Resistance to Strobiliurin Fungicides

Today (20 October), a report out of the University of Illinois confirmed that a field in Tennessee where frogeye leaf spot was found and sprayed twice with a strobilurin fungicide but still had high levels of the disease was because the pathogen that causes the disease (Cercospora sojina) was resistant to the fungicide. This finding was based on laboratory assays that examined the sensitivity of the isolate obtained from the field in Tennessee with baseline isolates and compared against active ingredients like azoyxstrobin, pyraclostrobin, and trifloxystrobin. These are the active ingredients that are found in fungicides such as Quadris, Headline, and Stratego.

What does this mean for Wisconsin? Most importantly, this serves as a very important reminder that the use of fungicides should be done based on several factors, including knowledge of the variety planted and if there is resistance to the targeted diseases of interest, followed by active scouting during the growing season to assess if conditions would warrant a fungicide application. Misuse or overuse of a foliar fungicide can increase the risk for resistance. Specifically for frogeye leaf spot in 2010, we did see symptoms in many fields, but severity was low on average. However, this is the sort of information that should be used to build a working knowledge of the specific diseases that may affect production fields in order to most effectively build a long-term management program.

Based on our data from Wisconsin over the past several years, in the majority of situations a foliar fungicide was not found to be needed and would have been an additional cost to production.

Combine and Tractor Fires . . . A Burning Problem

Combine and tractor fires cause over $20 million in property losses each year and millions more because of lost time and downed crops during the busy harvest season. Fires not only cause huge losses and waste time . . . they also cause 40 or 50 serious injuries each year, and occasionally a person is killed because of a farm machinery fire. As we move into harvest remember there are two keys to preventing series machinery or life loss.

1. Prevention
2. Preparation in case a fire does break out.

Machinery Fire Prevention

For a fire to occur, three things must be present: air, a material to burn, and a heat source. Since it is impossible to eliminate air around a farm machine we must focus on keeping the machine clean of possible fire-causing materials and eliminating all possible sources of heat that could lead to a fire.

Cleanliness and Maintenance

Begin every harvest season with a clean machine. Pay special attention to the engine and engine compartment, since about 75% of all machinery fires start in that area. Use a pressure washer to remove all caked-on grease, oil, and crop residue. A clean engine will run cooler, operate more efficiently, and greatly reduce your chance for fire.After starting the season, make sure you frequently blow any dry chaff, leaves, and other material off the machine with compressed air. Also, clear off any wrapped plant materials on bearings, belts, and other moving parts.Pay close attention to your machine operator's manual and follow all instructions and schedules for lubrication and routine maintenance. If you notice any leaking fuel or oil hoses, fittings, or metal lines, make sure to replace or repair them immediately!

Eliminate Heat Sources

Combine and tractor fires can be caused by several heat sources. The most common is exhaust system surfaces that contact any flammable material. Make sure your exhaust system including the manifold, muffler, and turbocharger are in good condition and free of leaks.When checking your oil and performing other daily maintenance, quickly scan any exposed electrical wiring for damage or signs of deterioration. Replace any worn or malfunctioning electrical component with proper parts from your dealer. If you are blowing fuses, or have a circuit that intermittently cuts out, it's a good sign that there's a short or loose connection in the system. The arcing electrical wires on a farm machine will generate extremely high temperatures.Also keep an eye out for worn bearings, belts, and chains. A badly worn bearing can glow red-hot. Any rubber belt subjected to intense heat from a worn part can burst into flames.

Being Prepared

Despite your best intentions and good maintenance, a fire on a tractor or combine can still occur. Your best source of protection for a combine is at least one fully charged ten-pound ABC dry chemical fire extinguisher. A five-pound unit is recommended for tractors. Select only extinguishers with an Underwriter's Laboratory approval. Having two extinguishers on the machine is even better in case one malfunctions or loses pressure. Keep one mounted in the cab, and one where it can be reached from the ground.Check your extinguishers periodically, paying special attention to the pressure gauge. To function effectively, the gauge must show adequate pressure to expel the powder inside.Extinguishers should also be checked periodically by someone from your local fire department or insurance company. Any extinguisher that has been even partially discharged must be fully recharged before it's used again. During even a brief discharge, the tiny dry chemical particles will create a small gap in the internal seal of the extinguisher valve. This tiny opening will cause any remaining pressure to leak out in a few hours or days.

What If I Have A Fire?

If a fire does break out on a machine you're operating, quickly shut off the engine, grab your extinguisher, get out, and get help. If you forget to grab the extinguisher, don't go back in after it unless the fire is extremely small or confined to an area well away from the cab.Having a cellular phone or two-way radio nearby will help get professional assistance to the field more quickly.Approach any fire with extreme caution. Even a small fire can flare up dramatically as you open doors, hatches, or other areas to gain access. These types of fires are especially dangerous when liquid fuels are involved. If possible, use the extinguisher's flexible hose to shoot the chemical from a safe distance at the base of any flames you see. Continue to blanket flames to allow the fire to cool and prevent a reflash. Remember that it may not be possible to put out every fire. If it is in a difficult-to-reach area or seems out of control DON"T RISK the chance of injury or even DEATH....wait for help to arrive.

Post Authored by John Shutske at jshutske@cals.wisc.edu

Assessing hail damage in mature soybeans

Significant yield loss can occur when hail events strike mature soybeans (Image 1). One such event occurred this past week in Dane County. Though the damage was relatively isolated to a few fields we measured yield losses nearing 7.5 bushels per acre. If you run into similar hail events this fall below is an equation to help you estimate the possible damage to your field. If you believe significant yield loss did occur to your field remember to call your hail adjuster before you combine.

Image 1. Shattered soybeans.

To estimate soybean yield losses from seed that has fallen on the ground:

1. Select several random areas of the field
   
2. Use a hoop or other device of known size to delineate an area and count the number of seeds in that have fallen to the ground in that area
   
3. After counting the seeds that have fallen, use the following formula to calculate the yield loss:
   

Estimated yield loss (bu/a) = ((#of seeds on ground/average seed number per pound)/60 lbs. per bu)/((3.14 x radius x radius of hoop in ft.)/43,560 sq. ft per acre)

For example:

A 3' diameter hoop was used to determine soybean losses after a hailstorm (Image 2). An average of 220 seeds were counted inside the hoop:

((220 seeds/3000 seeds per pound)/60 lbs. per bu)/((3.14 x 1.5' x 1.5')/43,560 sq. ft per acre) = ~7.5 bushel per acre yield los

Image 2. 3' Diameter Hula Hoop

This will determine your pre-harvest losses. Any losses from the harvesting operation will be in addition to this.

Current Statewide Findings for SDS and BSR

With additional reports of sudden death syndrome (SDS) in soybean fields including areas of the state we have not previously detected SDS, we are receiving increased numbers of questions if we have detected brown stem rot (BSR) as well in these fields. First off, not every field will have SDS as we have seen several other diseases in 2010 that might have similar looking symptoms to SDS or BSR. One of the general things we are noting, however, is the following sort of statement: "we are seeing yellow patches in some of the fields." Given our own observations from research trials both on our UW research farms as well as our on-farm locations, when you see the yellow patch, stop and take a closer look at the symptoms.

In regards to the question about BSR, to date, the samples we have received into the Field Crops Plant Pathology lab and tested have had only SDS. We use a molecular approach to our diagnostics to differentiate SDS from BSR and the results have been very clear when examining these samples. As an additional piece of information, we are also working to isolate the respective pathogen(s). We will continue to monitor the situation for both diseases as the season progresses. Lastly, we want to emphasize that if you have a positive field for SDS take a soil sample to look for the presence of Soybean cyst nematode.

Get Your Wheat Seed Order in Early

Local cash and futures prices topping $6.10 and $7.00 per bushel, respectively coupled with the strong likelihood of early corn and soybean harvest have many growers considering winter wheat in 2010. Seed availability of elite varieties will begin to tighten so it is imperative to get your seed orders in early. To date, all of the wheat seed samples that have come into the Wisconsin Crop Improvement Association have been blue tag certified (>85% germ). This is good news to growers as certain areas of the state had difficulties with harvest and sprouting. It is still premature however to fully know the total amount of certified wheat seed from the 2010 crop available for planting in 2010. I strongly caution growers from planting bin run seed in 2010 given the sprouting issues and low test weights, both of which can negatively impact germination, tillering, and overwintering.

Reports of Frogeye Leaf Spot in Soybean

Over the past week, we have had reports of Frogeye leaf spot in soybean. Frogeye leaf spot is caused by the fungus Cercospora sojina. DATCP noted finds of this disease in some fields in the southern part of the state. While Frogeye leaf spot has been documented in Wisconsin, it is still a disease that for many is a relative unknown. As you scout soybean fields late in the growing season, symptoms of Frogeye leaf spot can be recognized as angular, brown to reddish brown spots that are irregularly shaped and have a light brown to gray center. While lesions on stems and pod can occur later in the season they are less common and distinctive than lesions on the leaves. If there are pod infections, seeds near those lesions can be infected and develop conspcuous light to dark gray or brown areas.

Why 2010? The prolonged warmer, more humid and rainy periods we have seen this year are very favorable to development of this disease. Management recommendations for Frogeye Leaf Spot include the use of resistant soybean varieties, crop rotation that is 2 years or longer (the pathogen overwinters in soybean debris). Foliar fungicides can be effective for control of this disease, but timing of application is important.

For more information about Frogeye Leaf Spot, there are several good fact sheets like:

http://www.ces.purdue.edu/extmedia/BP/BP-131-W.pdf

http://www.soydiseases.illinois.edu/index.cfm?category=diseases&disease=119

http://www.planthealth.info/frogeye_basics.htm

Late Season Stem Diseases - Look Closely...

We are receiving questions and also samples this year that are similar to fields we visited during the 2007 and 2008 growing seasons. As a reminder, the focus for many of those field visits were specifically if there was a breakdown in the Rps 1K gene for Phytophthora. A summary of that information is available here.

Similar to those two years, samples we have looked at this year have not necessarily been typical and it has not been easy to identify a primary disease of interest (i.e., the primary cause). Samples submitted to the Plant Disease Diagnostic Clinic have often yielded evidence of multiple pathogen species in a given sample. Recent results from the Wisconsin DATCP Phytophthora root rot survey of 45 fields between 16 June and 9 July indicated presence of Phytophthora in 15 fields (33%), which was an increase from the previous two years (20% in 2008 and 18% in 2009, respectively). In spite of the increase, the results still indicate that it is important to make sure you have a proper diagnosis of suspect soybean plants. Two diseases that can often be confused during the later stages of soybean development are Northern stem canker and Phytophtora. Below are a description of the two diseases and associated symptoms/signs:

Northern stem canker (Diaporthe phaseolorum var. caulivora): reddish brown to black discoloration on stems and petioles that can first appear around flowering. Lesions originate at the nodes and appear sunken and may girdle the stem. There can be a yellow and brown discoloration of leaves around the veins and plant death is associated with petiole and leaf retention.

Phytophthora stem and root rot (focus is on symptoms after V4): brown to black lesion that extends above and below the soil surface. A root rot can be found. Leaves turn yellow and petioles will droop. Wilting where tip of the plant forms a shephard's hook. Plant death associated with petiole and leaf retention.

For further information about soybean diseases, please consult Soyhealth.

For a field diagnostic guide of common soybean diseases in Wisconsin, please click here.