Posts Tagged ‘barley yellow dwarf virus’

Agronomic Crop Insects

Friday, September 21st, 2012

Joanne Whalen, Extension IPM Specialist; jwhalen@udel.edu

Small Grains
As you make plans to plant wheat, be sure to review our article on aphid and barley yellow dwarf management in the Aug 3, 2012 newsletter (http://agdev.anr.udel.edu/weeklycropupdate/?p=4595). The following link to the May 1, 2012 Kentucky’s Pest News also provides additional management information, especially as it relates to the weather conditions in the 2012 season (http://www.ca.uky.edu/agcollege/plantpathology/extension/KPN%20Site%20Files/kpn_12/pn_120501.html).

Aphids Prevention and Barley Yellow Dwarf Management

Thursday, August 2nd, 2012

Joanne Whalen, Extension IPM Specialist; jwhalen@udel.edu, Phillip Sylvester, Kent Co., Ag Agent; phillip@udel.edu and Nancy Gregory, Plant Diagnostician; ngregory@udel.edu

As discussed in the article, Review of Barley Yellow Dwarf in 2012, the spread of barley yellow dwarf virus (BYDV) is completely dependent on aphids transmitting the virus which causes the infection. There are four aphid species occurring in Delaware that are capable of transmitting BYDV from infected grasses into wheat including the English grain aphid, bird cherry-oat aphid, corn leaf aphid, and the greenbug. For photos to help you identify aphids go to: http://kentagextension.blogspot.com/2007/10/know-your-small-grain-aphids.html

Aphids can infest small grain fields in the fall and again in the spring. The number of aphids arriving in fields in the fall is often dependent on the growing conditions the preceding summer. In general, cooler summer conditions with adequate rainfall followed by a warm, dry fall favors aphid development, especially in early planted fields. In drier summers, fewer aphids are produced due to reduced host plant quality. It should be noted that greenbug aphids (which cause direct damage to small grains as well as transmit BYDV) are favored by cool, late summer conditions. Aphid population densities in the fall are also affected by when the first hard frost occurs in relation to wheat seedling emergence. Crops that emerge long before a hard freeze have a greater potential for aphid infestation (and exposure to BYDV). Planting after the fly free date can help to help to manage aphids as long as the freeze occurs when expected. Aphids arriving in the fall will continue to feed and reproduce as long as temperatures remain above 48°F.

In areas where you have seen BYDV in the past, where you are planting early (before the Hessian fly-free date), or you have seen direct damage by greenbug aphids, a commercial applied seed treatment which includes an insecticide would be a good control option for fall infestations. Another option would be to scout fields and apply a foliar insecticide. Information from Kentucky indicates that planting date is the most important factor determining the intensity of an aphid infestation. The most important time for controlling aphids in the fall is the first 30 days following emergence. The second most important time is the second 30 days following emergence. So it will be important to scout wheat starting at plant emergence if you plan to use a foliar insecticide for fall aphid management. The following link to a fact sheet from Kentucky provides more information on aphids and BYDV in wheat (http://www.ca.uky.edu/entomology/entfacts/ef121.asp).

Since the incidence of BYDV has not been widespread in past years in Delaware and Maryland, we do not have current data from our area evaluating thresholds to time sprays for fall aphid management. The following thresholds from Kentucky (included in the above fact sheet) could be considered when making a decision to apply a fall foliar insecticide : (a) the first 30 days after planting treat if you find an average of three or more aphids per row-foot, (b) from 30-60 days after planting treat if you find six or more aphids per row-foot, and (c) more than 60 days after the plants emerge treat if you find ten or more aphids per row-foot. Depending on weather conditions, a second application could be needed, especially if temperatures remain warm. As we saw this past season, aphid populations remained high throughout the winter and early spring so you will need to continue scouting if conditions remain mild again. They also indicate that in some years these thresholds may be too high and in others too low but currently this is the best available information. In addition, the risk of BYD infection varies from year to year. At this point, we are still not certain if the 2012 season was just an unusual one for BYD or if we will continue to see an increase in problems. We hope to survey for aphids this fall and evaluate these thresholds under our conditions.

Review of Barley Yellow Dwarf in 2012

Thursday, August 2nd, 2012

Phillip Sylvester, Kent Co., Ag Agent; phillip@udel.edu, Joanne Whalen, Extension IPM Specialist; jwhalen@udel.edu and Nancy Gregory, Plant Diagnostician; ngregory@udel.edu

As we approach the upcoming small grains planting season, it is a good time to discuss barley yellow dwarf management. Barley yellow dwarf (BYD) can be found most years in a few wheat fields in Delaware. It is not uncommon to see a few infected plants, primarily in the spring. In 2012, the number of fields with infected plants appeared to be generally higher compared to most seasons. Impact on yield was variable, though it was estimated that some fields experienced a 5% yield loss. The dry spring weather in Delaware had a larger impact on yield, therefore it was difficult to estimate the true impact of BYD. It is important to understand the causal agents, symptoms, and disease cycle in order to best manage BYD. Barley yellow dwarf is the most widespread virus disease of cereal crops worldwide and can infect other crops such as rye, barley, oats, and corn, though the greatest concern in our area is in wheat.

Causal Agents
There are numerous virus types that actually cause BYD. While the taxonomy of BYD can be complicated, it’s important to note that some strains are more severe than others. The ones that are of greatest concern in our area are (in order from least severe to most severe): BYDV-MAV, BYDV-PAV (severe strain), and CYDV-RPV. CYDV-RPV, cereal yellow dwarf, was named and then later found to be a related strain of BYD. Both CYDV-RPV and BYDV-PAV were confirmed in the samples submitted this past spring from wheat fields in Delaware.

Vector
The BYD viruses are limited to the phloem and can only be transmitted from plant to plant by aphids which have piercing/sucking mouthparts. The infection occurs after aphids feed on infected hosts, such as wild grasses, and then move into and feed on wheat fields. The wild grasses may be infected yet show no symptoms. It can take as little as 12-48 hours from the time aphids feed on the infected grasses until infection has occurred in wheat plants. This can occur anytime that aphids are actively feeding, which would typically be in the fall and spring months when the weather is warmer. Since the spread of barley yellow dwarf depends on aphids, management of the aphids may be helpful in fields with known problems of barley yellow dwarf in the past. Remember that the viruses causing BYD are only transmitted by aphids and are not known to be seed-borne. Read the Aphids Prevention and Barley Yellow Dwarf Management article in this issue of WCU for more on management.

Symptoms
Symptoms include leaf discoloration (Figures 1- 3), shortening of the internodes, and general stunting of the plant. Leaf discoloration typically has a characteristic purple to yellow color. Symptoms become exacerbated by cool weather and high light intensity. Hot spots (cluster of infected plants) may occur near field borders, field corners, or near woods depending on how the aphids moved. To further complicate matters, the plant’s reaction to the infection may vary depending on when the plant was infected and the variety of wheat. Fall infections usually result in more stunting and less tillering while spring infections tend to discolor the flag leaf and are thought to cause little yield loss. Other viruses such as wheat spindle streak and/or wheat soil-borne mosaic virus may infect the plant causing additional symptoms (see Figure 4). The other viruses are not transmitted by aphids. To learn more about the other viruses we encounter in Delaware, read Bob Mulrooney’s article on Viruses in Winter Wheat at: http://agdev.anr.udel.edu/weeklycropupdate/?p=2745.  It’s difficult to identify viruses in the field and samples should be submitted to a lab for testing to confirm virus infection.

Figure 1. Wheat plant infected with barley yellow dwarf (BYDV-PAV).

Figure 2. Wheat plants infected with barley yellow dwarf (BYDV-PAV).

 Figure 3. Wheat plants infected with barley yellow dwarf (BYDV-PAV).

 Figure 4. Wheat Plant infected with BYDV-PAV, CYDV-RPV, wheat spindle streak mosaic virus, and wheat soil-borne mosaic virus.

Figure 5. Close up of wheat infected with BYDV-PAV, CYDV-RPV, and wheat spindle streak mosaic virus.

Small Grain Disease Updates – May 11, 2012

Friday, May 11th, 2012

Bob Mulrooney, Extension Plant Pathologist; bobmul@udel.edu

Stripe rust in wheat has been seen in both DE and MD this week. The outbreaks at this time are small and for most of the state wheat is past flowering, so the impact of increased rust development at this time should be minimal. Anyone who applied a fungicide such as Tilt, Prosaro, or Caramba at boot stage or heading will have 2-3 weeks of control, depending when it was applied and when stripe rust spores arrived from the south of us. We have not seen stripe rust in our region for several years. There have been population changes in the rust and it may be more aggressive than what we have seen in the past. We would be interested to know if you see it and what varieties get infected and the severity of the infection. Initially it might be found in a small area or several small areas but if the continued rain and cooler temperatures prevail it could spread quickly. If the wheat is past flowering, check fungicide labels for timing. See the next article for more information on stripe rust and effect on yield as well as fungicide choices.

 Close-up of stripe rust symptoms showing rust pustules in a line or stripe.

 Stripe rust on wheat.

Several more wheat samples were confirmed with Barley yellow dwarf virus. Most of the symptoms are mild but very widespread when it is found in a field. There is little impact on yield as best we know, but there is still much to learn about this virus in this region.

 Barley yellow dwarf showing reddening of flag leaf.

Wheat Disease Update
The following was written by Arv Grybauskas, Extension Plant Pathologist, University of Maryland and adapted for Delaware by Bob Mulrooney, Extension Plant Pathologist, University of Delaware

The risk of scab development this season has been very low and most of our wheat will be scab‐free or, at worst, have infection levels well below 10%. Vomitoxin levels should therefore be well below the 2 ppm threshold for acceptance at mills for most of the crop. The last few days, however, indicate that there are a couple of regions in the state that might still develop some scab. Much of the wheat in the hot spots in eastern Sussex County should be past flowering, and therefore past the label growth stage limitation for treatment with fungicides. However, there may be late planted fields or later developing varieties that can be treated. Leaf rust has been present on susceptible varieties since early spring but has been kept in check by unfavorable temperature or moisture conditions. It still has the potential to develop and spread if temperatures warm into the 80s at daytime and drop only to the mid‐60s at night as long as showers continue or dew and RH is high. Treatment of susceptible varieties may be warranted if leaf rust is present and is threatening to reach the flag leaves.

Stripe rust has also made an appearance this season. It was just confirmed in Dorchester and Caroline Counties in Maryland as well as in Delaware on Monday, May 7. These outbreaks are in small pockets (foci) in fields and their appearance is consistent with long‐distance spore transport from either NC or KY on storm fronts that came through about 2 weeks ago. Stripe rust, unlike leaf rust, requires cooler temperatures. In fact, at temperatures above 77°F lesions will stop producing spores and secondary spread is reduced, and at temperatures above 85°F the pathogen dies. The question now is, what is the potential damage and do I need to apply a fungicide? The short answer is, in my opinion, the worst‐case scenario for either rust disease (susceptible variety, and continuous disease favorable conditions through grain‐fill, and a focus of rust is present in the field now) would potentially produce a 10% yield loss. Realistically the weather will probably be less favorable sometime during grain fill so losses are more likely in the 1‐7% range (Table 1). For either rust disease it takes 7‐14 days to go through an infection cycle (infections giving rise to more spores that cause new infections) under ideal conditions. With that in mind, by the end of the grain‐fill period it is possible that the plants will look nasty (100% of the plants with 40 to 65% flag leaf severity) but between hard and soft dough stages this typically only produces 1 to 7% yield losses.

Table 1. Approximate Yield Loss in Relation to Severity of Rust on the Flag Leaf at Various Stages of Growth

Growth Stage Flag Leaf Area Infected with Rust
10% 25% 40% 65% 100%
Flowering 10 15 20 30 35
Milk 2 5 8 14 20
Soft dough 1 3 4 7 10
Hard dough 1 1 1 3 5

From: Hunger, B. and K. Jackson. Foliar Fungicides and Wheat Production in Oklahoma.

At this stage the only products that can be considered are triazole fungicides. The products registered for scab management, Prosaro and Caramba, are also effective against leaf and stripe rust. Rust susceptible wheat varieties that are still eligible for a fungicide application (pre‐ or just at flower) that are not at risk of developing scab may be sprayed with Folicur or a properly labeled generic tebuconazole product for rust control. Note that Prosaro, Caramba and Folicur have a 30 day Pre‐Harvest Interval as well as the growth stage restriction. Tilt has a 45 day PHI, and therefore would only be an option on earlier stage wheat where the risk of scab was low.

Wheat Disease Update – April 27, 2012

Thursday, April 26th, 2012

Bob Mulrooney, Extension Plant Pathologist; bobmul@udel.edu

BYDMV
We have had several more reports and a sample of Barley yellow dwarf mosaic virus in wheat. Irregular patches of varying height reductions, yellowing and purple flag leaves indicate BYDMV infection. Since this virus is aphid transmitted there are no controls at this time.

Fusarium Head Blight
With the much needed rain that came and the forecast for more Thursday and possibly Saturday as well some have been asking about the possibility of head blight or scab appearing. The forecast at the present time is the probability is low. The corn residue on the surface needs to be wet for a long time before spores are produced that can infect the wheat at flowering and the temperatures need to be in the mid-70s for significant infection to occur. The temperatures have been and are too low now for infection. As long as the wheat flowers between now and next Wednesday when the forecast is for warmer temperatures the wheat will no longer be in a susceptible stage of development for scab to infect. I think the risk of scab it very low and specific sprays for scab control are unwarranted at this time.

Keep up to date with scab by visiting the website and using the 2012 Predictor. http://www.wheatscab.psu.edu/ This will be important if we should get more rain later in the week.  Make sure the predictor says 2012 across the banner. For some reason my browser is going back to the 2011 site. If you run into the same problem here is the 2012 link http://www.wheatscab.psu.edu/riskTool_2012.html

Leaf Rust & Stripe Rust
More of a possibility is the occurrence of some late season leaf rust and stripe rust. There has been stripe rust reported in NC earlier in the week and now a report of leaf rust and stripe rust from Mt. Holly, VA in university test plots. These reports are fairly close and after a big rain event like we had with some more possibly on the way we may see some develop within the next two weeks. If growers have a variety that is susceptible to leaf rust or stripe rust, there is a chance that we could see more rust two weeks from now depending on the temperatures. Again that might justify application of a fungicide at flowering if you have rust present now or are growing a susceptible variety. With the lack of water there may be undetected leaf rust in the lower canopy and with the recent rain there could be spread to the upper canopy. Be sure to get out and check the wheat before making a spray decision. Prosaro plus a non-ionic surfactant can be applied to wheat until 30 days before harvest; for scab control it needs to be applied at early flowering in 5 gal/A if applied by air. Tilt can only be applied until full head emergence. With the low risk of scab, strobilurin fungicides such as Headline and Quadris could also be considered for protection against leaf and stripe rust as well as tan spot, and the Septoria complex if those diseases are present, which have not been seen because of the dry weather. Be sure to check labels for application restrictions. Our past experience has shown that diseases that appear late (after flowering) usually do not have time to infect the upper leaves that are important for grain fill and reduce yield. If diseases are present in the canopy at flowering there is more of a risk of diseases reducing yield and/or quality of the grain.

Some information from Dr. Christina Cowger from USDA at NC State Unversity indicates that the following varieties are susceptible to stripe rust and might warrant spraying especially if any rust is present now. There are some gaps in our knowledge about susceptibility to stripe rust, so this is a very limited list of known susceptibility for varieties that are grown in the Mid-Atlantic:

Coker 9436, DG Shirley, NC Cape Fear, NC Neuse, NC Yadkin, P26R12, SS520, SS560, USG3209, USG3592, USG3665, SS8404

Freeze Injury
We just received a wheat sample from Kent County, DE with random bleached awns as well as tips of some heads. If you see some irregular bleaching of heads don’t panic about scab. We suspect at this point since no fungus appears to be present on this sample that the damage is from freezing. From spike emergence through flowering, freezing can cause symptoms that range from minimal bleaching of the awns to severe grain yield loss, depending on the duration and degree of freezing.(See Photo 3 in the article by Richard Taylor, “Another Risk of Frost on the Small Grain Crop”, which is in this issue of WCU) If normal kernel development does not occur, then freeze injury can be suspected.

Small Grain Disease Update

Thursday, April 12th, 2012

Bob Mulrooney, Extension Plant Pathologist; bobmul@udel.edu

The dry weather and low humidity has been very unfavorable for diseases at the present time. There are still some fields of barley with powdery mildew and leaf rust. If they needed treatments they should have been treated by now. Wheat is looking a bit better in that powdery mildew levels are low and except for some barley yellow dwarf mosaic virus in some areas the crop looks good. Rainfall is desperately needed. The risk for Fusarium head blight or scab is low at the present time. To keep track of the threat of scab be sure to check the website http://www.wheatscab.psu.edu/.

Viruses in Winter Wheat

Friday, April 1st, 2011

Bob Mulrooney, Extension Plant Pathologist; bobmul@udel.edu

The first winter wheat sample with virus symptoms arrived last week. It was sent for confirmation and was determined to be wheat soilborne mosaic virus. Wheat on the Delmarva can be infected by four possible virus diseases. The aphid-transmitted barley yellow dwarf mosaic virus is probably the most common, depending on how high aphid populations are in the fall and early spring. Often irregular patches of stunted wheat occur in wheat fields and as the season warms up infected young leaves will become yellow, and then turn red. Wheat spindle streak mosaic causes a yellow discoloration to wheat seedlings. This yellow discoloration is often most intense in low areas of the field. Leaves of infected plants have long, yellow streaks that are slightly wider in the middle than at their ends. Symptoms are similar to wheat soilborne mosaic and plants often are infected with both diseases. Winter wheat infected by wheat soilborne mosaic develops a pale-yellow discoloration shortly after breaking dormancy in the spring. The incidence of wheat soilborne mosaic is often greater in low areas of the field where moist soil conditions favor growth of the protozoa that spread this viral disease. Leaves of infected plants often have a mosaic pattern of dark green blotches on a pale greenish-yellow background. Symptoms will normally fade when warm temperatures slow the activity of the virus within infected plants. Control of both these soilborne diseases is by planting resistant varieties.

The least common virus disease of wheat that we see is wheat streak mosaic. Leaves of plants infected with wheat streak mosaic have bright yellow streaking. Symptoms are often most severe near the tip of the leaf. The virus that causes wheat streak mosaic survives in volunteer wheat and spreads by wheat curl mites. The disease is often most severe in areas of a field that are closest to these sources of the disease and mites.

Barley yellow dwarf mosaic virus

Wheat spindle streak mosaic virus

Wheat soilborne mosaic virus

Wheat streak mosaic virus
(Last three photos from Wheat Disease Identification published by NCERA-184, which will be available soon.)

It can be very difficult to positively identify these virus diseases especially early in the spring. They can look like other diseases or nutritional disorders. Testing of infected plants can help diagnose the problem to avoid repeating it in the future or eliminate other possible causes of the symptoms. Unfortunately by the time you see symptoms of these virus diseases there is no control of any of these diseases.

Agronomic Crop Insects

Friday, September 18th, 2009

Joanne Whalen, Extension IPM Specialist; jwhalen@udel.edu

Soybeans
At this point, the decision to treat for corn earworms should have been made by now. If you have not scouted, be sure to check the latest planted fields. We are seeing a decline in trap catches so hopefully we will not see another hatch. Soybean aphids continue to be a problem in later planted fields. With the projected cool weather, they could be a problem for the next few weeks. Please refer to previous newsletters for treatment thresholds.

Small Grains
Be sure to sample all fields at emergence for aphids, true armyworm and fall armyworm feeding. In past years, we have seen economic damage from all three insect pests.

When it comes to armyworm, we have seen fields destroyed in past years, especially in no-till situations. In many cases it has been true armyworm, although fall armyworm can also cause damage. Although there is no threshold available, you will need to watch for larvae feeding on small plants.

As you make plans for small grain planting, you should consider the following factors when making a treatment decision for aphids. In general, cooler summer temperatures with adequate rainfall, followed by a warm, dry fall are conditions that favor aphid development in small grains, especially in early planted fields. Early fall infestations of the greenbug aphid (which cause direct damage to small grains as well as vector BYDV) are favored by cool, late summer conditions. Since weather has been favorable, be sure to watch fields closely for aphids.

The main reason one would consider aphid control in the fall (except for greenbug aphid that causes direct damage) is the potential for Barley Yellow Dwarf Viral (BYDV) transmission. In areas where you have seen BYDV in the past, where you are planting early, or you have seen direct damage by greenbug aphids, a seed treatment that control aphids (i.e. Cruiser and Gaucho) would be a good control option. Information from Kentucky indicates that planting date is the most important factor determining the intensity of an aphid infestation. If you have a history of aphids transmitting viruses in the fall and you plan to scout for aphids, data from the South indicates that the most important time for controlling aphids to prevent BYDV is the first 30 days following emergence. The second most important time is the second 30 days following emergence. The following link to a fact sheet from Kentucky provides more information on aphids and BYDV in wheat (http://www.ca.uky.edu/entomology/entfacts/ef121.asp). Please refer to the Pest Management Recommendations for Field Crops for materials labeled for aphid control in small grains (http://extension.umd.edu/publications/EB237online/).

Agronomic Crop Insects

Friday, September 19th, 2008

Joanne Whalen, Extension IPM Specialist; jwhalen@udel.edu

Soybeans
In general, the decision to treat for corn earworms should have been made by now. If you have not scouted, be sure to check the latest planted fields. We are finally starting to see a decline in trap catches so hopefully we will not see another hatch. Overall, control has been good – especially if treatments were applied to threshold levels of small worms and the correct rate was used. If you sprayed last week for the first time, you will want to re-check fields this week to be sure you do not have another hatch of larvae.

Small Grains
Be sure to sample all fields at emergence for aphids, true armyworm and fall armyworm feeding. In past years, we have seen economic damage from all three insect pests.

When it comes to armyworm, we have seen fields destroyed in past years, especially in no-till situations. In many cases it has been true armyworm, although fall armyworm can also cause damage. Although there is no threshold available, you will need to watch for larvae feeding on small plants. With higher trap catches for true armyworm throughout the summer, you will want to watch fields since damage can occur very quickly.

As you make plans for small grain planting, you should consider the following factors when making a treatment decision for aphids. In general, cooler summer temperatures with adequate rainfall followed by a warm, dry fall are conditions that favor aphid development in small grains, especially in early planted fields. Early fall infestations of the greenbug aphid (which cause direct damage to small grains as well as vector BYDV) are favored by cool, late summer conditions.

The main reason one would consider aphid control in the fall (except for greenbug aphid that causes direct damage) is the potential for Barley Yellow Dwarf Viral (BYDV) transmission. As indicated in past newsletters, the plant pathologists in our area still do not feel that we are seeing a significant increase in the incidence of BYDV. However, in areas where you have seen BYDV in the past, where you are planting early, or you have seen direct damage by greenbug aphids, a seed treatment that control aphids (i.e. Cruiser and Gaucho) would be a good control option. Information from Kentucky indicates that planting date is the most important factor determining the intensity of an aphid infestation. If you have a history of aphids transmitting viruses in the fall and you plan to scout for aphids, data from the South indicates that the most important time for controlling aphids to prevent BYDV is the first 30 days following emergence. The second most important time is the second 30 days following emergence. The following link to a fact sheet from Kentucky provides more information on aphids and BYDV in wheat (http://www.ca.uky.edu/entomology/entfacts/ef121.asp).

Small Grain Diseases

Friday, May 9th, 2008

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://agdev.anr.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.