ISSUE 6   June 18, 2009

NDSU DISEASE FORECASTING SITE UPDATE

Leaf Disease Predictions: The NDSU Small Grain Disease Forecasting site at: www.ag.ndsu.nodak.edu/cropdisease/ is showing risk of tan spot infections and possible need for fungicide application at many NDAWN locations, because of recent rains at these locations. For example, the following tables show risk predictions of tan spot infection at Dickinson and Jamestown for recent days. The Dickinson weather table also shows how longer hours of wet periods correlates with higher risk of tan spot.

The flagging leaf growth stage was chosen, as it is the earliest available on the model, but the data would also be indicative of risk of infection for other leaf growth stages.

Fusarium head blight (scab) Predictions: At the same above web site, when the flowering growth stage is chosen, risk maps for Fusarium head blight infection also are available. The user of the web site also may pick the susceptibility of the variety to this disease. For a very susceptible variety, such as Jagalene winter wheat, the risk on June 14th was fairly high in some areas of the state. Growers should check the website in the near future as recent rains will increase risk.

Risk of FHB infection for a very susceptible,
flowering wheat variety on June 14.

 

FUNGICIDES FOR FUSARIUM HEAD BLIGHT (SCAB) MANAGEMENT

Winter wheat growers in the region will soon be making a decision on fungicide use for Fusarium head blight (scab) control. Reductions in scab severity of 50 percent to 60 percent can be achieved when fungicides are applied at early flowering for wheat and durum, and at early heading in barley. Triazole fungicides (fungicide resistance group 3) are recommended for scab suppression because they are locally systemic and have been shown to reduce both FHB and DON. The following table provides a comparison of the most frequently used and best products registered for scab suppression in wheat and barley:

Fungicides for Fusarium head blight (head scab) suppression

 

Fungicide

Product name

Rate/A
(fl oz)

Head Scab Efficacy*

Preharvest Interval for grain

Tebuconazole

Folicur, Orius, Embrace, Monsoon, Tebustar, others

4.0

F

30 days

Prothioconazole

Proline

5.0 - 5.7

G (VG)

30 days (32 for barley)

Prothioconazole + Tebuconazole

Prosaro

6.5

VG

30 days

Metconazole

Caramba

10 - 13.5

G (VG)

30 days

* F= Fair; G = Good; VG =Very Good: (VG) rating only when higher rateused for Proline and Caramba

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

 

GROWTH STAGE IS CRITICAL FOR SCAB CONTROL WITH FUNGICIDES

The intent of this article is to describe the optimum growth stage to apply fungicides for management of scab in wheat and barley. For information on the forecasting models and fungicide options refer to Marcia McMullen’s articles in this issue.

Growth stage in wheat: Early flowering is the optimum growth stage for applying fungicide for scab control in all classes of wheat (winter, spring and durum). Applying fungicide during early flowering helps to protect vulnerable florets during fertilization and early grain-filling. The center spike in the following photo is at the ideal stage for applying fungicide. The spike on the left has emerged from the boot, but has not yet started to flower (there are no visible anthers extruded from the glumes) and will likely be at the optimum stage in about two days. The spike on the right is past the optimum stage; the anthers are bleached and dried, unlike the turgid, yellow anthers in the center spike. The length of time from head emergence to the beginning of flowering usually takes about three days. Experience has shown that it is better to apply fungicide too early rather than too late.

       

Growth stage in barley: Flowering in barley begins just before head emergence, so barley florets are not overly susceptible to scab infection. Scab infections do not generally impact yield. The scab fungus, however, is able to infect the glumes and produce DON which impacts the value of the grain in the market. The optimum stage for applying fungicides to protect the glumes of barley from infection is when the spike is fully emerged from the boot. The spike third from the left demonstrates the optimum stage, with those further to the left too early and the one on the right too late. With barley the appearance of the first spikelet from the boot is a good indication that the best stage for spraying is only a few days away.

Joel Ransom
Extension Agronomist for Cereal Crops
joel.ransom@ndsu.edu

 

NDSU IPM FIELD SURVEY

NDSU IPM field scouts surveyed 117 wheat fields and 29 barley fields across the state this past week. Of the wheat fields surveyed, half had symptoms of tan spot. Since the start of the survey, severities of tan spot in symptomatic fields have ranged from 1 to 28%, with the highest average severities in the southwest region of the state (see figure):

Fungicide applications in fields with early season tan spot are still taking place this week in spring wheat. See information on risk of tan spot infections under Disease Forecasting information.

Only 3 wheat fields were observed to have light wheat streak mosaic virus symptoms this past week and a few had symptoms of fungal leaf spots other than tan spot.

In barley, just a few fields had some symptoms of fungal leaf spots, but severities remained generally less than 5%.

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

 

SUGARBEET – MANAGING RHIZOCTONIA ROOT ROT

Rhizoctonia solani can infect all growth stages of sugarbeet and may cause wilting and death of plants. Rhizoctonia can cause infection even in dry soil, but prefers wet conditions and soil temperatures above 68ºF. The fungus may cause damping-off at the seedling stage when it infects the hypocotyl which results in rapid collapse of seedlings before soil emergence or post-emergence. Damping-off affects the plant population and ultimately reduces root yield. Crown and root rots infection are more common and occurs in older plants when the pathogen infects petioles or roots. Characteristic symptoms of Rhizoctonia crown and root rot include sudden wilting of leaves, and petioles of outer leaves are blackened at the point of attachment to the crown. The crown rot extends to the root causes root rot. The disease may also produce dry rot cankers on the root surface. Rhizoctonia crown and root rot are becoming more widespread and disease severity appears to be increasing. Research done by Dr. Carol Windels and others show that sugarbeet grown in Minnesota and North Dakota are affected by both R. solani AG2-2 4, and the more aggressive AG2-2 IIIB. Rhizoctonia crown and root rots need to be managed since they cause significant yield reduction.

Fields with a known history of heavy Rhizoctonia should be planted to a tolerant variety. Crop rotation with non-hosts such as wheat, early planting, avoidance of throwing soil at cultivation into crowns of plants, and improved drainage will assist in managing the disease. The use of the fungicides Quadris at 9.2 fl oz/A or Proline at 5.7 fl oz/A in a 7 inch band at the 4 to 6 leaf stage or when the soil temperature at the four inch depth is about 65ºF will also help to control Rhizoctonia crown and root rots.

 

SUGARBEET CROP UPDATE

The 2009 sugar beet crop is finally planted. American Crystal Sugar Company (ACSC) planted about 441,881 acres, Minn-Dak Farmers Cooperative (MD) 115,360 acres, Sidney Sugars 24,776 acres, and Southern Minnesota Beet Sugar Cooperative (SMBSC) 116,000 acres. At SMBSC, most fields were planted by mid-May, and at this time about 75 to 80% of the crop is looking good to excellent. In some areas, inadequate rainfall in May resulted in non-uniform emergence. Recent rainfall throughout the district will facilitate good crop growth. About 70% of growers at SMBSC plant a cover crop, mainly oats. Unfortunately, it appeared that some of the oats were contaminated with herbicide tolerant canola. Affected growers are using mainly hand labor to rogue infested fields since chemical control is more costly.

Planting was also done early at Sidney Sugars. However, about 4,000 acres had to be replanted because of frost damage.

At ACSC and MD, because of wet conditions, most fields were planted in late May and early June. Timely weed control is imperative, especially in a short growing season, to prevent any competition from weeds. The sugarbeet plants need warm, sunny days to quickly get full canopy to make maximum use of sunlight for the remainder of the season to produce a profitable crop.

Mohamed Khan
Extension Sugarbeet Specialist
701-231-8596
Mohamed.khan@ndsu.edu

 

SUGARBEET: TANK-MIXING FUNGICIDES, INSECTICIDES WITH HERBICIDES

Late planting may result in the need for applying insecticides and glyphosate at the same time on Roundup Ready sugarbeet. Please note that for Roundup Ready sugarbeet, the glyphosate manufacturers do not recommend or endorse mixing insecticides with glyphosate (Please Read Label). Thus, growers are responsible for any loss, damage, or unsatisfactory weed or insect control that may result from using mixtures of glyphosate with insecticides. One year of research at NDSU showed that Lorsban 4E at either 1 or 2 pt/Ac mixed with glyphosate (1 qt) did not result in any phytotoxicity or reduction in sugarbeet root maggot control. Similarly, no phytotoxicity was observed when Asana at 5.8 oz/Ac was mixed with glyphosate (1 qt). If choosing to apply such combinations, risk of crop injury may be reduced by making the application during cooler parts of the day.

Growers may also need to control Rhizoctonia crown and root rot with fungicides. Quadris at 9.2 fl oz/A, or Proline at 5.7 fl oz/A with a non-ionic surfactant at 0.125% v/v, applied in a 7-inch band when the mean soil temperature at the four inch depth is 65 F will provide effective control. We do not recommend mixing fungicides with glyphosate for Rhizoctonia control on Roundup Ready Sugarbeet since the fungicide has to be banded. Please note that research done by Dr. Andrew Kniss at the University of Wyoming in 2005 showed that Quadris (0.15 lb/A) mixed with Roundup Ultra Max II (0.75 lb/A) and AMS (10 lb/100 gal), and applied to Roundup Ready sugarbeet at the 6 to 7 leaf stage did not result in any phytotoxicity. For conventional sugarbeet, Quadris should not be mixed with conventional herbicides because it is highly likely that plant growth will be adversely impacted. For additional advice, call your agriculturist or researchers at NDSU.

Mohamed Khan
Extension Sugarbeet Specialist
Mohamed.khan@ndsu.edu

Mark Boetel
Research & Ext. Entomologist
Mark.boetel@ndsu.edu

 

SUNFLOWER RUST UPDATE

Last week I wrote an article about sunflower rust, and wanted to re-emphasize a couple points. The early spore stages of rust have been found in volunteers in last years fields. To my knowledge, we haven’t found rust in any commercial fields yet. The most important thing to do, right now, is to control the volunteers in the fields that had sunflower last year, some of them are being hit hard with rust (Figure). Secondly, we may be looking at fungicide applications for rust again, but right now is too soon. It is important to scout for rust, but I would be somewhat surprised if it is found in commercial fields before the last week of June or first week of July.


Volunteer sunflower cotyledons infected
with an early stage of sunflower rust (Photo: LoAyne Voigt)

 

SOYBEAN RUST ACTIVE IN SOUTHERN STATES

To no-ones surprise, soybean rust has successfully survived the winter in the gulf coast states. The disease has been found in Alabama, Georgia, and Florida, Louisiana, and in two states in Mexico (Figure).


Occurrence of soybean rust in the United States
as of June 17, 2009. Red indicates counties in
which sentinel plots were scouted and soybean
rust was found and green indicates counties in
which sentinel plots were scouted and soybean r
ust was not found.

Soybean rust is a serious concern for growers in the United States. However, for soybean rust to cause problems in North Dakota, it will have to spread north from an overwintering site, and it will have to occur prior to the beans being in R6.

The North Dakota Soybean Council and the North Central Soybean Research Program are supporting a monitoring effort for the disease in the United States, called the ipm-PIPE program. Sentinel plots (designated soybean fields) are scouted on a weekly basis and tissue from the sentinels are brought into the lab and examined for disease. In 2009, North Dakota will have eight designated sentinel plots along with five to ten mobile sites (randomly scouted fields in designated counties). Scouting will begin around the first of July.

Information concerning the spread of soybean rust in the United States, disease management, and other soybean-rust related issues are available online at www.sbrusa.net.  

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


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