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ISSUE #11  July 12, 2001

 

DIAGNOSIS AND CONFIRMATION OF ROUND UP (AND OTHER HERBICIDE) INJURY

Since June 2001, the Plant Diagnostic Lab has processed 10 Round Up tests and made herbicide injury diagnoses on 33 other samples, based on visual assessment. The number of herbicide injury complaints is not different from any other year. What is different is the increase in Round Up injury complaints, and the interest in confirming other herbicide diagnoses by biochemical testing methods. The reasons for the increased interest in testing for herbicide injury confirmation include the availability of technology, but most likely many other factors worthy of both casual and serious debate.

The responsibility of the lab is to answer questions, both specific and general, and provide growers and producers with reasonable information from an unbiased perspective. To meet that goal, we now offer plant residue testing to confirm exposure to glyphosate, the active ingredient in Round Up (see below for sampling information). We will still do assessments based on visual symptoms for the standard ND Resident fee of $15.00. The plant tissue test for confirmation of exposure to glyphosate is $150.00 per sample.

The NDSU Plant Diagnostic Lab is able to offer Round Up residue testing through a cooperative project with another lab at the university. Neither this lab nor others at the university are equipped to offer more extensive herbicide residue testing. There are other labs, both public and private, that do offer these services. A partial list of those labs is available in the ND Weed Control Guide on page 119, table Y25. A complete listing of those labs that offer more extensive herbicide testing is available on the Plant Diagnostic Lab website, http://www.ag.ndsu.nodak.edu/diaglab , or by request. Recently, I have been recommending the lab at SDSU. They offer an extensive list of herbicide residue testing services, and they are the closest lab to our region. The address is: Olson Biochem Lab, SDSU, PO Box 2170, 134 ASC, Brookings, SD 57007. The phone number for the SDSU lab is 605.688.6171. It is a good idea to call the lab before sending a sample to get specific instructions on sampling and mailing. As with any lab that offers herbicide residue testing, including SDSU and NDSU, some specific information will be required. Testing methods vary for different herbicides, and testing for multiple products will be costly. It is best to know which herbicide might have caused the injury. The NDSU Plant Diagnostic Lab may be able to provide assistance determining at least which family of herbicides may have caused the injury symptoms to narrow the number of possibilities.

Instructions for Submitting Plant Material for Round Up Testing

Plant material suspected of being damaged by Round Up can be brought directly to the lab or mailed. Either way, select a minimum of 10-15 plants, roots and all if possible, showing symptoms of suspected Round Up injury. Also submit 10-15 plants of the same crop, at approximately the same growth stage, that have not been exposed to the herbicide. If the plants are to be mailed, do not wrap them in plastic. Enclose the plant material in paper or simply in a box of the appropriate size, and mail to the NDSU Plant Diagnostic Lab, Walster 306, Box 5012, Fargo, ND 58105.

Instructions for Submitting Other Suspected Herbicide Injury Samples

Plant material suspected of injury from other herbicides should include a minimum of 5-10 symptomatic plants. It is helpful to have 3-5 unaffected plants as well. Also include a description of the pattern of injury in the field, herbicides applied to the current crop, last year’s crop and herbicides applied to that crop, and a description of neighboring fields including herbicide use that is known.

Cheryl Biller
Plant Diagnostician
diaglab@ndsuext.nodak.edu

 

DOWNY MILDEW IN SUNFLOWERS

NDSU IPM crop scouts are also looking at sunflower fields now for levels of downy mildew. Preliminary reports from Jeanna Jambor indicate that in 10 sunflower fields examined in the SW, the incidence of downy mildew ranged from 0-8.4%, with an average of 3.2% of plants infected. Of six fields examined in Morton county, four had levels of 5% or greater.

Jerry Schneider examined 25 fields in the central and south central part of the state and found a range of downy mildew infections from 0-4%, with an average of 1% of plants in a field showing downy mildew symptoms.

 

DRY BEANS AND WHITE MOLD CONTROL

Potential economic return from spraying fungicides for white mold control in dry beans has been correlated to rainfall accumulations from June 1 to 10 days after initiation of bloom. In research done by the late Dr. Richard Meronuck extension plant pathologist, University of Minnesota, it was determined that if total rainfall from June 1 to 10 days after bloom initiation was 3-5", a fungicide was economic 20% of the time; when total water was 5-7 inches, a fungicide was economic 67% of the time; when total water was over 7" for this time frame, a fungicide was economic 85% of the time.

The following was rainfall totals from June 1 through July 10 for NDAWN weather sites (other locations may have had more or less rain, of course):

Location

Rainfall 6/1-7/10

Location

Rainfall 6/1-7/10

Baker

3.45"

Hazen

3.85"

Beach

4.89"

Hettinger

3.38"

Berthold

0.73"

Hillsboro

2.49"

Bottineau

2.29"

Hofflund

3.92"

Bowman

5.18"

Horace

2.28"

Brorson, MT

7.67"

Humbolt, MN

2.36"

Cando

4.39"

Jamestown

3.79"

Carrington

4.95"

Langdon

4.62"

Cavalier

3.13"

Linton

3.63"

Columbus

3.07"

Mandan

4.73"

Crary

5.19"

Mayville

2.32"

Dazey

2.83"

McHenry

3.89"

Dickinson

6.45"

McLeod

4.54"

Edgeley

3.90"

Mohall

3.25"

Eldred, MN

1.68"

Northwood

2.57"

Fargo

2.73"

Oakes

2.00"

Felton, MN

1.69"

Prosper

2.70"

Forest River

2.54"

Robinson

3.48"

Galesburg

1.89"

Rolla

3.15"

Grand Fks.

2.16"

Turtle Lake

3.23"

Streeter

4.18"

Watford City

4.00"

St. Thomas

2.31"

Williston

4.71"

Towner

4.40"

Wyndmere

2.44"

Twenty-six (in bold in table) of the 46 NDAWN sites listed recorded rainfall above 3", where white mold control may be economic 20 to 67% of the time. No ND or MN site had rainfall over 7" for this time frame.

Many of the sites in traditional dry bean production areas have had less than 3" of rain.

Other factors that affect spray decisions for white mold control in dry bean include variety; row closure; and history of white mold. Some varieties are more susceptible to white mold; row closure favors wet canopies; and a history of white mold in the area may mean a higher potential of the disease this year.

 

POTATO LATE BLIGHT HOTLINE

The latest report (July 11, 2001) on the Blightline indicates that late blight has not been found yet, and they attribute this lack of disease to fair weather, lack of inoculum, fungicide applications, and luck, plus give credit to the producers and growers for destroying inoculum sources and proper disease management. The pathologists urge growers, however, not to become complacent, continue to scout fields, and apply fungicides on a regular basis for those sites with index values above the threshold. A new reporting site has been added to the blightline, Hofflund, ND, which covers the Nesson Valley near Williston.

The second annual potato field day at the irrigated research site near Dawson, ND, will be held on Tuesday, August, 7, from 9-12 am.

 

SMALL GRAIN DISEASE UPDATE, 7/10

Rusts: Wheat leaf rust has been observed more frequently this past week. Jerry Schneider, NDSU IPM crop scout, observed leaf rust at trace severity levels in spring wheat fields in central and south central counties. A field of winter wheat in Benson county now has 35% severity of leaf rust on the flag leaves. Terry Gregoire, NDSU Extension area specialist, observed a trace level of leaf rust in Ingot wheat in variety plots at Devils Lake and a private crop consultant observed leaf rust in Gunner wheat in the Devils Lake area. I observed a trace amount of leaf rust in a commercial field of ‘2398' in Hettinger Co. on July 10. The NDSU Crop Forecasting Model indicates conditions have been favorable for leaf rust infection in some sites across the state.

Stripe rust: One new observation of stripe rust was made by a crop consultant observing Norpro spring wheat in McIntosh Co. Trace amounts were observed. A private crop consultant from north central SD indicates that fungicide treatment arrested stripe rust development in that area, but now that several weeks have passed since treatment, leaf rust is developing on the crops in the milk stage.

Crown rust of oats was observed by Terry Gregoire in wild oats in Ramsey county, while I observed no crown rust in oats or wild oats in Fargo.

Leaf spots: Tan spot is still the most frequent leaf spot disease observed in wheat fields by NDSU IPM crop scouts, with severity on the flag leaves ranging from 0% to 28%. However, Septoria infections are now being observed by crop scouts, crop consultants, and myself. In wheat variety plots in Hettinger Co., Roger Ashley, NDSU Extension area specialist and I observed some extensive Septoria infections in variety plots and a commercial field on July 10. A crop consultant observed some extensive Septoria on spring wheat in Devils Lake area. Kelly Novak , NDSU IPM crop scout, observed Septoria infections in barley in Burke county, as well. She also observed spot blotch in barley in Burke and Renville counties. Severity levels of spot blotch n the top leaves was generally only 1%.

Bacterial leaf blight: This disease was observed in wheat by Kelly Novak in Ward county, by NDSU IPM crop scout Holly Semler in McHenry county and by Nathan Carlson in McLean county. These scattered observations of symptoms were related to rainstorms in these areas that favored the bacterial infections.

Overall, disease incidences and severities on wheat and barley are higher in areas of the state that have had greater than 3" of rain since June 1 (see table in dry bean white mold discussion). Disease observations by Matt Gregoire, NDSU IPM crop scout working the Red River Valley areas, indicate that the dry conditions in these areas are slowing disease development substantially. The NDSU Disease Forecasting model of Dr. Len Francl’s also indicates that favorable infection periods for diseases have been much less in these dry areas of the valley. He also has had very little detection of scab spores in the recent week.

Field scouting and attention to the Disease Forecaster ( http://www.ag.ndsu.nodak.edu/cropdisease/ ) are still important, as Septoria and leaf rust can develop very rapidly when favorable environmental conditions occur.

Marcia McMullen
Extension Plant Pathologist
mmcmulle@ndsuext.nodak.edu

 

CERCOSPORA CONTROL IN SUGARBEET

Cercospora leafspot is the most damaging foliar disease of sugarbeet resulting in lower tonnage, reduced sucrose content, poor storageability, and increased impurities resulting in higher processing costs. The fungus Cercospora beticola causes Cercospora leaf spot. The most common source of the Cercospora fungus is infected sugarbeet debris in the field. The fungus is spread mainly by wind and water. Cercospora leaf spot develops rapidly in humid, warm and rainy weather. Spore release is effected by rain and dew. Optimal spore germination and infection occurs when the temperature is 75-77° F at 100 % relative humidity for at least 8 hours. Day temperature of 80-90° F and night temperatures above 60° F is favorable for disease development. Leaf spot symptoms may occur about 5-7 days after infection. Cercospora leaf spot is a multi-cyclic disease; that is, it has many infection cycles during the growing season. As such, it is important to have early control of Cercospora leaf spot.

An integrated approach is recommended for controlling Cercospora leaf spot, involving cultural practices such as burying infected tops by tillage in the fall, planting more tolerant varieties, plant in fields with a rotation interval of at least three years, select fields as far away as possible from the previous year’s infected field, and the timely and proper use of recommended fungicides. Alternate Eminent 125 SL with other registered compounds such as triphenyl tin hydroxide (TPTH), Mancozeb, Quadris, and Topsin or Benlate in order to delay the development of resistance to these products. The benzimidazole fungicides, Topsin and Benlate, should not be used in stand-alone applications since the Cercospora fungus has developed resistance to this class of fungicide. Topsin or Benlate can be used in a tank mix with Mancozeb or Tin, but only once in a season.

Since sugarbeet planting was generally late in most growing areas, it follows that canopy closure will also be later than in normal years. Consequently, the micro-climatic conditions necessary for disease development will probably occur in mid- to late July. As a result, disease symptoms for Cercospora have not been observed to date in sugarbeet fields in North Dakota and Minnesota.

Dr. Mohamed F. Khan
NDSU Extension Sugarbeet Specialist
mkhan@ndsuext.nodak.edu


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