C.O.R.N. Newsletter 2005-39

Soybean Aphid Prediction for 2006 and Insecticide Seed Treatments

Authors: Ron Hammond, Bruce Eisley

Researchers throughout the Midwest recently met to thrash out the soybean aphid situation this past year, and make predictions for 2006. There are two topics of concern for Ohio growers that can be discussed. The first is what might happen in 2006. Based on limited adult flight during September and October in Michigan and eastern Indiana, we are predicting that soybean aphids will NOT be a problem, at least in Ohio, in 2006. The low number of winged adults collected the past few months is similar to 2003, which was followed by the low soybean aphid year of 2004. Thus, for Ohio, we feel that the 2-year cycle of a high year followed by a low year will continue. We should point out that this prediction is only for Ohio, and is just that, a prediction. We will still need to monitor soybeans closely for the aphid next year, and react if populations begin to increase.

Why is this information important at this time, and how does this relate to seed treatments? There are two commercially applied seed treatments labeled for control of soybean aphid, Cruiser and Gaucho. We had plots this past summer at numerous locations throughout Ohio, including at OARDC research stations and on on-farm sites. The research suggests two things related to control of the aphid. The first finding is, although we placed all the studies at sites that had soybean aphid problems in 2003, only half of them had soybean aphids reach densities that suggested control was necessary. Put another way, half of the sites did not need any type of treatment; seed treatments would have been unnecessary. The second finding is that at those sites where aphids reached threshold numbers of at least 250 aphids per plant, all the plots including the seed treatment reached it, and then went well above threshold. The seed treatments were not able to keep aphids below the economic threshold, and all needed a foliar treatment.

Based on these observations and findings, we do NOT recommend seed treatment for soybean aphid control. First, it is too hard to predict which fields might have soybean aphids. Second, because our prediction is for a low soybean aphid year, we do not expect aphid numbers to reach economic levels in Ohio. Third, even if they do, our research (along with data from other Midwestern states) indicates that seed treatments do not offer long-term management of this pest. We will still recommend scouting and treating with a foliar material if and when the threshold of 250 aphids per plant is reached.

Additionally, these seed treatments are labeled for the bean leaf beetle. These same studies showed that seed treatments will control overwintered adult populations in late May and June, greatly lowering the amount of beetle leaf feeding. However, control of the first and second generation in mid and late summer, respectively, was NOT achieved. Whether control of the overwintered adult population will result in lowering the transmission of bean pod mottle virus is still unclear. However, those growers who choose to control the beetle to reduce bean pod mottle virus, especially those seed and food grade producers concerned with seed quality, might consider a seed treatment to help reduce early season feeding. We would point out that the best management for virus control, taken from recommendations out of Iowa State University, is to control both the overwintered population and the first generation population in July.

This is not to say that seed treatments do not have other places in pest management. Our studies indicate that they do control certain soil insects. In our tests in Ohio, we found that these seed treatments do an excellent job preventing stand loss and subsequent yield loss from seedcorn maggot. However, seedcorn maggots are only a problem when a green living crop, such as a cover crop, an old alfalfa field, or perhaps significant weed growth, is incorporating into the soil in the spring. Research over the past 20 years shows that no-till does NOT increase seedcorn maggot problems.

Northern Corn Rootworm Extended Diapause in Ohio

Authors: Alan Sundermeier, Ron Hammond

In July of 2004, a Wood County, Ohio, first year corn field was found to be heavily infested with adult northern corn rootworms (NCR)http://ohioline.osu.edu/icm-fact/images/38.html. Sticky traps placed on corn plants removed on August 16, 2004 averaged 5.5 NCR /trap/day compared to 1.1 per trap/day with western corn rootworms (WCR)http://ohioline.osu.edu/icm-fact/images/39.html. Research was conducted in 2005 on the same field to better determine the rootworm problem.

Northern corn rootworm extended diapause may be occurring in this field. Previous crop rotation had corn rotated with soybeans. Most rootworm larvae hatching during the soybean season fail to survive due to lack of food. However in extended diapause, the majority of northern rootworm larvae will wait to hatch until the second year and survive in that year’s corn, passing the trait on to the next generation. This problem, only with the northern rootworm, has been occurring in Iowa, Minnesota, and South Dakota.

To analyze the amount of rootworm pressure and differentiate between western corn rootworms and northern rootworms, part of the same field in Wood County was planted to second year corn. Adult emergence traps were placed in July, 2005 by removing five feet of corn stalks and placing a metal housing over the row. Escape holes in the housing allowed emerging adult rootworm beetles to be trapped in jars lined with tanglefoot. Trap jars were counted twice weekly during emergence. Yellow sticky traps were placed in surrounding corn plants to catch flying rootworm beetles. Also, corn roots were dug, inspected, and rated for corn rootworm damage.

Results of 2005 soil trap counts:
July 18: WCR-0.5, NCR-0.7
July 22: WCR-2.7, NCR-1.3
July 26: WCR-4.1, NCR-1.1
August 2: WCR-1.2, NCR-0.2
August 9: WCR-0.3, NCR-0.1.

Results of 2005 sticky traps placed in corn plot as number of beetles/trap/day:
August 2: WCR- 11.4, NCR- 3.1
August 9: WCR- 10.1, NCR- 2.3.

Results of root ratings were 2.5 on the Iowa 1 – 6 scale. These ratings were taken from 48 samples in the plot area. No corn lodging was observed in the plot area. In 2005, this plot did not have significant rootworm damage. The NCR was not the dominant type, opposite of what was observed in 2004. At this time we cannot accurately determine if extended diapause is present at this site. Research will continue in 2006 to better analyze this situation.
Growers should scout corn fields and note the number of NCR versus WCR present to determine if extended diapause may be occurring in their fields.

Agriculture Fall/Winter Outlook & Policy Meetings

The economic outlook and related policy concerns for agriculture are the focus of the recently announced series of OSU Policy & Outlook Meetings set to begin in December. This year's program includes traditional outlook discussions on grain, livestock, input costs, policy and consumer factors effecting Ohio agriculture. Details on locations, topics and background material are all available through the OSU Policy & Outlook Program website (http://aede.osu.edu/programs/outlook). A direct link to currently scheduled meetings is at http://aede.osu.edu/programs/outlook/2005-06schedule.html.

It’s Not Too Late to Spray Those Winter Annuals and Dandelions

Despite last week’s and the current cold spell, winter annual weeds can still be effectively controlled with herbicides. Unlike summer annual weed species in the spring, winter annual weed species grow more actively at temperatures near freezing. As long as leaf tissues are green and rigid on winter annuals, simple perennials such as dandelion, and biennials, herbicides can effectively control these species. However, when the leaves of dandelions turn purple, control is usually reduced compared to spraying dandelions with green leaves during warm weather. Based upon last week’s cold spell and the current forecast, effective control of Canada thistle may not be possible. However, we do not know that for sure. If the leaf tissues are still green and rigid some control may be possible.

Ohio State University researchers have applied herbicides in December after cold spells and obtained effective control of winter annual species. As long as soils are not frozen for an extended period of time and the spray mixture is capable of reaching the weeds, it is better to make an herbicide application this fall to control winter annual, biennial, and simple perennial species than to wait until the spring, especially for dandelion.

Statistics and Agricultural Research, Why Statistical Analysis Matters

Authors: Robert Mullen

When a state Extension specialist or Extension educator makes a presentation, the individual will occasionally make reference to “statistical significance” or some variant that alludes to statistical analysis and its use in determining treatment differences. So what is meant by statistical significance? Why should a producer, consultant, or retailer care about statistics? Can the average of treatment effects be used alone to evaluate differences? These are often asked questions that need clarification. Over the next several CORN Newsletters, we will attempt to explain why researchers use statistics as a tool, why statistics are useful and necessary, and why split field unreplicated information is difficult to draw conclusions from.

Useful Terms

Observation– a measurement that is made for some output(s) of interest (yield, plant stand, nutrient status, disease incidence, insect infestation, etc.).

Treatment– controlled input factor applied to an experimental plot (seeding rate, fertilization rate, insecticide application, fungicide application, etc.) that will hypothetically have an impact on an output(s) of interest. Obviously multiple treatments are needed to conduct a well-designed experiment.

Error – deviation of a measurement from the true value (usually caused by variation in the measuring device being used or uncontrolled factors that affect the measurement directly).

Experimental error –differences in observations from treatments due to environmental conditions that can not be controlled by the experimenter (differences in soil texture, topography, soil compaction, rainfall, nutrient status, disease infestation, etc.).

Statistics 101

Any observation made within an experiment has a certain amount of error associated with it. In fact, there is error associated with any measurement. Statistics allows us to quantify and assess this error. If only a single observation is made can you get an estimate of error? Some would argue this point with a complicated mathematical model, but for the sake of argument we will agree that a single observation will not provide an estimate of error. In order to estimate the error of an observation, multiple observations need to be made. We call these multiple observations replications. Replication allows us to estimate the experimental error associated with the observations that are being made (and evaluation of the tools we are using to measure the observation). In a field experiment, the observations can be confounded with a multitude of soil and environmental factors therefore we must replicate the treatments across the landscape. To ensure the estimates of experimental error for each treatment are unbiased (not systematically influenced by underlying environmental conditions (i.e. soil type, topography, etc.)), the replications should be randomly placed within the field. We have just discovered the two most important things (in our humble estimation) in statistics – 1) to estimate the experimental error of treatments requires replication and 2) to ensure an unbiased estimate of experimental error requires randomization of the treatments.

Statistical Significance

This is often mentioned but seldom explained in an extension venue. When an experiment is conducted (properly replicated and randomized), the experimental error (average variance within treatment observations) is computed and used to assess whether or not treatments differ “significantly” from one another. Statistics is based on probability, and researchers select what level of probability constitutes significance. The probability level selected is solely at the discretion of the researcher. The scientific community general prefers a probability level of 95%. So a researcher can state with 95% probability that one treatment is different from another. If the 95% probability criterion is met, then the treatments are “significantly” different. This is where some gray area enters into research, what is the appropriate probability level? Each researcher has their own set of criteria. The next time you hear a speaker discussing some research data, think about what level of probability is being used to evaluate treatment differences.

Statistics is a tool that allows researchers to assess the error associated with conducting an experiment and to separate real treatment differences from differences caused by uncontrollable environmental factors. Researchers can separate the grain from the chaff as it were. Like any tool, it must be used properly to be effective (replication and randomization). Statistics is not a hard and fast science. It does require some direction from the researcher conducting the experiment.

In the next CORN Newsletter article, we will continue our discussion on statistics and look at some actual data.

Ohio Corn and Soybean Performance Trials Available

The Ohio Corn and Soybean Hybrid/Variety Performance Trials are now available in Adobe Acrobat (pdf) format. The Corn Trial can be found at https://agcrops.osu.edu/research/OCPT%202005%20DATA.pdf. The Soybean Trials can be found at https://agcrops.osu.edu/research/2005%20OSPT%20DATA.pdf. The searchable website that many have found useful in past years will soon be available. To access this data base you can check for posted information at http://www.ag.ohio-state.edu/~perf/ or look for further announcements in the next CORN newsletter.