Posts Tagged ‘wheat powdery mildew’

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/.

Small Grain Diseases

Friday, March 2nd, 2012

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

Powdery Mildew on Small Grain
Be on the lookout for powdery mildew on ‘Thoroughbred’ barley and wheat. Powdery mildew has been seen on both within the last several weeks. ‘Thoroughbred’ barley is very susceptible to PM as you know and if the stand is thick and lush you will more than likely see it. Does it need to be controlled this early in the season? I think it depends on how many times you are willing to spray it. Dr. Arv Grybauskas did a trial last season looking at fungicide applications at jointing (GS6), flag leaf emergence (GS9) and flowering (GS10.5) Tilt (4.0 oz/A) was applied at GS 6 or 9 and Prosaro (6.5 fl. oz/A) was applied at GS 10.5. While all treatments gave a positive yield response in two trials, only the later applications gave a significant yield increase. It confirms what we have been saying about the importance of keeping the top two leaves free of disease and the positive relation to grain fill. This is true in wheat and susceptible barley like ‘Thoroughbred’. If you spray to control mildew at jointing you may have to come back again later because the control will not last season-long. Disease control later is more important for protecting the yield potential of the crop.

For powdery mildew on wheat, check areas of rank growth first to see if the disease is present in the field then revisit to see if it spreads. It is too early to consider control of powdery mildew (PM), but if it is present, keep scouting. Unless the variety is very susceptible the mildew does not move fast depending on the weather.

Rank areas, like the one pictured here that was infected with powdery mildew, should be checked often.

Close-up of powdery mildew as it looks now

Rust on Small Grain
Everyone has been wondering about the possible consequences of the warm winter and one consequence might affect wheat. Both leaf rust and stripe rust have been found in the South this winter. It has been mild and relatively moist depending on the location. This scenario is conducive for rust infections that get started in the southern production regions and blow north as the season progresses. With the early appearance down south, the mid-Atlantic area may see rusts early enough to be a threat. Keep your eyes open as the season progresses.

Small Grain Disease Prevention

Friday, September 23rd, 2011

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

Be sure that you plant wheat and barley varieties with high levels of disease resistance. Select varieties with high levels of resistance to powdery mildew, leaf rust and stripe rust. Seed should be treated with Baytan, Raxil, Dividend or other labeled product to protect plants from loose smut and common bunt. Varieties that are susceptible to powdery mildew should be treated with Baytan, Dividend, or other seed treatment fungicide that will protect them from early infection.

Small Grain Disease Update – May 27, 2011

Friday, May 27th, 2011

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

Barley
The most prevalent diseases that can still be seen in areas where the barley has not returned yet are the spot blotch form of net blotch and powdery mildew. After checking the barley varieties today near Sandtown in western Kent County I don’t believe that net blotch will be affecting yields, but powdery mildew on unsprayed ‘Thoroughbred’ will reduce yields if the flag leaf is infected. There is some scab infected barley in Kent County.

Wheat
The wheat in the Kent County variety trial has tan spot moving in rapidly on some varieties. Most of the varieties are in the watery ripe stage of development and will not likely be adversely affected. Leaf rust was easily seen on a public variety ‘Rumor’. Powdery mildew in general was low in most varieties but was in the upper canopy on SS8302, Milton, Bravo, and USG3770. There is a low level of scab in the trial as well. If scab is going to appear it should be evident now or very soon depending on location. Low levels of scab (less than 1% of the heads infected and most of the infected heads were only partially infected) were present in 8 out of 45 varieties (around 18%).There is some sort of physiological spotting that could look like a disease but is probably a resistance reaction by the variety in response to a fungal infection. This spotting was evident on the following varieties at this Sandtown location: Merl, Sunburst,USG3665, USG3409, USG3251, and Grow Mark FS627.

 

Small Grain Disease Update – May 6, 2011

Friday, May 6th, 2011

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

Wheat
Be sure to keep scouting for the presence of diseases, especially powdery mildew, at this time. With the return of cooler temperatures and risk of showers and cloudy weather as well, powdery mildew could become a problem, especially in very thick stands of susceptible wheat. It is important to keep the uppermost two leaves as free of diseases as possible to protect yields. At the most, you can wait until you see 5-10% of the upper two leaves infected before applying a fungicide. Tilt, Stratego, Twinline, and Quilt can be applied as late as heads emerged but not yet flowering. If scab should be a concern this year it may be best to use only a triazole fungicide at heading through flowering to avoid mycotoxin issues if scab infection occurs. There is evidence that if fungicides containing strobilurins (Quilt, Twinline, Stratego) or strobilurins alone are applied during heading up to flowering, they can increase mycotoxin production if scab occurs during flowering. If a fungicide is needed as late as flowering for powdery mildew, Septoria leaf blotch, tan spot, or other disease and conditions are favorable for scab development consider applying Prosaro, Caramba, or Folicur for scab suppression and control of the other diseases just mentioned. For a table that rates the efficacy of fungicides for use on wheat diseases see the following link to the Kansas State fact sheet with the NCERA-184 ratings. This is a group of wheat pathologists from across the country that collaborates on wheat disease control. http://www.ksre.ksu.edu/library/plant2/ep130.pdf

Head Scab Risk Assessment Tool
Scab is still the one wheat disease that can cause major economic losses if weather conditions are favorable prior to and during flowering. The tools that we have to manage scab are limited but the use of rotation, resistant varieties and fungicides can help reduce the losses from scab should it appear. One of the tools that we have to help predict its occurrence and aid in making fungicide application decisions is the Head Scab Risk Assessment Tool that is found on the wheat scab website http://www.wheatscab.psu.edu/. The site provides information on how to use the tool and its limits.

 

Small Grain Disease Update – April 29, 2011

Friday, April 29th, 2011

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

Wheat is developing rapidly with the recent increase in temperature. Be sure to keep scouting for the presence of diseases, especially powdery mildew, at this time. It is important to keep the uppermost two leaves as free of diseases as possible to protect yields. At the most, you can wait until you see 5- 10% of the upper two leaves infected before applying a fungicide. Tilt, Stratego, Twinline, and Quilt can be applied as late as heads emerged but not yet flowering.

If scab should be a concern this year it may be best to use only a triazole fungicide at heading through flowering to avoid mycotoxin issues if scab infection occurs. There is evidence that if fungicides containing strobilurins (Quilt, Twinline, Stratego) or strobilurins alone are applied during heading up to flowering, they can increase mycotoxin production if scab occurs during flowering. If a fungicide is needed as late as flowering for powdery mildew, Septoria leaf blotch, tan spot, or other disease and conditions are favorable for scab development consider applying Prosaro, Caramba, or Folicur for scab suppression and control of the other diseases just mentioned. For a table that rates the efficacy of fungicides for use on wheat diseases see the following link to the Kansas State fact sheet with the NCERA-184 ratings. This is a group of wheat pathologists from across the country that collaborates on wheat disease control. http://www.ksre.ksu.edu/library/plant2/ep130.pdf

Head Scab Risk Assessment Tool
Scab is still the one wheat disease that can cause major economic losses if weather conditions are favorable prior to and during flowering. The tools that we have to manage scab are limited, but the use of rotation, resistant varieties and fungicides can help reduce the losses from scab should it appear. One of the tools that we have to help predict its occurrence and aid in making fungicide application decisions is the Head Scab Risk Assessment Tool that is found on the wheat scab website http://www.wheatscab.psu.edu/. The site provides information on how to use the tool and its limits.

 

Agronomic Crop Diseases

Thursday, April 22nd, 2010

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

Wheat
The first disease of the season on wheat is usually powdery mildew. In general, powdery mildew has not been a problem for several years. Once wheat reaches jointing (Growth Stage 6) it should be scouted regularly for powdery mildew. As always, planting the highest yielding resistant varieties is the best control strategy, but if mildew threatens to rob yields later, fungicide control is the best control measure. Tilt, Propimax EC, Stratego, Quilt, Proline, and Caramba (the new Group 3 triazole from BASF) are suggested for control when and if fungicides are needed. These fungicides are also very effective for control of tan spot and Septoria leaf spot and glume blotch. It is common for powdery mildew to infect the lowest leaves and remain there for some time. The critical time to scout for powdery mildew is GS 8-10 (when the last leaf just appears until head emergence) to determine if fungicides are needed.

Barley
We have had reports of increasing amounts of powdery mildew on barley. ‘Thoroughbred’ looks to be the most susceptible variety but others should be scouted as well. Regionally we have no data to evaluate fungicides for control of barley diseases because barley rarely needs to be sprayed for diseases and the cost has been prohibitive. Times have changed, and if the heads are emerging and the top two leaves are infected there may be some benefit to controlling powdery mildew on a susceptible variety such as ‘Thoroughbred’ if the weather continues to favor powdery mildew. Stratego, Tilt, Quilt (10.5 – 14.0 oz/A) would be suggested for control if necessary. A beneficial non-target effect will be brighter straw if straw is being baled.

Powdery mildew on barley.

Soybean Cyst Nematode
It is still not too late to check for soybean cyst nematode, especially if susceptible soybeans are going to be planted. Soil test bags with the submission form can be purchased at the Extension offices. If you have a fax machine and need results quickly, test results can be sent via FAX if you provide the number on the Nematode Assay Information Sheet. This information sheet can be found on the web at the Plant Clinic Website http://ag.udel.edu/plantclinic .

Wheat Disease Scouting

Friday, May 1st, 2009

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

Be on the lookout for several wheat diseases now. Powdery mildew is appearing in very dense stands and in headrows and on susceptible cultivars. The small white-to-tan spots of fungal growth are getting easy to spot when present. Most of what I have seen has been in the lower canopy and does not require treatment. Keep scouting. The second disease worth looking for is stripe rust (Figure 1). I am seeing some reports of it in the South and there might be low levels in our area that go undetected until some yellowing of the leaves appears. Stripe rust is getting more aggressive so it is important to identify it early and apply a triazole fungicide, such as Tilt or Caramba; a strobilurin, such as Quadris or Headline; or a combination product like Quit or Stratego. If these products are applied from flag leaf fully expanded until head emergence very good to excellent control should be achieved. None of these products labeled for powdery mildew or rust control, except Caramba, will aid in scab control.

Stripe Rust of Wheat

Figure 1. Stripe rust pustules on the underside of the leaf

Scab or Fusarium head blight suppression is achieved with well-timed applications of Prosaro (Proline + Folicur) 6.5 fl oz/A , Caramba 14 fl oz/A, or Proline (alone) 5.7 fl oz/A. None of the other fungicides labeled for wheat will give the same level of suppression as the above three, according to work done by Arv Grybauskas at the University of Maryland. No fungicide provides the level of control that most growers would like to see, but they are the best that we have and can provide suppression of the disease, especially if conditions are favorable. Suppression of scab depends on very precise timing of the application. For the fungicides to work to the best of their ability they need to be applied when the anthers first appear (Figure 2). The fungus infects through the flower parts of the wheat so it is the newly flowering wheat heads that need to be protected. Once pollination takes place the fungus is only susceptible to the fungicides for a very short time.

Wheat is at risk when temperatures are warm and wet during flowering, the risk increases when the wheat crop is planted in no-till corn stubble and there is no rotation. The new risk management tool is located at the Fusarium head blight website http://www.wheatscab.psu.edu. It can be useful once heading begins and the risk of scab increases as flowering approaches. The new version that is running now has the ability to give a 24-72 hour forecast looking at the previous several days as well as the weather forecast for the next several days. Those buttons are at the top left side of the forecast page.

 timing

Figure 2. Correct timing for fungicide application for scab suppression

Prevention of Disease in Small Grains

Friday, September 12th, 2008

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

Be sure to plant fungicide treated seed for control of loose smut and common bunt especially if you saved your own seed for planting. Select varieties that are high yielding as well as resistant to powdery mildew, leaf rust and stripe rust.

Scout Wheat for Diseases

Friday, April 11th, 2008

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

Continue scouting wheat for powdery mildew. The cool weather has been ideal for disease development. In cases where too much nitrogen was applied or extra carry-over from last year was not taken into consideration, resistance can be overcome. Lush wheat should definitely take priority when scouting. In areas that had good moisture in the fall keep an eye out for wheat spindle streak mosaic virus. This virus is vectored by a root infecting fungus that needs plenty of water in the fall when the initial infection takes place. We have had reports of it occurring but have not seen any plant samples yet in the lab. Wheat generally grows out of it once warm weather gets here and stays. Symptoms on leaves appear as yellow-green mottling, dashes, and streaks. It can occur widely in fields not just wet areas. Wheat soil-born mosaic virus can often be confused with WSSMV but is generally more limited to wet spots in the field.

wheat spindle streak mosaic virus

Wheat spindle streak mosaic virus