Since last week, the critical period of fifteen to eighteen days for wheat crop grain quality and quantity has been underway in much of south-central New Jersey and Pennsylvania. This period occurs when heads begin to emerge from the flag leaf (flowering) followed by pollination through to dough stage. While we can’t rule out bacterial and pest damage going forward, we can anticipate how fungal pathogens might impair wheat yields by looking back at the weather since the flag leaf emerged and this week’s coming forecast as pollination completes.
Current predictions for the fungal grain pathogen of wheat known as fusariums as of May 13th are low for much of the region with just a few areas along the Delmarva Penninsula considered at high risk. The Fusarium Risk Tool developed by researchers at Ohio State, Penn State, and Kansas States can be found at https://www.wheatscab.psu.edu/
Fusarium’s are naturally occuring fungi in soil that can infect small grain seed heads when conditions are ideal for infection. For high yielding wheat, ideal weather includes humidity in the range of 50 to 60%. Ideal conditions for fusarium risk are when humidity levels rise to 100% and stay there during this critical period of grain development. While they may sporulate at lower temperatures and humidity levels, they rarely mature until humidity climbs above 85%.
Let’s take a look back and see how the weather has favored the winter wheat crop in our area using local conditions for Woodstown, NJ.
Weather May 1 to May 10. Coming into head emergence, the low humidity periods on May 1 (below 40%) for six hours, three hours on May 3 and five hours on May 5 were offset by the number of hours and days above 68% humidity but mostly below 89% humidity except for a high of 93% on May 4. Chances for diseases to sporulate were highest on May 6 through May 8, but humidity levels did not rise above 90% and temperatures were below 60F degrees even dropping into the low 40’s. Yellow rust Puccinia striiformis in particular if present might have sporulated under these conditions. Powdery mildew could also have sporulated as these conditions were in the lower end of it’s ideal range. The key consideration is that sporulating conditions did not remain so for a long period of time on May 9 and May 10 when humidity dropped into the mid to low 20% range and temperatures hovered in the low 70’s, less than ideal for most fungal pathogen development of concern.
To learn more about specific wheat diseases see USDA’s Guide to Wheat Diseases and Pests at https://wheat.pw.usda.gov/ggpages/wheatpests.html
Weather May 11 to May 13. Most fields in Salem County are nearly fully headed and shedding pollen with little signs of flag leaf disorders. Other than uneven canopy heights on some poorly drained heavy clay soils, much of the sandier loam fields are sporting a good rating at this time. The critical period for any required fungicide applications is now through the next few days. Humidity levels stayed well below 80% until 11 pm on the 12th but have remained above or near 90% for the last twelve hours.
What’s in store? Today with overcast skies and a steady light rainfall this morning in Woodstown, NJ, the humidity rose into the low 80’s and temperatures hovering around 75F degrees. The forecast for Saturday has humidity at 80 to 88% then dropping on Sunday to below 83% and below 76% on Monday, and below 54% for the rest of the week. All things considered, a good forecast this next week going into a critical period of wheat quality and grain fill.
Keep in mind these observations are under natural conditions and non-irrigated. Those who rely on irrigation and have been using irrigation on winter wheat during flag leaf development must pay particular attention to humidity levels in the wheat canopy, especially when cloud cover and higher air temperature persist for long periods of time.
