Have Kentucky’s Corn Yields Become More Variable With Time?

J.H. Grove¹, E.M. Pena-Yewtukhiw², and A.A. Marchi³

            We often hear that Kentucky’s climate is quite variable. “If you don’t like today’s weather, just wait until tomorrow” is commonly said. But the current climate debate has serious implications for rainfed agriculture – corn, wheat and soybean need water to mitigate heat stress – and a changing climate could impact Kentucky’s air temperature, rainfall or both.

            There have been numerous statements that climate has become more variable, subject to more extreme events, statements made in the local restaurant, the university classroom, and over the home dinner table. Recently, a grower asked: Have Kentucky’s corn yields become more variable with time?” The answer to that question is: “It depends.” What follows is the answer to that question.

Economic and Policy Update

The 2012 March edition of the Economic and Policy Update written by faculty in the Department of Agricultural Economics is now available at:
http://www.ca.uky.edu/cmspubsclass/files/EconPolicyUpdateMarch%202012.pdf
The current edition provides articles on the following topics:
1) A Glimpse at the Upcoming 2012 USDA Prospective Plantings and Quarterly Grain Stocks Reports. By Cory Walters
2) Profitability Projections for Corn and Soybeans in 2012. By Greg Halich
3) Form 1099 - MISC Information Returns. By Jerry Pierce
4) Kentucky and the Economic Recovery. By Alison Davis
5) Understanding Year-to-Year Changes in the ACRE Guarantee. By Cory Walters

Historical updates can be found at: http://www.ca.uky.edu/agecon/index.php?p=209

March Weather is a Poor Indicator of Late Spring Freeze

Chad Lee, Extension Agronomist, University of Kentucky

With all of the warm weather there have been questions about whether there is any correlation between that warm weather and the last spring freeze event. The quick answer is No!

Tom Priddy, our meteorologist ran some numbers from Paducah and Lexington on the warmest months of March over the last 100 years or so. He ranked the top 23 warmest and then identified when the final freeze event occurred. For Paducah, the average was April 12, which is four days after the median freeze date for Paducah. In Lexington, it was April 16 which is one day after the median freeze date. For those 23 warmest March months, the range on final freeze was March 22 to May 27 in Paducah and April 3 to May 4 in Lexington. In only two years out of those listed for Paducah did the last spring freeze occur in March. For Lexington, the last spring freeze always occurred later than March.

Burndown Weed Control for Corn and Soybeans

Jim Martin and J.D. Green, Extension Weed Scientists, University of Kentucky

The status of weedy vegetation in corn and soybean fields ranges from very clean to very weedy. Burndown treatments applied last fall or during the last few weeks have created a clean seedbed. Burndown treatments that had a soil-residual herbicide look cleaner compared with those that did not have a soil-residual herbicide. This is especially true with marestail. However, do not expect these fields to remain clean for long since the warm temperatures will likely degrade soil-residual herbicides sooner than normal and allow weeds to emerge.

The amount of weedy vegetation in fields that have not yet received a burndown will vary depending on weeds present. With the warmer temperatures cool-season broadleaf weeds such as henbit, purple deadnettle, and common chickweed are maturing earlier than normal and will soon dieback and not likely to be a significant factor unless cooler weather conditions return. However, such weeds as marestail, giant ragweed, ryegrass, and volunteer wheat are growing well and need to be monitored. This may motivate growers to apply burndown treatments earlier than normal in order to manage weeds before they become too large.

2012 Armyworm Flights Earlier Than Normal.

UK-IPM pheromone baited traps for armyworm captured 49 moths for the week ending Friday Mar. 9th. This is the earliest capture date and the largest initial capture for this insect in 19 years of trapping. What this may tell us about the season is difficult to know at present. Nevertheless, it appears that if this weather trend continues we will see armyworm populations much earlier than we would normally expect.

Armyworms, (Mythimna unipuncta) also commonly called “True armyworm” prefers feeding on grasses and in Kentucky can be an early season pest of small grains , corn and occasionally forages grasses. Our concern this year may be that both the plants and the pests will appear earlier than we would normally expect. We will monitor the moth flights and compare them to past year’s captures to try and estimate the potential for a problem population.

At this point it is important to remember three points:

It is not the moths that cause damage. The moths appear first and after mating lay eggs that hatch into caterpillars. It is the caterpillars, feeding on the plants that causes the damage.

Comparing moth capture numbers with captures in past years that have resulted in known crop damage can give us an indication of what might happen in the current year.

Using a predictive model, we can roughly calculate when the caterpillar stage will appear by using the date of moth capture and calculating the development rate of the caterpillars using daily maximum and minimum temperatures.

At present it is too early to get really worried about this insect. We will need to look at the captures for several more weeks to understand if a trend is truly developing. Nevertheless, the early counts are larger and earlier than normal, are greater than the rolling 5-year average, and appear to be following the trend line for the 2006 outbreak year. If this continues I will begin running the model to predict the appearance of the damaging caterpillar stage.
At present it is sufficient to understand that something out of the ordinary is happening. We have plenty of time to figure out whether or not it is important.

Corn Planting this Spring

Chad Lee, Extension Agronomist, University of Kentucky

Young corn plant killed by freezing temperatures. 

The weather is warm, the soil is warm, the redbuds are blooming... it seems like we should be planting corn! Some producers have sprayed their burndown herbicides, which is a good thing this season considering how large weeds could get. Some have finished applying anhydrous ammonia, which is good because soil conditions are good. Now that these major tasks are done, all that is left is to plant corn. The fields are ready, but the calendar is not.



Last season, the rains came in early and stayed late. Every farmer was pushed to get corn planted at all, let alone in a timely fashion. Late plantings, especially on soybeans did better than "early"plantings last year. The calendar says late plantings hurt yields. This spring, something internally says that everything else is ready, let's plant some corn! The fresh memory of the previous planting season says let's plant some corn! But, the calendar says not to plant corn, yet.

Which Fertilizer Recommendation is Best?

Lloyd Murdock, Extension Soil Scientist, University of Kentucky

There are two concepts for making fertilizer recommendations. Both take the same soil test but they usually result in two very different fertilizer recommendations. One is the Sufficiency concept and the other is the Cation Saturation Ratio (CSR).

The Sufficiency concept is based on local or regional research on similar soil types that find a level of each plant nutrient resulting in maximum yield. When a soil test is below this Sufficiency level, crops respond to the addition of the nutrients.

The CSR was developed in the 1940’s to create an ideal balance of calcium (Ca), magnesium (Mg) and potassium (K) that would result in maximum crop yields.

Stripe Rust in Wheat: Time to Scout

Scientists in Arkansas are really sounding the alarm about the unusually early and extensive appearance of stripe rust in wheat. Based on our mild winter, it is very likely that stripe rust has overwintered in KY, too, but I do not know the extent. It is a very easy disease to identify and it would be prudent to scout your fields for the disease now. Scientists in AR are recommending (and I concur) that growers finding stripe rust at any level may want to add a fungicide to the mix as they go over the field to apply any early insecticide and/or herbicide sprays. Most modern fungicides are very effective against wheat rusts. The fungicide, tebuconazole (Folicur and generic products), is extremely effective against rust diseases and the cost is very low. This is one case where an early application of a fungicide could be helpful (assuming stripe rust is observed!).

Should Lime and Phosphorus be applied at the Same Time?

Lloyd Murdock, Extension Soils Management, University of Kentucky

No matter how phosphorus (P) is applied or when it is applied it will be tied up with something. A soil pH of 6.5 is the very best one can do to reduce this fixation of P. If fertilizer P is applied below a pH of 6.5, especially below 6.0, more of it will be tied up with aluminium and iron in the soil. So not applying lime would be bad also. If the pH is above 7 then more of the P will be tied up by calcium in the form of insoluble calcium phosphates (rock phosphate). So you cannot win either way. If you have a low pH, say in the high 5’s, and you apply lime and you add P also. You would have to get the soil pH where the lime is placed above 7 for much of this additional fixation to occur and it is going to be difficult for this to happen since you are starting at a low pH and lime is a rock and is only slowly soluble.

Bottom line is do not worry about P fixation and keep the soil pH about 6.5. Under the best of circumstances, you are only going to get about 30% of the P you apply in the crop. Very small differences in P fixation would happen with or without the lime.