2024 Wheat Tour Predicts Variable Yields and Vomitoxin

On Monday, June 3, local millers, grain brokers, and agronomists toured Pennsylvania wheat growing regions in an annual effort to estimate new crop yield and quality.

Average yields presented were estimated several weeks before harvest, and randomly sampled from a few locations in large fields using the protocol outlined at "Home Stretch: Evaluating Your Small Grain Crops" (Image 1). One yield component that we did not measure in the tour is kernel weight, as it was too early in the plant's development for that. Our yield estimate formula assumes a fixed kernel weight. This is a yield component that is affected by drought at the grain filling stage, so our yield estimates are likely an overestimate. Additionally, heavy rainfall and wind we have come to expect in this time of year may cause lodging losses in some fields, which will lower yields. Therefore, these estimates may not reflect actual harvest yields. 

Image 1. The first step to yield estimates is counting the number of viable tillers in 5 feet of row. Photo Credit: Heidi Reed, Penn State Extension

Adams, Franklin, and York Counties:

• 10 fields
• Planting date: September 25 to November 3, most October 7-15
• Seeding rate: 1.2 to 2.9 million seeds per acre
• Estimated yield: 85 bu/A (range 55-159 bu/A)
• 2023 - 103 bu/A (84-123 bu/A)
• 2022 - 101 bu/A (85-131 bu/A)
• 2021 - 103 bu/A (81-140 bu/A)
• 2020 - 110 bu/A (81-139 bu/A)
• 2019 - 81 bu/A (60-120 bu/A)

The number of spikelets per head, and number of kernels per spikelet were lower in Adams, Franklin, and York Counties than in the last several years. These factors in addition to thinner stands than desired result in the disappointing yield estimates for the region. This is somewhat surprising, as all toured fields in the region received fall fertility (manure or synthetic), along with growth regulator and split nitrogen applications in the spring. Despite timely planting, all but two of the locations failed to reach the desired 3 million heads per acre for maximizing yield. 

Fusarium head blight (scab) incidence was generally low (below one percent) in Adams and York Counties, but higher in Franklin County (approximately 5% incidence), with one unsprayed field showing higher levels. Fungicide applications occurred during the vegetative stage at all but three fields, and at flowering in all but one field, with Prosaro being favored for late applications. According to the Fusarium Head Blight Prediction Center, scab risk was moderate to high for varieties with moderate resistance to scab during the week or two around flowering, due to, in some locations, near daily rainfall during that window. Despite this risk, the fact that most growers chose favorable genetics and accomplished timely sprays meant that only minimal scab is showing itself in the field in most locations. However, fields were at the milk stage transitioning to soft dough, so it was a bit early to detect scab at the time of the tour for some fields.

Cereal leaf beetle damage was present in several fields, but very minor. Glume blotch (Image 2) was widespread at low to moderate levels, and leaf blotch was noted at multiple fields in Franklin County. Yellowing and purpling of newer leaves was noted at several sites, some at severe levels. One explanation could be barley yellow dwarf virus (BYDV) (Image 3). Fall infection by the barley yellow dwarf virus, transmitted by several species of aphid, is usually associated with planting before the Hessian fly-free date. BYDV can lead to significant yield losses from reduced kernels per spikelet and smaller heads, and could explain those observations from this region. Our mild winter and early, mild spring would be a contributing factor, if it is indeed BYDV. It is possible that, as our growing season lengthens, we can no longer be assured that aphids will be minimal after the historical Hessian fly-free date, and wheat planting dates may need to be adjusted. Read more about BYDV and its management in this factsheet from the University of Kentucky Extension.

Image 2. Stagnospora glume blotch in wheat. Photo credit: Heidi Reed, Penn State Extension.

Image 3. Barley Yellow Dwarf Virus appears as yellow and purple streaks on wheat leaves. Photo credit: Bayer Crop Science UK

However, our pathologists have shared widespread reports about unusual wheat and barley symptoms this year, including leaf discoloration and uneven stands in patterns in the field that don't match what we would typically expect for BYDV or fertility issues. Cold injury and some root diseases including pythium have been identified to be part of the picture, but these do not explain the symptoms in all fields. The only way to know for sure whether your field is suffering from abiotic issues like cold injury or poor fertility versus a disease issue is to send samples to the lab for testing. Penn State's Plant Disease Clinic can test for fungal and bacterial diseases, while Agdia can test for viruses, including BYDV.

Berks, Lancaster, and Lebanon Counties:

• 7 fields
• Planting date: By mid-October
• Seeding rate: 1.1 to 1.9 million seeds per acre
• Estimated yield: 104 bu/A (94-132 bu/A)
• 2023 - 106 bu/A (74-165 bu/A)
• 2022 - 103 bu/A (90-118 bu/A)
• 2021 - 79 bu/A (68-111 bu/A)
• 2020 - 105 bu/A (44-119 bu/A)
• 2019 -99 bu/A (88-106 bu/A)

Contrary to the south central region, southeast yield estimates are in line with the average from the last several years.  Most of the fields in the region received fall fertility (manure or synthetic), and growth regulator in the spring. However, there was discussion on reduced spring N rates and/or doing single spring N applications instead of split applications at some sites due to lodging concerns.

Fusarium head blight (scab) incidence was significantly higher than in recent years due to consistent rainfall around flowering. Miravis ace was the preferred fungicide for late application, and despite widespread use, weather during the critical flowering window was perfect for scab infection. Estimates for multiple fields were about 7% infection, which means vomitoxin levels could be an issue. If you suspect you may have scab, North Carolina State Extension recommends adjusting the combine fan speed to 1,375 to 1,475 RPM and the shutter opening to 90 millimeters or 3.5 inches to reduce discounts due to low test weight, percent damaged kernels, and vomitoxin in the harvested grain. Note that, similar to the south central region, plants were at a somewhat early growth stage (milk to soft dough) to clearly detect scab at the time of the tour, and we may have underestimated infection levels.

Similar to the south central region, minor cereal leaf beetle damage was present in several fields. Additionally, participants in the tour also noted moderate levels of the suspected barley yellow dwarf virus (purpling and yellowing) and glume and leaf blotch at several fields. Powdery mildew was noted at one field in Berks County.

Summary

With harvest still several weeks on the horizon, we hope yield and quality will not deteriorate, save some lodging from expected scattered thunderstorms. Overall, we expect some elevated vomitoxin levels due to the higher scab presence this year. Other quality parameters such as test weight and falling number could be impacted by the widespread suspected BYDV and glume blotch.