Posts Tagged ‘Take-all of wheat’

Corn and Wheat Disease Update – June 5, 2009

Friday, June 5th, 2009

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

Corn
No need for me to tell you how bad the weather has been so far for corn. Stands are still being reduced by excessively wet soils and the Pythium and Fusarium damping-off that is occurring as a result of the wet soils. Fungicide treated seed, good drainage and some warm temperatures would help considerably in getting the plants out of the ground and growing.

Wheat
Fusarium head blight or scab is being seen in some fields in Kent and Sussex counties. The occurrence and severity so far has been variable but, in general, I think we dodged a bullet this time. Our wheat for the most part was already in flower before the most favorable weather came for scab (Figure 1).

fusarium head blight 

Figure 1. Fusarium head blight or scab.

Take-all was diagnosed this week as well from two fields. Take-all is characterized by patches in the field that can vary in size but the wheat is generally stunted and the heads bleach out prematurely. Infected plants can be easily pulled out of the ground due to the extensive root rot that occurs. The other symptom is the dark streaking at the base of the stem (lowest node under the leaf sheaths), see Figure 2. Take-all can be controlled by rotating out of wheat for a year. However planting wheat followed by double crop soybeans followed by wheat is not an effective rotation for take-all control. Manganese levels also interact with take-all. Be sure that soil levels of manganese are adequate for the crop and check pH so that the managanese is available. High pH makes manganese unavailable.

takeall

Figure 2. Take-all symptoms on the lower nodes. Note lack of roots as well.

Tan spot (Figure 3) has been present for almost three weeks in wheat. This foliar disease can look like Septoria (Stagnospora) leaf and glume blotch. It is caused by the fungus Pyrenophora tritici-repentis.

 tanspot

Figure 3. Tan spot symptoms on wheat.

It has been widespread on Delmarva this season because of the amount of rainfall that we have had. It is too late for any control, but this disease is favored by wet, warm weather. Most of the spots are in the lower canopy and may reach the flag leaf before the plants begin to dry down. Applications of foliar fungicides at heading or earlier have been providing good control of this disease. At present most of the infection is in the lower canopy and the effect on yield should be minimal if the disease does not move up to the flag leaf or the leaf below the flag leaf.

Wheat Diseases

Friday, June 6th, 2008

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

The wet weather and the warmer temperatures will accelerate the development of scab if it is present and the symptoms will become more evident as the temperatures get warmer this weekend. Some scab is present on Delmarva. The first symptoms of Fusarium head blight include a tan or brown discoloration at the base of a floret within the spikelets of the head. As the infection progresses, the diseased spikelets become light tan or bleached in appearance. The infection may be limited to one spikelet, but if the fungus invades the rachis the entire head may develop symptoms of the disease. The base of the infected spikelets and portions of the rachis often develop a dark brown color. When weather conditions have been favorable for pathogen reproduction, the fungus may produce small orange clusters of spores or black reproductive structures called perithecia on the surface of the glumes. Infected kernels are often shriveled, white, and chalky in appearance. In some cases, the diseased kernels may develop a red or pink discoloration.

 

Fusarium head blight or scab on wheat.

 

Fusarium head blight or scab on wheat head.

 

Grain produced in heads damaged by Fusarium head blight is often shriveled, white, and chalky in appearance.

Fusarium graminearum is known to produce two important mycotoxins, deoxynivalenol (DON) and zearalenone, which can contaminate the diseased grain. The mycotoxin DON can cause reduced feed intake and lower weight gain in animals at levels as low as 1-3 ppm, especially in swine. Vomiting and feed refusal can occur when levels of DON exceed 10 ppm. Humans are also sensitive to DON, and the FDA has recommended that DON levels not exceed 1 ppm in human food. Ruminant animals, including dairy cows and beef cattle, are less sensitive to the toxin. The fungal toxin zearalenone has estrogenic properties and produces many reproductive disorders in animals. Swine are the most sensitive to the toxin, but cattle and sheep may also be affected. Zearalenone concentrations of 1-5 ppm can result in negative effects in animals and humans. Producers concerned about these mycotoxins should have grain tested prior to feeding to animals. Contact the state department of agriculture or local extension office for more information about testing for mycotoxins.

When high levels of Fusarium head blight are present in fields, precautions can be taken to reduce mycotoxin contaminations of the grain. The mycotoxin contamination is often highest in the severely diseased kernels. Adjusting the combine to blow out the small, shriveled kernels can help reduce mycotoxin levels. Harvested grain should be dried to 13.5% moisture as soon as possible to limit continued fungal growth. Grain suspected to have been damaged by Fusarium head blight should be tested for DON and zearalenone. Do not mix contaminated grain with good grain prior to a mycotoxin analysis. The mixing will result in more contaminated grain, which may be difficult to sell. Edited from Penn State fact sheet on Head Blight authored by Eric DeWolf. http://www.wheatscab.psu.edu/PDF/Fusarium_Head_Blight_.pdf

Other wheat diseases that we are seeing are take-all and, just recently, tan spot. Take-all is characterized by patches in the field that can vary in size but the wheat is generally stunted and the heads bleach out prematurely. Infected plants can be easily pulled out of the ground due to the extensive root rot that occurs. The other symptom is the dark streaking at the base of the stem (lowest node under the leaf sheaths). See picture. Take-all can be controlled by rotating out of wheat for a year. However planting wheat followed by double crop soybeans followed by wheat is not an effective rotation for take-all control. Manganese levels also interact with take-all. Be sure that soil levels of manganese are adequate for the crop and check pH so that the managanese is available. High pH makes manganese unavailable.

 

Take-all symptoms on the lower nodes. Note lack of roots as well.

Tan spot was identified in my wheat fungicide trials near Middletown. This foliar disease can look like Septoria (Stagnospora) leaf and glume blotch. It is caused by the fungus Pyrenophora tritici-repentis. It is too late for any control but this disease will be favored by the wet and warm weather. Most of the spots were in the lower canopy and may reach the flag leaf before the plants begin to dry down. Applications of foliar fungicides at heading or earlier should provide pretty good control of this disease. At present most of the infection is in the lower canopy and the effect on yield should be minimal if the disease does not move up to the flag leaf or the leaf below the flag leaf.

 

Tan spot symptoms on wheat.