Bob Mulrooney, Extension Plant Pathologist; bobmul@udel.edu
Wheat
Last week we did identify barley yellow dwarf virus on wheat in two locations in Sussex County. One was identified as BYDV-pav strain and the other tested positive for BYDV-pav as well, but also tested positive for cereal yellow dwarf virus CYDV-RPV. This used to be BYDV-RPV, the most serious strain. Both are transmitted by aphids, and there isn’t much that can be done for management except resistant varieties.
Information from an Illinois bulletin:
BYDV and cereal yellow dwarf virus (CYDV). Aphids spread BYDV and CYDV disease. Aphids carrying the virus transmit it to wheat plants through their saliva when they feed. The most serious yield loss results from fall infection by viruliferous aphids’ feeding on wheat seedlings. Fall infections typically result in stunted plants and fewer tillers when spring growth resumes. Leaf discoloration is usually the most notable early-season symptom. Leaves may be varying shades of red to purple, pinkish-yellow to brown. As the plant continues to grow, older leaves typically begin to die back from the tip and may feel somewhat leathery, while the new leaves begin to discolor. Spring infections occur as well, but they commonly discolor only the flag leaf and typically do not cause significant yield reductions.
There were three strains of BYDV: MAV (mild), PAV (serious), and RPV (more serious). This was probably confusing enough, but for numerous biological reasons the BYDV-RPV strain has been renamed and put in the cereal yellow dwarf group; its acronym is now CYDV-RPV. Testing of plant material for BYDV or CYDV should include tests for both BYDV-PAV and CYDV-RPV (formerly known as BYDV-RPV) to be certain, first, whether a virus is causing the symptoms and, if so, which one it is responsible.
Barley yellow dwarf virus-PAV strain
Proline for scab suppression was featured in an article in WCU Volume 16, Issue 6 (http://extension.udel.edu/weeklycropupdate/?p=130). Now, Caramba (metconazole) from BASF and Folicur (tebuconazole) from Bayer CropScience have also received section 3 federal registration for use in wheat. In terms of efficacy against head scab and vomitoxin, Proline, Caramba and a tank mix of Proline + Folicur are very comparable. Data from studies conducted across the US show that on average Proline + Folicur, Caramba, and Proline alone, when sprayed at flowering (Feekes 10.5.1), had about 50% reduction in scab and about 42% reduction in DON when compared to the untreated check. Proline is recommended at rates between 4.3 – 5.7 fl oz/acre, Caramba between 14 – 17 fl oz/acre, and the tank mix of Folicur + Proline at 3 fl oz/acre of each product (commonly referred to as Proline 3+3). I am not sure if Folicur and Caramba are available or if state labels have been issued yet for use this season, but if scab control is needed these three products are the products of choice.
For scab suppression, the best results were achieved when these products were: applied at flowering (Feekes 10.5.1), forward and backward mounted nozzles were used to achieve maximum coverage of the heads, and the products were applied to moderately resistant wheat varieties. With the hope of controlling as many diseases as possible with a single fungicide application, producers may be tempted to apply these products as early as boot (Feekes 10). However, for head scab management, treatments applied at Feekes 10 are much less effective than those applied at Feekes 10.5.1. It should be noted that even when applied at the correct growth stage none of these products will provide complete scab control, especially if prolonged periods of wet conditions occur during and after flowering. The term here is SUPPRESSION. What producers can expect is a reduction of head scab and vomitoxin, but NOT total 100% control.
Reprinted in part from “More Fungicides Registered for the Suppression of Head Scab in Wheat” by Pierce Paul and Dennis Mills in the May 5 edition of the Crop Observation and Recommendation Network newsletter from the Ohio State University agronomic crops team.