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06
May
2011
Wheat Condition and Disease Update
Author: Jason Kelley, Wheat & Feed Grains Extension Agronomist

Crop Update – Jason Kelley

Many wheat producers are still struggling with flood water or water logged soils.  Over the last two weeks, we have had areas report as much as 20 inches of rainfall, mainly in central and Northeast Arkansas.  Many fields have been completely submerged with water for several days and little hope exists in these fields for much/if any type of yield.  For other fields that had flood water on them, but where it quickly receded, the verdict is still out.  But, they likely will still suffer some damage.  Other fields that were never flooded but have poor drainage are now showing signs of water damage in the last few days (see photo below).  Fields with good drainage on high ground appear to still be in decent shape.

Water Damage on Wheat in Poorly Drained Field

Wheat Disease Update – Dr. Gene Milus

At Kibler near Fort Smith, wheat is generally in early milk stage.  Stripe rust only developed to about 30% severity in plots of Armor Renegade that was very susceptible last year and did not spread much from where it overwintered. No hot spots were found, and stripe rust is about finished for the season. Leaf rust is present at trace levels on several varieties, but the level is too low to rate plots at this time. Stagonospora leaf blotch is present on lower leaves of several varieties but has not spread to upper leaves yet. Only low levels of Septoria leaf blotch were seen.  Bacterial streak was the most serious disease in some plots but was not uniformly distributed among or within plots. Barley yellow dwarf was only at low levels.

In inoculated plots at Fayetteville, stripe rust is >80% severity on susceptible lines. Recent overnight low temperatures ranged from the low 30s to low 40s with day temperatures in the 50s to 60s, making conditions close to ideal for stripe rust. Only a few scab infections were noted in inoculated nurseries, likely because temperatures have been too cold for scab. Powdery mildew developed to high levels in susceptible plots. Barley yellow dwarf is present in plots not treated with an insecticide in the fall, but incidence and severity appear to be lower than in previous years.

Scab appears to be the greatest disease threat statewide at this time.  In inoculated and irrigated plots at Newport, scab severity is greater than 50% in plots of susceptible lines. Scab pressure here is likely much higher than commercial fields in the area because infested corn kernels were spread throughout the plot in March, and the plot was irrigated 3 times per week during the drought period to promote spore development in the inoculum. Given the recent wet weather, there are likely plenty of Fusarium spores around the state now, especially in fields following corn. Scab development from now through harvest will be favored if we have warm, wet weather. It is too late to apply any fungicide.

Diagnosing bacterial streak:   Bacterial streak appears to be widespread across the state and at higher severity levels than we have seen in several years. The most common symptoms at this time are dead, tan to brown streaks and blotches on upper leaves. In severe cases, most of the flag leaf will be dead. Bacterial streak can be easily confused with Septoria leaf blotch, Stagonospora leaf blotch, or other moderately resistant stripe rust infections. Given the low fungal disease pressure this year, it is not likely that moderately resistant stripe rust infections, Septoria or Stagonospora are causing problems on flag leaves. If a fungicide was applied between flag leaf emergence and heading, then it is even less likely that stripe rust, Septoria or Stagonospora are causing problems on flag leaves. Fungicides have no effect on bacterial streak.  Septoria and Stagonospora develop first on lower leaves and move up the plant to the flag leaves. Bacterial streak tends to skip the lower leaves, develop suddenly after flowering on the upper leaves, and then does not develop much more during the rest of the season. The damage you see now is not likely to get worse if bacterial streak is the problem. If Septoria or Stagonospora blotches are the problem on flag leaves, the lower leaves likely will be completely dead, and the disease will continue to get worse until the end of the season.

Wheat Status Reports: 

Central Arkansas:   Hank Chaney, Faulkner County Extension Agent.  Bacterial Streak was our main disease however, our wheat acreage is either underwater or has had water in it at varying levels on the plant.  Most of the wheat that was flooded for 4+ days looks ok now, but as the temperatures increase, I think damage will be more evident.  Stinkbugs were noted prior to all of the rain and flooding.

Brent Griffin, Prairie County Extension Agent, reports we do have acreage under water at this time, hard to tell how many acres are under water because river is still rising.  Fields on high ground are in soft dough to late milk.  There is a little bit of stripe rust, but not blown out the top. We do have some lodging issues from past weekend storms. Head scab is showing up in southern end of county where the crop is further along.

Northeast Arkansas:  Chris Grimes, Wheat Research Verification Coordinator notes that most of the wheat is in the milk stage.  I have not seen any armyworms as of yet.  There are several fields with wheat that is leaning, but have not seen a lot of fields with severe lodging problems. 

Randy Chlapecka, Jackson County Extension Agent, says most of our wheat is in the milk to soft dough stage.  I’ve seen head scab starting to show up and have gotten a few calls from consultants about head scab.  We have significant acreage completely ruined by water.  We will have to see on some of the wheat that had water on it but has receded.   

Southeast and Southwest Arkansas:  Steve Kelley, Wheat Research Verification Coordinator says verification fields in south Arkansas are mostly in the soft dough stage.  None have been treated for armyworms.  Lodging is spotty at some locations with the worst in Lafayette County in Southwest Arkansas.  Hail damage has occurred in the Arkansas County (South Field) and Lincoln County fields.  Hail damage was estimated at 10-15%.


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