There is a lot of yellow wheat causing concern in the state. I’ll go through a few causes, below.
1. Powdery mildew on lower leaves is drying up in most cases and the leaves, attacked by frost events, are flaring off. A very characteristic sign of powdery mildew are these ‘green islands’ in the picture below (left side). The question now is, what affect is this going to have on the crop? Well, if it’s dry, probably nothing. But, if there is significant moisture and favorable temperatures (59‐72F), this disease could flare up again. A great fact sheet is at http://www.ianrpubs.unl.edu/pages/publicationD.jsp?publicationId=1262 and updated fungicide recommendations are in the fungicide efficacy table, included with this agalert. Consider all of our common varieties susceptible. Yield losses can be 20‐45{f2533179b7c7e7cbdbc11018732de14c82f3d44c9f1e829e9a046cc47141a2e6} in wetter wheat‐ growing areas. I don’t know what yield losses we can expect; likely not much from early infections, but later season infections could damage the crop.
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2. Nutrient issues. Every spring we get a flush of nitrogen, iron, and various deficiencies due to cold temperatures. Usually the crop grows out of them with some moisture and sun. We’ve gotten a number of samples that had obviously been fertilized with urea, but the granules hadn’t dissolved (and the samples smell like urea). This tells me the nutrients haven’t gotten into the plant! I think a complicating factor could be high plant densities due to the incredible growth some earlier planted winter wheat got last fall.
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3. Frost. Winter wheat is tough, but it’s trying to joint in some areas and is very actively growing. Some varieties are more susceptible to frost damage. A pretty typical picture is below – the lower leaves are all dying and the next upper leaf has burned tips. A key for frost damage is that it’s all at one level, where the plant tissue was young and tender when the frost event occurred. Sometimes it will be in the middle of a leaf, but on all the plants. No or minimal yield losses are expected from early frost events.
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4. Cephalosporium stripe. Some growers are seeing a lot of Cephalosporium stripe, from the triangle down through the Yellowstone valley. The plants will have a yellow or lime‐green cast from far away. When you look close, there is a distinctive stripe from the base of the leaflet to the tip, and on one side is a thin brown border.
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Plants at tillering infected with Ceph stripe (c. Jeff Johnston) and a closeup of the leaf symptoms (http://visualsunlimited.photoshelter.com/image/I0000n8x.5T5VFeM)
Cephalosoporium stripe is a disease of winter wheat. Likely you’ll see the plants recover, but symptoms will reappear at flag. A great fact sheet is at http://pnw‐ ag.wsu.edu/smallgrains/Cephalosporium{f2533179b7c7e7cbdbc11018732de14c82f3d44c9f1e829e9a046cc47141a2e6}20Stripe.html This seems like a banner year for this disease; I have some old variety trial data from Alan Dyer, below, and I’ll try to get an update.
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5. Wheat viruses. Wheat streak mosaic virus and concern about Barley yellow dwarf. The key for WSMV is to look at the youngest leaves – do they have the streaky yellow symptom present on the lower leaves? It can be easily confused with bad powdery mildew infections. Then, look for wheat curl mites, or think about the field history: was there a lot of volunteer or cheatgrass that was not killed prior to planting? Was the upwind crop infected, or late maturing spring wheat? Both can be good sources of the disease.
Barley yellow dwarf is a big concern in Idaho but I haven’t seen widespread infection here in Montana, but our crop is behind Idaho right now. Bright Agindotan has offered to ELISA or PCR samples for BYDV‐PAV, the most common species, for $50 per sample for ELISA test and/or $100/sample to PCR.
His contact information is:
Bright Agindotan, PhD, MBA, PMP
Manager/Diagnostician
Regional Pulse Crop Diagnostic Laboratory
Dept. Plant Sciences & Plant Pathology Montana State University,
P.O. Box 173150,
Bozeman, MT 59717‐3150
E‐mail:pulsediagnostics@montana.edu
Tel: 406‐994‐5162 Fax: 406‐994‐3786
Shipping Address:
C/0 Bright Agindotan
Montana State Seed Laboratory (Marsh Lab Rm 40)
1911 W. Lincoln St.
Bozeman, MT 59718‐3145
As always, call with questions. ‐‐Mary Burrows, mburrows@montana.edu, 994‐7766
Source: Montana Ag Alerts
