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19
Jul
2013
Answers to recent questions regarding rice disease management
Author: Yeshi Wamishe, Extension Rice Plant Pathologist

Sheath Blight:

Q.  I want to spray 2-4-D for duck salad, and I see active sheath blight at green ring in my semi-dwarf variety but do not want to risk damage.  Could I tank-mix the strobi fungicide with 2-4-D and spray?

A.  It has successfully been done before, but always check the new labels for restrictions before you tank-mix.

Q.  I have a large but not-uniformly planted field due to mishaps with the planter.  Some spots in the field have thicker canopy than others.  I see sheath blight moving actively in the thicker spots.  Should I spray for sheath blight?

A.  In such a field it may be difficult to know the threshold level.  Therefore, it is a judgment call.   Historically, controlling sheath blight is most advantageous in fields with high yield potential, so this field may not be a good candidate for treatment.

Q.  If sheath blight appears at green ring, is moving fast and reaches threshold level, how many times do I need to spray for sheath blight in a season to minimize yield damage?

A.  If sheath blight is this aggressive at green ring, which is before canopy closure on a well-managed field, then it is very likely that the field has been excessively fertilized with N at the preflood stage, or the field is suffering from severe potassium deficiency.  These factors need to be addressed over the long term.  In general, spraying more than once for sheath blight is not economically justifiable, but in this case, an application of Quadris would be warranted, then scout at booting to see if the disease is active again.  If so, and yield potential seems good, then a logical judgment could be made to address late sheath blight and smut if the field has this history.  Our concern would be why sheath blight is active so abnormally early in this field though.

Q.  If I plan for just a one-time application for sheath blight control on a susceptible variety, what is the optimum developmental stage I should spray the fungicide?

A.  In Arkansas, it is usually not economical to treat for sheath blight more than once, if the field is well managed and the fungicide rate and timing is correct.  Naturally, there may be exceptions, but these would be rare in our experience.  Typically, a fungicide for sheath blight would be applied from 5-20 days after mid-season (1/2 inch IE), developmentally 2 inch IE to mid-booting.

Blast:

Q.  If I see leaf blast early in the season and treat field with Quadris, do I need to spray twice later in the season to control neck blast?

A.  You should keep permanent flood to at least 4 inches.   A deep flood is 4 inches in the shallowest part of the paddy.  The effective fungicides work best if applied twice for blast.  The first application should be made at late boot to beginning panicle tip emergence and the second when panicles are 50-75% out of the boot on most of the main tillers.  Higher rates are best.

Q.  Do I need to worry about blast when I hear reports of its occurrence in LA, TX, or even in AR?

A.  No.  But scouting of fields historically prone to blast is always warranted.  Leaf blast should be scouted for during June or early July.  We recommend integrated disease management practices including deep flood, clean and high quality seed, resistant varieties, proper N and K fertilizer management, and disease scouting and fungicide applications when needed.  Staying alert and on top of irrigation is really necessary for blast control in areas prone to the disease.

Q.  If there is no blast in my field but I know my variety is susceptible to blast, do I need to spray fungicide for protection?

A.  Depends.  If there is truly no blast in the field, why would we spray?  Accurate scouting pays off with this disease.  Any blast history in the field is a good indicator of potential disease problems, so these fields should be monitored accordingly.  Leaf blast and neck blast occur at different times during the season, and leaf blast tends to dry up or “disappear” after midseason in many fields.  While preventative applications to all acres of susceptible varieties is simple, they are not as economical or as sustainable as IPM applications based on monitoring and field to field judgement.

Smuts (kernel and False):

Q.  If I already know the variety is susceptible for these smuts but my field has no history and my nitrogen fertilization is based on NSTAR recommendation, do I need to spray fungicide?

A.  No

Q.  My other field is just as the one described in the previous question except that it had high pre-flood nitrogen. Do I need to worry about it?

A.  Yes. High nitrogen level is bait for the smuts.

Q.  I need to prevent smut infection because my field has history.  Sheath blight pressure at the moment is low.  Should I use Stratego to suppress both the smuts and sheath blight or or just use Tilt for the smuts?

A.  The full rate of Stratego (19 oz) has 5.5 oz Tilt in it and is close to the research recommended rate (6 oz) to suppress smuts.  Since there is no 100% smut control that may work, research has shown Stratego at 19 oz could give 21-24 days protection from sheath blight.  However, Tilt (Propimax, Bumper) alone would be good enough for the smuts only.  Timing and rate of the fungicides to suppress the smuts are critical.  The fungicides need to be applied during booting, but do not wait until boot split or later.  If sheath blight is not aggressively moving at this stage and if the variety is tall and the weather forecast is not favoring its development, I would worry less about sheath blight and apply Tilt (Propimax, Bumper) at the right rate.  

Bacterial Panicle Blight:

Q.  When is the earliest I will start seeing symptoms of panicle blight?

A.  At grain-fill, when the florets at the tip of the panicles are the oldest. When they fill, the panicle starts to tip-down but if infected, the panicles stick up and remain like that until harvest.  There is also typical discoloration you may see (http://www.arkansas-crops.com/2011/12/19/downloadable-quick-id-guide-for-panicle-blight-in-rice/).  Later the color changes as other fungi grow on it. Sometimes healthy-looking panicles could also show the symptoms on the younger florets at the base of the panicle.  Rarely, we also have seen some typical discoloration on the stem below the panicle.

Q.  Is there anything I can do to stop further spread of the disease after this point?

A.  No, it is too late.

Q.  If my field gets severe bacterial panicle blight, was there anything I could have done differently?

A.  The bacteria that are known to cause this disease are seed-borne.  They could also live in residue in the soil.  If you knew the soil had a history, planting Jupiter or hybrids could have been a better choice.  A clean seed source would be a good way to start, but you cannot be sure how clean is clean.  An adequate level of potassium fertilizer, lower rates of pre-flood nitrogen, recommended seeding rate, and possibly good water management would also help to grow strong and healthier plants that may withstand the bacterial infection.

 Fungicides:

Q.  Do you have information on fungicide rates and for how long they could protect?

See the table below:

Fungicides for Major Rice Diseases

Min – Max oz /acre Strobi Triazole
Quadris 8.5-12.5 Azoxystrobin
Stratego 16 -19 Trifloxystrobin Propiconazole
GEM RC 3.8-4.7 Trifloxystrobin
Quilt 14-34.5 Azoxystrobin Propiconazole
Quilt Xcel 14 – 27 Azoxystrobin Propiconazole

Research has shown that about 12 fl oz of Quadris or its equivalent rate in Quilt or Quilt Xcel suppresses sheath blight more than 28 days.  Lower rates obviously don’t last as long, with a 6-7 oz rate in the past lasting about 10-14 days.  The 19 oz rate of Stratego has been shown to suppress sheath blight from 21-24 days.

Q.  What are the rates of the active ingredients in Stratego?

See the table below:

Rice

Labeled

Contains Quadris Equiv Rate

Contains Tilt Equiv Rate

Contains GEM 500 SC or

Fungicide

 Rate (fl oz/A)

Fl oz/A

Fl oz/A

GEM RC Equiv Rate (Fl oz/A)

Stratego

16.00

0.0

4.6

4.0

Stratego

17.00

0.0

4.9

4.2

Stratego

18.00

0.0

5.2

4.5

Stratego

19.00

0.0

5.5

4.7

Q.  What are the rates of the active ingredients in Quilt?

See the table below:

Rice Labeled Contains Quadris Equiv Rate

Contains Tilt Equiv Rate

Contains GEM 500 SC or

Fungicide

Rate (fl oz/A)

Fl oz/A

Fl oz/A

GEM RC Equiv Rate (Fl oz/A)

Quilt

14.00

4.2

4.0

0.0

Quilt

15.00

4.5

4.3

0.0

Quilt

16.00

4.8

4.6

0.0

Quilt

17.00

5.1

4.9

0.0

Quilt

18.00

5.4

5.2

0.0

Quilt

19.00

5.7

5.5

0.0

Quilt

20.00

6.0

5.8

0.0

Quilt

21.00

6.3

6.1

0.0

Quilt

22.00

6.6

6.4

0.0

Quilt

23.00

6.9

6.6

0.0

Quilt

24.00

7.2

6.9

0.0

Quilt

25.00

7.5

7.2

0.0

Quilt

26.00

7.8

7.5

0.0

Quilt

27.00

8.0

7.8

0.0

Quilt

28.00

8.3

8.1

0.0

Quilt

29.00

8.6

8.4

0.0

Quilt

30.00

8.9

8.7

0.0

Quilt

31.00

9.2

9.0

0.0

Quilt

32.00

9.5

9.2

0.0

Quilt

33.00

9.8

9.5

0.0

Quilt

34.00

10.1

9.8

0.0

Quilt

34.50

10.3

10.0

0.0

Q.  What are the rates of the active ingredients in Quilt Xcel?

See the table below:

Rice Labeled Contains Quadris Equiv Rate

Contains Tilt Equiv Rate

Contains GEM 500 SC or

Fungicide

Rate (fl oz/A)

Fl oz/A

Fl oz/A

GEM RC Equiv Rate (Fl oz/A)

Quilt Xcel

15.75

8.9

4.5

0.0

Quilt Xcel

16.00

9.1

4.5

0.0

Quilt Xcel

17.00

9.6

4.8

0.0

Quilt Xcel

17.50

9.9

5.0

0.0

Quilt Xcel

18.00

10.2

5.1

0.0

Quilt Xcel

19.00

10.8

5.4

0.0

Quilt Xcel

20.00

11.3

5.7

0.0

Quilt Xcel

21.00

11.9

5.9

0.0

Quilt Xcel

22.00

12.5

6.2

0.0

Quilt Xcel

23.00

13.0

6.5

0.0

Quilt Xcel

24.00

13.6

6.8

0.0

Quilt Xcel

25.00

14.2

7.1

0.0

Quilt Xcel

26.00

14.8

7.4

0.0

QuiltXcel

27.00

15.3

7.6

0.0

Note: All Equivalent rates are rounded to nearest decimal point.

Q.  Is there difference in potency among the strobi fungicides to control sheath blight or blast?

A.  The difference is considered slight by researchers.  Trifloxystrobin (GEM) is considered slightly more effective on blast than Azoxystrobin (Quadris).  Azoxystrobin (Quadris) is considered somewhat more effective on sheath blight than Trifloxystrobin (GEM).

Note that only propiconazole (Tilt) has been shown to have activity in suppressing kernel and false smut.

For more information on fungicides for rice diseases, visit Arkansas plant disease control product guide at: http://www.uaex.edu/Other_Areas/publications/PDF/MP154/RiceFung.pdf.  See current labels for restrictions for directions.

Acknowledgement:

The genuine help of Dr. Rick Cartwright for the information and experience shared towards answering these timely and pertinent questions is highly appreciated.


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