We have attached the most recent edition of Sangamon-Menard Extension’s “Crop Update” for your use.

In This Issue:

• SPORES: A CAUTIONARY TALE – Suzanne Bissonnette, IPM Educator
• WHAT DOES DENNIS MEAN FOR RUST? Reviewing the facts for insight.
• NITRATE TOXICITY CONCERNS – David Fischer, Animal Systems Educator

SPORES: A CAUTIONARY TALE – Suzanne Bissonnette, U of I Extension
Been reading the Ag press for the latest soybean rust information? Been checking the official USDA website that gives information on rust spread and individual state information on their scouting observations? Been wondering what one actually means when a Plant Pathologist says ‘there are rust spores in a spore trap’?

Some background in fungal identification is needed to correctly interpret such observations. The word ‘rust’ refers to a huge family of fungi that infect plants. There are many hundreds of “rust” species that infect green plants. For example, some fungal rust species infect corn, some infect wheat, some infect hollyhocks, Etc. The list goes on and on. Fungi in the rust family have numerous microscopic features that look similar and they thus are organized into the rust family for purposes of identification by a mycologist or plant pathologist. Next, you need to carefully read or listen to what was actually said or written. If a Plant Pathologist says “there are rust spores in a spore trap in my state” it only means that spores that look like they are in the rust family are in the trap. Any rust spores (not just soybean rust spores) could be in there. If the Plant Pathologist says “there are soybean rust spores in a spore trap in my state,” that statement is an indication that the spores have been identified microscopically by an individual trained in rust taxonomy and properly identified as one of the species of soybean rust.

Even then, the identification process is not over. Remember there are 2 species of soybean rust, a severe one Phakopsora packyrhizi (Asian soybean rust), and a mild one P. meibomiae of little concern. Lab tests, based on proteins on the outside of the rust spores, must be done to differentiate between the two known soybean rust species. Before firing up the sprayer, be certain the information in hand is from a reliable site and that the rust species is actually Asian soybean rust not one of the innumerable other rust species floating in the air at any given time. You will save yourself time, money and will be a good steward by getting the right information before reacting.

WHAT DOES DENNIS MEAN FOR RUST?
Hurricane Dennis brought some needed rain to much of Illinois, but as it moved north, producers began to ask the inevitable question “did it bring soybean rust with it?” Bluntly stated, “no one knows” the answer. Those claiming that we are “on the verge” of rust and those claiming that we are “safe” from rust, speculate at best.

QUESTION: Did Dennis pass over an area declared “positive” for soybean rust?

ANSWER: Yes, the “center” of hurricane Dennis did pass over Baldwin County, Alabama, which was declared positive for Asian soybean rust (in a monitored sentinel plot) last month. HOWEVER:

• Soybean rust has not been confirmed (as of July 13th) in any other Alabama counties. (Note: one additional field was noted just one mile north of the sentinel plot on July 14th in the same county)
• Neither has soybean rust been found (as of July 13th) in any of Alabama’s other monitored soybean fields (nearly 25 soybean fields are monitored weekly throughout that state).
• Neither has soybean rust been found in any of the dozen-monitored kudzu “patches” in that state (also monitored weekly).

Soybean rust has only been confirmed in one of the two “southern most” counties that make up Alabama’s “boot heel.” In other words, the entire state of Alabama has apparently not yet been a “hot bed” for Asian soybean rust and may not yet have been a “hot bed” for widespread Asian soybean rust spore production. No one knows if “many” or “few” “Alabama born” spores were picked up and carried by this storm.

QUESTION: Could Dennis have picked up Asian soybean rust (ASR) spores from other “non-Alabama” locations?

ANSWER: If other “non-Alabama” locations displayed ASR, those locations may have provided spores that could be carried with the storm. HOWEVER:

• Soybean rust has not been confirmed within approximately 200 miles of the Alabama location. Nearly due east of Baldwin County, Alabama that site is located in Seminole County, Georgia.
• Soybean rust has not been confirmed west or north of the Alabama location.
• Outside of Alabama and Georgia, Asian soybean rust has only been confirmed in Florida (seven locations).

In other words, ASR, while prevalent has not been an “easy find” outside of Alabama. Once again, no one therefore knows if “many” or “few” spores were picked up from “extra-Alabama” locations.

QUESTION: If spores were brought into Illinois by this storm, could we see Asian soybean rust?

ANSWER: If ASR spores have been deposited in Illinois, our producers could experience soybean rust in coming weeks. HOWEVER:

• “ASR-like” spores (reference Dr. Bissonnette’s article above) were noted in one Louisiana-based trap almost three weeks ago. Yet as of July 13th, Asian soybean rust had not yet been confirmed in Louisiana.
• Even if “ASR-like” spores are confirmed in our area following this depression, confirmation of “ASR-like” spores is only a “part” of the overall story. Rust spores were confirmed in Kentucky and Tennessee traps “pre-Dennis” BUT those spores were only collected in one trap out of several traps monitored in each state. In other words, some spores were found but spore distribution in the state was very limited and the amount of material collected in those traps was also limited.
• ASR, like any other disease, not only requires inoculum (spores) to develop, but it also requires a suitable environment. Anyone care to “bet the farm” on the remainder of the season/next week being “prone to moisture?” In other words, we do not know if the environment will be conducive, in coming days, for this disease to “take hold” even if ASR spores get to Illinois.

SHORT STORY: Nobody knows what Dennis means for ASR in Illinois this year. While spores would be noteworthy, the presence of “rust-like” spores would not necessarily equal a coming problem with Asian Soybean Rust. Current conditions may “raise the eyebrows” over ASR, but no one can accurately predict or refute “ASR favorable” conditions in coming weeks. Producers are left with one option…namely vigilant scouting of soybean fields. Don’t panic, just scout, ask lots of questions, and watch for reliable updates regarding ASR progress.

NITRATE TOXICITY CONCERNS – David Fischer, U of I Extension.
We have received a number of producer calls on drought-stressed corn and sudan grass. In particular, we have had many questions related to nitrate poisoning concerns in livestock. Following adequate rainfall, the ability of the plant to convert nitrates to plant protein resumes and nitrate levels in the plant return to “more normal” levels in about 5 days.

However, drought-stressed corn, sorghum, and sudan grasses must be managed to avoid potential nitrate poisoning. Nitrate (NO3) interferes with the animal’s ability to carry oxygen in the blood. The nitrate afflicted animal dies from lack of oxygen and/or the fetus dies due to lack of oxygen. Following are helpful management tips to avoid nitrate problems:

• Do not graze or feed “green chop” corn or sudan grasses, especially within the first 5 days following rain. A good shower on droughty plants will cause plants to uptake soil nitrates quickly. One must allow at least 5 days for the nitrates to convert to plant proteins.
• Ensiling the corn or sudan grass as silage and allowing it to ferment for 3-4 weeks (before start feeding) can reduce NO3 by about 50 percent. Silage must be ensiled at the proper moisture (60 to 70 percent depending on storage structure) in order for proper fermentation and dissipation of NO3.
• I prefer ensiling versus baling since baling does not significantly reduce NO3. If drought damaged crops are baled or fed green chop it is extremely important to test feedstuffs for NO3 pre-feeding.
• Properly sample and test plants/hay/silages for NO3 before feeding. As a general rule, NO3 levels should be less than 0.44 percent, or 1000 ppm nitrate nitrogen to be without risk. Levels greater than 1.76 perecent NO3, or 4000 ppm should not be fed.
• Be careful of human exposure to silo gas. Even short-term breathing in of nitrogen dioxide gas (NO2) can injure the lungs and cause sudden death. This gas is detected by the bleach-like odor and visible reddish-brown haze. Since NO2 is heavier than air, it is seen at the base of the silo chute and on/at the silage surface. Always run the silo blower for 10-15 minutes before entering the upright silo to help ventilate the area and blow off the NO2.
• Nutritive value of drought-damaged corn or sudan grass will generally be about 70-80 percent of normal and can still be a good feed source when the diet is balanced with other energy and protein sources.
• If the producer is going to feed high NO3 feeds, they will need to know what level of NO3 is in the feedstuff and limit the amount fed per day. When fed with other safe feedstuffs, they will be able to dilute the total NO3 intake to acceptable levels. Avoid feeding high nitrate feeds to young calves and pregnant animals. Goal of NO3-N/ppm: <1000 ppm is safe; 1000 – 2000 ppm generally safe when fed with balanced diet and limit to 1/2 of total dry matter to pregnant animals and young calves; 2000 * 4000 ppm be cautious and limit dry matter intake to less than 1/3 of diet for non-pregnant animals (steers, open heifers); >4000 ppm potentially very toxic-do not feed.

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