Last year it was too cold, and this year it’s been too dry. Until recently, weather in the Southern states has been hot and dry, so soybean rust is off to a slow start again. No new soybean rust has been found in Georgia despite recent rainfall and favorable temperatures. Similarly, there has been no rust found in Louisiana. Soybean rust has been found in northern Florida on kudzu and on kudzu in the southeastern corner of Alabama. Despite reports of rust in Mexico on soybeans grown for seed production and recently harvested, so far, no new soybean rust had been reported in Texas.

Sentinel plots will be monitored again this year in Michigan. Michigan’s sentinel plot locations for 2006 have been determined with input from the Michigan Soybean Promotion Council. Plots will be located in Allegan, Clinton, Gratiot, Saginaw, Tuscola, Sanilac, St. Clair, Shiawassee, Eaton, Ingham, Van Buren, Kalamazoo, Calhoun, Berrien, Cass, St. Joseph, Branch, Hillsdale, Lenawee and Monroe counties.

On the soy bean rust information front, the http://www.sbrusa.net/ has been renamed – Pest Information Platform for Extension and Education (PIPE) to reflect expanded coverage beyond rust. A number of new features have been added, including soybean aphid reporting, discussed in this issue by Chris DiFonzo. One of the features is a pest management toolbox, containing tactics, guidelines, a GFP (Good Farming Practices) tool, insurance documents and a chronological commentary of soybean rust reports for each state. Currently, under Tactics - USA you’ll find national soybean rust fungicide guidelines updated for 2006. Clicking on Guidelines -USA brings up information related to good farming practices. States have the option to add individual tactics or guidelines.

The GFP tool is a printable, interactive form that can be filled in to generate a report to document good farming practices taken by a grower to control soybean rust and/or aphids, information that is needed for crop insurance claims. Under Insurance Docs, you’ll find a list of documents needed to substantiate best management practices or to file an insurance claim. The chronological commentary allows you to view or print state commentaries and guidelines for a particular date or range of dates

Many of you are aware of the soybean rust web site (http://www.sbrusa.net/) sponsored by USDA last year. That site provides a map that shows soybean rust detections in sentinel plots and on kudzu, an alternate rust host. There is also commentary provided by state specialists. Knowing the progression of the disease north will help producers target scouting and apply preventative fungicide applications.

For 2006, there is a new feature on the web site – maps for soybean aphid. When you enter the site, simply go to the drop down menu in the top right corner, under the date and select soybean aphid. Two maps appear on the right side of the screen. The top map shows “SB Aphid Observations.” As of this writing (May 25) this map is blank (it isn’t active yet), but once reports of soybean aphid come in, dots will appear. While USDA is funding the sampling some sentinel plots for aphids, additional research plots and production fields may be sampled in certain states by Extension educators, state government, university entomologists and others. Unlike the rust map, which only has two colors (green for no detection, red for detection), the color of the dots on the aphid map will reflect the number of SBA per plant with purple dots indicating fields or plots over the 250 per plant threshold. The second map has the “SB Aphid State Update,” commentary by state specialists. Note that the color of the state reflects when the commentary was last updated.

By clicking on Michigan, you can read commentary by me on aphids. I will also include my detailed management recommendations, if aphid populations increase. Some of this information may be redundant of the Field Crop CAT Alert, but I since can update the rust web site daily if needed, the information will be more up-to-date.

A note of caution about the soybean aphid web site – entomologists in the region agree it should not be used to make spray decisions in your individual fields. This is different from how the rust maps are used. Detections of rust near your location will help to time preventative fungicide applications across a region. However, detecting soybean aphid in your area and even having fields go over threshold do not necessarily indicate your individual fields should be treated. We definitely know from 2005 that soybean aphid populations during an outbreak differ dramatically from field to field and that some fields need to be treated while other do not. We also know from 2005 that optimal timing of insecticide applications protects yield, which argues for scouting as needed and making field-by-field decisions. Use the soybean aphid maps to get information about aphid populations in general, but do not use the maps to make a decision about whether or not to treat your own fields.

The following article is from the September 8, 2005 Field Crop CAT Alert.

Nine scouting reports were filed from the 20 soybean sentinel plots during the reporting week. Two of those were final reports, as the fields no longer have leaves.

No soybean rust has been found on soybeans or other plants in Michigan or anywhere in the North Central Region, including Ontario, Canada.

Plant height: Ranged from 24 to 40 inches.

Degree of canopy closure: Ranged from 0 to 100 percent. Fields are ripening and losing leaves.

Soybean diseases present: Brown spot, bacterial blight and downy mildew were the diseases found most often. There were occasional reports of Phytophthora stem canker and brown stem rot.

Insects present: Soybean aphid populations were either non-existent or extremely low. Bean leaf beetles were present in one field.

Soybean: Charcoal rot

Poster viewing to start 8:00 PM on November 14; Technical program begins at 8:00 AM Eastern Time (9 a.m. CT) on November 15 and ends at 4:00 PM on November 16

Website: http://www.apsnet.org/online/sbr/

The following article is from the August 25, 2005 Field Crop CAT Alert.

Twelve reports were filed from the 20 soybean sentinel plots during the reporting week.

No soybean rust has been found on soybeans or other plants in Michigan or anywhere in the North Central Region, including Ontario, Canada.

Plant height: Ranged from 24 to 40 inches. Ten plots are in the 36- to 40-inch range.

Degree of canopy closure: Ranged from 84 to 100 percent.

Soybean diseases present: Three-fourths of the plots report multiple diseases ranging from one to seven diseases per plot. Low levels of Septoria brown spot, low to high levels of downy mildew and low levels of bacterial blight are the most common diseases. Also noted were powdery mildew, Phytophthora stem canker, sudden death syndrome, white mold and soybean cyst nematode.

Insects present: Soybean aphid levels are dropping in fields that haven't been sprayed. The highest count came from two plots, each reporting about 100 aphids per plant. Japanese beetles, Western corn rootworm and spider mites, all at low levels, were also reported.

Soybean: Soybean cyst nematode

The following article is from the August 11 , 2005 Field Crop CAT Alert.

Ten reports were filed from the 20 soybean sentinel plots during the reporting week.

No soybean rust has been found on soybeans or other plants in Michigan or anywhere in the region, including Ontario, Canada.

Plant height: Two plots ranged from 20 to 30 inches, and eight plots ranged between 36 and 48 inches.

Degree of canopy closure: All plots ranged between 95 and 100 percent closure.

Soybean diseases present: Downy mildew is present in half the plots at low to moderate levels but the incidence is increasing. Brown spot remains at low levels in three plots.

Insects present: Two plots have recently been sprayed for soybean aphids, three plots have per plant populations of soybean aphids ranging from 250 to 420 with honeydew and sooty mold present, two plots have low incidence of soybean aphids and three plots report no soybean aphids. Spider mite damage was noted on 5 to 10 percent of the leaves in one plot.

There is no MSU Diagnostic Services report this week.

The following article is from the July 28 , 2005 Field Crop CAT Alert.

Fourteen reports were filed from the 20 plots during the reporting week.

No soybean rust has been found in Michigan or anywhere else in the region, including Ontario, Canada.

Plant height: Ranged from 20 inches to 40 inches, 4 plots = 20 in., 1 plot = 22 in., 2 plots = 24 in., 3 plots = 30 in., and one plot each at 35, 36, 38 and 40 inches.

Degree of canopy closure: Ranged between 90 and 100 percent.

Soybean diseases present: Eleven plots = low brown spot, 2 plots = low bacterial blight, 7 plots = low downy mildew, 2 plots = low Phytophthora stem canker.

Insects present: Four plots = a few soybean aphids per plant, 8 plots = 0-50 per leaf, 2 plots = 0-10 spider mites per leaf, and 2 plots = low levels of Japanese beetles. One plot had been recently sprayed for soybean aphids and 3 plots reported that soybean aphid numbers were increasing.

No soybean samples were submitted to MSU Diagnostic Services to be assayed for soybean rust during the reporting period.

MSU Diagnostic Services reports the following pests and problems found on field crop samples submitted in the last 2 weeks:

The following article is from the July 14 , 2005 Field Crop CAT Alert.

There were 19 reports filed from the 20 sentinel plots during the reporting week.

Following is a compilation of the reports.

Growth stage: Six plots=R1, 10 plots=R2, 1 plot=R3, 1 plot=R4.

Plant height: Ranged form 13 to 26 inches with the majority between 16 and 20 inches.

Degree of canopy closure: Ranged from 50 to 100 percent and averaged 85 percent.

Soybean diseases present: Low levels of brown spot (13 plots), low levels of bacterial blight (7 plots), low level of downy mildew (1 plot) and low levels of phytophthora stem canker (2 plots).

Insects present: Soybean aphid remains at low levels in 16 of the plots. One plot recorded 250+ aphids, and two of the fields containing sentinel plots have been sprayed for soybean aphids.

Comments: Drought seems to be having a significant impact on soybean plant growth. In one sentinel plot within an irrigated field, canopy cover was 100 percent where water reached the plants and only 75 percent where water did not reach.

One soybean sample from a sentinel plot was submitted to MSU Diagnostic Services and tested negative (using real-time PCR) for soybean rust. The symptoms – small chlorotic flecks – were caused by downy mildew (Peronospora manshurica). Under high relative humidity grayish tufts of sporangiophores may be visible on the lower surface of lesions. Older lesions that are necrotic do not have these tufts. The sporangiophores are best seen with a hand lens or a dissecting microscope. According to the University of Wisconsin (http://www.plantpath.wisc.edu/soyhealth/minordiseases/downy.htm), downy mildew commonly occurs wherever soybeans are grown but rarely causes yield loss.

MSU Diagnostic Services reports the following pests and problems found on field crop samples submitted in the last week:

No new soybean rust detections have been made on soybeans in the last week. The USDA soybean rust web site (http://www.sbrusa.net/) forecast dated July 13 states the following: “The soybean rust model indicates that light deposition of inoculum is possible over eastern Ohio, and extreme western Pennsylvania for the next two days. Greater deposition is indicated over Alabama, Georgia, South Carolina, North Carolina, eastern Tennessee and eastern Kentucky, Virginia, West Virginia from now until the end of the week. Infections in new deposition areas will not be observable for approximately two weeks, assuming favorable weather conditions.” Check the web site at: http://www.sbrusa.net/ daily for changing forecasts and predictions.

Following is a compilation of the 13 reports
Growth stage: Ranged from V5 to R3.

Plant height: Ranged from 12 to 24 inches.

Degree of canopy closure: Ranged from 40 to 98 percent and averaged 75 percent.

Soybean diseases present: Ten plots reported low incidence of Septoria brown spot and three plots reported low to moderate incidence of bacterial blight.

Insects present: Soybean aphids were present in small quantities (a trace to 6/leaf) in eight plots and one plot reported 20 per leaf (150 per plant).

MSU Diagnostic Services reports the following pests and problems found on field crop samples submitted in the last week:

The following article is from the June 30 , 2005 Field Crop CAT Alert.

MSU has established 20 sentinel plots around the state to be scouted weekly looking for the first appearance of Asian soybean rust (SBR) in Michigan. Scouting is occurring in at least 25 soybean-growing states and, to date, rust infection has been reported on volunteer soybeans in one county of southwest Georgia (those plant have been destroyed) in one sentinel plot in northern Florida and at one site in Alabama. Six counties in Florida have reported Asian soybean rust infections on kudzu – a rampantly growing invasive vine found in the South. The kudzu infections are of concern because kudzu is an alternate host on which SBR can overwinter and serve as a reservoir for infections that could spread to soybeans. A United States map with the scouting locations and SBR detection locations can be found at http://www.sbrusa.net/

The Michigan sentinel plots are located in Berrien, Cass, St. Joseph, Hillsdale, Lenawee, Monroe, Van Buren, Calhoun, Jackson, Washtenaw, Eaton, Ingham, St. Clair, Saginaw, Tuscola, and Sanilac counties. The scouting is being done by 12 Extension educators with field crops area of expertise.

In the last week six soybean samples have been submitted to MSU Diagnostic Services and tested for SBR. Two samples came from sentinel plots. All six samples tested negative for SBR using real time PCR technique. The diseases found on the leaves were Septoria brown spot and bacterial blight, both common diseases found on soybeans in Michigan.

Following is the compilation of the 15 scouting reports submitted between June 22 and 29.

Growth stage: ranged from V4 to R1.

Plant height: ranged from 7 to 18 inches.

Degree of canopy closure: ranged from 20-95 percent.

Soybean diseases present: Diseases were indicated on 13 reports. Brown spot was predominate (12 reports) with bacterial blight and Phytophthora stem canker each indicated twice.

Soybean insects present: Soybean aphids were indicated in nine of the reports. Quantities ranged from less that 1 per leaf up to 0-100 per leaf.

No Asian soybean rust was found in any of the sentinel plots.

MSU Diagnostic Services reports the following pests and problems found on field crop samples submitted in the last week:

Soybeans – In addition to the Septoria brown spot and bacterial blight diseases mentioned above, samples were submitted with herbicide injury, poor root development due to soil compaction, and mealybug.

Sugar beets – Severe bacterial leaf spot (Pseudomonas syringae pv. aptata) on two sugar beets samples.

The following article is from the June 9 , 2005 Field Crop CAT Alert.

Soybean rust still has only been found on volunteer soybeans in a single county in Georgia and on kudzu in four counties in Florida. Scouting for soybean rust continues in states south of Michigan, and if found would trigger intense scouting of soybean sentinel plots planted throughout Michigan.

There has been some suggestion by members of the chemical industry sales community that spraying fungicides for soybean rust should begin in Michigan when the disease is found in soybeans as far south as Louisiana. This is not true and would be a waste of money and time. Due to the intense monitoring for soybean rust throughout the United States, Michigan soybean growers will have sufficient warning to apply fungicides in a timely manner and not before the disease has appeared in northern Ohio and Indiana.

The following article is from the June 9 , 2005 Field Crop CAT Alert.

The Extension Plant Science, Econ and Ag Engineering specialists at South Dakota State University recently collaborated to produce an eight-page publication on Asian soybean rust. It also includes a section on soybean aphid.

To download a copy of the publication in pdf, visit:
http://agbiopubs.sdstate.edu/pub_description.cfm?Item=ABS20

The following article is from the June 2 , 2005 Field Crop CAT Alert.

Soybean rust still has only been found on volunteer soybeans in a single county in Georgia, and on kudzu in four counties in Florida. Scouting for soybean rust continues in states south of Michigan, and if found would trigger intense scouting of soybean sentinel plots planted throughout Michigan.

The following article is from the May 12, 2005 Field Crop CAT Alert.

Soybean rust (SBR) has only been found on kudzu in four counties in Florida and on volunteer soybeans in one county in Georgia. Growers should be developing an action plan for the possibility that rust will move into Michigan this summer. However, no specific actions are recommended at this time. Refer to the April 21 issue of the Field Crops CAT Alert for more information.

 As a reminder, daily updates on the movement of SBR can be found at:
http://www.sbrusa.net/. Forecasts for the movement of SBR can be found at:
http://www.ces.ncsu.edu/depts/pp/soybeanrust/

The following article is from the May 5, 2005 Field Crop CAT Alert.

Soybean rust has been found on volunteer soybean in Georgia. The disease is spreading slowly, so please check back in future Field Crop CAT Alerts for updates, or check the web site at: http://www.usda.gov/soybeanrust

The following article is from the April 21, 2005 Field Crop CAT Alert.

Ohio State University has a web site with links to just about every site anyone would need to keep them informed about the movement of soybean rust in the United States, predictions for movements, and a current list of available fungicides (http://www.oardc.ohio-state.edu/ohiofieldcropdisease).

The web site along with the following list for general information will provide most growers and Extension agents with the information they need to keep informed about soybean rust in the United States.

Also, daily updates on the movement of SBR can be found at http://www.sbrusa.net/. Forecasts for the movement of SBR can be found at http://www.ces.ncsu.edu/depts/pp/soybeanrust/.

A good site for soybean rust information is at www.ncpdn.org, which has links to other soybean rust sites of interest. If you go to this site, use the links on the left side of the page to go to first detectors, and then follow the link to Michigan. This site has two recent power point presentations on soybean rust, including one on fungicide use.

Another good source of information on soybean rust is: http://www.plantmanagementnetwork.org/infocenter/topic/soybeanrust/.

Farm Radio Network is a good resource for rapidly emerging events.

Growers should not change planting practices or varieties this year.

Early stages of rust are difficult to identify and distinguish from other soybean leaf diseases. Growers should rely on a person who has received training in the identification of SBR.

Wait for official confirmation of SBR from MSU Extension before applying any fungicides for SBR control. Applying fungicides too early could mean the difference between one and two applications. Other resources would be Ohio State University, Purdue University and the University of Illinois. They should be able to give Michigan an idea of how fast rust is moving north.

Most states are recommending a strobiluron (Headline, Quadris), a Triazole (ie Folicur, Domark, Bumper, Laredo, Propimax, Tilt) or a premix (Quilt, Stratego) for the first application. A strictly preventative spray such as a strobiluron applied by itself must be applied before the rust exceeds 2% of the leaf area in the lower canopy. Earlier is better, but not before rust in imminent. Too early, and the fungicide will not provide enough protection for later growth stages, possibly resulting in a need for a second fungicide spray. If rust exceeds 2% leaf area infection in the lower canopy, then apply either a triazole or a premix. Don’t let the rust move into the mid- and upper canopies before applying a control. Timing of the first fungicide application is critical to good control. More information on fungicides available for rust control can be found at: http://www.ca.uky.edu/agcollege/plantpathology/PPAExten/SoybeanRust.htm.

Soybean rust will not survive the Michigan or Midwest winters, it moves up from the south every year.

Be sure to know how to qualify for crop insurance payments.

Don’t panic, keep informed, and use official web sites and MSU Extension notifications for making your decisions, especially this first year when we don’t know what to expect from this disease.

Scouting

General information

The following article is from the April 7, 2005 Field Crop CAT Alert.

With all the talk about soybean rust in the last few months, I’d like to switch from the glass being half empty to the glass being half full. Although rust may cost producers time and money over the next few seasons, it may also encourage people to take soybean pest management more seriously. Since the discovery of rust in the United States, producers have started to think seriously about scouting, spray timing, and application methods in soybean. So in an odd way, rust may make a positive impact on soybean aphid management. There are at least four important similarities between rust control and aphid management.

Scouting
The threat of rust has lead to an increased interest in scouting beans, as well as funding of sentinel plots sampled by MDA inspectors and university Extension agents. Recommendations for soybean aphid management already include a scouting plan and an action threshold for treatment – the trick is getting out to fields frequently enough to catch aphid populations as they increase towards the threshold. Scouting for rust and soybean aphid can be done at the same time, so the more times someone is in a field to scout for rust, the more opportunities there are to look for aphids.

Timing
Given that rust will have to move from the southern United States up to Michigan, and then find favorable environmental conditions (such as high humidity) to infect soybean, July and August will likely be the critical scouting and application window. This coincides nicely with the timing of aphid populations going over threshold in Michigan, which occurred between mid-July and mid-August in 2001 and 2003. The current action threshold for soybean aphid (250 aphids per plant) is recommended in beans in the late vegetative stage up to early R6, a similar spray window recommended for rust fungicides. Thus, the timing and plant stage at treatment may be similar for rust and aphids.

Tank mixes
Given a similarity in spray timing and application method, tank mixes of fungicides and insecticides may be economical. This at least would save the cost of going over the field a second time.

Bottom line? Many of the techniques being recommended to maximize rust control will also improve aphid management in soybean.

The following article is from the April 7, 2005 Field Crop CAT Alert.

With the confirmation of Asian soybean rust (SBR) in the Southern United States last November, there has been much speculation, hand-wringing, and even fear mongering as to its potential affect on United States soybean production this year. The main source of this anxiety is that we simply do not know how the disease will behave here, both in terms of severity and incidence. Much of the speculation on how the disease will progress in the United States is based on the experience of the disease progression in Brazil, where SBR was first confirmed in 2001. However, the environmental conditions in Brazil are very different from those found in the United States soybean-growing areas and care should be taken in basing recommendations on Brazilian experiences. However, there are some generalizations we can make from the experience that other parts of the world, including Brazil, have had with SBR.

From a management perspective of SBR, the Brazilians often refer to three basic pillars:
1)      Correct fungicide application timing
2)      Product (fungicide) efficacy
3)      Application quality

Following are generalizations of these management “pillars” that may have applicability in Michigan.

If and when the disease progresses north towards Michigan, the frequency of scouting should increase to several times per week. SBR is aggressive once infection occurs and conditions are mild and moist. Be diligent in scouting for it, both in fields and on disease progression charts. The threshold for treating is zero for protective fungicides, and low (10% of leaves with lesions or less) for curative fungicides. Therefore, the decision to pull the protective fungicide application trigger is made when scouting (website disease progression charts and field-based) show the disease appearing in your countywide geographic area. The most likely time for SBR to arrive in Michigan will be between flowering and pod fill. On the flip side, you do not want to pull the fungicide application trigger too soon either. Fungicides have a limited active period on the leaf depending upon the weather, so you do not want to apply too early and miss the infection period entirely. Scouting and watching the national disease progression maps will be critical to ensure correct fungicide application timing.

Product efficacy
Until we have United States- and Michigan-based fungicide efficacy trials it will be somewhat speculative to make fungicide recommendations. The main products available will be from the strobulurin or triazole chemical families. Strobulurins are protective only, whereas triazoles are primarily considered curative. (Please see the March 1 Cat Alert issue and the above mentioned website portal for a more detailed summary on fungicides.) Again, due to the aggressive nature of SBR, it is likely that by the time you scout lesions in your field, it is too late for a protective fungicide alone and you will likely need curative and protective properties in a fungicide for maximum yield protection. This will likely lead to premix products or tank-mixes of strobulurins and triazoles, and indeed this type of application has become very common in Brazil. Michigan State University Extension is working with the Michigan Department of Agriculture in developing an easy to use SBR fungicide reference chart. The chart will be completed once the Section 18, special use permits are obtained for the 2005 growing season and will be made readily available to growers throughout the state.

Application quality
Penetration of the fungicide to the lower leaves of the soybean canopy is important since the disease appears first in the lower canopy. To achieve maximum canopy coverage and penetration, medium droplet size, relatively high carrier volumes (20 to 25 gpa) and high pressures (see nozzle manufacturers suggested pressure to achieve medium droplet size at the indicated carrier volume) are recommended. Be sure to check manufacturer specifications to ensure that your sprayer pump has the capacity to deliver the pressure and volume required for your nozzles and boom width. There is general agreement that optimum canopy coverage and penetration can be obtained with the double configuration of flat fan nozzles (twin jets). A detailed discussion on nozzle selection for fungicide application can be found in the March 1 Cat Alert issue, referenced above. Given the necessity to spray immediately once SBR is confirmed in your area, it is important to have your sprayer equipped and field-ready on a moment’s notice.

The following article is from the April 7, 2005 Field Crop CAT Alert.

In addition to soybeans, there are a number of forage legumes, beans, weeds and ornamental plants in Michigan that could potentially serve as hosts of Asian soybean rust (Phakopsora pachyrhizi). Worldwide, there are more than 30 species of legumes reported to be hosts of soybean rust in nature and more than 60 species when considering successful inoculation under greenhouse conditions. Many of these host plants are not found in Michigan. For this reason, a list was compiled of plants in Michigan that could be infected with soybean rust (Table 1).

Kudzu (Pueraria lobata) is a weedy legume that infests roadsides, fencerows, abandoned fields and non-crop areas throughout the southeastern United States. It has been described as the “vine that ate the south” because of its aggressive, climbing and trailing habit. Kudzu is a susceptible host of Phakopsora pachyrhizi. Due to the prevalence and location of kudzu, it is believed that this weed will serve as a continual source of soybean rust inoculum for southern soybean growers. The good thing – kudzu is not believed to exist in Michigan.

There are occasions when only a plant genus is listed in Table 1. In these cases, there is not sufficient information on the potential host range of soybean rust in the United States. Keep in mind that other potential soybean rust hosts could be species in the same genera as those listed in
Table 1.

It is our goal to make this host list as complete as possible. If you are aware of other “legumes” or “beans” grown in Michigan fields or greenhouses, please contact Steve Gower at 517-432-9693 or sgower@msu.edu

The following article is from the March 1, 2005 Field Crop CAT Alert.

In November 2004 soybean rust was identified on soybeans in at least nine states in the southern United States. It is expected to overwinter on alternate hosts in the southern United States, primarily kudzu, and spread to the Midwest in 2005 (http://www.aphis.usda.gov/ppq/ep/soybean_rust/index.html). The rapid spread of soybean rust and the potential for severe yield losses makes this the most destructive foliar disease of soybean in the United States.

Asian soybean rust, Phakopsora pachyrhizi, significantly reduces yields in Asia, Africa, and South America. In areas where the pathogen commonly occurs, yield losses up to 80 percent have been reported (http://www.apsnet.org/online/feature/rust/). The pathogen had been limited to the Eastern hemisphere until it was found in Hawaii in 1994. Since then, the distribution of P. pachyrhizi includes Africa, Asia, Australia, South America and Hawaii. There has never been a soybean disease in the United States with the potential economic destructive power as soybean rust. Soybean rust will have a major impact on both total soybean production and production costs in the United States and Michigan. A conservative prediction indicated yield losses greater than 10 percent in nearly all the United States soybean growing areas with losses up to 50 percent in the Mississippi Delta and southeastern coastal states. These estimates are for large geographic areas – individual fields would vary from 0 to 80 percent losses. These estimates do not include the cost of fungicides and applications.

Resistant or tolerant soybean varieties are not available, nor likely to be available in the near future, making management with fungicides the only viable option available to growers. The Michigan Department of Agriculture applied and has received approval for at least five fungicides under the Section 18 Quarantine Emergency Exemptions. Application timing will be critical. The first fungicide applications should be made shortly before the rust is expected or immediately after soybean rust symptoms are evident. Unfortunately, identifying soybean rust is difficult in the early stages because of similarity to several other common diseases occurring at the same time. In Brazil, identifying soybean rust early continues to be a challenge for growers. However, after my recent trip to Brazil I think this can be accomplished with proper training

What nobody knows is how soon or how fast the soybean rust will move north this spring and summer. Soybeans are planted in southern states in March and April, and in Michigan, most soybean plantings occur during late May and early June. Even under the most optimum conditions it is unlikely that soybean rust would move into Michigan before the middle of July. But at this point no one really knows what is going to happen or when. The best defense against soybean rust is keeping informed about the problem, so that if it does arrive in Michigan in 2005, we will be prepared. It is important to remember that soybean rust may not make it to Michigan in 2005, or it could come in so late that it does not become an economic problem. For these reasons, growers should follow their normal agronomic practices for soybeans. This is especially true when it comes to buying fungicides. Chemical companies are assuring us that we will have more than adequate supplies of fungicides available for Michigan in 2005, and early stock piling is not necessary.

Detailed information on soybean rust, including alternate host crops, how and where the pathogen overwinters, and the current status of the disease in the United States can be found at http://www.ncpdn.org/.

Click on “first detectors” (See navigation bar on the left of the screen.) and then on Michigan to find links to Power Point presentations on soybean rust. Information on fungicides available for soybean rust, our current state of knowledge on the best way to manage soybean rust with fungicides, and links to other important sites can be found here.

Plant pathologists around the country and at Michigan State University are gearing up so that we will be prepared to deal with soybean rust on a national and regional scale. In 2005, the Field Crops CAT Alert publication will provide weekly updates on the soybean rust situation in the United States and what it means for Michigan. By April, web sites will be up and running that will predict when and where soybean rust will occur. Other sites will provide information on where soybean rust has actually occurred. As the addresses for these sites become available the Field Crop CAT Alert will make this information available, in addition to posting the information at http://www.ncpdn.org/

A manual on fungicide management of soybean rust has been put together by plant pathologists in the North Central Region, and will be available as a hard copy and on the web in the very near future. This rather long document will be reduced to an easy-to-read two to four page bulletin. More information on soybean rust can also be found at the Michigan Farm Bureau, and the Michigan Soybean Promotion Committee web sites. During the coming month Michigan State University will continue to prepare materials that will assist growers in making management decisions related to soybean rust. Michigan State University will also be continuing with research and extension activities over the summer.

The following article is from the March 1, 2005 Field Crop CAT Alert.

The confirmation of Asian soybean rust in the continental United States last fall has elicited a flurry of activity by researchers, regulators and producers. While no one knows how rapidly the disease will spread nor how significant an effect it will have on crop growth and yield, climatic conditions during the much of the growing season in Michigan are suitable for the disease to develop should inoculum arrive in Michigan. Currently, the only method available to control the disease is through the application of foliar fungicides.

Soybean rust fungicides may be classified either as preventative (protective) or curative (eradicant). Preventative fungicides such as the strobulurins (azoxystrobin, pyraclostrobin, trifloxystrobin) and chlorothalonil have the ability to prevent the fungus from infecting plant tissue or to stop spore germination on the plant surface. Protective fungicides must be applied prior to infection, and their efficacy depends upon the plant foliage being adequately coated by the fungicide. Curative fungicides have the ability to inhibit or stop the development of established infections by limiting the reproductive potential of the soybean rust fungus. Curative fungicides, most of which are classified as triazole fungicides, include propaconazole, tebuconazole, tetraconazole and myclobutanil. Curative fungicides are effective if soybean rust is present at low levels in the field, but have little effect if the soybean rust is firmly established in the field.

Soybean rust infects the lower leaves of the soybean plant first. If not controlled, the disease will proceed to infect upper leaves, causing premature leaf death and defoliation of the plant. To prevent the fungus from infecting the plant or to control the disease while it is present only at low levels, it is critical that the fungicides reach the lower canopy and coat as much of the plant foliage as possible. This will require different application techniques than those used for most herbicide applications. We will consider three main factors: spray volume, spray nozzles and spray pressure.

Both aerial and ground applications of fungicides have been effective at controlling soybean rust. However, higher volumes of water must be applied with fungicides than with most herbicides. Aerial applications of soybean rust fungicides should be in a minimum of 5 gal/A, and ground applications in a minimum of 15-20 gal/A. This is about double the rate used for most herbicides, but the extra water helps to insure complete coverage of the plant canopy.

The current recommendation is to select nozzles that will produce a medium-size droplet at the spray volume, pressure and speed you will be using. If the droplet is too fine, it will not penetrate the canopy and may drift. A droplet that is too coarse will penetrate the canopy, but not cover the leaf surface completely. Twin jet, hollow cones and flat fan nozzles are acceptable for fungicide application. However, fungicide deposition trials in peanuts showed that TurboDrop and twin jet nozzles penetrated the peanut canopy more than hollow cones and flat fan nozzles. With twin jet/TurboDrop nozzles two streams are emitted from the nozzle, one at a slight angle forward and the second at a slight angle backwards. It is believed that this spray angle disturbs the upper canopy, enabling the spray to penetrate to the lower parts of the canopy more effectively.

When it is indicated on the label, fungicide labels recommend setting spray pressures at 35 to 40 psi. Some nozzle manufacturers are recommending spray pressures of 60 to 120 psi. As the applicator it will be important that you set the pressure high enough to ensure good canopy penetration, but not so high that the droplet size becomes too small. Nozzle manufacturers can provide information that will help you to determine the proper speed, pressure and nozzle size to maintain medium-size droplets for the nozzles you select.

Good pesticide application practices are critical for effective fungicide application. As a reminder, inspect your sprayers to make sure all the nozzles are the same and replace nozzles that show excessive wear. Calibrate your sprayer to make sure that you are able to accurately apply a uniform amount of product across the field.

And finally, be safe. Stay tuned for more information on soybean rust and fungicides in future CAT Alerts.