New and Revised Disease Fact Sheets

A new UW Extension disease fact sheet on Aphanomyces root rot has recently been developed and ready for download.  The fact sheet describes symptoms of Aphanomyces root rot, gives details about the pathogen that causes the disease, and gives some management ideas. You can download the fact sheet by visiting the ‘Fact Sheet’ section of the UW-Madison Field Crops Pathology website or CLICK HERE.

Revisions to fact sheets describing symptoms and management of Ergot of small grains and Fusarium head blight of wheat are also now available for download. To access these fact sheet, visit the ‘Fact Sheet’ section of the Field Crops Pathology website or CLICK HERE FOR THE ERGOT FACT SHEET or CLICK HERE FOR THE FUSARIUM HEAD BLIGHT FACT SHEET.

Evaluation of fungicides for control of foliar diseases of Alfalfa at cutting #1 in Wisconsin, 2014

Alfalfa 1Damon L. Smith, Extension Field Crops Pathologist, University of Wisconsin

Scott Chapman, Research Associate, University of Wisconsin

Bryan Jensen, IPM Program, University of Wisconsin

An evaluation of foliar applied fungicides for control of diseases of alfalfa was implemented in Wisconsin in 2014.  This work is a continuation of fungicide evaluation that has been ongoing since 2011.  In previous trials, yield advantage by using fungicide was only observed about 20% of the time when fungicide was used. In addition, the yield advantage is often not high enough to cover the cost of the fungicide application.  In 2014 we wanted to continue to evaluate some newer products on the market and determine if there was a yield increase and added value when used.  Methods and results from the first cutting in 2014 are below.

The trial was established at the Arlington Agricultural Research Station located in Arlington, WI. The alfalfa cultivar ‘Spring Gold’ was seeded on 20 Aug 2012 in a field with a Ringwood silt loam soil (6 to 12% slopes). The experimental design was a randomized complete block with four replicates.  Plots were 40 ft long and 10 ft wide.  Standard alfalfa production practices as described by the University of Wisconsin Cooperative Extension Service were followed. Treatments consisted of a non-treated control and five fungicide treatments. Fungicides were applied using a CO2-pressurized backpack sprayer equipped with 8001 TurboJet flat fan nozzles calibrated to deliver 20 GPA.  Fungicides were applied once plants had reached a height of 6 in. Date of fungicide application was 4 May 2014. Natural sources of pathogen inoculum were relied upon for disease. Disease and defoliation was evaluated immediately after harvest by visually estimating both parameters with the aid of standard area diagrams. A small-plot harvester was used to cut a 31-in wide by 37.4 ft long area of each plot to determine wet yield. A subsample of alfalfa was also collected from each replicate (~0.50 lb.), weighed, then dried and weighed again to determine dry matter yield. Value added per acre was also determined for each treatment using the following method. First yield differences compared to the control were calculated (yield advantage). Price advantage per acre was then determined by multiplying the yield advantage by $0.10/lbs dry matter (price based on June 13, 2014 hay report). Finally, $30 (average price for a fungicide application) was subtracted from all price advantages to determine the value added to each acre by using fungicide. All disease, defoliation, yield, and added value data were analyzed using a mixed model analysis of variance (P=0.05).

Weather was very wet and cool prior to the first harvest. Based on these weather patterns the primary disease present at the first harvest was spring black stem. No significant differences in average severity of spring black stem were identified among all treatments (Table below). No significant differences in defoliation were identified among treatments. Dry matter yield was significantly higher than the non-treated check for all plots that received fungicide. Added value was not significantly different from the non-treated control for all plots that received fungicide. While there was an average yield increase when fungicide was used for this cutting, significant added value over the non-treated control was not observed when fungicide was applied. Phytotoxicity was not observed with any treatment.

**Note: Aproach is not yet labeled for use on alfalfa.  A label is anticipated in Wisconsin on alfalfa in the near future.

Treatment and Rate/Acre

Spring Black Stem Severity (%)z

Defoliation (%)z

Dry Matter Yield (Tons/a)y,x

Added Value by using Fungicide (USD/a)v

Non-treated Check

10.6

10.0

1.74 b

$0.00

Quadris 6.0 fl.oz. + Warrior II 1.6 fl.oz. + Induce 0.25% v/v

5.6

7.5

1.92 a

$6.30

Aproach 12.0 fl.oz. + Induce 0.25% v/v

4.4

5.0

1.93 a

$7.93

Aproach 12.0 fl.oz.

6.3

6.3

1.95 a

$11.00

Quadris 6.0 fl.oz. + Induce 0.25% v/v

4.3

7.5

1.95 a

$10.89

Aproach 6.0 fl.oz.

5.6

6.3

1.97 a

$14.73

Aproach 6.0 fl.oz. + Induce 0.25% v/v

6.3

7.5

1.99 a

$19.00

EXP 2

5.6

6.3

1.99 a

$18.84

EXP 1

5.6

7.5

2.01 a

$23.44

Headline 6.0 fl.oz. + Induce 0.25% v/v

4.4

6.3

2.05 a

$31.50

LSD (α=0.05)

nsw

nsw

     0.15     nsw

zValues are based on the average disease severity or defoliation prior to harvest on 3 Jun.

yMeans followed by the same letter are not significantly different based on Fisher’s Least Significant Difference (LSD; α=0.05).

xYield based on harvest on 3 Jun.

wns = no least significant difference (α=0.05).

vValues determined after accounting for hay yield compared to the non-treated control and subtracting average price of fungicide application ($30/a); prices based on $0.10/ lbs. dry matter; June 13, 2014 Hay Report

Stamina Seed Treatment for Aphanomyces Root Rot Control On Alfalfa

Aphanomyces euteiches growth on agar media

Aphanomyces euteiches growth on agar media

Damon L. Smith – Extension Field Crops Pathologist, University of Wisconsin

Quinn Watson – Hilldale Undergraduate Scholar, University of Wisconsin

Many alfalfa farmers in the state of Wisconsin often find themselves struggling with root rot diseases of alfalfa. One of the increasingly more prevalent pathogens that cause root rot is the fungal-like organism Aphanomyces euteiches. To learn more about Aphanomyces root rot (ARR), you can click here to download an informational disease profile.

One of the main methods to manage ARR is through the use of host resistance. One of the complicating factors with ARR management, however, is that there are three races of the pathogen. Alfalfa varieties can differ in their performance to each race, with some varieties having only race 1 resistance or sometimes race 2 resistance. Resistance to race 3 seems less common, but does exist in a few cultivars.

Because of this complication of races and resistance interactions in alfalfa varieties, it would be nice to have some other management strategies that might be useful across races. One approach is to use fungicide seed treatments. Lately, seed treatments have gained popularity in the agronomic crops. Much interest has been paid in corn and soybean production. To learn more about the types of seed treatments available in agronomic crops, click here.  Now seed treatments are becoming more common in alfalfa. Probably the most common fungicide seed treatment on alfalfa is Apron XL®. This product contains the active ingredient mefenoxam, which is active against the ‘water-mold’ organisms in the groups Phytophthora and Pythium. Interestingly, A. eutieches is also a ‘water-mold’ but Apron XL® has been shown to not be active against this organism. Because of this shortfall, the industry has sought seed treatments that might be effective against A. eutieches.

Interest has grown in the seed treatment Stamina® for control of ARR in alfalfa. Stamina® fungicide seed treatment contains the active ingredient, pyraclostrobin.  This is the same ingredient that is in the popular foliar fungicide, Headline®. This is a FRAC group 11 compound, or what we commonly call a strobilurin fungicide. To dust up on your fungicide knowledge, you can visit an informational page, by clicking here.

I have received a lot of questions on the topic of using Stamina® on alfalfa. In order to answer questions about the efficacy and performance of this product against A. eutieches, we completed several experiments over the winter to compile some non-bias datasets.

Figure 1. Growth of Two Races of Aphanomyces euteiches on Agar Media Amended with Six Rates of Stamina Seed Treatment

Figure 1. Growth of Two Races of Aphanomyces euteiches on Agar Media Amended with Six Rates of Stamina Seed Treatment

Two experiments were conducted. The first experiment involved simply growing a race 1 and race 2 isolate of A. eutieches on agar media amended with different concentrations of Stamina® (0 ppm – 2000 ppm). We measured the growth of the resulting colonies for 6 days. We then converted the daily growth data into a single number by doing an area-under-the-growth-curve transformation. This is a conversion that plant pathologists often use for data taken over multiple days. Figure 1 shows the results of the growth studies at each concentration for race 1 and race 2 isolates of A. eutieches. The race 2 isolate used in this study was a bit more sensitive to Stamina® than the race 1 isolate (shorter bars as the concentration increased for the race 2 isolate, compared to the race 1 isolate). However, growth was inhibited to a certain degree at higher concentrations of Stamina® for both races. These data suggest that Stamina® seed treatment has efficacy toward A. eutieches, but the level of efficacy might be dictated by the race of the isolate.

In another study we used our routine alfalfa bioassay to test the performance of Stamina® on treated alfalfa seed. We chose to use ‘Vernal’ as an Aphanomyces-susceptible cultivar of alfalfa and ‘WAPH 5’ as an Aphanomyces-resistant cultivar. Seed of each cultivar were treated with the high rate (3.1 fl ozs/100 lbs. of seed) of Stamina®. Seed were placed in the bioassay using the mycelial fragment inoculation method. Details about how the bioassay is conducted can be found here. Each treated variety was inoculated using isolates of all 3 known races of A. eutieches. We also included a set of plants that were not treated with Stamina®. This trial was conducted twice in a growth chamber.

Figure 2. Percentage Survival of Emerged 'Vernal' Alfalfa Plants After Aphanomyces euteiches Inoculation

Figure 2. Percentage Survival of Emerged ‘Vernal’ Alfalfa Plants After Aphanomyces euteiches Inoculation

We evaluated several parameters including plant emergence, proportion of emerged plants that survived to the end of the study, root length, root area, and visual severity. Figures 2 and 3 show the proportion of emerged plants that survived to the end of the study, for each treatment. Interestingly, in the susceptible cultivar ‘Vernal’, the effect of Stamina® was highly significant (Figure 2). There was an interaction of race on survival, with race 3 causing severe damage on treated and not treated ‘Vernal’ plants. However, Stamina® significantly improved the survival in this cultivar in the presence of race 1 and race 2 isolates over the non-treated plants. In ‘WAPH 5’, the resistant cultivar, the effect of Stamina® treated plants was not significant over the non-treated plants. The superior genetic resistance in ‘WAPH 5’ against all races of A. eutieches trumped the effect of Stamina® in these trials.

These data are preliminary, but it appears that Stamina® fungicide seed treatment might have efficacy toward ARR in alfalfa. However, based on the bioassay results in this trial, the positive effect of that

Figure 3. Percentage Survival of Emerged 'WAPH 5' Alfalfa Plants After Aphanomyces euteiches Inoculation

Figure 3. Percentage Survival of Emerged ‘WAPH 5’ Alfalfa Plants After Aphanomyces euteiches Inoculation

Stamina® might provide could only be observed in the more susceptible variety of alfalfa. In highly resistant varieties, Stamina® may not provide much added benefit to ARR management.

We are curious if similar results might be observed in the field. Therefore, we are conducting a Stamina® seed treatment trial in the 2014 growing season. We are planting replicated field plots of a known A. eutieches race 2 susceptible alfalfa variety treated with Stamina®,or not treated.  This will be conducted at the Lancaster Agricultural Research Station in a field with a confirmed A. eutieches race 2 population. Stay tuned for results of this trial later this season.