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Monthly Archives: May 2013

Watch for armyworms in wheat

We have a late-maturing wheat crop that has fought its way through freezes, howling winds and it is now receiving some needed rain.  This cool weather is also helping slow the maturity of the wheat.  Right now, wheat is vulnerable to infestation from armyworms.  Armyworm infestations typically occur in late April through the first two weeks of May, but obviously, the cooler spring we have experienced this year has delayed their development.

Armyworm infestations occur more frequently around waterways, areas of lush growth, or areas with lodged plants. These areas should be checked first to determine the size of the infestation. Armyworm 2 Royer 2007

Early signs of an infestation include leaves with ragged margins that have been chewed.  You may find “frass” i.e. the excrement from armyworm caterpillars, around the base of wheat stems.  They also tend to clip heads from developing wheat plants. The head clipping I have noticed over the years us usually restricted to secondary tillers with very small, green heads that would not likely contribute much to yield.

Armyworm damaged wheat heads

Armyworm damaged wheat heads

Scout for armyworms, at 5 or more locations looking for “curled up worms”.  Armyworm caterpillars tend to feed at night, so a good strategy is to bring a flashlight and look at fields after dusk when they are feeding up on the plant stems.  The suggested treatment threshold for armyworms is 4-5 unparasitized caterpillars per linear foot of row.

Clipped heads from armyworm feeding

Clipped heads from armyworm feeding

Armyworms have a number of natural enemies that help keep populations in check, if given a chance.  In particular, parasitic wasps and flies attack them.  If you find small white cocoons littered on the ground that are about ¾ the size of a cue tip, the natural enemies have already taken care of the problem.

 

 

Parasitized armyworms

Parasitized armyworms

I have noticed that there has been some fungicides being applied during the past few weeks. If an insecticide was added to that spray, it is likely to have reduced any armyworm population already established in the field. Still, it is important to check the field.  Generally if wheat is past the soft dough stage, control is not warranted unless obvious head clipping can be seen, and caterpillars are still present and feeding.  Worms feeding on the awns when plants are past soft dough will not cause enough yield loss to justify the expense of an insecticide application.

Consult CR-7194 Management of Insect and Mite Pests of Small Grains for information on insecticides registered for control of armyworms.

For more information on this topic, contact Tom A. Royer, Extension Entomologist at tom.royer@okstate.edu

Wheat disease update 25 May 2013

Wheat disease updates are written by Dr. Bob Hunger, Extension Plant Pathologist

I and Nathalia Grachet (OSU Graduate Student) returned Friday from a trip and field days in the panhandle of Oklahoma.  Wheat at Lahoma (25 miles west of Enid) ranged from full berry (watery) to the milk stage.  Driving further to the northwest after about Alva was depressing as the condition of the wheat and the landscape in general deteriorated with what seemed like each passing mile.  The field days we attended were at Balko (40 miles east of Guymon) and Hooker (20 miles northeast of Guymon).  Wheat in these trials ranged from flowering to full berry (watery).  Rick Kochenower (Panhandle Area Specialist – Agronomy) related the story that demonstrates the resilience of wheat.  The Balko area was hit hard by the last freeze in April such that he felt there would be no wheat there.  However, a mild May with just a little moisture allowed secondary tillers to come back, and if some rainfall and mild temperatures occurs for the next couple of weeks, some wheat will be harvested in the area.  This is not the scenario over the entire panhandle.  According to Rick, wheat in Cimarron County (far western county in the panhandle) is all but gone primarily due to drought whereas in Texas and Beaver County freeze and drought have both played a role in severely impacting wheat production.

Leaf and stripe rust were found this past week around Stillwater but not at a typical incidence or severity; leaf rust is especially lacking.  Dr. Art Klatt reported being able to easily find leaf rust in his plots near Perkins, OK (15 miles south of Stillwater) in the range of 5-20S, which is lighter than typical.  At Lahoma, Nathalia and I found both leaf and stripe rust but at low incidence and severity (especially leaf rust).  Leaf spotting was more common, but it was difficult to determine if this was Septoria, Stagonospora, tan spot and/or physiological.

Signs of wheat streak mosaic and barley yellow dwarf can still be observed, especially around Lahoma where flag leaves are still mostly green.  In the panhandle and northwestern OK it is difficult to discern virus damage from freeze and drought.

 

Reports/excerpts of reports from other states:

Nebraska – Dr. Stephen Wegulo (Small Grains Extension Pathologist, Univ of Nebraska, Lincoln, NE) 24-May-2013:  Wheat in Nebraska is mostly in the boot to heading growth stages.  There have been no new reports or observations of rust diseases since the observation of stripe rust at Mead on May 7.  On May 21 and 22, I surveyed wheat fields in Lancaster, Saline, and Saunders Counties in southeast Nebraska.  I did not find any rust diseases.  The stripe rust that was observed at Mead on May 7 stopped activity following the high temperatures we had during the week of May 13 (including 100+ deg F on May 14), and never spread, similar to Carl Bradley’s observation in Champaign County, IL.

 

Bacterial streak found in Oklahoma

Widespread leaf spotting symptoms in wheat in the variety trial near Chickasha, OK (40 miles southeast of Oklahoma City) now is believed to be caused by bacterial streak (aka black chaff – see pictures below).  Bacterial streak/black chaff is occasionally observed in Oklahoma but typically is not widespread or severe.  This disease is more severe in warm (80 F or so) and humid climates or in wheat grown under irrigation, and often appears after an event such as a late freeze or other event that can cause wounds to facilitate entrance of bacteria into plants.  Lesions on leaves initially appear water-soaked but become elongated dead bands and streaks as time proceeds.

Bacterial streak lesions on leaves initially appear water-soaked but become elongated dead bands and streaks as time proceeds.

Bacterial streak lesions on leaves initially appear water-soaked but become elongated dead bands and streaks as time proceeds.

These dead areas tend to be more common on leaf “bends” where dew forms to enhance infection.  Symptoms on heads and on the stem immediately under the head include dark discoloration, and awns typically show a dark banding.These symptoms often can be confused with leaf spotting caused by the fungi Septoria (Septoria tritici blotch) or Stagonospora (Stagonospora nodorum blotch).

Symptoms on heads and on the stem immediately under the head include dark discoloration

Symptoms on heads and on the stem immediately under the head include dark discoloration

Bacterial streak/black chaff is seed transmitted, so grain from a badly infected field should not be kept for seed wheat.  There are no commercial seed treatments available, and although varieties vary in reaction to this disease, no resistant varieties are known in Oklahoma where bacterial streak/black chaff is not commonly widespread.  This disease may be occurring in other parts of Oklahoma this year, but will be difficult to discern from all the other factors that contribute to general browning and leaf spotting including other diseases (tan spot, septoria, etc), freeze, and drought.

Bob Hunger
Extension Plant Pathologist

Jeff Edwards
Small Grains Extension Specialist

Awns affected by bacterial streak/black chaff typically show a dark banding

Awns affected by bacterial streak/black chaff typically show a dark banding

Wheat disease update 18 May 2013

Wheat disease updates are written by Dr. Bob Hunger, OSU Extension Plant Pathologist

Oklahoma:

Wheat in southern/southwestern Oklahoma is maturing and will speed up with the warmer (>90 F) over the last couple of days.  In central Oklahoma, around Stillwater and to the north, wheat is just finishing or has just past flowering and kernel development is starting.  As you head to northwest Oklahoma, wheat also is in late flowering or has just finished flowering.  I’m not sure about out toward the panhandle but know there is not much wheat that will be harvested as you move west of Woodward and Buffalo.  I’ll be taking a trip to the panhandle the end of the coming week and will report more after that trip.

Disease-wise, not a lot changed over the past week in Oklahoma.  Leaf rust remained practically absent although infections in the 15-40S range were observed in Jagalene (or Jagger) guard rows in breeder plots at Stillwater.  However, little to no leaf rust was found elsewhere around Stillwater and no reports were observed or reported from north-central and northwestern Oklahoma.  Stripe rust is slight more prevalent.  Several “hot spots” were noted around trials at Stillwater and occasional “stripes” (but not hot spots) were noted at field days west of Enid, north of Ponca City, and north of Stillwater.  Leaf spotting diseases, barley yellow dwarf, and wheat streak mosaic (WSM) are the most commonly observed diseases in samples seen at field days and submitted to the Plant Disease and Insect Diagnostic Clinic.  This past week a few samples also tested positive for High plains virus.  Several reports from ag educators, consultants, and growers have indicated that WSM has devastated wheat in fields in northern and western Oklahoma.  In all cases where I talked to the person, there was an indication that volunteer wheat was involved either in the field or adjacent to it.

Reports/excerpts of reports from other states:

Arkansas – Dr. Gene Milus, (Professor/Small Grains Pathologist, Univ of Arkansas, Fayetteville, AR) 17-May-2013:  Visited plots at Kibler near Fort Smith today. Wheat is in soft dough. Stripe rust is still active. Leaf rust was present at mostly low levels. Also Septoria, bacterial streak, powdery mildew, and Stagonospora on flag leaves depending on the line. Most lines in the variety test had resistance to most or all of the above diseases. Weather is hot and humid. Plenty of soil moisture.

Kansas – Dr. Erick De Wolf (Professor/Small Grains Extension Pathologist, Kansas State Univ, Manhattan, KS) 17-May-2013:  Stripe rust continues to be reported at low levels in Kansas this week with new finds in Sedgwick, Kingman, Sumner, and Pratt counties. The wheat in this area of the state is still heading or flowering. Generally, only trace levels could be found in these fields.  Tom Maxwell, Central Kansas District agent, reported finding low levels of stripe rust in Saline County on May 17. The wheat there is generally in the early heading stages.  I have found a few fields and a demonstration plot in Pratt County where the disease is at high enough levels to justify a fungicide application. This area of the state has received more rain than others in recent weeks and some fields in Pratt County have good yield potential. The affected varieties included Everest and Armour, which were found to be susceptible in 2012. A lot of wheat in this area of the state is struggling with continued dry weather.

I encourage farmers to carefully check fields for symptoms of disease. Fields where stripe rust can be readily found on the flag leaf (one lesion every 2-3 feet) will likely benefit from a fungicide application. The wild card on this decision is the weather.  Low temperatures in the upper 60’s are generally thought to be suppressive to stripe rust development. High temperatures in the upper 80’s or above for several days in a row also tend to suppress stripe rust. But if temperatures in that range last only last a few days or so, followed by cooler weather, stripe rust can resume activity.

Wheat disease update 11 May 2013

Wheat disease updates are written by Dr. Bob Hunger, OSU Extension Plant Pathologist

Oklahoma:  As you move from southern to northern/northwestern Oklahoma, wheat ranges from past flowering to flowering to heads emerging/approaching flowering (depending on variety and planting/emergence date).  It is highly variable.  Weather continues to be cool and moist except in southern, western and northwestern Oklahoma where it continues to be dry.

There were no reports of leaf rust over the last week in Oklahoma, but reports of stripe rust increased.  However, none of these stripe rust sightings indicated a widespread, severe outbreak anywhere in the state.  Bryan Vincent (Crop Consultant – northern Oklahoma) reported seeing strip rust on Everest wheat just west of Orienta, OK (about 40 miles west of Enid).  Dr. Brett Carver (OSU Wheat Breeder) reported in his visit early in the week to his breeder nursery at Lahoma (north central OK – 10 miles west of Enid), that, “35 swipes, just one 1″ sporulating Yr lesion at Lahoma, f-3. Otherwise nothing. Will keep looking.”  On Friday (10-May) at the Lahoma field day in the variety trial, I found an occasional active stripe in expected varieties (Pete, Garrison, Iba, Everest, and Armour), but these stripes were rare – only one or two per plot.  However, our weather over the last couple weeks and the near forecast is for weather favorable for stripe and leaf rust, so we may begin to see more of these rust diseases.  Powdery mildew continues to be found but I have not seen it yet on flag leaves or even F-1 leaves.  Leaf spotting diseases (tan spot, septoria, stagonospora) are more severe in Oklahoma than typical but vary by location.  For example, Dr. Jeff Edwards (OSU Smalll Grains Extension Agronomist) indicated that at his variety trial at Chickasha, leaf spotting was widespread, severe, and was on the flag leaves of specific varieties in the trial.

Regarding viruses – barley yellow dwarf is commonly observed at all locations, but is not associated with severe stunting indicating a later infection.  Numerous reports have been received and many samples have now tested positive for wheat streak mosaic virus from many areas of Oklahoma.  None of these samples have tested positive for either High plains virus or Triticum mosaic virus.

Reports/excerpts of reports from other states:

Arkansas – Dr. Gene Milus, (Professor/Small Grains Pathologist, Univ of Arkansas, Fayetteville, AR) 10-May-2013:  Most wheat has flowered or is flowering now. I found a low level of leaf rust at Rohwer in the southeast corner, and this is the first confirmed leaf rust here. Stripe rust is still active. Bacterial streak showed up on several varieties in the variety test. Leaf blotch is moving up the plants. There is abundant soil moisture across most of the state.

Kansas – Dr. Erick De Wolf (Professor/Small Grains Extension Pathologist, Kansas State Univ, Manhattan, KS) 11-May-2013:  The wheat is heading and flowering in southeastern and south central Kansas this week.  Wheat in central Kansas is mostly in the boot stages of development with the most advanced fields beginning to head this weekend. The wheat in southwestern KS continues to struggle with drought and freeze damage and growth stage varies widely among fields.

Disease scouting this week suggests the risk of severe rust epidemics remains low in Kansas this year.  I had a few more reports of trace levels of stripe rust in southeastern KS where the wheat is flowering. The levels of stripe rust are very low at this time.  Temperatures are forecast to reach the upper 80’s early next week with low temps at or above 60 F. Temperatures in this range often slow the development of stripe rust but farmers in this areas should monitor the disease carefully.

I was able to find a single pustule of leaf rust in Stafford county Kansas this week, but the wheat at this location was thin from recent dry conditions.  I suspect the leaf rust will not increase rapidly at this location.  Other fields that I checked in southwest KS (Finney and Kiowa counties) show significant drought stress and no sign of rust.  In south central and central Kansas (Pratt, Reno, and McPherson counties), the wheat is in better condition with thick canopies and good moisture recently.  I found no leaf rust, stripe rust or stem rust in these areas; however, several fields had moderate levels of powdery mildew. Symptoms of barley yellow dwarf remain low or absent in all fields I have check to date.

Stripe rust on wheat at Lahoma

Stripe rust on wheat at Lahoma

Wheat disease update 04 May 2013

Wheat disease updates are written by Dr. Bob Hunger, OSU Extension Wheat Pathologist

Oklahoma:  Over the last week I, Nathalia Grachet (OSU graduate student), and Brian Olson (OSU A&P) extensively looked at wheat around Stillwater, and in central (Minco, Apache), southwestern (Granite), and north central (Lahoma) Oklahoma.  Additionally, OSU Wheat Breeder Brett Carver examined his plots at numerous locations in central, southwestern OK as well as at Stillwater, and Dr. Art Klatt (OSU Wheat Geneticist) examined trials around Stillwater and Perkins.  Wheat in southwestern Oklahoma was damaged from drought and freeze, and little disease was discernible.  Wheat in southwestern Oklahoma (where it was possible) appeared to be at various states of head emergence, and in a few cases was just starting to flower.  In central OK, wheat was in various stages of heading.  Around Stillwater, wheat was just starting head emergence, while at Lahoma wheat was mostly just approaching GS 10 (boot stage).  However, there seems to be quite a bit of variability regarding stage of maturity depending on variety and planting date.

No leaf rust was observed at any location.  The “hot spot” of stripe rust we found at Minco is still active, but my previous update incorrectly identified ‘Duster’ as the variety with the most severe stripe rust.  Actually that was ‘Garrison’.  Stripe rust also was on Duster but not to the same severity nor was significant stripe rust on the flag leaves of Duster.  This is the only location where we observed significant stripe rust.  We also observed powdery mildew and leaf spotting on lower to mid leaves at many locations.  Primarily the leaf spotting appeared to be septoria/stagonospora with some tan spot mixed in, and as expected is usually somewhat more severe in no- or low-till fields.

Barley yellow dwarf was commonly observed at many locations with variable severity, but it was often difficult to differentiate damage between BYD, freeze, and drought.  Wheat streak mosaic also was observed across the areas examined (see photo below).  An increasing number of samples from around western OK have kept Jen Olson (Plant Disease Diagnostician) busy.  Most of these samples have tested positive for BYDV, WSMV, or both, but no high plains virus or Triticum mosaic virus has been detected.  This includes the Stillwater area where I have never before (since 1982) observed WSM.  Another interesting find here at Stillwater included occurrence of Russian Wheat Aphid, which was confirmed by Dr. Rick Grantham (Director of the Plant Disease and Insect Diagnostic Lab –  photos below taken by Rick).

Wheat showing symtoms of Wheat Streak Mosiac Virus. There are no curative sprays for this virus, but it can be avoided by ensuring volunteer wheat and other grasses are dead at least two weeks prior to planting

Wheat showing symtoms of Wheat Streak Mosiac Virus. There are no curative sprays for this virus, but it can be avoided by ensuring volunteer wheat and other grasses are dead at least two weeks prior to planting

Symptoms of Russian wheat aphid feeding

Symptoms of Russian wheat aphid feeding

Russian wheat aphids on wheat

Russian wheat aphids on wheat