Sclerotinia Stem Rot (White Mold) Beginning to Show Up
Sclerotinia stem rot is beginning to show up in a few fields in northern Ohio. This is very surprising due to the hot, dry conditions that occurred across the state during flowering. As I recall, there were heat indexes of over 100 F as we took stand counts and as we talked about the lack of canopy closure in many areas of the state. We pulled some weather data from August, and there was a cold spell, with 70 F during the nights of the first week of August with some light rains. The fields where we are spotting white mold are also those fields that had very high incidence during 2009. They were planted to corn last year. We need another week to see if the fields are as badly affected as in 2009 and if the affected fields stretch as far south as they did in 2009. Based on observations from fields last week, we saw a few lesions on the main stems on a few plants, while the majority of plants had lesions further up the plant or on side branches. Lesions that are on the lower part of the main stem have the greatest impact on yield as the whole plant is killed. Lesions on the upper stem, tend to be slower to develop and do not reduce yields to the same extent. But some losses will undoubtedly occur.
Symptoms of Sclerotinia are quite striking. There will be dead plants standing straight above the canopy. The leaves start off with a gray-green color and wilt. When you open the canopy you will see white cottony growth of the fungus on the affected area. Sclerotinia will produce hard-black structures that resemble rat droppings. These will fall onto the soil during harvest and provide inoculums for the next soybean crop. It is important to note the fields that have white mold now, and mark those fields. Save these to harvest last. This will avoid contaminating more fields as combines will move sclerotia from field to field.
There is an excellent new publication on white mold from the North Central Soybean Research Program’s Plant Health Initiative http://www.planthealth.info/whitemold_basics.htm. You can download it from the website.
Tips for Evaluating Corn Hybrid Demonstration Plots
This is the time of year when many farmers visit and evaluate hybrid demonstration plots planted by seed companies and county Extension personnel, among others. When checking out these plots, it’s important to keep in mind their relative value and limitations. The much later than normal corn plantings in 2011 may result in hybrid performance and responses to various to treatments (e.g. seeding rate, fertilizer rates) that are not be representative of a typical growing season - when crops are planted much earlier.
Demonstration plots may be useful in providing information on certain hybrid traits, especially those that are usually not reported in state corn performance summaries. The following are some hybrid characteristics to consider while checking out hybrid demo plots.
PLANT/EAR HEIGHT. Corn reaches it maximum plant height soon after tasseling occurs. Remember that although a big tall hybrid may have a lot of "eye appeal," it may also be more prone to stalk lodging in the fall. Unless your interest is primarily silage production, increasing plant height should not be a major concern. Generally later maturity hybrids are taller than earlier maturity hybrids. Big ears placed head high on a plant translate to a high center of gravity, predisposing a plant to potential lodging. The negative effects of stalk rot on stalk lodging in the fall may be worsened by high ear placement. Plots that have been subjected to early season (V7 or earlier) defoliation caused by hail or frost often have lower than normal ear height.
STALK SIZE. Generally speaking, a thicker stalk is preferable to a thinner one in terms of overall stalk strength and resistance to stalk lodging. As you inspect a test plot, you will see distinct differences among hybrids for stalk diameter. However, also check that the hybrids are planted at similar populations. As population increases stalk diameter generally decreases. Also keep in mind that uneven emergence and development, which affected many corn fields this year, may make such comparisons difficult because late emerging plants are “spindlier”.
DISEASES. During the grain fill period, leaf diseases can cause serious yield reductions and predispose corn to stalk rot and lodging problems at maturity. Ear rots can also impact yield and grain quality. The onset of leaf death shortly after pollination can be devastating to potential yield, since maximum photosynthetic leaf surface is needed to optimize grain yield. Hybrids can vary considerably in their ability to resist infection by these diseases. Demonstration plots provide an excellent opportunity to compare differences among hybrids to disease problems that have only occurred on a localized basis. Look for differences in resistance to northern corn leaf blight, gray leaf spot, and diplodia ear rot. Symptoms of these diseases and others are available online at the OSU Field Crop Disease Website (http://oardc.osu.edu/ohiofieldcropdisease/t01_pageview2/Home.htm)
Check to see if foliar fungicides have been applied and what crop rotation has been followed. Typically you’ll encounter more severe foliar disease problems in no-till, continuous corn.
STALK ROTS. Hybrids will likely differ widely when faced with strong stalk rot pressure. Begin checking plants in late August or about 6 weeks after pollination by pinching lower stalk internodes with your thumb and forefinger. Stalks that collapse easily are a sure indicator of stalk rot. Remember that hybrids with thicker stalks may be in plots having thin stands.
LODGING. Perhaps as important as stalk rot resistance is the stalk strength characteristics of a hybrid. Sometimes, superior stalk strength will limit the adverse effects of stalk rot. If your variety plot is affected by stalk rot in late August and early September, evaluate stalk lodging of the different hybrids. Most agronomists characterize plants with stalks broken below the ear as ‘stalk lodged’ plants. In contrast, corn stalks leaning 30 degrees or more from the center are generally described as ‘root lodged’ plants; broken stalks are usually not involved. Root lodging can occur as early as the mid-to- late vegetative stages (as it did this year) and as late as harvest maturity. Both stalk and root lodging can be affected by hybrid susceptibility, environmental stress (drought), insect and disease injury.
Root lodging may be associated with western corn rootworm injury. However, much root lodging in Ohio occurs as the result of other factors, i.e. when a hybrid susceptible to root lodging is hit by a severe windstorm, like those we experienced in mid-July. A hybrid may be particularly sensitive to root lodging yet very resistant to stalk lodging. A cornfield may exhibit extensive root lodging in July but show little or no evidence of root lodging at harvest maturity in September (except for a slight “goose necking” at the base of the plant). This year some of our plots were subjected to more than one wind storm that caused root lodging. Some hybrids showed less recovery following the second wind storm, especially when plant populations exceeded 34-35,000 plants/A.
TRANSGENIC TRAITS: Because damage from European corn borer (ECB) and western corn rootworm (RW) can be very localized, strip plot demonstrations may be one of the best ways to assess the advantages of ECB Bt and RW Bt corns. The potential benefit of the ECB Bt trait is likely to be most evident in plots planted very early or very late; the potential benefit of the RW Bt trait is likely to be most evident in plots planted following corn or in a field where the first year western corn rootworm variant is present.
HUSK COVERAGE/EAR ANGLE. Hybrids will vary for completeness of husk coverage on the ear as well as tightness of the husk leaves around the ear. Ears protrude from the husk leaves are susceptible to insect and bird feeding. Husks that remain tight around the ear delay field drydown of the grain. Hybrids with upright ears are often associated with short shanks that may be more prone to ear and kernel rots than those ears that point down after maturity. This relationship received considerable attention in 2009 when Gibberella ear rot problems were widespread across the Eastern Corn Belt. However, we’ve observed that differences in ear “orientation” among hybrids can be strongly influenced by growing season and plant density. Also, under certain environmental conditions, some hybrids are more prone to drop ears, a major problem if harvesting is delayed.
The following are some additional points to consider during your plot evaluations:
1. Field variability alone can easily account for differences of 10 to 50 bushels per acre. Be extremely wary of strip plots that are not replicated, or only have "check" or "tester" hybrids inserted between every 5 to 10 hybrids. The best test plots are replicated (with all hybrids replicated at least three times).
2. Don't put much stock in results from ONE LOCATION AND ONE YEAR, even if the trial is well run and reliable. This is especially important this year given the tremendous variability in growing conditions (e.g. planting dates) and crop performance across the state. Don't overemphasize results from ONE TYPE OF TRIAL. Use data and observations from university trials, local demonstration plots, and then your own on-farm trials to look for consistent trends.
3. Initial appearances can be deceiving, especially visual assessments! Use field days to make careful observations and ask questions, but reserve decisions concerning hybrid selection until you've seen performance results.
4. Walk into plots and check plant populations. Hybrids with large ears or two ears/plant may have thin stands.
5. Break ears in two to check relative kernel development of different hybrids. Use kernel milk line development to compare relative maturity of hybrids if hybrids have not yet reached black layer. Hybrids that look most healthy and green may be more immature than others. Don't confuse good late season plant health ("stay green") with late maturity.
6. Differences in standability will not show up until later in the season and/or until after a windstorm. Pinch or split the lower stalk to see whether the stalk pith is beginning to rot.
7. Visual observations of kernel set, ear-tip fill, ear length, number of kernel rows and kernel depth, etc. may provide some approximate basis for comparisons among hybrids but may not indicate much about actual yield potential. This year we’ve seen differences in tip kernel abortion (“tip dieback” or “tip-back”) among hybrids and heard reports of “zipper ears” (missing kernel rows). Even if corn ear tips are not filled completely, due to poor pollination or kernel abortion, yield potential may not be affected significantly, if at all, because the numbers of kernels per row may still be above normal.
8. Find out if the seed treatments (seed applied fungicides and insecticides) applied varied among hybrids planted, e.g. were the hybrids treated with the same seed applied insecticide at the same rate? Differences in treatments may affect final stand and injury caused by insects and diseases.
Diagnostic Stops at the Farm Science Review
As you read this you are on the way out the door to the Ohio State University Farm Science Review being held this week, September 20, 21 & 22, near London, Ohio at the Molly Caren Ag Center. The review is at the intersection of US 40 and SR 38. On your way out the door you remember that unknown weed down by the creek, or the weird shaped corn ear you saved from last fall, or that strange bug on the tomatoes. All these and more can be delivered to the OSU Extension professionals at the Review.
Where to take that specimen?
Horticulture and home gardening insects and disease specimens – go to the Utsinger Gardens, right in the center of the FSR grounds at OSU central. Pick up a program at the gate and head on over. Look for the OSU Master Gardeners.
That weird weed or strange corn ear – take those to the Agronomic Crops Team demonstration plot area and ask an agronomist to take a look. The agronomy plots are between the public parking lot and Gate C – the main entrance to the show.
Have a hay or pasture question – you can ask the Forages Team also in the tent at the agronomy plots near Gate C.
And if you have a wildlife, fish, or conservation planting question – then head up to the Gwynne Conservation Area and visit with all the varied specialists there from Ohio State, Purdue, and the Department of Natural Resources.
Certified Crop Advisors – CEUS are available at several places around the Review, all three days: http://go.osu.edu/2011FSRCCA.
For a map and more see: http://fsr.osu.edu.
Fall Scouting for Soybean Weed Management
As soybeans approach maturity now is the time to evaluate this year’s herbicide program. Weeds that escaped 2011’s herbicides are currently setting seed which will be the source of problems in subsequent years. Most weeds are still green with leaves and seed heads attached so they are very easy to identify. Proper identification of weeds that survived this year’s program will allow selection of herbicides for next year’s crop and for future planning in that particular field. Also be sure to look below the canopy to see what weeds have emerged this fall.
There are several reasons that weeds are not managed by an herbicide program. The first is timing of application as it relates to weed size and weed lifecycle. Herbicide labels list the weeds controlled and the average size of weeds for various herbicide rates. For example the Roundup Powermax label lists the maximum height for control of giant ragweed at 12 inches for the 22 oz rate. Allowing ragweed to exceed this height reduces the efficacy of the herbicide, so escapes are more likely to happen. Increasing the rate of glyphosate can help increase control, but a better option is to apply the herbicide when weeds are smaller.
Application timing can also occur to early and miss certain weeds that are late emergers. Weeds like waterhemp and morningglory can emerge well into July and August, past the time of most POST herbicide applications. There isn’t much to do about late emergers unless a residual herbicide is included with the POST. There are very few herbicides labeled for this purpose and they are very limited in the number of weeds they control. One example would be to include Warrant with a POST application to control pigweeds.
The second reason for weed escapes is an herbicide program that is not comprehensive enough. With the advent of Roundup Ready production systems, farmers shifted to a single application of glyphosate. However, certain weeds like marestail can survive a postemergence application of glyphosate. Marestail management requires a spring herbicide application with a strong burndown combination and a residual herbicide with activity against marestail.
The third reason weeds can escape an herbicide program is resistance. In Ohio many weeds are resistant to both glyphosate and ALS-inhibiting herbicides. This list includes marestail, giant ragweed, and common ragweed. Other weeds like waterhemp and common lambsquarters are showing less susceptibility to glyphosate. A shift from a single application of glyphosate to a PRE + POST program can reduce the impact of herbicide resistant weeds on crop yields. Adding a PRE with several modes of action and another herbicide mode of action to the POST can greatly improve control of resistant weeds. For example adding a PPO inhibitor like Flexstar, Cobra, or Phoenix to a POST program can control glyphosate-resistant giant ragweed and waterhemp. However, utilizing a contact herbicide like a PPO or Ignite often comes with shorter weed height limits and different application methods. Be sure to read the label.
Understanding what weeds made it through this year’s program and why they survived will help increase weed control next year. Extra time this fall can also add money to your pocket next fall. Dr. Mark Loux’s research showed a 16 bushel increase from proper management of marestail in soybeans. That is $210 extra dollars in your pocket at today’s prices. While you are out scouting fields keep an eye out for your local extension educator. We will be out doing our annual fall weed survey and seeing what weeds made it through this year’s herbicide program. The last few surveys have shown that in most counties marestail, giant ragweed, and volunteer corn make up the top three weeds that survive until fall. For more information on what to look for in the field Dr. Vince Davis, Weed Management Specialist for Univ. of Wisc. has a three part series on fall scouting. Part I, Part II, Part III. Also when making plans for weed management be sure to consult the Ohio and Indiana Weed Control Guide available from the Agronomic Crops website at https://agcrops.osu.edu under publications.
The best chance of rain the next two week is Monday Sept. 19, with most locations getting 0.25 to 0.50 inches with isolated totals mostly south of 0.75 to 1.00 inches. A few more showers may occur around Wednesday. Otherwise expect mostly dry conditions this week with high pressure. Temperatures will be close to normal.
Next week there will be a few weak weather systems with a few chances for light rain. Overall, nothing out of the normal for this time of year. Temperatures will remain near normal.
For the next two weeks expect near normal temperatures and near normal rainfall. Normal for a 2 week period is 1-1.5 inches. Expect 0.75 to 1.5 inches.
The chances for any widespread freeze or frost events are slim for the next two weeks. Most lows will be in the 40s and 50s.
If we see any significant frost or freeze, we will let you know.
- Glen Arnold (Nutrient Management Field Specialist),
- Nathan Douridas (FSR Farm Manager),
- David Dugan (Adams, Brown, Highland),
- Mike Gastier (Huron),
- Greg LaBarge (Agronomy Field Specialist),
- Mark Loux (Weed Science),
- Pierce Paul (Plant Pathology)
- Anne Dorrance (Plant Pathologist-Soybeans),
- Peter Thomison (Corn Production),
- Harold Watters, CPAg/CCA (Agronomy Field Specialist),
- Mark Loux (Weed Science),
- Justin Petrosino (Darke),
- Jim Noel (NOAA/NWS)