ISSUE 4 May 31, 2007
WHEAT LEAF RUST DETECTED IN ND
Wheat leaf rust was detected by IPM field scouts in winter wheat in Cass Co. and Ransom Co. on May 25th. These winter wheat fields were in the jointing stage, and incidence of tillers with symptoms ranged from 1 to 12%, and leaf severity ranged from 1-3 %. Tan spot incidence in these same fields ranged from 10 to 46% of plants infected and severity ranged from 3 to 14% of leaf area infected.
NDSU IPM CROP SURVEY
NDSU Extension’s IPM summer survey program began last week with training of field scouts at the Carrington Research Extension Center on May 24th. Field scouts will be scouting for insects and diseases of wheat, barley, soybean, canola, and sunflower, with some additional insect trapping for corn and soil sampling for nematodes. Scouts will be looking at fields in each county, and will be operating in their respective regions under the direction of Area and State Extension Specialists.
The scouts and their scouting coordinators are:
operating out of the Dickinson Research Extension Center, Roger Ashley, Area Extension Specialist, coordinator;
Brandt Lemer: operating out of the Carrington Research Extension Center, Greg Endres, Area Extension Specialist, coordinator;
Miriam Miller: operating out of the Devils Lake Area Extension Office, Terry Gregoire, Area Extension Specialist, coordinator;
Tracy Samson and Ty Hanson: operating out of the North Central Research Extension Center, Denise Markle, Area Extension Specialist, coordinator;
Jaycie Klabunde: operating out of NDSU at Fargo, Jan Knodel, Marcia McMullen, and Sam Markell, Extension Entomologist and Extension Plant Pathologists, coordinators.
IPM scouting reports will be summarized weekly, with timely reports of pest problems provided on the web, through Ag Alerts, and the NDSU Crop and Pest Report.
CORRECTION TO LAST WEEK’S ISSUE
In last week’s Crop and Pest Report , I had presented a table of fungicide products available for early season tan spot control in wheat. In the rate column for mancozeb products, the rate should have been:
1-1.5 lbs/acre (1-11/2 lbs/acre), not 1-1/12 lbs/acre.
Ext. Plant Pathologist
FUNGICIDE RESISTANCE LEADS TO NEW MANAGEMENT RECOMMENDATIONS IN CHICKPEA
Managing the disease Ascochyta blight on large kabuli chickpea often is a challenge for producers. Ascochyta blight is caused by a fungal pathogen and can result in yield and quality losses if conditions are favorable for disease development. A fungicide program of three to four fungicide applications usually is needed through the growing season.
The strobilurin fungicides (QoI), such as Headline and Quadris, have been very effective in reducing the disease in past years. However, recent lab tests indicate that spores from some 2005 and 2006 Ascochyta blight samples collected in North Dakota can germinate in the presence of high concentrations of Headline and Quadris. Preliminary experiments also indicate that applications of QoI fungicides may not reduce chickpea disease caused by fungicide-resistant spores. These data support observations by some chickpea producers that QoI fungicides are not as effective as they used to be in controlling Ascochyta blight and indicate the pathogen causing Ascochyta blight is resistant to QoI fungicides.
These results have led researchers at NDSU to recommend that QoI fungicides not be used on chickpea in North Dakota in 2007.
To reduce QoI fungicide resistance and still manage disease, following these guidelines when managing disease in this year's crop is critical:
Small kabuli and desi-type chickpea generally are less susceptible to Ascochyta blight and usually only one or two fungicide applications are needed to manage the disease. To reduce QoI fungicide resistance and still manage disease, follow the previous guidelines when managing disease in this year's crop. In a two-spray program, preventative fungicides, such as chlorothalonil and maneb (Manex), should be applied prior to flowering and disease development, followed by Proline or Endura at flowering or pod-set. If conditions are dry and low levels of disease are present, only one fungicide application likely will be needed during the growing season.
To stop or slow the progress of fungicide resistance, and in the hopes that the QoI fungicides can be used again in the future for Ascochyta disease control, avoiding the use of any QoI fungicide on chickpea alone or in combination with other chemistries this year is important.
HOW DID ASCOCHYTA BLIGHT BECOME RESISTANT TO QOI FUNGICIDES?
To understand how fungicide resistance develops, it helps to understand how the fungicide works and how the pathogen reproduces.
Fungicides are effective because they disrupt basic biological processes in fungi. Some fungicides interfere with multiple metabolic sites (termed multi-site mode of action) while others interfere with only one metabolic site (termed single-site mode of action). Fungicides with a single-site mode of action, such as the QoI fungicides, are usually very effective at managing disease. However, the disease only needs to have a single mutation that will overcome one site of action to develop resistance to the fungicide.
The biology of Ascochyta blight contributes to the likelihood of developing resistance to fungicides because it can reproduce sexually and asexually in one growing season. Sexual reproduction allows the fungus to exchange genetic information that may help it overcome the fungicide. Asexual reproduction produces spores that can cause repeated infection cycles in a growing season. These repeated infection cycles increase the amount of fungus exposed to fungicides.
The level of fungicide resistance in a pathogen population increases when sequential or back-to-back applications of fungicides with the same mode of action are applied in a field. These applications increase fungicide resistance in the population by removing the sensitive fungi and "selecting" for fungi that can reproduce in the presence of the fungicide. This "builds up" the resistance population, which can then spread to other areas where fungicide resistance may not be established.
Until recently, the only systemic fungicides labeled for use on chickpea Ascochyta blight were Quadris and Headline. However, these fungicides have the same mode of action and are in the same group of fungicides (Group 11). Since systemic fungicides with alternative modes of action have been limited, sequential or back-to-back applications of these chemicals have been used in a single growing season for several years. The repeated use of the QoI fungicides without rotation, the single-site mode of action of these fungicides, and the biology of the fungus have all contributed to the development of QoI fungicide resistance in Ascochyta blight.
For additional information please contact Sam Markell or Kent McKay.
Graduate Research Specialist
Neil C. Gudmestad
Extension Plant Pathologist
Area Extension Specialist
North Central Research Extension Center
POTATO BLIGHTLINE OPERATIONAL
The Plant Pathology Department at North Dakota State University will again be providing the potato blightline service at no charge to the potato industry of North Dakota and western Minnesota in 2007. This will be the thirteenth year that this service has been provided and sponsored by Syngenta Crop Protection. The hotline uses local weather data collected from weather stations throughout our area to forecast the occurrence and spread of late blight in fourteen non-irrigated and nine irrigated production areas in ND and western MN. The data is processed by the North Dakota Agricultural Weather Network (NDAWN) and analyzed by a computer program (WISDOM) to forecast when conditions are favorable for late blight to occur.
The forecast information is used by plant pathologists Gary Secor and Neil Gudmestad to make late blight management and fungicide recommendations. The recommendations are made Monday, Wednesday and Friday of each week during the growing season. The first late blight hotline will be Friday June 1st, and the hotline will continue through mid September depending on disease pressure. The hotline will also be used to confirm late blight infection and serve as clearing house for national late blight information. In addition to late blight forecasting, the hotline also provides cumulative P-values for early blight disease forecasting and management recommendations. Finally, it serves to alert growers of other disease and insect news, as well as posting messages of general interest such as potato field day dates.
The hotline recommendations can be accessed by phone or website.
The toll free phone number is 888.482.7286
The NDAWN website for potato disease forecasting contains colored maps of ND to pictorially illustrate the late blight severity values (both two day and seasonal), favorable day values and P-day values for early blight throughout ND. That site is:
www.ndawn.ndsu.nodak.edu Go to applications and then click the drop down box for potatoes.
Growers and scouts are encouraged to send suspect late blight samples to us for positive identification. Late blight is a community disease and proper identification and prompt notification is important. Leaf samples should be placed in a slightly inflated zip-lock plastic bag without a wet towel and sent to:
Plant Pathology, Walster Hall 306
North Dakota State University; Fargo, ND 58105
We look forward to a successful potato year.