two diseases. This trend was echoed in canola which is also susceptible to AY.
Another disease, stripe (or yellow) rust caused by Puccinia striiformis then became evident. This disease is also rarely seen in Minnesota and is more commonly seen in the Pacific North West, as conditions in the typical growing season here are more favorable to leaf rust. The stripe rust infections were able to continue despite warm daytime temperatures and little rain, probably due to much cooler night temperatures and the high humidity in late June. The difference between plants that had been sprayed at Feekes 5 with fungicide and those which had not became marked as the stripe rust infections continued. However, once temperatures really warmed up to the low to mid 90s F, stripe rust entered a decline and went in to its resting phase.
Tan spot as always, was ever present in many fields with the worst affected being those fields which had minimal fungicide inputs to control foliar diseases.
Fusarium head blight (FHB) did make an appearance later in the season but this year conditions were not optimal for FHB to really take hold as it has in previous years.
In addition to diseases this year, there were many reports of herbicide injury in the wheat crop. Again this was probably in part due to high temperatures and lack of moisture which left plants stressed and less able to cope with the demands placed on their metabolism by pesticide applications.
Despite such an atypical - and in parts of the State - extremely dry growing season, some farms are averaging 60-70 bushels an acre.
We wait with baited breath to see what next year
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Terms
of Use before utilizing this site. This Fusarium Head Blight (FHB, or
'scab') model is a pre-flowering model. It is meant to be applied using weather
conditions during the week leading up to flowering. Therefore, the epidemic
risk for a particular field should be determined by selecting a time coinciding
with or just prior to the initiation of flowering in that field. A growth stage
estimator is available on this website, but you should still monitor growth in
your own fields to better estimate the date on which flowering begins.
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