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Around the County

Frequent information updates for agricultural audiences

Wheat Diseases - from Mike Roegge

Posted by John Fulton -

The wheat crop this year is so much improved over last years' crop. It's much thicker and healthier, and as of today (April 26) there is little to no sign of disease, even though the weather we've been experiencing of late would have been ideal for disease development. Constant wetness is one of the necessary factors to allow any disease to progress. And we've certainly had our share of wet weather of late.

The wheat crop is progressing nicely. We have to remember that wheat is a cool season crop, and does well in cooler temperatures. So temperature wise, the weather the past few weeks has been ideal. Some sunshine would certainly help to provide necessary "energy" through photosynthesis, but the critical time of necessary high energy need is at heading and after.

Some wheat fields have the second node above ground, which means that after another two or three leaves emerge, the head will appear.

The flag leaf and flag minus one leaf are responsible for approximately 75% of yield, so it's important that the top part of the plant be free of any disease lesions to able to maximize photosynthesis. Keep a watch on lower leaves to determine if any disease is present in fields, as the most significant diseases will make their way up the plant from lower leaves. Leaf blotch and glume blotch are the most common fungal diseases to be concerned about until heading takes place, and then the concern is of scab (fusarium head blight).

Leaf blotch will initially turn the foliage a tan color, then a brown color. There will be very small black dots within the lesion, those are the fruiting bodies that will potentially cause further disease spread. The lesion will be perhaps ¼ to ½" in diameter and if numerous could converge together on the leaf. There are many fungicides available that will control this disease.

Head scab can be a much more devastating disease. And over the past few years we've seen this disease take quite a few dollars per acre away because it shrinks the developing grains and causes test weights to be lower than normal. It can only infect when the flower is open, so you really need to spend less than a week watching for this disease. And it can only infect if moisture (or high humidity) is available during flowering, so if it's not raining during bloom, you probably don't need to worry about it.

There are no resistant varieties, but some wheat varieties have better tolerance to the disease. Fungicides can be effective in lowering the amount of scab, but won't control it entirely. And you have to be careful not to use the strobilurin fungicides for control of scab because they can actually increase the levels of toxin in the grain.

Two fungicides, Prosaro and Carumba fungicides are useful tools to help prevent excessive loss due to scab if applied at flowering and environmental conditions warrant the use of fungicides to help reduce scab losses. They also do a great job at providing control of the other major foliar diseases.

There is a web site that can be utilized to help producers determine the need to use a fungicide to help protect against scab. Utilizing it during bloom can make your decision pretty easy. The tool looks at past temperatures and precipitation and determines if favorable conditions exist for scab to develop. All you need to do is verify if your wheat is flowering. http://www.wheatscab.psu.edu/ Click on "risk map tool" and follow the directions.



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