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C.O.R.N. Newsletter : 2014-27
WHITE MOLD OR SCLEROTINIA STEM ROT IS HEREAuthor(s): Anne Dorrance
This disease is caused by the fungus, Sclerotinia sclerotiorum and it is favored by cool damp conditions. Remember those morning fogs this summer and the fact that you hardly used your air conditioner? Perfect conditions for infection. This fungus forms hard black irregular shaped bodies called sclerotia. (photo of sclerotia inside stem) They are actually a mass of hyphae and if you break them open they will be pink inside. They can be mistaken for mice or rat droppings as well, the inside is a different color! When the conditions are cool and the canopy is closed, this fungus produces a very small mushroom (photo). This usually occurs during flowering and the spores then land on the dead flowers. This provides a perfect point of entry. This fungus produces oxalic acid – which degrades the tissue as it colonizes the plant. The infections that you see now occurred 2 to 4 weeks ago. Symptoms from the road will look like standing plants with a gray-green appearance. Eventually these plants will lodge. Once the leaves fall off – the plants will stand back up to some extent.
Some things to keep in mind:
1. There is nothing to spray at this time to stop the infection. The plants that have stem lesions will die and that yield will be lost. The plants that lodge on top of one another, we have seen the mycelium keep colonizing the upper stems – “plant-to-plant”. But overall this will be minimal. Again, nothing can be sprayed on the plants at this time.
2. It takes at least 20% incidence to begin to measure yield loss. We have had several trials out over the past several years, we can measure differences in disease severity/incidence – but in all cases we could not measure yield loss as we were at 15 to 20% incidence.
3. Not all fields have inoculum – there must be sclerotia in the field from a previous crop to have Sclerotinia develop – so farmers should note this field as they will now have this “forever”.
4. Make note of the variety – and remove this from the list. There are more resistant varieties out there, but this year was VERY conducive for infection and I expect that some moderately resistant varieties are going to have a tough time. As I like to say, it is a good year to get data and some of these varieties will be dumped.
5. Plan to harvest these fields last. The reason is the sclerotia, they will get everywhere in those combines and then become introduced into more fields. Let’s keep the spread to a minimum.
6. After harvest, practice no-till. The sclerotia that are left on the surface will degrade more quickly than those that are buried.
7. For severely infested fields, we have tried fall applications of a biocontrol fungus called Contans. Interestingly, in subsequent years, we did not observe white mold developing – but I can’t be certain it was from the Contans or the fact that the environment was not favorable in the years that followed or if the varieties were more resistant. So I am sharing the information but not backing the practice.
8. Practice good weed management. This fungus has a very wide host range including many weeds, alfalfa, and other legumes. So best to plan for wheat or corn for the next crop.
9. Choose varieties with better resistance levels.
SOYBEAN APHID UPDATE FOR 2014Author(s): Andy Michel
For the most part, soybean aphids have been a problem only in odd numbered years. Several other states have broken this two-year cycle, but it has held in Ohio for over 10 years. Recently, we have been noticing the presence of soybean aphids in soybean, mostly in the northern and central part of the state. While the majority of fields have extremely low numbers, a few fields have reached 75-100 aphids per plant. Usually, in even numbered years, non-economic soybean aphid populations are found in soybean—these aphids will provide the migratory populations needed to overwinter on buckthorn and form populations the following year. Additionally, natural enemies such as lady beetles have already responded and are in many of these fields (photo). Keep in mind, the economic threshold to manage soybean aphid is a rising population of at least 250 aphids per plant. While the expectation is that soybean aphid populations will remain under threshold, growers should keep a watchful eye on their fields, especially in late planted soybean fields that may take some time before reaching the R6 stage (when the soybean aphid economic threshold can be increased).
WARMER WEATHER AHEAD
The weather pattern has been modifying some the last several weeks to not as wet overall. We will monitor this trend but all indications are near normal rainfall can be expected the next 4 weeks. At the same time, it appears the much cooler than normal weather the last six weeks will trend toward a "slightly" warmer than normal period for the next 4 weeks. It will be mainly the night-time lows which will cause the above normal conditions. Normal highs now are in the upper 70s to lower 80s with normal lows in upper 50s to lower 60s.
The latest NOAA/NWS/Ohio River Forecast Center 16-day rainfall outlook of an average of weather models can be view at:
The next update will take a look at autumn 2014 frost and freeze risk.
BLUE MOLD IN TOBACCO
The first report that I have heard about blue mold in tobacco this year and it is just on the Kentucky side of the Ohio River. It was first reported in Lewis County on Friday (Aug. 15) but was not confirmed on Friday. On Monday morning (August 18) the Mason Co. Extension Agent also found what he believed to be blue mold in a patch. This was found in a patch that has been topped and sprayed for nearly a week. However, from talking to Dr. Bob Pearce, University of Kentucky Tobacco Specialist, the belief is that the lesions are probably nearly two weeks old, so it has been there a while and it is now confirmed.
The weather patterns have been swirling with low fronts. Most likely this is not just a Mason and Lewis County KY issue. More than likely we can expect that spores have spread throughout Southern Ohio Counties, too. The weather conditions on Monday (August 18) are ideal for blue mold to thrive. Tobacco that has been topped and sprayed with a MH product for sucker control for at least 10 days will probably see very little damage. However, tobacco that has not been topped, or topped in the past few days could have damage. It is recommended that these later crops be sprayed to prevent or reduce the issues with blue mold. If Quadris has been applied recently for the prevention of Target Spot, you have provided the crop with some protection. Depending on the amount of time since the Quadris application and the current stage of the crop, another application may need to be made. Keep in mind, another product should be used between any two applications of Quadris according to the label.
Crop Observation and Recommendation Network
C.O.R.N. Newsletter is a summary of crop observations, related information, and appropriate recommendations for Ohio crop producers and industry. C.O.R.N. Newsletter is produced by the Ohio State University Extension Agronomy Team, state specialists at The Ohio State University and the Ohio Agricultural Research and Development Center (OARDC). C.O.R.N. Newsletter questions are directed to Extension and OARDC state specialists and associates at Ohio State.
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