WheatWatch 2012: Wheat Disease Update, Week Ending March 16Fri, 16 Mar 2012 17:33:50 CDT
Oklahoma’s unusually warm weather continued last week favoring wheat growth and, in some cases, growth of disease and pests. Bob Hunger, Extension Wheat Pathologist with Oklahoma State University compiles a weekly report on crop disease progression in Oklahoma and surrounding states. These WheatWatch 2012 reports are a service of the Oklahoma Wheat Commission. Check out their website by clicking here for more wheat news and marketing information.
OKLAHOMA: Although not severe, powdery mildew (PM) can be found with ease in most trials on susceptible varieties if the growth is thick. Weather this week was favorable for wheat growth and disease development with highs between 75-85, lows in the mid 60s, and with high humidity and dew formation most mornings. This should lead to a dramatic increase in PM levels and also provides favorable conditions for leaf rust; it actually may be a little warm for stripe rust (one day this past week reached 88). Our early foliar fungicide application was done on 14-Mar at GS 7. Two nodes were easy to find on most tillers with emergence of the flag leaf not all that far away on some tillers (variety is Jagger). Still no leaf rust observed this far north in Oklahoma, but observation of sparse pustules were reported to me last week by Gary Strickland (Extn Educator, Jackson County - SW Oklahoma). Septoria is evident on lower leaves but is not severe. Soilborne-spindle streak symptoms are disappearing quickly in that nursery. As indicated below and also confirmed by other Extension Educators around the state, aphids are abundant. I have seen both BCO aphids and greenbug around Stillwater. Symptoms of BYD continue to develop.
Dr. Jeff Edwards (Small Grains Extension Specialist - OSU) 15-Mar-2012: “I did not see much disease at all. Just a little PM at McLoud (just east of Oklahoma City) in wheat that should have been loaded with it. Plenty of aphids, though!
Dr. Brett Carver (OSU Wheat Breeder) 15-Mar-2012: “Even with a loaded canopy at Granite (SW Oklahoma), Marshall (30 miles west of Stillwater), and Lahoma (15 miles west of Enid), diseases are AWOL, only some minor leaf spotting in the lower canopy. Jeff is right about the aphids - BCO, I presume, was out in full force at Lahoma. Where we got a jump on planting at Lahoma (Oct. 6th) after a fallow year, I'm pretty confident we'll be taking heading notes there in less than 10 days. Not so in the variety trial - it looks more normal.”
Reports/excerpts of reports from other states:
TEXAS: Dr. Amir Ibrahim (Associate Professor, Small Grains Breeding & Genetics, Texas A&M University): 14-Mar-2012: I toured our rust evaluation nursery located 12 miles west of San Antonio, TX on March 14, 2012. This is a 25 acre land with yield trials, segregating populations, and head-rows. Winter and spring types were planted in mid- November and December, respectively. The nursery looks great and the growth is lush. All entries have satisfied their vernalization requirements, including those from Nebraska and South Dakota. Spring wheat has not headed yet, but the early winter types have already done so. None of the northern Great Plains entries have headed yet. The wheat crop is early by at least a week this year. Leaf rust is developing rapidly and uniformly in the spreaders, ranging from 60S - 80S. Consistent with previous years, there is more leaf rust in the observation head-rows as compared to the yield trials. Some entries were rated 100S. I have found yellow rust in some of the head-rows with ratings as high as 60S. No indication of leaf or yellow rust race change but it is early to tell at this point. The highest rating I could find in the Texas Uniform Variety Trial (UVT) for leaf rust was 60S. Powdery mildew is very heavy on some lines.
James Swart (IPM Entomologist, Texas AgriLife Extension, Texas A&M University, Commerce) 13-Mar-2012: The following are quotes from James’ report, which covers northeast Texas:
“To describe this year as unusual would be an understatement. Although, most fields were planted around the optimum planting date (November 1), plants have progressed rapidly due to one of the mildest winters on record. The earliest maturing varieties are approaching the boot stage (Feekes 10), while the latest maturing varieties are in Feekes 7 (two nodes above ground). By our estimate, wheat development is 10 days to two weeks ahead of normal.”
“Bird cherry oat aphid populations have virtually exploded in many area fields. This has been a recent development, as there were very few aphids observed as late as the end of last month. These aphids are usually considered minor pests that are kept under damaging levels by beneficial insects (parasitic wasps, ladybeetles, and lacewings). But I have seen populations in excess of 1000 aphids per foot of row this week, causing visible plant stunting.”
“Stripe rust (Puccinia striiformis) has infected some experiments in our research trials. Leaf rust (Puccinia recondita) has not yet been observed in this region, but the warmer than normal temperatures we are observing are ideal for leaf rust development.”
ARKANSAS: Dr. Gene Milus (Professor of Plant Pathology, University of Arkansas) 14-Mar-2012: “I looked at wheat plots in Fayetteville yesterday. Growth stage ranges from tillering to 1 node for most of the commonly-grown cultivars to close to flag leaf emergence for earliest lines in nurseries. This wide range in maturity may be due to presence or absence of photoperiod sensitivity among the cultivars and lines. Freeze damage occurred on stems of some of the earliest lines, as we had frost this past weekend.
A trace of leaf rust was found for the first time here this season. Leaf blotch is at a low level. No powdery mildew or BYD yet. A stripe rust inoculation on January 31 in our breeder’s head row nursery was very successful, but there has only been very limited spread to new leaves since then. Currently, overnight lows are too warm for stripe rust infection, and we may break all-time daily high temperature records across the region with temperatures forecast to be in the mid 80s F.
In eastern Arkansas where there has been a lot of early stripe rust, additional fields with hot spots continue to be found. In general, fields with hot spots are being sprayed with a fungicide as weather permits. (Last week was too rainy and windy for aerial applications.) Current warm temperatures should help slow stripe rust development.
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