ISSUE 12    July 21, 2005

DRY BEAN DISEASES

As dry bean fields move into flowering, the risk of disease (esp. white mold) increases. Some of the potential diseases that could be found this year are listed below.

White mold. White mold is a "wet weather" disease. Soil moisture is needed for the apothecia (mushroom-like structures) to emerge from the soil and release ascospores. Wet foliage provides a conducive environment for disease progression to occur more rapidly. Thiophanate-methyl (Topsin M, T-methyl, Farmsaver.com Thiophanate methyl 85 WDG) and Endura have been shown to provide good control of white mold if applied correctly. These fungicides should be applied at the onset of bloom to 7 days after. For ground application, a pressure of 100 psi along with the use of drop nozzles may allow for better coverage and control. Research conducted at the University of Minnesota to determine the potential for a fungicide to be profitable on dry bean when total water (rainfall and irrigation) from June 1 until 10 days into bloom was recorded showed that:

3 to 5 inches = fungicide profitable 20% of the time

5 to 7 inches = fungicide profitable 67% of the time

7+ inches = fungicide profitable 85% of the time

Common bean rust. With the shortage of seed early in the spring, many of the rust-resistant varieties may have not been available. A fungicide to control common bean rust may be needed on susceptible varieties. Products registered for rust control include Amistar, Quadris, Quadris Opti, Headline, chlorothalonil products, and maneb products. All of these fungicides should be applied prior to onset of disease for maximum efficacy.

Anthracnose. Although anthracnose has been found sporadically since 2001, it is unlikely to be established in North Dakota. Most of the incidences of anthracnose since 2001 have been traced to infected seed sources. Even so, scouting for the presence of anthracnose is still a good idea as it is a destructive disease. Foliar symptoms appear as reddish-brown lesions that occur on the leaf veins on the underside of the leaf. Pod symptoms appear as sunken tan lesions with dark borders.

Fungicides registered for control of anthracnose include Amistar, Quadris, Quadris Opti, Headline, chlorothalonil products, and thiophanate-methyl products.

Antracnose lesions on veins
Anthracnose lesions on veins of bottom-side of a leaf.

Antracnose lesions on pods.
Anthracnose lesions on pods.

Common blight. With all of the hail and damaging winds, common blight has been prevalent this season. Because common blight is caused by a bacteria, only the copper-hydroxide bacteriacides (Basicop, Champ, Kocide, etc.) will provide some control of this disease. In regular production fields, protection against common blight may not be needed; however, in seed production fields, an application of a copper-hydroxide compound may help reduce the number of pods with common blight lesions. Results from a trial conducted in 2003 at Prosper, ND in collaboration with Dr. Luis del Rio are below. The product used in this trial was Champ DP.

Rate (lb/A)

Plant stage

Yield (lb/A)

% Pods with disease % severity of:

0%

1%

10%

25%

0

 

1955

86

11.7

1.9

0.25

2

V8

2155

84

12.8

22.4

0.45

2

V8, R3

1966

86

11.2

22.4

0.18

2

V8, R3, R6

1953

90

8.1

1.4

0.48

2

R3

2244

91

8.3

1.0

0.15

2

R6

1967

92

6.8

1.5

0.23

1

V8, R3

1837

91

7.6

1.1

0.08

1

V8, R3, R6

1996

83

13.0

2.9

0.83

 

LSD 0.10

281

7

5.5

1.8

0.50

 

SOYBEAN RUST FOUND IN AL AND GA COMMERCIAL FIELDS

Soybean rust was found in a commercial field in Georgia and in a commercial field in Alabama within the last week. The only states with confirmed soybean rust this year are Alabama, Florida, and Georgia. Soybean rust spores have been found in spore traps in a few other southern states; however, disease has not been found in those states as of yet. Once soybean plants reach the R6 stage, research has shown that a fungicide application would no longer be needed. Soybean fields in North Dakota are generally in the R1 to R2 stage right now. Soybean rust will likely not be an issue for North Dakota this year. To track the spread of soybean rust in the United States, go to:

http://www.sbrusa.net/

Carl A. Bradley
Extension Plant Pathologist
carl.bradley@ndsu.edu

 

NDSU IPM SURVEY, JULY 11-15

The NDSU IPM field scouts surveyed 103 wheat fields, 32 barley fields and 38 sunflower fields the second week of July. Wheat leaf rust severity ranged from zero on flag leaves to 45%. Tan spot severity ranged from 0 to 70%, while the Septoria severity ranged from 0 to 44%. In some fields, the combination of leaf rust and leaf spot diseases approached 100% severity on the flag leaves, while in other fields total leaf disease severity remained low. The NDSU scouts do not have information on variety scouted or whether or not fields were treated with fungicides, as they randomly choose fields across a county. Differences in leaf disease severity could be due to fungicide application or variety grown, as most areas of the state had ample rain fall for leaf disease development.

Barley fields surveyed this week were in the central, northwest, and southwest districts. Barley leaf diseases were common, as well. They included net blotch, spot blotch and Septoria infections.

Bacterial leaf blight (also called bacterial stripe) was also recorded in some wheat and barley fields. Bacterial leaf diseases are not controlled by fungicide application, and in some cases, bacterial infections are severe in fields that were treated with fungicide.

During this second week of July, the NDSU IPM field scouts observed head scab (Fusarium head blight) in 35% of the wheat fields surveyed, primarily in the south central, central and southeast districts. Field severities of head scab (incidence of infected tillers x % of individual head infected) ranged from <1% to 8%. Head scab was observed in 25% of the barley fields surveyed, but field severities were <1%. These barley fields surveyed were primarily in the western counties.

 

HEAD SCAB (FUSARIUM HEAD BLIGHT)

Observations of head scab in spring grains on Monday, July 18th increased substantially from the week before. In central, south central and southeast counties, head scab infections became very obvious in many spring wheat fields. These infections weren’t obvious a week before. Reports from area extension agents Terry Gregoire, Devils Lake, and Kent McKay, Minot, indicate that scab infections are becoming obvious now in their areas, as well. Very frequent rains and high humidities and dew points favored these infections in spring grains, as they did in winter wheat, as reported in earlier Crop and Pest Reports.

At small grain demonstration trials at Lisbon and Casselton, spring wheat varieties were quite variable in scab response. Some varieties had high numbers of heads infected and the % head severity also was high, from 50 -100%. Some heads had infections extending into the stem below the head, giving the stem a purple to bleached color.


Individual spikelets of wheat infected with
scab and discoloration of stem due to fungus
spreading from head into stem.

In other varieties, incidence of infected stems was scattered, about 1%, and the number of spikelets infected was low, 1 or 2. Alsen and Glenn, releases from NDSU with scab tolerance, looked very good at these two sites, with low incidence and severity. These two varieties are not immune, and scab will be visible in them, but overall severity is low.

Spring wheat variety trials at Lisbon are being evaluated for scab differences this week, and other trials across the state also will be evaluated soon, by plant breeders and area agronomists. Producers are urged to look at these variety trial results as they become available this fall, before planning next year’s varieties. This year’s levels of scab are a reminder that this disease is still a huge potential problem across the state, and variety choice is one of the good management tools, even in the face of overwhelming environmental conditions. Information from fungicide trials across the state also will be available later this summer or early fall.

 

BLACK CHAFF IN WHEAT

Last week’s Crop and Pest Report indicated that bacterial leaf blight (bacterial stripe) was common in some wheat fields. This bacterial infection is caused by the bacterium Xanthomonas translucens pv translucens. The bacteria infect with wounds caused by wind driven rains that also move tiny soil particles that cause small wounds in the leaves. The disease appears to be endemic in North Dakota.


Bacterial Leaf blight (Stripe)

Bacterial infections start as water soaked streaks on the leaves, but under recent hot temperatures, these streaks dried up, leaving brown streaks and dried, shiny bacterial exudate on the leaf surfaces. The bacterial cells also may splash onto the glumes and kernels after head emergence. Bacterial infection on the glumes is called black chaff (see figure to the left). Black chaff is characterized by dark brown to black shiny streak along the length of the glume. Continued wet weather could cause the bacteria to spread to the kernel, under severe conditions, causing discoloration of the kernel and also causing seed infection.

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

 

NDSU PLANT DIAGNOSTIC LAB

Is It Really Growth Regulator Herbicide Injury on Soybean?

The NDSU plant diagnostic lab has seen quite a few soybean samples, both conventional and RoundUp Ready varieties, with symptoms that resemble those associated with growth regulator herbicide injury. However, the reported patterns in the field don’t fit with what we expect to see with a drift event or a tank contamination. Sometimes, an affected plant will reportedly be adjacent to a nonaffected plant, and symptoms are throughout large fields. Typically, only one growth stage is affected, and the new growth appears normal, suggesting that yield will not be significantly negatively affected. The actual cause is unknown, but others have speculated that the strange symptom may be a result of a stress response to high temperatures during active growing periods. Other areas in the Midwest have reported similar symptoms over the years. The following links to publications from the University of Illinois and Iowa State University provide more information on this strange ‘symptom’:

www.ag.uiuc.edu/cespubs/pest/articles/199916g.html

www.ipm.iastate.edu/ipm/icm/2002/7-22-2002/pgr.html

 

How to send samples to the NDSU Plant Diagnostic Lab:

General Sample Submission. When collecting samples to submit to the lab, a good rule of thumb is to bring or mail to the lab within just a few hours of collecting the sample. Include roots, if possible, and keep the entire plants intact. Prevent soil on roots from contacting the foliage by wrapping the roots in a separate paper towel (slightly dampened, if desired, but not wet) and enclosing in a plastic bag. Surround foliage with dry paper towels (not dampened in any way), and then place the entire intact sample (with separately wrapped roots and foliage) in a plastic bag. Seal the plastic bag or fold over the top, and place in a sturdy box or envelope. Usually, several plants are needed. A single plant is almost always insufficient. At least 6 plants is a good rule of thumb to follow. Regular mail is sufficient for most parts of North Dakota, but if the sample is being mailed from the extreme western side of the state, priority or express mail may be preferred, especially in very hot weather. Avoid sending samples by mail late in the week, to prevent samples from sitting in a hot warehouse over the weekend (what some diagnosticians refer to as ‘sample soup’ is the result). If you are sending samples from outside of North Dakota, the NDSU Plant Diagnostic Lab has a special permit that allows the lab to receive these samples for diagnostic purposes. However, out-of-state samples must be double bagged, using zippable plastic bags, and packaged in a sturdy box or envelope (with seams sealed with tape) in order for the lab to be in compliance with the requirements of this permit.

A sample improperly collected and stored is as useful as no sample at all. If there is any delay in mailing or bringing a sample to the lab, collect and prepare as above, but keep in a cooler or in a refrigerator until it can be sent.

Soybean leaf samples. Samples of plants with foliar diseases, such as suspect soybean rust, usually need consist only of about 15 to 20 symptomatic leaves, rather than entire plants. Layer the leaves between dry paper towels and place in a zippable plastic bag. Seal, place in another zippable plastic bag, and place in a sturdy box or envelope. Tape the seams and submit to the lab as soon as possible.

Arthropod ID samples. Insect specimens can also be received by the lab. Please, don’t send live insects, if possible! Most insects can be preserved by placing in a vial of alcohol (isopropyl or ethanol, found in drug stores or the medicine aisles of retail/grocery stores). Delicate insects, such as moths, can be wrapped in paper towels to prevent damage during shipping. Whole insects or other arthropods are best. Animal parts seldom lead to a satisfactory diagnosis.

Plant ID samples. Weed samples or other plants for identification can be sent to the lab in the same manner as a regular plant sample. To preserve a plant sample for identification later, press the plant. Include all plant parts with the sample – roots, foliage, reproductive parts.

Mold ID samples. The NDSU Plant Diagnostic Lab evaluates samples for the presence of molds, which is a relatively common problem in dwellings in the Red River Valley. This type of evaluation is limited to at the very least determining if a mold contaminant is present. Occasionally, if a mold contaminant is detected, the mold is identified to genus, and sometimes, the mold(s) can be identified to species. Samples should be collected with care. Please call the lab for more information on sampling for mold in your home or workplace. The following website may provide additional information:

http://www.homemoisture.org

 

Directions to the NDSU Plant Diagnostic Lab

From I-29, take the 12th Ave North exit, and head East on 12th Ave North to the NDSU campus (approximately 1.5 miles). Turn left (North) onto Bolley Drive. Near the end of Bolley Drive is a sky walk that connects Loftsgard Hall (on the East side of Bolley Drive) with Waldron Hall (on the West side of Bolley Drive). The lab is located in Waldron Hall, second floor, rooms 206 and 208. Parking is available on the south side of the building.

Minimal Services July 29 through August 2, 2005

The NDSU Plant Diagnostic Lab will not be accepting samples July 29 (Friday) through August 2 (Tuesday), 2005. Exceptions will be made for samples suspected to be infected with soybean rust or other ‘suspicious’ malady. Please plan accordingly. If a sample must be submitted during these times, a delay in processing the sample is likely. Thank you for your understanding and support of the lab!

Kasia Kinzer
Plant Diagnostician
kasia.kinzer@ndsu.edu


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