Posted 22 May 2011. Plant Health Progress.
Wheat Disease Management Reaches Critical Stage; Spray Timing Key
Source: The Ohio State University Press Release. www.oardc.ohio-state.edu
Wooster, Ohio (May 13, 2011)--Cool, wet weather in the past few weeks and warmer weather expected in the next few days may spell trouble for wheat growers in some parts of Ohio, as conditions become favorable for head scab and vomitoxin as well as a host of foliar diseases such as powdery mildew, Ohio State agronomic crops experts reported today.
Pierce Paul, wheat disease specialist with Ohio State University Extension and the Ohio Agricultural Research and Development Center (OARDC), said that despite a relatively slow start due to cool, wet conditions, the wheat crop in Ohio has developed well and is now between the jointing (in the north) and boot (in the south) growth stages.
“At this rate of development, and with warmer weather in the forecast, flowering should begin within the next 10 to 20 days,” Paul reported in this week’s issue of Ohio State’s C.O.R.N. Newsletter (corn.osu.edu). “More rain is also forecasted for later this week and early next week (May 13-18). Rain plus warmer weather plus wheat flowering equals an increased risk for head scab and vomitoxin. Early flowering fields in southern Ohio may be at risk within the next week or so, and growers in those areas should be prepared to apply a fungicide at flowering to suppress head scab.”
However, Paul warned that with flowering still several days away, things could change quickly, either increasing or decreasing the risk of head scab. Growers should keep their eyes on the weather and the forecasting system (www.wheatscab.psu.edu) as their fields approach flowering.
Details on vomitoxin suppression strategies via fungicides can be found at go.osu.edu/DB3.
The abnormally wet conditions experienced this spring in Ohio and beyond, combined with temperatures in the 60s and 70s expected in the next several days, are also creating a conducive environment for foliar diseases such as powdery mildew, Septoria and Stagonospora blotch. Powdery mildew and Septoria are already very prevalent in some locations, Paul said. He advised growers to continue scouting their fields and to be prepared to apply a fungicide to prevent these diseases from spreading and reaching the flag leaf stage, especially if the varieties planted are susceptible to those diseases and wet and humid conditions persist.
“Damage to the flag leaf caused by foliar diseases could result in reduced grain yield and quality,” Paul explained. “A foliar fungicide application between flag leaf emergence and heading usually provides the best control of these diseases. However, this relatively early application will not provide adequate protection against scab and vomitoxin if favorable conditions occur during flowering and early grain fill. Fungicide application for scab and vomitoxin suppression must be made at flowering.”
An updated fungicide efficacy chart with a list of products labeled for wheat, efficacy against foliar and head diseases, application rates, and pre-harvest intervals can be found on Ohio State’s field crops diseases website: www.oardc.ohio-state.edu/ohiofieldcropdisease/wheat/OFCDwheatfungicides.pdf.
Adding insecticide to wheat fungicide sprays?
Paul and Dennis Mills, a plant pathology program specialist with OSU Extension and OARDC, warned against growers adding insecticide to the fungicides they will be spraying on wheat over the next month -- a strategy some growers may be planning to employ since adding insecticide to the spray application is relatively cheap to do.
“We want to make it clear that this is not a very good integrated pest management approach to managing insect pest populations,” Paul and Mills indicated. “Indeed, in most wheat fields, there are no pests that will even get close to economic levels, assuming that they are in the field in the first place. Aphid populations are rarely high enough to cause concern, and any virus transmission would have already occurred. Although we had an initial concern with armyworm, word from Kentucky suggests that they perhaps will not be that high, and an insecticide spray might kill off all the predators and parasitoids that help keep armyworm under control. Cereal leaf beetle problems are still infrequent in Ohio, and we would point out that all of these pests can be scouted for and managed if necessary.”
While it may be easy and cheap to apply insecticides, Paul and Mills urge growers to think about the overall benefit of not applying an insecticide.
OSU Extension and OARDC are the outreach and research arms, respectively, of Ohio State’s College of Food, Agricultural, and Environmental Sciences.