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July 16 July 22, 2002
C.O.R.N. 2002-22
In This Issue:
A) Wheat Yield And Grain Quality Excellent
B) Ohio's 2002 Wheat Crop
C) 2002 Soybeans: Some Good, Some Bad & Some Ugly
D) Flea Beetles In Corn
E) Rootworm Beetles Make Their Appearance
F) Twospotted Spider Mites
G) Soybean Aphid
H) Water Stress Effects On Corn Growth And Development
I) Are We In A Drought Yet?
J) Reminder On Osu Weed Science Field Day
Weather conditions over the past two to three weeks has not been good for corn and soybeans, but the persistent dry conditions has helped wheat producers harvest the crop quickly and maintain excellent grain quality. Yields from around the state have been quite variable with reports ranging from less than 10 bu/A to over 100 bu/A. The Ohio Crop Reporting Service has estimated the state average yield to be 62 bu/A, down 5 bu/A from the 2001 crop. Acres harvested were estimated at 800,000, down 11 % below 2001. The extreme variability in yields across the state was due to very low yields in fields with frost injury in the southern Counties. Remarkably, the late planted and replanted wheat fields in Northwest Ohio had very respectable yields with reports ranging from 60 to 75 bu/A for fields planted in November. The warm late fall weather significantly influenced the ability of these fields to develop adequate tillers and reasonable yields.
Test weights reported so far have been uncommonly high for Ohio ranging from 58 to 63 lb/bu. These high test weights indicate grain quality is excellent. The lack of diseases on the flag leaves and the wheat heads, the cooler weather during early grain fill, and little or no rainfall to weather the grain after ripening promoted the development of high test weights. Additional evidence of the lack of weathering due to dry conditions is the bright colored straw that has been baled in fields throughout Ohio. Wheat producers should begin now to plan for the 2003 crop by obtaining information about variety performance from various sources.
A wheat crop produces from 3 to 6 bushels per acre per day during the grain fill period depending on the weather and disease pressure. The grain fill period in Ohio is from 12 to 21 days long with 15 to 18 days being typical. With poor weather or heavy disease and 3 bu/ac/day, yields would be in the range of 36 to 63 bu/ac depending on the length of the grain fill period. With no disease and ideal weather the crop can produce up to 6 bu/ac/day. In 2002, the weather was not ideal but there was very little disease and the crop produced about 4.5 bu/ac/day, but the grain fill period was short in many areas due to the high temperatures. These factors account for the wide range in Ohio's 2002 wheat yield.
The Bad: Much of the crop was planted later than ideal due to wet weather. Some fields had to be replanted because of poor stands due to disease and/or flooding. Flowering in many fields is starting in mid-July instead of late June or early July. Therefore, yield potential for 2002 is lower than normal.
The Good: This high temperature and dry weather will cause less damage now than if it occurred in late July or in August. Generally, stands are good and weeds have been controlled. The crop will flower for about four weeks, and if we get some good rains anytime during the flowering period, the plants will set enough pods to make a good crop. The critical time when we must have rain is the grain fill period which will extend from about mid-August till late September for much of the crop this year.
The Ugly: Dry weather stress is allowing other problems such as nematodes, root rot diseases, and some insects to extract a toll on the crop. When we get the crop established early, and there is little disease and the weather is ideal, the yield potential for most fields is 50 to 100 bu/ac. The final yield that we harvest is that yield potential less the effect of all the stresses the crop endures during the growing season. Stress before flowering generally has very little effect on yield. The same stress during flowering has a greater effect on yield. Stress during the grain fill period is the most devastating. Every year, stress reduces yield 25 to 50 percent.
Eliminating or reducing stress, no matter the cause, will save yield. We can control much of the possible stress with variety selection, fungicide seed treatments, timely weed and insect control, proper fertility, and the proper use of other cultural practices. This is the essence of good management.
We have had a number of reports during the last week about flea beetles feeding on corn. The corn is 4 to 6 feet in height and there have been reports of 15 to 20 beetles per plant in some instances. The beetles are feeding on the leaf tips resulting in leaves with brown tips. The heavy flea beetle feeding at this time is unusual and an economic threshold for this type of damage is not available. We have talked with other entomologists and do not think it would be economic to spray for this type of damage.
We have been finding both northern and western corn rootworm beetles during the past week. Their emergence is right on schedule for this year. Since silks are not available in most of the corn fields at this time, the beetles are feeding on the corn leaves. This is a good time to dig roots to see if rootworm larvae have damaged the roots in continuous cornfields that may not have received a soil insecticide.
The soybean aphid has been confirmed in Ohio as of last week, with large colonies of over 100 aphids per leaf being found on individual plants in Wayne County. In all likelihood, it is probably occurring in other parts of the state. Whether it is occurring in economic populations in Ohio is unknown, but it is essential that growers monitor their fields for their presence and possible large populations. Reports from other northern soybean-growing states indicate that aphids are beginning to reach economic populations. Current thresholds and treatment recommendations are available in last week's CORN newsletter. Briefly, treatment is recommended when aphids are common and abundant, averaging at least 30-100 per single top leaflet. This level of aphid infestation should be on most plants throughout the field. Growers should check the upper most leaves of the plant, especially the newer trifoliolates that are still expanding. Most aphids will be found on these top leaves. The presence of aphids will often be noticed by the occurrence of ants on those leaves. There is a close association with aphids and ants, and often they will be on the leaves together. Additionally, we found numerous multicolored Asian lady beetles with these plants. The following insecticides are labeled for soybean aphid control, although additional ones might be labeled later. The current insecticides are Asana XL (5.8 to 9.6 fl oz per acre), Furadan (0.25 to 0.5 pt per acre), Lorsban 4E (1 to 2 pts per acre), Mustang (3.4 to 4.3 fl oz per acre), Penncap-M (1-3 pts per acre), and Warrior (1.92 to 3.2 fl oz per acre).
High temperatures and limited rainfall in recent weeks have raised the possibility of drought damage to corn in many areas of the state. Much of the corn planted in April and early May is at or rapidly approaching the tassel stage, which begins the reproductive phase of corn development. This is the period of development (i.e. tasseling, silking and pollination) which is most sensitive to moisture stress. To get a better understanding of why this period is so sensitive to drought let's consider the water requirements of corn during the growing season.
A corn crop in Ohio typically uses 20 to 22 inches of water during the growing season. Water requirements of corn vary according to the stage of development as shown in Table 1. Corn reaches its peak water use during pollination when plants are silking.
Table 1. Water Use Rates for Corn at Different Growth Stages.
Growth Stage Water Use Rate (inches/day)
Prior to 12-leaf stage < 0.20
12-leaf 0.24
Early Tassel 0.28
Silking 0.30
Blister Kernel 0.26
Milk 0.24
Dent 0.20
Full Dent 0.18
In last week's C.O.R.N. newsletter, yield losses to moisture stress were related
to the number of days that the crop shows stress symptoms during different growth
periods. Through the late vegetative stage, corn is fairly tolerant of dry soils,
and mild drought during June may even be beneficial because roots generally
grow downward more strongly as surface soils dry, and the crop benefits from
the greater amount of sunlight that accompanies dry weather. (Unfortunately
in 2002, surface compaction caused by planting wet fields plus excessive rainfall
after planting has limited deep root development, and this may predispose the
crop to greater drought damage.) During the two weeks before and two weeks following
pollination, corn is very sensitive to drought. Dry soils during this period
can cause serious yield losses with most of these losses due to failure of pollination.
How does moisture stress impact grain yield determination at pollination? A typical corn plant produces between 2 and 5 million pollen grains, which means there are about 2000-5000 pollen grains for each silk. Pollen shed does not usually begin until the tassel has fully emerged from the whorl. Under normal weather conditions, pollen shed begins about 2 to 3 days prior to silking and continues 5 to 8 days. The corn ear of a non-stressed plant generally has between 750 and 1000 potential ovules or kernels arranged in even numbered rows around the cob. Each kernel produces a silk that must receive pollen to be fertilized. Under favorable weather conditions, silks first emerge from the base of the ear and progress upward toward the tip over a period of 3 to 5 days.
Under drought stress conditions, however, silk emergence is often delayed 1 to 3 days even though pollen shed remains on schedule. This delayed silk emergence may cause the plant to run out of pollen before all the silks have emerged and result in kernel blanks and lack of tip development. If fertilization does not occur, the yield loss for that potential kernel is 100%. Losses increase proportionately as more kernels fail to fertilize. The high temperatures often associated with water stress conditions may also affect the pollination process. Temperatures in excess of 95 degrees, especially when accompanied by low relative humidity can result in silk desiccation but have little direct effect on silk elongation. Pollen viability may also be reduced as temperatures approach 100 degrees. However, pollen shed normally occurs during the cool hours of the day (i.e. 9 a.m. to 11 a.m.).
Many people have been asking whether we are currently in a drought. The way to answer this question is to look to the Palmer Drought Severity Index (PDSI) and other information from the Climate Prediction Center, an arm of the National Oceanic & Atmospheric Administration (NOAA) and the National Weather Service.
According to NOAA - common to all types of drought is the fact that they originate from a deficiency of precipitation resulting from an unusual weather pattern. If the weather pattern lasts a short time (e.g., a few weeks or a couple months), the drought is considered short-term. But if the weather or atmospheric circulation pattern becomes entrenched and the precipitation deficits last for several months to several years, the drought is considered to be a long-term drought.
Many quantitative measures of drought have been developed in the United States, depending on the discipline affected, the region being considered, and the particular application. The most frequently used indicators of drought are those developed by Wayne Palmer in the 1960's. These include the Palmer Drought Severity Index (PDSI), the Palmer Hydrological Drought Index (PHDI), the Palmer Z Index and the Crop Moisture Index (CMI). These indices have been used in countless research studies as well as in operational drought monitoring during the past 35 years. The Palmer drought index has proven to provide one of the best indications of drought for much of the United States. It is superior to other drought indices in many respects because it accounts not only for precipitation totals, but also for temperature, evapotranspiration, soil runoff and soil recharge.
The Palmer Drought Severity Index is an index of the relative dryness effecting
water sensitive economies. The data is provided in graphical and tabular formats,
for the contiguous United States. The following is a link to the Drought Severity
Indices for the week ending July 13, 2002:
http://www.cpc.ncep.noaa.gov/products/analysis_monitoring/regional_monitoring/palmer.gif
While the PDSI does not currently show that Ohio and especially Northwest Ohio
is in a drought, looking at topsoil moisture can also be helpful. According
to the Climate Prediction Center topsoil moisture for Ohio on July 7 was 60%
dry in the top 6 inches this can be compared to the 5-year mean of 23%, this
puts current conditions in the very dry category. Listed below is a link to
the Climate Prediction Centers Topsoil Moisture Monitoring page for July 7,
2002:
http://www.cpc.ncep.noaa.gov/products/monitoring_and_data/topsoil.html
The Northwest Branch of the OARDC in will host it annual Agronomic Field Day
on Thursday, July 25, 2002, at the research farm located at 4240 Rangeline Road,
northeast of Hoytville, Ohio. The program begins at 6:00 p.m. with wagon tours.
The program will include:
Management of phytophthora root and stem rot -- Dr. Anne Dorrance
Soybean aphid -- Dr. Ron Hammond
New Technologies in precision Ag - Dr. Reza Ehsani & Matt Sullivan
How weed populations change with tillage, rotation, and herbicides
-Dr. John Cardina
Certified Crop Advisor credits offered: 1.0 crop mgnt, 1.0 pest mgnt
Commercial PAT Credits: Core-30', cat. 2a-60', and cat. 2c-30".
Free and open to the public. Contact Matt Davis at 419-257-2060 for more information.
Readers can subscribe electronically to this newsletter by sending an e-mail message to: corn-out-on@postoffice.ag.ohio-state.edu. A successful subscription message will receive by an automatic reply from the listserv. Contact your local Ohio State University Extension Office or e-mail labarge.1@osu.edu if you have problems subscribing.
Past versions of C.O.R.N. can be found on the World Wide Web at: http:/www.ag.ohio-state.edu/~corn/archive/
C.O.R.N. is a summary of crop observations, related information, and appropriate recommendations for Ohio Crop Producers and Industry. C.O.R.N. is produced by the Ohio State University Extension Agronomy Team, State Specialists at The Ohio State University and Ohio Agricultural Research and Development Center. C.O.R.N. Questions are directed to State Specialists, Extension Associates, and Agents associated with Ohio State University Extension and the Ohio Agricultural Research and Development Center at The Ohio State University.
State Specialists: Pat Lipps, Anne Dorrance & Dennis Mills (Plant Pathology), Peter Thomison (Corn Production), Jim Beuerlein (Soybean & Small Grain Production), Mark Loux & Jeff Stachler (Weed Science), and Bruce Eisley & Ron Hammond (IPM). District Agronomist: Ed Lentz (Northwest) Extension Agents: Steve Bartels (Bulter), Steve Prochaska (Crawford), Howard Siegrist (Licking), Jim Lopshire (Paulding), Glen Arnold (Putnam), Ray Wells (Ross), Clark Hutson (Seneca), Roger Bender (Shelby), and Dave Jones (Allen).Editor: David Jones Web Editor: Tom Rosati
Information presented above and where trade names are used, they are supplied with the understanding that no discrimination is intended and no endorsement by Ohio State University Extension is implied. Although every attempt is made to produce information that is complete, timely, and accurate, the pesticide user bears responsibility of consulting the pesticide label and adhering to those directions.
All educational programs conducted by Ohio State University Extension are available to clientele on a nondiscriminatory basis without regard to race, color, creed, religion, sexual orientation, national origin, gender, age, disability or Vietnam-era veteran status.
Issued in furtherance of Cooperative Extension work, Acts of May 8 and June 30, 1914, in cooperation with the U.S. Department of Agriculture, Keith L. Smith, Director, Ohio State University Extension.
TDD # 1 (800) 589-8292 (Ohio only) or (614) 292-1868
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