Tar spot and fungicide application timings

Although tar spot was detected in Ontario in the first week of July the past two years, 2022 is much different than 2021 and shows the importance of environmental conditions for disease development. Remember, this holds true for any disease! The big difference was the dry conditions early and shortened leaf wetness periods which delayed tar spot establishment until later (post-tassel). Areas along the north shore of Lake Erie (Essex through Haldimand-Norfolk) are seeing tar spot at higher levels compared to other areas. 

OMAFRA and UG Ridgetown Campus results in 2021 supported U.S. data that fungicides applied between tasseling (VT) and silking (R1) provided optimum control of tar spot. Fortunately, the optimum application timing for effective tar spot fungicides is the same for other common leaf diseases like northern corn leaf blight and especially Gibberella ear rot (DON). 

This year there have been a lot of questions around fungicide application timing for fields at risk of late season tar spot infection. In OMAFRA tar spot trials in Rodney, ON with Dr. Dave Hooker (UGRC) there are definite differences in tar spot control as expected since fungicide efficacy is largely dependent on fungicide selection and application timing. The images below illustrate some of the differences to date. The pre-tassel applications (7 to 12 leaf) did not reduce visual symptoms of tar spot compared to non-sprayed check and plants are prematurely shut down which is expected since product wouldn’t be available when needed. The VT/R1 application again provided good control for those fungicides which have demonstrated good tar spot control, but some late tar spot is present. Similarly, later applications at R3 (milk) and R4 (dough) either alone or as a second application have shown good control.  

Will these observations between VT/R1 and later applications result in significant yield differences and will the “Return on Investment (ROI)” cover a late or second fungicide application? We cannot wait till these and other tar spot trials are harvested so we can answer these questions and more! Stayed tuned for updated fungicide performance information!!

Fall is the best time to sample for SCN!

Soybean harvest has begun and for many growers, managing soybean cyst nematode means planting SCN resistance varieties BUT effective SCN management does not end when you have selected your soybean varieties! It is imperative to not only know your SCN population levels in each of your fields but what is happening to those levels over time and it begins with SCN soil testing!

The fall is a perfect time to sample harvested soybean fields or those which will be planted to soybeans in 2022. A fall sample takes into account any significant SCN population changes that have occurred during the growing season. If it’s the first-time sampling a field, the results provide you a baseline for future comparison. If you already have a baseline, the SCN test provides critical information.

If your SCN levels are decreasing, this could indicate your management program is working. If your is SCN levels are rising, this is a big red flag that the problem is getting worse and could get out of hand, costing you significantly in lost yield, dollars and sleep! If you do not know what is happening to your SCN population levels in your fields over time, your efforts may be wasted. One of the most important decisions a producer can make concerning this devastating pest is to take a SCN soil test.

For more information, visit the SCN Coalition website at thescncoalition.com or OMAFRA Agronomy Guide Publication 811.

Ontario nematode survey request for samples

OMAFRA specialists Albert Tenuta (Field Crop Pathologist) and Katie Goldenhar (Horticultural Crop Pathologist) are coordinating a nematode survey, targeting field crop and horticultural crop fields across the province. Nematodes present a significant and ongoing threat to plant health in Ontario and can result in significant economic and production losses. The primary objective of this 2-year CAP funded project is to update provincial nematode distribution maps as well as establish baseline data, for six different nematode species including soybean cyst nematode, root lesion or other nematode species. These results will support the enhancement of current nematode Best Management Practices for field and horticultural crop farmers, helping to improve the economic and sustainability of crop production in Ontario. Participating in the nematode survey is FREE, easy and soil samples can be collected specifically for nematode testing such as SCN or alternatively, soil samples collected for soil fertility can be split, with subsamples submitted for nematode testing. If you would like more information on the Nematode Survey, please contact Albert Tenuta ([email protected]) or Katie Goldenhar ([email protected]).

– Click here to read the Sept. 14 field crop report at the Field Crop News website.