Late Dry Weather is Hurting Corn and Soybean Yields

Chad Lee, Extension Agronomist, University of Kentucky

The USDA NASS lowered their estimates for Kentucky corn yields by 10 bushels per acre and soybean yields by 2 percent in their latest report. The negative numbers reflect calls and comments we are receiving from producers across the state.

In August, most of our corn and soybean fields looked great. The foliage was lush, canopies were closed and the crop looked to be in excellent condition. Now, farmers are getting surprised about low yields in some fields. Just to clarify, these reports do not reflect all fields. There are some really good yields being reported. But, there are some really bad yields as well and these fields were the surprise. I think the biggest contributor to these bad surprises is the weather. Most of Kentucky was wet early and dry late. The wet weather encouraged shallow root systems. The dry weather late penalized crops with shallow roots.

Watch for Mites in this Dry Weather!

Doug Johnson Extension Entomologist, University of Kentucky

At least one soybean field in the Jackson Purchase area has suffered from mite damage. The weather that we are now experiencing is what I would expect for mites to become a problem. There is no guarantee that mites will be a problem in any particular field, but dry (low humidity) weather and drought stressed plants increase the probability of a problem occurring.If you are in an area that has had sufficient rainfall you can probably ignore this warning.

More Is Not Better: Nitrogen, Corn and Dry Weather

John Grove, Professor of Agronomic Soil Science, University of Kentucky

The 2014 season has been dry in many places in Kentucky – corn in these areas not growing as well, or looking as good as desired. Many fields are showing less than optimal color and there have been several calls regarding possible need for more N to ‘green things up a bit’. Without evidence of substantial loss of fertilizer N applied earlier, additional N is not a good idea. Extra N (N above and beyond the recommendation) can do more harm than good – especially if the season stays dry.

The Worst Drought Since the Dust Bowl, but Where is the Dust?

Chad Lee, Extension Agronomist, University of Kentucky

The 2012 Drought left Kentucky corn in tatters, but the soil is mostly intact. 

The 2012 drought rivals the droughts of the 1930's, or the "Dust Bowl". But, there is one major difference in the drought of 2012... there's relatively no dust. I remember my grandfather talking about the Dust Bowl and saying that he couldn't see the sun for days. He lived in southeast Ohio, yet some of that soil he saw in the sky was from Nebraska, Kansas and Oklahoma. We certainly see a very different story today. While there have been reports of massive dust storms in Arizona and similar desert climates, there has been relatively no evidence of dust storms in the Midwest in 2012. So, if our 2012 drought is similar in size and intensity to those of the 1930's, what happened to the dust this time?

Know when to say when on corn yields

Chad Lee, Extension Agronomist, University of Kentucky

While many farmers have already given up on the corn crop this season, others are waiting a little longer. Identifying the success of pollination in a field can go a long way to determining whether or not to give up grain yield goals.

Figure 1. Pollination on this plant is completed
based on  the exposed stamens. A shake of
the tassel shows no evidence of additional pollen. 

Anthers fully exposed across the entire tassel indicates that pollination is nearly complete (Figure 1). Pollen release normally begins near the middle of the tassel and then upwards and downwards. If the plant is still pollinating, a gentle shake of the tassel should release some of the small pollen grains. If there are no pollen grains, then pollination is probably complete.

Brown silks on are an indication that pollination is complete as well (Figure 2). These indicators are important, because in many fields, pollen drop has occurred before silk emergence.

Gently cutting open the husks around the ear can reveal the silks and developing ear. Once pollen travels down the silk and fertilizes and ovule, the silks detach from the young kernel. A gentle shake of the ear will help you identify the amount of pollination that has occurred. As kernel development progresses, identifying pollination success becomes easier. Developing kernels are easy to see (Figures 3 and 4) while the blanks are easy to see as well. An ear where all almost all kernels are developing is evidence of excellent pollination (Figure 5).

Temperatures near 100 F can kill pollen. Since June 28, 2012, many corn fields in Kentucky, including the ones in these pictures, have experienced seven days above 100 F.  Pollen drop normally occurs for about a week or two. However, peak pollination is normally about the third day of pollen drop. Based on the ears in Figures 3 and 4, pollination was severely impaired by the high temperatures. In both of these cases, those ears represented less than half of the ears in the field. The other half had not released silks, yet. With pollination complete in those fields, that means that half of the ears will not be fertilized at all. In fields such as these, salvaging the crop as a silage is probably the best option. Be sure to check with your crop insurance agent before making any decision to cut the crop for silage. 

Drought Resources for 2012

Chad Lee, Extension Agronomist, University of Kentucky

We have put together a new website to house the 2012 drought information for corn and soybeans. This drought is widespread and we have included articles from other states as well as our resources here in Kentucky.

Websites that monitor the drought conditions and include some other information about weather are near the top of the page. Timely articles, including date published, from Kentucky are listed below the websites. Articles from other states come next. States as far north as Wisconsin are reporting drought concerns. Finally, there are some links to websites about irrigation and crop water use.

If you know of other resources that should be on this 2012 drought website, please let me know. Thanks.

2012 Drought Resources.

Drought Stress and Corn Pollination

Chad Lee, Extension Agronomist, University of Kentucky

Drought-stress corn in western Kentucky. Photo: June 25, 2012. 

Most of western Kentucky is in a severe drought status and that severity is likely to spread to central Kentucky on the next report. Most of the corn is going through tassel and pollination, which is well ahead of the five-year average, and the worst possible time to experience temperatures in the high 90's F (35 C or more). The high temperatures and low humidity dry out pollen and silks faster, both of which need moisture for successful fertilization of the ovules.

In addition to the need for moisture for pollination, the corn plant simply needs more water. Corn around tasseling and silking demands about 0.3 inches (7.7 mm) per day. Most of our fields were at a water deficit prior to tasseling and the water deficit is increasing. The lack of water could lead to the abortion of kernels.

Dry conditions prior to tasseling often result in the tassel emergence and pollen drop before silk emergence. In many cases, the resulting ears may have a few kernels develop near the base of the ear but very few to no kernels near the tip of the ear.

I Hate Crying Wolf…… But Forewarned is Forearmed !!

Doug Johnson, Extension Entomologist

Twospotted spider mites (TSSM) are an occasional pest of soybeans and corn in Kentucky (KY). They are present every year but only important during hot, dry periods. Unfortunately, this is the type of weather we currently have and have had for several months. Additionally, states to the north of us, including Nebraska and Iowa, are already experiencing some problems. I have not received information about spider mites on KY field crops but have seen some large populations in fruit trees (different mite but same circumstances). I, therefore, think it wise for those with field crops interest to keep an eye peeled for this pest.

Twospotted spider mites on soybean leaf
Photo: Frank Peairs, Colorado State Univ.,
 Bugwood.org

TSSM are greenish-white with two dark spots on the back. Adults are about the size of salt grains. Juvenile TSSM have six legs, but adults have eight legs. Other species of spider mites also attack field crops.

Spider mites become active early in the spring and remain active throughout the summer. They live in thinly webbed colonies on the underside of leaves. Occasionally, you will see web strands between leaves. Hot, dry weather allows rapid population growth with each generation taking about five to seven days to complete.

Infestations tend to start on field margins near broadleaf weeds and/or the side from which the wind is blowing, as they may drift on a breeze. They may then spread out in ever enlarging spots if the weather allows.

In corn, damage presents as yellow stippling on the upper surface of the leaves. Heavy and / or prolonged infestations may cause premature drying resulting in loss of tissue, stalk breakage and kernel shrinkage.

In soybean, injury could resemble herbicide damage, foliar disease or nutrient deficiency. Feeding results in tiny yellow spots or stipples which may turn orange. Multiple damaged spots may merge in to larger areas of damage. With severe damage, leaves may turn brown and eventually fall off. Spider mites reduce yields by causing pod shattering, wrinkled seed and early maturity.

Scouting is best done in times of prolonged hot, dry (low humidity) weather. In soybeans the most important time is during the reproductive stages of R1-R5 and where a synthetic pyrethroid insecticide has been used. Shake plants over a piece of white paper and look for tiny white moving specks. A hand lens is very useful in determining if the specks are actually mites. In corn, scouting is much more difficult and less is known about making a control decision. The mites are no harder to find, simply follow the instructions for soybean but using corn leaves. One simply wishes to determine if the infestation is only on the outer edges or is across the field.

Large and widespread, mite infestations usually happen when hot, dry and low humidity conditions have occurred early in the season (like this year!). In these circumstances, scouting should start well before R1 (soybean) and in younger corn. Cooler temperatures and high humidity allow a natural fungus to control spider mites. Rainfall will help the plant tolerate the infestation but will not reduce the mite population. Application of synthetic pyrethroid insecticides and fungicides may worsen the infestation because these insecticides don’t work well on mites and the fungicide may hamper the natural occurring fungus that kills the mites.

If direct control is required, consider using an organophosphate insecticide like chlorpyrifos or dimethoate. If you must use a pyrethroid consider bifenthrin. An application is warranted when most plants are infested with spider mites and leaf speckling and discoloration are apparent.

Reference: Field Crop Insects. Iowa State Univ. CES. CSI 0014. Jan. 2012

White Grub Damage Evident on Corn.

Doug Johnson, Extension Entomologist



White grubs; photo courtesy of Iowa State University.



Questions concerning corn root pruning by white grubs have surfaced across the state. A number of Ag. & Natural Resources agents have noticed typical damage and found white grubs in place, along with typically pruned roots. Certainly, given the drought status of most of our corn production area, it is within reason to believe that these grubs are placing an unusual stress on an already stressed crop.

Early white grub damage typically appears as stunted, wilted, discolored, or dead seedlings and/or as gaps in rows where plants fail to emerge. White grubs prune roots and can feed on the mesocotyl causing plant death. Obviously we are far past this early damage stage. In larger corn, grub feeding simply prunes the roots resulting in the reduced ability to move water and thus nutrients. The plants simply have an unthrifty look.

While there are some soil insecticides labeled for grub control, their control is somewhat erratic. These products must be applied before or at planting. No insecticides are recommended for rescue treatments. Even if soil applied rescues were available, we would likely need some rainfall to move the insecticide into the soil, especially in no-till. If we got the rain needed for that, we would have the rain we need for vigorous growth in the corn crop; which would likely outgrow the problem.

Consequently, even though one might be looking for a pesticide remedy for this problem, what we really need is rain. In the presence of rain the problem is likely to go away. In the absence of rain…… well the damage just will not matter.

When does soil get too dry for young corn?

Chad Lee and John Grove, Extension Agronomist and Agronomic Soil Scientist, University of Kentucky

Young corn seedlings require very little water. 

When does soil get too dry for young corn? Or, when will you know that the young corn seedlings will not make it? Variations of these questions have been coming in as the lack of rain continues and the temperatures rise on young corn plants. The quickest, and perhaps most practical answer, is to scout fields regularly and identify areas where plants are not recovering from drought stress. In other words, the best indicator of when the plants will not make it is when they have died.


A more technical answer is that a soil gets too dry when the ‘permanent wilting point’ is reached - the level of soil moisture at which plants will fail to recover(Taylor and Ashcroft, 1972, Physical Edaphology: Physics of Irrigated and Non-Irrigated Soils, Freeman and Co., San Francisco).
Most plants will display drought symptoms long before the permanent wilting point is reached. Most silt loam soils will reach the permanent wilting point around 8% moisture content (weight/weight), while a clay loam will reach the permanent wilting point around 10% moisture content (weight/weight).The permanent wilting point varies with temperature, compaction/structure/pore arrangement, and the resulting ability of the soil to conduct water.

Drought Expanding Across Kentucky - and Midwest

Chad Lee, Extension Agronomist, University of Kentucky

The dry weather is expanding across the state according to the drought monitor posted on Aug. 16, 2011. About 50 percent of the state - and 90 percent of the grain crops area - fall into the "Abnormally Dry" category. The map from a week earlier estimated that about 17 percent of the state was in the same category. Similar trends can be seen across the Midwest as well.

One of the Driest Years Ever in Kentucky

Tom Priddy, University of Kentucky Ag Weather Center

According to preliminary data, since August 1st through November 9, the state has only received 6.10 inches of rain, which is over 5 inches below normal. Some west and west-central locations are 9 to 10 inches below normal for that time period.

Here's the latest map of US Drought Monitor for Kentucky: http://www.drought.unl.edu/dm/DM_state.htm?KY,MW

Unless Kentucky receives some rain before the end of the month, this August 1 through November 9 is the second driest on record (over 110 years)...surpassed only by 1953 with 5.17 inches. (See driest Aug-Nov 10 years below). Notice some very important dry years in the list, such as 1930 (the granddaddy of droughts) and recently 2008, 1998 & 1999 in the top ten list.

Rank	Value*	Year
1	5.17	1953
2	6.62	1904
3	7.11	1908
4	7.24	2008
5	7.28	1963
6	7.29	1939
7	7.54	1943
8	7.93	1998
9	7.95	1930
10	8.43	1999

* Value is total rainfall (inches) between August and November.

Two rainfall events are in the forecast...Saturday, November 13, 2010 and again late Monday/Tuesday. The latest models indicate the Saturday event is weak and falling apart. Tuesday's event looks very promising. Also, the winter outlook is calling for above normal rainfall for Kentucky: http://www.cpc.ncep.noaa.gov/products/predictions/long_range/seasonal.php?lead=02

Drought Expands Across Kentucky

Tom Priddy, University of Kentucky Ag Weather Center

Drought conditions continued to expand and deepen this past week across the
Bluegrass state. Get the latest update and webcast concerning these dry
conditions
in the state at the below listed UKAWC link:

Kentucky Climate Update:
http://wwwagwx.ca.uky.edu/weather_presentation.shtml

And, expanded drought info on UKAWC's Drought page, at:
http://wwwagwx.ca.uky.edu/drought.html

Hot, Dry Weather at the Worst Time for Corn

Chad Lee, Extension Agronomist, Plant and Soil Sciences

Much of Kentucky has turned hot and dry at the worst possible time for corn. About half of the corn crop was silking or complete with silking as of July 5, 2010, according to the USDA Crop and Weather Report.  Corn is most sensitive to stress around silking and blister development. In addition, corn uses the most water at silking, as much as 0.35 inches per day. 

Pollen shed and pollination is improved when temperatures are mild. The majority of pollen is shed in the morning after the dew has dried. A second release of pollen may occur in the late afternoon or early evening as temperatures cool again. The hot, dry weather we are currently experiencing does not favor good pollination. The hot weather will tend to dry out both the pollen and the silks. Temperatures above 100 F can kill pollen. 

The good news is that most corn fields will pollinate for about 14 days and most pollen shed occurs when temperatures are a little cooler. So, even when conditions are hot and dry, the corn plant will attempt to work around those poor conditions. The bad news is that high temperatures seem to quicken pollen shed. Taking the good with the bad: each field still has a chance for successful pollination.

For corn that was through pollination before things turned dry, abortion of kernels is a possibility. The corn plant will recognize that water reserves are low and abort kernels near the tip of the ear, first. Very high plant populations can increase the water stress and increase kernel abortion.

What can you do about it? Unless you have irrigation, not much can be done on the agronomics. If you are marketing the current crop on the futures, you might want to be more cautious with your yield targets. Of course, a good rain in the next couple days will solve most of our problems.

Sources:

R.L. Nielsen, Tassel Emergence and Pollen Shed, July 2010. Purdue. http://www.agry.purdue.edu/ext/corn/news/timeless/Tassels.html

R. Elmore. Corn Development from R1 to R6. Iowa State. http://www.agronext.iastate.edu/corn/production/management/growth/yield.html

Kentucky Weekly Crop and Weather Update. July 5, 2010. 

http://www.nass.usda.gov/Statistics_by_State/Kentucky/Publications/Crop_Progress_&_Condition/cw10/cw0706.pdf