ISSUE 10   July 15, 2010

SUNFLOWER RUST IN NORTH DAKOTA

Last week I scouted six fields between Minot and Langdon on Hwy's 83 and 5.  Five of them had the dusty-brown uredinia pustules on them (Figure 1).  The disease was only found on the lower leaves, and with one exception, was very light in severity (approximately one pustule or less per leaf).  Additionally, calls and pictures of sunflower rust have been coming in from these and other areas in the state.


Figure 1. Sunflower rust pustules.

It will be important to scout fields for rust this year.  Research data collected over the last two years indicate that a fungicide application is economical when the rust severity on the upper leaves is approximately 1-3% before R6.  Fungicide applications during the bloom stages have been very effective at managing rust, as long as severity was not higher than 3%.    R6 applications have had little effect on yield.  When rust is severe in the vegetative stages, two applications may be beneficial, the first in the early reproductive stages and the second in the bloom stage.  Although they may exist, I did not see any fields that had high severity on my brief trip.  My recommendation for growers who are beginning to see rust is to scout and anticipate that a fungicide application may be warranted near or at bloom.

Folicur and tebuconazole generics, Headline and Quadris are all labeled for rust.  When severity is approaching 3%, tebuconazole will have an edge over strobilurin products (Headline and Quadris).    Fungicide trial data is available at the National Sunflower Association website: go to research, then to research forum papers and/or research forum presentations.  Search for Markell or Friskop.  Additionally, a rust seminar given at the National Sunflower Association summer meeting is available at the National Sunflower Association website at

http://www.sunflowernsa.com/uploads/Markell_ControllingRust_10.pdf

More scouting will be done this coming week, and I will post another update in next week's Crop and Pest Report.

 

FUNGICIDE APPLICATIONS FOR WHITE MOLD ON SOYBEANS

I have been getting lots of calls about white mold fungicide applications on soybeans.  This is typical for dry beans, which are very susceptible, and fungicide applications are frequently necessary.  However, we had white mold in soybeans last year and it is clear that people have taken note.

Soybeans are susceptible when they begin to bloom, though not as susceptible as dry beans.  The pathogen uses flowers as initial nutrition sources, and from there moves into the stems and branches of the plant.  Thus, the environmental conditions during bloom are very important for disease development.   Conditions have been mixed for white mold in soybeans.  For most of the state, we have had enough soil moisture for inoculum to be produced.  We have generally had enough rain to be favorable for infection as well.  However, favorable temperatures hover in the 60's and 70's, and at about 85 F the white mold pathogen gets uncomfortable and disease is unlikely.  

If you determine conditions are favorable and intend to apply a fungicide, the most important aspect is timing.  An application at R1-R2 is much more likely to be effective than an application at R3.  I am including some data (Table 1) from a fungicide trial that was conducted at the Carrington Research Extension Center in 2009 under the direction of Blaine Schatz.  Endura is the only chemical that I am presenting, but timing (as opposed to chemistry) is the critical component.  The trial was misted and inoculated with spores so disease pressure may be artificially high.  This data does a good job of illustrating the importance of an application at the R1-R2 growth stage. 

There is limited data on head to head comparisons of fungicide efficacy on soybeans, simply because epidemics have been relatively rare.   However, I am including a link to a trial conducted by Dr. Carl Bradley at the University of Illinois.  Many chemicals that are available in soybeans (Proline, Endura, Domark, Topsin, etc.) are tested under a very high disease environment.  My recommendation would be to focus on the disease incidence for the first rating date; this would generally translate into a yield increase.  This trial quickly became overwhelmed and few treatments resulted in any yield increase.  Remember, this is only one trial and under very high disease pressure.  Chemicals may look different in different environments.  http://bulletin.ipm.illinois.edu/article.php?id=1252

Table 1.  Soybean fungicide trial at Carrington 2009.  Courtesy Blaine Schatz. 

Fungicide Treatment

Product Rate (oz) /Acre

Timing

Incidence  % Plants

Viable Plants (%)

Seed Yield
bu/ac

Non-treated

NA

NA

56.3

53.4

20.2

Endura

11.0 oz

R1 to R2

23.8

53.6

28.0

Endura

11.0 oz

R3

33.8

52.9

21.0

Endura

11.0 oz

R5

60.0

53.0

21.4

LSD.05

 

 

13.1

1.0

4.5

R1 = beginning bloom, R3 = beginning pod, R5 = seed 1/8” in upper 4 nodes
Variety = ProSoy.  All treatments had NIS at 0.25% v/v.  Pivot Irrigation was used.
Fungicide applied in 17 gpa.  Disease rated Sept 28

Sam Markell
Extension Plant Pathologist
samuel.markell@ndsu.edu

 

SUGARBEET CROP PROGRESS

The sugarbeet crop is off to its best start ever!  More than 90% of the acres were planted by the end of April.  Soil temperatures and moisture were favorable for uniform germination and emergence.  Although there was a spell of cold weather in early to mid-May, and many days with heavy winds, the sugarbeet crop has fared well with minimal replanting.  Most fields have already closed rows – this means that the crop can make optimal use of the long days of summer to maximize photosynthesis and to increase yield.  

More than 90% of the sugarbeet acreage in North Dakota and Minnesota were planted to Roundup Ready sugarbeet.  Weed control in the Roundup Ready sugarbeet is excellent.  Growers have done a good job at weed control in the conventional sugarbeet as well.

There are reports of some fields with Rhizoctonia and Fusarium.  Records should be kept of fields with root diseases so that appropriate varieties and necessary management decisions are used the next time these fields are planted to sugarbeet.

Mohamed Khan
Extension Sugarbeet Specialist
NDSU and University of Minnesota
mohamed.khan@ndsu.edu

 

COMMON ROOT ROT AND TAKE-ALL IN WHEAT

I have received several reports in the past week on patches of prematurely white plants in wheat fields, both in spring and winter wheat.  In all cases, the wheat has been planted into previous wheat ground.  The symptoms observed include the whole plant getting a silvery to white color and the heads are white and empty.  The affected plants also show the characteristic brown discoloration of the crown area, the subcrown internode and the feeder roots.  These symptoms are diagnostic for the common root rot disease caused primarily by the fungus Bipolaris sorokiniana (synonyms Helminthosporium and Cochliobolis). 

 
Patch of prematurely whitened spring wheat due to common root rot infection.


Comparison of common root rot infected subcrown internode (left)
and healthy subcrown internode (right) of ‘Sabin’ hard red spring
wheat in Fargo.
  Note chocolate brown discoloration of subcrown
internode of infected plant vs. almost white subcrown internode of
healthy plant.

The common root rot fungus is abundant in ND soils.  The fungus generally infects plants when soils are wet, but if soils have enough moisture for root growth and temperatures stay cool, the above ground symptoms of prematurely whitened heads or patches of these plants may not be visible, as the plants can move adequate water to the grain head.  But if infection has occurred and the plants are subsequently exposed to heat stress or hot, drying winds, the unhealthy roots are not able to move water to the grain heads fast enough, and the heads and plants dry up and result in the characteristic above ground symptoms.

Another root disease of wheat, called take-all, caused by the soil-borne fungus Gaeumannomyces graminis, also causes similar above ground symptoms of patches of white plants with white, prematurely ripened heads.  This fungus often infects only under irrigated conditions, as it prefers very wet soils for infection, but it is sometimes seen under dryland wheat production when excessive rains have occurred.  Take-all infection and symptoms were observed in Fargo this year on ‘Oklee’ spring wheat.  With take-all root disease, the root development is very poor and the disease is characterized by a shiny black discoloration of not only the subcrown internode, but also the lower stem (see picture).  Again, like with common root rot, take-all symptoms often show up in wheat that has had a sudden heat or drying stress.


Take all infection causing shiny black discoloration
of lower stem area of wheat plant and poor root development.
 
Note black color and almost absence of feeder roots.

For common root rot and take-all root rot, the best management strategy is to lengthen rotations between wheat/and or barley crops (barley is also susceptible to these root diseases).  Information on variety responses to these diseases for the most recently released varieties is not available. 

  

NDSU IPM SURVEY RESULTS, JULY 9

Wheat:  NDSU IPM scouts looked at 97 wheat fields during the past week, with the average growth stage of these crops at early flowering.  The range of growth stages surveyed were from boot to soft dough.  As in previous reports, tan spot infection is by far the most common disease observed, with an average severity on the flag leaf now at 4%, with higher levels observed in winter wheat.  Three winter wheat fields were observed with leaf rust.    Six fields had symptoms of Fusarium head blight (scab), with an average severity of 4.3%.  Twelve fields were observed with wheat streak mosaic symptoms and four with barley yellow dwarf symptoms.  Barley yellow dwarf observations may increase as the crop develops.  I observed a big jump in the degree of barley yellow dwarf symptoms in spring wheat plots of certain varieties in the past few days after the recent heat stress put on the crop in Fargo.

Barley: Seven barley fields were surveyed and the average growth stage in these surveyed fields was fairly young, only kernel watery-ripe.  No observations of scab were made this past week, and net blotch remained the most common disease observed.  The scouts did not record any powdery mildew infections, but plots in and around Fargo are showing some substantial powdery mildew infections.

Marcia McMullen
NDSU Extension Plant Pathologist
marcia.mcmullen@ndsu.edu


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