FCN Logo College of Agricultural Sciences Penn State

May 29, 1998 Vol. 98.6

IN THIS ISSUE:

Production:

DOUBLE CROPPING SOYBEAN IN SHORT SEASON AREAS

This year winter grain harvest will probably occur one to two weeks earlier then normal in many parts of Pennsylvania. This offers the opportunity for double cropping soybean in shorter season areas; areas that do not traditionally have enough heat units remaining to mature soybean when planted after winter grain harvest. There are several points to ponder when planting double crop soybean in these areas.

Planting Date - of course this depends on the harvest date of the preceding crop. This soil can be very dry following a small grain crop. Remember that if the soil is dry do not try to plant soybean. It is very sensitive to soil moisture levels. This could delay planting past the point for successful soybean production.

Variety Selection - We suggest planting varieties that have a similar maturity to those planted for full season production in a given area.

Inoculation - Use the same procedure for inoculating double crop as used for full season soybean.

Fertilization - Soybean seed is very sensitive to fertilizer, therefore any required fertilizer should be broadcast prior to planting. If the soil test is in the optimum level for P205 and K20, apply no fertilizer and apply the estimated amount removed by the soybean when fertilizing the next crop in the rotation.

Row Space - Plant in narrow row spaces, 15 inches or less.

Population - Plan to establish approximately 225,000 plants per acre.

Herbicides - Consider using a herbicide that has no restrictions on using the soybeans for forage as well as the weed spectrum it controls. This offers another use for the crop if a frost should occur before the soybean is mature enough to harvest for grain.

Elwood Hatley,
CCA, Agronomy



USING PLANT ANALYSIS TO DIAGNOSE NUTRIENT DEFICIENCY PROBLEMS

Plant analysis is a valuable tool for diagnosing suspected plant nutrient deficiency problems. There are two ways to use plant analysis for this purpose. The first method is to compare the analysis of the plant tissue with standard tables of interpretive values. Since the table values are for specific plant parts sampled at a specific stage of growth, it is critical that sampling guidelines be strictly followed. The following table provides general sampling guidelines for common agronomic crops. Check with the lab you use for more specific sampling instructions.

The problem with this method is that book values are only available for the few specific stages of growth given in the table below. For annual crops the recommended sampling times are often not for the stage of growth when the problem is observed and usually they are too late to take corrective action. For example, most nutritional problems with corn are observed when the corn is short and you can look out over the field.

Table 1. Sampling Guidelines for Plant Analysis
Crop Sampling Time Plant Part
Corn Silking Earleaf
Forage Legumes Bud to 10% bloom Top 1/3 of plant
Small Grains Just prior to heading Uppermost leaves
Soybeans Prior to or early flowering Uppermost full leaves
Forage grasses 3-4 weeks between cuttings Top of the plant

This is also early enough that corrective action could be taken for some problems. Thus waiting until silking to take samples of problem corn plants for plant analysis is of questionable value except as a postmortem. For perennial crops, corrective action can often be taken during the next season or next cutting. A final problem with this method is that there are many environmental and cultural factors that can influence the level of a nutrient in plant tissue. Thus, book values are only ball park estimates of sufficiency for nutrients and actual sufficiency levels can vary significantly depending on the specific conditions.

The better alternative for using plant analysis to diagnose nutrient deficiency problems is to take comparative samples. With this method two samples are taken for analysis. One sample is taken from the problem area and the second sample is taken from a nearby area that is as near to identical to the problem area as possible, but is showing normal growth. This method can be used at any stage of growth and it eliminates the confounding effects of most of the cultural and environmental factors. When using this method the two samples must be taken at the same time and the same plant part must be sampled. Usually the newest fully developed leaves or stems are the best plant part to sample for this method. If the problem is nutritional, comparison of the nutrient levels in the two samples usually gives a direct indication of the problem.

Regardless of the method used, it is important to use all available information to interpret the plant analysis for diagnosing a nutrient deficiency. Look carefully at the symptoms on the plants, note any patterns in the field, consider the timing of the appearance of the problem. Keep in mind that not all nutrient deficiencies in plants are the result of nutrient deficiencies in the soil. Soil tests and plant analysis are often complementary. They can confirm each other, but they can also indicate when the cause of the problem is something other than a soil deficiency of the nutrient. If the soil test level is adequate but the plants are deficient this indicates that some other factor is limiting the plants ability to take up the available nutrients. Some areas to consider include: possible interactions with other cultural practices such as tillage or pesticides; pest injury such as root worm feeding; differences in varieties or hybrids; or soil physical conditions such as compaction.

If used properly plant analysis can be a very useful tool for diagnosing plant nutritional problems and suggesting solutions to these problems.

Douglas Beegle,
Agronomy, Soils

Pest Management:

HERBICIDE PERFORMANCE AND LACK OF RAINFALL

In the last issue of Field Crop News we discussed wet weather woes, while two weeks later it's dry weather problems again. Dry weather can affect both soil applied and postemergence herbicide performance. All soil applied herbicides require rainfall to mobilize them for effective weed control. In general, rainfall should occur within 7 to 10 days after application or before weed emergence. As a general rule of thumb, 1/2 inch of rain is considered the minimum depending on current soil moisture levels and the herbicide used. The less mobile materials (Prowl, Atrazine, Scepter) and deeper germinating weeds (e.g. yellow nutsedge, cocklebur, velvetleaf, ragweed, etc.) will require even more rainfall for effective control.

If the 10 day limit has gone following a Pre treatment and weeds are starting to break, consider using a rotary hoe, making a post herbicide application, or start tuning up that old cultivator that you have been dying to try again.

Although some "reach back" can be expected on small annual weeds (esp. broadleaves) with some herbicides when rainfall occurs, depending on this is a little like gambling in Las Vegas. As for post herbicide applications, remember that small annual weeds are easier to kill than large ones and examine adjuvant options to maximize activity under dry weather conditions. Delaying the herbicide application until after a rainfall rarely increases your chances of success unless you're making that decision while watching a large storm front move in from the west.



PERENNIAL WEED CONTROL IN SUMMER ANNUAL CROPS

Last year I included an article on the potential for perennial weed management in Roundup-Ready soybeans. The article was written by some colleagues at Iowa State University and included some data from a Wisconsin study. In general the research found that hemp dogbane control increased as Roundup applications were delayed although the effect of hemp dogbane maturity on control could be partially overcome by increasing the rate of Roundup (Table 2). The researchers also evaluated the impact of the Roundup Ultra treatments on hemp dogbane the year following application. While all treatments reduced hemp dogbane populations the year following application, applications made at flowering provided more effective control than Roundup applications made earlier in the season. For example, the 2 pint per acre rate at early or full flowering reduced hemp dogbane populations by 95 percent the year following application, whereas, the bud stage treatment reduced populations by 80 percent.

Can we expect similar results with other perennials and what about Roundup applications in Roundup-Ready corn? First, hemp dogbane is one of the more susceptible perennial broadleaf weeds to Roundup. Other perennial weeds may require higher rates than is necessary for hemp dogbane. Also, the window of opportunity to make a timely application is less in corn than in soybeans. In 1998, Roundup may be applied to Roundup-Ready corn up to 24 inches tall. However, because of annual weed competition as well as effective spray coverage, most applications of post herbicides should occur to corn that is less than 15 inches tall. With the exception of perhaps Canada thistle and quackgrass, many perennials will not yet be in the reproductive stage of development and less than optimum control should be expected (however, excellent seasonal control or suppression can still be achieved). So, although Roundup-Ready provides an excellent opportunity to manage perennials, it will take efficient management of the product to achieve maximum performance. In order to maximize perennial weed control, keep in mind susceptible stages of growth and how both crop rotation and mechanical controls can improve management opportunities.

Table 2. Influence of Roundup Ultra rate and application timing on hemp dogbane control in Roundup-Ready soybeans.
Percent hemp dogbane control1,2
Hemp dogbane and (soybean) growth stage at application timing
Roundup Ultra
(pints per acre)		 Vegetative
(Unifoliolate)		 Bud
(1 trifoliolate)		 Early flower
(2-3 trifoliolate)		 Full flower
(5-9 trifoliolate)
1.5 22 73 64 88
2.0 58 72 93 99
3.0 43 91 92 100
4.0 57 78 100 100

Source: Jerry Doll, 1996, University of Wisconsin.
1 Control ratings made on August 1.
2 LSD 0.05 = 11%.

Bill Curran,
Agronomy, Weed Science



HERBICIDE DRIFT MANAGEMENT

With the windy spring and summer weather, spray drift is certainly on many commercial operators and farmers minds. The following are some tips to help reduce the potential of herbicide drift.

With the introduction of herbicide tolerant crops, drift management is even more critical. Although Roundup is an effective herbicide in Roundup Ready soybeans, it is also an effective herbicide on nearby corn. Also, products such as Banvel and 2,4-D can cause problems when they drift to nearby soybeans. Spray drift not only wastes your herbicide and money, but it may cost you more if legal action is taken by your neighbor or client.

Reference-"Spray Drift Control", D.R. Daum and J.D. Keener, PSU, 1991.

Dwight Lingenfelter,
Agronomy



POSTEMERGENCE HERBICIDE USE IN SOYBEANS

Postemergence herbicide programs are becoming widely used and can provide an effective weed control option. When using a POST program consider crop and weed size, necessary adjuvant(s) and rate, rainfastness, and application timing restrictions; see Table 3 for more information. Tank mixing not only broadens the control spectrum, but is generally necessary for planned POST programs; Table 4 shows approved tank mixes. Keep in mind that certain tank-mix combinations may cause antagonism. In most cases, grass control is reduced when a broadleaf plus grass herbicide mixture is used. To overcome this problem either increase the grass herbicide rate or apply the broadleaf product a day or two after applying the grass herbicide. See current herbicide label(s) for additional information on herbicide application information and precautions.

Table 3. Herbicide application rates, weeds controlled, spray additives, rainfastness, re-entry periods and application timings for postemergence soybean herbicides.
Herbicide Application rate (product/A) Weeds controlled Adjuvant(s)1 Adjuvant rate Rain fastness (hours) Re-
entry period		 Application timing2
Assure II or Matador 5-10 fl oz G nonionic surfactant or crop oil concentrate 1 qt/100 gal
4 qt/100 gal 		1 12 80 days before harvest and not after pod set
Basagran 1.5-2 pt B,N crop or vegetable oil concentrate or nitrogen solution or ammonium sulfate (for velvetleaf) 5 qt/100 gal (2 pt/A maximum)
2-4 qt/A
2.5 lb/A 		8 48 No statement
Blazer 0.5-1.5 pt B nonionic surfactant or nitrogen solution (for velvetleaf) 1 pt/100 gal
2 to 4 qt/A 		6 48 1-2 trifoliate to 50 days before harvest
Classic or Skirmish 0.5-0.75 oz B, N nonionic surfactant or crop oil concentrate plus nitrogen solution or ammonium sulfate (for velvetleaf) 1 qt/100 gal
1 gal/100 gal
2 to 4 pt/A or
2 to 4 lb/A 		1 12 1 trifoliate to 60 days before harvest
Cobra3 6-12.5 fl oz B nonionic surfactant or crop oil concentrate plus/or nitrogen solution or ammonium sulfate 1 qt/100 gal
1-2 pt/100 gal
4 qt/A or
2.5 lb/A 		0.5 12 1-2 trifoliate to 45 days before harvest
Concert SP4 0.5 oz (1 pack/4 acres) B nonionic surfactant or crop oil concentrate plus nitrogen solution or 10-34-0 or ammonium sulfate 1 to 2 pt/100 gal
4 pt/100 gal
2 to 4 qt/A or
1 to 2 qt
2 to 4 lb/A 		1 12 1 trifoliate to 60 days before harvest
FirstRate 0.3 oz B nonionic surfactant plus nitrogen solution or ammonium sulfate
or
crop oil concentrate
or
crop oil concentrate plus nitrogen solution 		1 to 2 pt/100 gal
2.5 gal/100 gal
2 lb/acre

1.2 gal/100 gal

1.2 gal/100 gal
2.5 gal/100 gal 		2 12 1 trifoliate to any time prior to 50% soybean flowering stage
Fusilade DX 6-12 fl oz G nonionic surfactant or crop oil concentrate plus nitrogen solution
or
10-34-0 (optional) 		1 to 2 qt/100 gal
2 to 4 qt/100 gal
1 gal/A
2 pt/A 		1 12 Prior to bloom
Fusion 6-10 fl oz G nonionic surfactant or crop oil concentrate plus nitrogen solution (optional) 1 to 2 qt/100 gal
2 to 4 qt/100 gal
4 gal/100 gal 		1 24 Prior to bloom
Liberty 8 16 to 28 fl oz B, G ammonium sulfate 3 lb/A 4 12 Emergence to bloom
Pinnacle4 0.25 oz B nonionic surfactant or crop oil concentrate plus nitrogen solution or ammonium sulfate (for velvetleaf) 1-2 pt/100 gal
2 qt/100 gal
4 gal/100 gal
or 2-4 lb/A 		1 12 1 trifoliate to 60 days before harvest
Poast
or
Poast Plus5 		0.75-1.5 pt
or
18-36 fl oz 		G crop or vegetable oil concentrate or Dash HC plus nitrogen solution or ammonium sulfate (for certain species) 2 pt/A
1 pt/A
2 to 4 qt/A
or 2.5 lb/A 		1 12 75 days before harvest
Pursuit 2S
or
70DG 		4 fl oz
or
1.44 oz 		G nonionic surfactant or crop oil concentrate or vegetable oil concentrate plus nitrogen solution or ammonium sulfate 1 qt/100 gal
2 pt/A
1.5 to 2 pt/A
1 to 2 qt/A or
2.5 lb/A 		1 12 85 days before harvest and prior to bloom
Raptor 4-5 floz B, G crop oil concentrate
or
nonionic surfactant
and
nitrogen solution or ammonium sulfate 		2 pt/A

1 qt/100 gal

1 to 2 qt/A 2.5 lb/A 		1 4 85 days before harvest and prior to bloom
Reflex
or
Flexstar 		1-1.5 pt B nonionic surfactant or crop oil concentrate plus nitrogen solution (optional) 1 to 2 qt/100 gal
2 to 4 qt/100 gal
4 qt/A 		4 24 Prior to bloom
Resource 4-12 fl oz B crop oil concentrate plus nitrogen solution (optional ) 2-4 qt/100 gal
2-4 qt/A 		1 12 60 days before harvest and not after pod set
Roundup Ultra
or
Roundup5 		16-64 fl oz G, B, N no NIS/COC required for Roundup Ultra nonionic surfactant plus ammonium sulfate (optional) 2 qt/100 gal
8.5-17 lb/100 gal 		1-2
(Ultra)

6 		4
(Ultra)

12		 cracking to flowering
Scepter 1.5S
or
70DG 		0.66 pt
or
2.8 oz 		B, G nonionic surfactant or
crop oil concentrate 		1 qt/100 gal1 qt/100 gal 1 gal/100 gal 1 gal/100 gal 1 12 90 days before harvest
Select 6-16 fl oz G crop oil concentrate plus nitrogen solution (optional) 2-4 qt/100 gal
1 to 2 qt/A 		1 12 60 days before harvest
Stellar 5 fl oz B crop oil concentrate or metylated seed oil plus nitrogen solution or ammonium sulfate (optional) 2 to 4qt/100 gal
2 to 4 qt/100 gal
2 qt/100 gal
2.5 lb/A 		1 12 60 days before harvest and not after pod set
Storm6 1.5 pt B nonionic surfactant or crop oil concentrate or nitrogen solution or ammonium sulfate (for velvetleaf or pigweed) 1 to 2 pt/100 gal
1 to 2 pt/A
2 qt/A
2 lb/A 		8 48 2-3 trifoliate to 50 days before harvest
Synchrony STS 42DF7 0.5 oz (1 pack/4 acres) B, N crop oil concentrate plus nitrogen solution or 10-34-0 or ammonium sulfate (for velvetleaf) 1 gal/100 gal
2 to 4 qt/A or
1 to 2 qt
2 to 4 lb/A 		1 12 1 trifoliate to 60 days before harvest
B=broadleaves, G=grasses, N=yellow nutsedge
1 In general, nonionic surfactants should contain at least 80% surface active agent; crop or vegetable oil concentrates should be non-phytotoxic containing at least 15% approved emulsifier; nitrogen solution is ammonium based fertilizer such as 28%, 30%, or 32% N; and ammonium sulfate should be spray grade dry ammonium sulfate (21-0-0). 10-34-0 may also be used with some products.
2 Earliest applications should be made when weeds are most susceptible to herbicide (refer to product label), otherwise apply at or after earliest soybean stage specified.
3 Adjuvants for use with Cobra depended on relative humidity and weed species.
4 Use crop oil concentrate under drought-stressed conditions.
5 For use on Roundup Ready soybean varieties only
6 For Poast Plus with Storm in a tank-mixture, include 1 gal/100 gal of crop oil concentrate.
7 For use on STS soybean varieties only
8 For use on Liberty Link soybean varieties only.


Table 4. Approved tank mixes for foliar-applied herbicides in soybeans
X = approved tank mixes.
1 See individual labels for specific mixtures that may be prohibited and for specific application rate, timing, and adjuvant information.
Herbicide Basagran Blazer Classic Cobra Concert First Rate Pinnacle Pursuit Raptor Reflex Resource Stellar Storm SynchronySTS3
Assure II X   X X X X X X X X       X
Basagran   X   X   X X X   X X X    
Classic   X   X           X   X    
Concert       X                    
FirstRate X X   X     X X   X        
Fusilade X X X X X   X X X X       X
Fusion X X X   X X X X X X     X X
Liberty4 X X     X   X X   X X X X X
Pinnacle X X X X   X   X   X X X X  
Poast(Plus) X X     X     X X X       X
Pursuit X X   X   X X     X X X X  
Resource X   X X     X X         X  
Roundup2           X         X      
Scepter X X   X       X   X X X    
Select X X X X X X X X X X X X X X
SynchronySTS3       X           X   X    
1 Tank-mix is approved on either one or both herbicide labels. See product labels for more information.
2 Roundup or Roundup Ultra for use on Roundup Ready soybean varieties only
3 For use on STS soybean varieties only
4 For use with Liberty Link soybeans only

Dwight Lingenfelter and Bill Curran



INSECT ALERT

The following insects can be active during this time period. This does not mean they have been seen in the State, but it is the period of time when they can injure crops. Insects that have been reported are shown in bold type and specifics about their management are presented in individual articles. Pictures of each corn insect species, economic thresholds, and scouting guidelines can be seen on the worldwide webpage, http://www.fra.cas.psu.edu/ (Note correction from the last newsletter).

Corn
black cutworm
corn root aphid
corn rootworm larvae
European corn borer adults 		flea beetle
garden symphylan
grape colaspis		 seed corn maggot
slugs
sod webworm
thrips
white grub
wireworm
Soybeans
potato leafhopper seed corn maggot thrips
Alfalfa
alfalfa weevil larvae
Clover root curculio		 Meadow spittlebug
Potato leafhopper		 Spotted alfalfa aphid
Small grains
cereal leaf beetle corn leaf aphid English grain aphid

Black cutworm - So far few reports of black cutworm have been received. Black cutworm larvae have been reported in sweet corn grown under plastic. According to degree day accumulations, we should be in the period of peak cutting activity (see Table 4 and 6). The warm spring temperatures have accelerated the insect's development, so they are about two weeks ahead of normal in reaching damaging stages. Continue to watch newly emerging corn fields and young seedlings. Both no-till and tilled fields that had significant populations of winter annual weeds (i.e. common chickweed, shepherds purse, yellow rocket, etc.) are at increased risk of the pest. These fields should be watched very closely over the next few weeks for evidence of cutworm injury and treated if the economic threshold is reached or a protective insecticide application applied at-planting or preemergence. See the Agronomy Guide for effective materials and rates.

Economic Threshold Values:

Slugs - Immature slugs are common in no-till corn fields this year. Also, many adult slugs appear to have successfully overwintered because of the mild winter conditions. Even though they are abundant, it is doubtful that slugs will be a significant problem this year. The late planting of corn and good growing conditions should allow corn plants to rapidly outgrow slug injury. However, if the weather should turn cooler for an extended period as corn seedlings begin to emerge, then some fields could suffer economic injury. Watch newly emerging corn seedlings for slug feeding, and treat if necessary.

Economic Threshold Values: 50% of leaf area removed per plant and plants are less than V6 (6 leaves with the collar showing outside whorl).

Corn Rootworm Larvae - Based on degree day accumulations and planting dates, the 1998 growing season is almost the complete opposite of the 1997 growing season. In most areas of the state, degree day accumulations are nearing, have reach or have passed the number needed for 5% hatch of western corn rootworm eggs. See Tables 4 and 6 for degree day information for your area. Last year 5% egg hatch was not reached until June 17 in central Pennsylvania. Therefore, hatch is about three or four weeks earlier this year. Egg hatch will continue to occur over the next three to four weeks. For those individuals interested in Furadan 4F application timing, the product should be applied within a week of 5% egg hatch. This allows time for the material to reach the corn's root zone and provide a high level of protection. Also, cultivation time treatments should be applied during the same window.

Although conditions were excellent for overwintering of corn rootworm eggs, the high amount of rainfall during May has caused some soils to become saturated. Saturation of soil eliminates air that the eggs need, thereby increasing mortality of eggs. In addition to increased mortality, the early hatch of eggs should allow soil insecticide applications applied at planting to provide high levels of protection. With the exception of fields that were untreated and have high overwintering populations, corn rootworm injury should be minimal this year.

European corn borer - Overwintering adult corn borers are beginning to emerge and should begin to lay eggs by next week. It is still early in the flight which will continue for about four weeks. First generation peak egg laying occurs at about 558 DD (See Tables 4 and 6). This should occur about the second week of June.

Because corn planting in many fields was delayed until mid or late May, corn fields that were planted in late-April will be extremely attractive to egg laying females. Females looking for a field to lay their eggs will not select a field less than V7. The taller the corn, the more attractive it is for egg laying. Because only a few fields were planted in late-April, significant first generation corn borer infestations will be limited to these fields.

Stalk Borer - Southern areas of the state are approaching the time when stalk borer larvae will be migrating from grasses around the field margin into corn plants. Based on degree day accumulations up to May 26, 1998, some areas should reach the 1400 to 1700 DD needed within the next one to two weeks. To adequately protect corn plants from this pest, it is important to apply an insecticide as soon as the first signs of injury are observed. In fields where corn is no-till planted into an old hay field where orchardgrass clumps are common, an insecticide should be applied when a herbicide is applied to control the orchardgrass and other annual weeds. As the orchardgrass dries down after treatment, the small stalk borer larvae leave the orchardgrass and seek out young corn plants. Once inside a corn plant the larvae can no longer be controlled. See the Agronomy Guide for insecticide options and the "Field Crop IPM Training and Reference Manual", for economic thresholds (This manual is available from Dennis Calvin, Dept. of Entomology, 501 ASI, Penn State University, University Park, Pa. for $75.00).

Economic Thresholds Values - See the "Field Crop IPM Training and Reference Manual" for specific thresholds which vary based on plant growth stage and market value of the crop.

Alfalfa Weevil Larvae - We are nearing the end of the alfalfa weevil larval feeding period. Reports of the fungal pathogen causing weevil populations to crash are common. In fields where the economic injury level has been reached, any of the following materials can be used: Sniper 50PVA, Furadan 4F, Lorsban 4E, Baythroid 2E, dimethoate formulations, malathion formulations, Lannate 90SP and LV, Penncap-M, Warrior 1EC, Pounce formulations, Ambush formulations. When possible, consider cutting early to avoid further damage and the need for an insecticide application. See the Agronomy Guide for specific insecticide rates and application methods.

Economic Thresholds Values - See the Publication, "A Pest Management Program for Alfalfa in Pennsylvania", for specific thresholds.

Threshold Ranges:
For 12 to 18 inch high alfalfa - 34 to 225 larvae per 30 stems
For 19 to 24 inch high alfalfa - 37 to 240 larvae per 30 stems
For 25 to 30 inch high alfalfa - 39 to 260 larvae per 30 stems

Spittlebug - Spittlebug larvae still can be found feeding on alfalfa plant stems and a number of other plants. Although, they are easily seen in alfalfa fields, the insect seldom causes economic losses in yield. Evidence of the pest in a field is plants that look like someone spit on them. Inside this mass of liquid is the spittlebug larvae.

Economic Threshold Values - One or more spittle mass per stem in mid-May

Potato leafhopper - Although I have not received any reports of the pest in Pennsylvania alfalfa fields, the presence of the first leafhoppers was reported in Maryland on May 14. The two weeks of dry weather has delayed their movement into Pennsylvania. We should expect them to arrive in the State at any time, so be on the outlook. It is a good idea to check a few fields after every storm system passes through the State for the pest. Early detection can help prevent significant losses from the pest.

Economic Threshold Values - See the Publication, "A Pest Management Program for Alfalfa in Pennsylvania", for specific thresholds.

Threshold Ranges:
For 0 to 4 inch high alfalfa - 0.2 to 1.0 leafhoppers per sweep
For 5 to 8 inch high alfalfa - 0.3 to 1.7 leafhoppers per sweep
For 9 to 12 inch high alfalfa - 0.8 to 5.0 leafhoppers per sweep

Dennis Calvin,
Entomology


Precision Vision:

WHAT ARE THESE THINGS CALLED GPS?

Where it all started

Since this is a column about Precision Farming or Site Specific Agriculture, the subject of GPS will come up as it is an important part of the total picture. GPS stands for Global Positioning System, and it can be complicated or very simple, depending on how we talk about it. Now for you men (and women, too) that like to gather in the coffee shop in the morning for sinkers and coffee, you too can be a space age whiz! What you need is some new technical jargon about GPS and every one will think you are the most advanced farmer in the county. You will be nominated for "Farmer of the Year". This is the information you can use to wow your friends about GPS.

The U.S. Air Force and Navy started space - based radio navigation systems back in 1960 and in 1973 the U.S. Secretary of Defense signed the official memorandum which conceived the NAVSTAR Global Positioning System. The GPS system consists of 24 satellites, a series of monitoring stations and ground antennas and a master control station. The first satellites were launched in March, 1978. These satellites are in constant communication with the master control station so they can be kept in the proper orbit and also for maintaining the electronics on each of the 24 satellites. The satellite orbits are about 12,400 miles above the earth's surface. They orbit the earth once each 12 hours at a speed of 9000 miles per hour. Each of these satellites contains a very accurate atomic clock (not radioactive). Very simply, each satellite sends out a timing signal that is received by the GPS receivers on the ground. The signal is very faint, and it takes some fancy frequency generation and transmission of these frequencies so that our little battery operated GPS receivers can receive these signals. Because of the way the satellite orbits are maintained, at any single location on the surface of the earth, our receivers can get a signal from about 5-6 satellites.

These Things do Geometry!

Now, why the orbits and why do we need all these satellites? With the length of this column, I can't go into a lot of detail, but the reason gets back to the geometry that you took in high school. Very simply, the satellites send out a very accurate timing signal. Since the velocity of light is 186,000 miles per second, it takes about 0.06 seconds for the signal to get from the satellite to your receiver if the satellite is directly overhead. If it is lower on the horizon, the distance is greater and it takes longer. So, if your GPS receiver knew when the signal was transmitted and when it was received, it could compute how far you are from the satellite. Now enters the geometry. Also transmitted with the timing signal is an "ephemeris" of data that tells the GPS receiver the location of each satellite in its orbit. So your GPS receiver knows not only the distance to each satellite, it also knows the relative position of each satellite in relation to your GPS receiver. It now has all the information to calculate some angles and position! Your GPS is actually a radio receiver, a small computer and memory chip, and trigonometry equations.

Since the GPS actually computes a three dimensional position, and theoretically, the GPS could work with three satellites for both elevation and latitude/longitude. In reality, there is a way for the calculated position to be more accurately computed if an additional satellite position were known. The GPS receiver is programmed to require four satellite signals if elevation and latitude/longitude is to be computed.

It tells you where you are!

The GPS receiver really does a very simple thing. It tells you where you are. The GPS electronics takes care of giving you the position and the accuracy estimate. So, what is the accuracy? The basic GPS receiver is dependent on the Department of Defense controlling the satellites. Normally, the DOD degrades the accuracy of the timing signal. This degraded signal is called "selective availability (SA)", and only in wartime is the SA turned off so that you get a more accurate signal. Working normally, your GPS is accurate to about 15 to 30 feet if there were perfect reception and all the satellites were in perfect position. Due to a lot of other interferences, and with the DOD degrading the signal, you can count on about 300 to 350 feet accuracy. So what does this 300-350 feet accuracy term mean? If you draw a circle on the ground, 350 feet in diameter, and stand in the middle of the circle, about 2/3 of the location readings from your GPS receiver would fall in the circle. Not too accurate, huh? If you are a hunter or a boater, that accuracy would be good enough to get you out of the woods or back to your dock. But for agricultural application or yield monitoring and mapping fields, that accuracy is not good enough. We have other tricks up our sleeve. Read on.

Differential Corrections to Get More Accuracy

Consider if you had a precisely surveyed location or a known location on your farm, like the property corner out in front of the house, and you put a GPS (let's call that GPS1) receiver on that point. Because of the inaccuracy of the GPS technology, you would know the error in distance and direction between the GPS1 receiver location and the property corner location. This is the differential GPS error correction at any single instant of time. Now, if you have another GPS receiver which is roving about the farm, (call this one GPS2) and you are moving about the fields and taking readings, the error in distance and direction for GPS2 is the same error introduced in GPS1. If you transmit the error correction from GPS1 with a radio signal to GPS2 and let GPS2 add or subtract the correction to its own location, then you have a differentially corrected GPS for the GPS2 location. With this differentially corrected location, the error in GPS2 is reduced to less than three feet. That's the basis of DIFFERENTIAL GPS; using the known error at one location to correct other GPS receivers. We can get these error corrections from radio beacons run by the Coast Guard, or from correction signal satellites, or from other GPS receivers on the farm hooked up to a low power radio transmitter that communicates with the roving GPS.

In concluding this column, the DGPS units used in combines with yield monitors and mobile computers for field scouting uses the principles outlines above. You can purchase a normal GPS for as low as $99.00 or spend about $2,000 to $6,000 for an agricultural differentially corrected GPS for precision farming. We will talk more about DGPS and farm mapping in forthcoming columns. Happy coffee drinking!

David Wagner,
Ag & Bio Engineering, Precision Ag


Agents Corner:


BERKS COUNTY

In the past week of May 18-22, significant advances have been made in getting the corn and soybean crop in, forage mowed, and some acres even baled for hay. For dairy producers, its been a time management nightmare, with most hay fields being cut, then corn planting to follow.

Some producers are reporting that they are 50 to 75% completed with corn planting. A minority of fields will not get planted in a timely fashion at all, because they are on the receiving end of water drainage in valleys. Corn fields planted in April now show emergence, about 2 to 3 true leaves, with some fields looking a bit chlorotic. There are no major reports of insects. The bigger worry is weeds, with temperatures this week reaching the 90's and good soil moisture. (Perennial weeds, such as thistles, are taking off!)

Small grains are growing rapidly in the heat. Rye has been harvested for straw. Barley is maturing (heads browning), with wheat in flag leaf to heading (stage 10). Some barley and rye fields showed heavy lodging around May 8.

In pastures, the shift between early cool season plants to warm season plants is occurring. Winter annual weeds are complete in their lifecycle. I noted puna chickory starting to bolt (no flowers yet) and brome grass heading out. Growth of one paddock measured, with one rotation intensively grazed, had 2700 pounds of dry matter (height up to my waist).

As I end this week, its been ironic that some producers (row crop growers and producers on shale soils) are wishing for a small shower as the high temperatures and winds have rapidly dried out fields with tillage.

Mena Hautau, Berks County

CRAWFORD/ERIE COUNTIES

Greetings from Northwestern Pennsylvania! The earliest opportunities for field crop activities, such as working ground and oats and forage seedings, were better than normal this year. (Some alfalfa seeding failures have occurred, and sclerotinia was suspect in a few cases.) Producers who were ready and took advantage of the drier than normal spring are undoubtedly gratified. As the soil temperatures and the calendar became optimal for corn planting in late April and early May, a couple of weeks of moderate but fairly steady rains held everyone at bay. Apparently only a few hundred acres of corn were planted before the rain.

As mid-May rolled around, the skies cleared and planting is now proceeding very well. Corn planted at that time was emerging in about seven days with a week of warmer than normal temperatures (both daily highs and lows). Temperatures have returned to more normal levels since then, and the scarcity of rains has generally slowed the pace some now. A lot of corn is now about at the 2 to 3 leaf stage.

Otherwise, pressure from winter annuals and biennials was fairly significant. Good burndown programs were in order for most no-till plantings. The first flush of annual weeds is just beginning and is apparently also being held back somewhat by limited soil moisture. Some weevil pressure in alfalfa has been observed.

A fairly significant portion of our winter wheat crop exhibited some yellowing mosaic that was apparently first noticed around growth stage 8 or 9 as the flag leaf was emerging. Observations suggested possible varietal differences. Samples sent to the Plant Disease Clinic were forwarded to an Indiana Lab for virus testing. The sample tested positive for the Wheat Spindle Streak Mosaic Virus. Ten other virus/strain tests were conducted. Other disease pressure in wheat, primarily mildew and/or Septoria was apparently slight to moderate. Hats off and thanks to the Plant Disease Clinic.

Perhaps one of the most notable characteristics of this season was the early development of the hay crop. Normally, especially with grasses (orchardgrass in particular), if we are mowing by the middle of May, we are in good shape for quality first-cutting forages. This year that time table was a week to two weeks ahead of schedule. Our dairy producers were well advised to pull the mower out of the shed when the rains stopped, but the corn planting urge is awfully tough to resist. Hay yields appear respectable.

Overall, it has been another "normal" season; that is, there is nothing normal about it! Seriously, in general, the season now seems to be progressing pretty well. Some rains for uniform germination (especially with soybeans) and for herbicide incorporation and activation will be needed before too long. Best wishes for good growing to all.

Joel Hunter, Crawford/Erie Counties

DAUPHIN COUNTY

Due to the milder winter and warmer weather during April, spring field work and crop growth were 1-2 weeks ahead of normal in Dauphin County. Most rye was cut during the last two weeks of April. Spring oats and forage seedings emerged quickly and are doing well. A lot of farmers were itching to plant corn during the last week of April but only a small percentage of corn was actually planted. This corn has emerged and like the other spring seeded crops is growing well.

The 12 days of "monsoon weather" in the beginning of May brought field work to a standstill. This has been followed by a stretch of excellent weather. After drying out, corn planting and haymaking are in full swing. Because the hay was ahead of normal, most producers who had to make a choice between corn planting and haymaking chose to make hay first.

Some producers are ready to plant soybeans. If the weather holds, soybeans will go in as soon as corn planting, pesticide applications and haymaking are completed. Finally, although hard to believe, we are actually dry and could use some rain. Grass growth for graziers has significantly slowed down.

Jerry Martin, Dauphin County

FAYETTE COUNTY

The corn planting season began rather slowly in April with fields too wet to perform mechanical tillage. Most primary tillage was completed in good order, but then the rains came. After two weeks of wet weather in May, many dairy farmers began harvesting the hay crop as silage and then baled hay during the third week of May. Some really good hay crop forages were harvested but this significantly hampered the corn planting progress. Considerably less than 50% of the corn was planted by mid May.

April planted corn, what little there was, managed to survive quite nicely and is looking really positive as of this writing (May 26). On the back side, if planting weather holds, most corn should be planted by the end of May.

Winter small grains also look quite well with only slight storm damage and grain formation looks positive at this time. Some flea beetle damage is occurring on wheat. Barley, although a minor crop for the area, looks very good with good vegetative growth and grain production. The spring oats crop is under siege from flea beetle and has caused significant leaf damage.

Pasture and hay crops are very good, but many are in need of surface moisture to sustain maximum growth. Some alfalfa weevil damage occurred, but mostly on new seedings.

Don Fretts, Fayette County

LYCOMING COUNTY

The rain finally cleared and a lot of crops went in the ground in short order! About 85% of the corn is now planted along with the majority of the soybeans. Much of the corn germinated in 4 to 5 days. Hay harvest is advancing rapidly due to the dry conditions but is running late due to the earlier rain period and the conflict with the condensed grain planting season. Alfalfa looks good to excellent in most places but some of the grass hay is starting to lose quality due to the later harvest. Alfalfa weevil was common on many of the south facing alfalfa fields and flea beetle is showing up in large numbers on corn fields observed (but still below threshold). Early planted oats are looking very good but I have seen a number of wheat fields infested with powdery mildew. Overall crop conditions at this point are good but we could use a shower or two for the late seeded crops (almost hard to say that after all that rain!).

Tom Murphy, Lycoming County

MIFFLIN/JUNIATA/PERRY COUNTIES

In our area we have gone from an extremely wet soil condition to mostly dry and very hard soil conditions. The dry weather has allowed farmers to harvest alfalfa and grass as hay or haylage at an extremely rapid pace. In fact, many dairy farmers have been letting their planters set while they harvest the forages. Most of the alfalfa is coming off at early bud stages with no blooms in sight.

The corn that was planted prior to the heavy rains looks good at this point, the biggest concerns in these fields is the weed control. Many fields were not sprayed before the weeds and the corn emerged. Corn fields that have been planted into the drier soils still seem to be germinating and emerging within 7 - 10 days. I have had two reports of cutworm activity, the warm winter and heavy growth of winter annual weeds should provide ideal conditions for this pest. Some growers I have talked to will be adding an insecticide to their herbicide mixture for cutworm control. Soybean fields that I have observed are showing somewhat spotty emergence. I feel sure this is a result of uneven soil moisture. No weed or insect problems have been reported so far. The small grains are doing well, with very little disease or insect pressure.

Even though most field activity started a little later than normal, I think the 1998 crop year is off to a promising start with no major problems showing up yet.

Greg Hostetter, Mifflin/Juniata/Perry Counties

YORK COUNTY

Field conditions are at extremes lately. After two weeks of almost constant rain beginning April 30 we now have very dry and hard soil. Luckily for many growers that took advantage of the early spring weather break and got started early they had a lot of corn acreage in before the wet period. Early planted corn looks good. Some areas of corn fields are drowned out. Spots in small grain fields looking bleached out caused by too much water laying are now accompanied by other areas of droughty soil hurting for moisture. Lots of disease seen on wheat. Not much one could do though. Hay making went full blast when the rain ended on the 13th. Still plenty of orchardgrass standing and getting old.

John Rowehl, York County

Degree Day Accumulations:

1998 DEGREE DAY ACCUMULATIONS

To track corn and insect development, compare the 1998 cumulative degree-days shown in Table 5 to the required values in Tables 6 and 7. Choose a location that is closest to your site when making a comparison.

Table 5. Cumulative Degree Days for Corn and Insects for the Period Ending May 25, 1998
  Corn Insects
County Location 1997 30-year ave. SCM/SB AW BCW CRW ECB
  50F 50F Diff 40F 48F 50F 53F 55F
Erie Waterford 283 218 65 950 504 415 302 240
Crawford Meadville 300 232 68 1016 541 448 329 262
Mercer Mercer 301 234 67 1033 549 455 334 267
Bradford Towanda 291 229 63 1022 539 446 325 257
Lycoming Montoursville 311 244 67 1108 585 487 358 285
Tioga Mansfield 275 216 60 957 503 413 299 236
Susquehanna Montrose 253 198 55 895 464 378 272 214
Butler Butler 316 246 69 1104 589 490 362 290
Indiana Indiana 311 245 66 1107 589 488 360 288
Lawrence Lawrence Jct 302 233 70 1014 542 450 330 263
Blair Martinsburg 299 237 62 1081 573 473 347 278
Centre State College 297 235 62 1062 561 464 340 271
Columbia Bloomsburg 314 247 67 1136 599 498 367 293
Clearfield Curwensville 296 233 63 1045 553 457 335 267
Dauphin Elizabethville 324 255 69 1190 629 524 387 310
Bedford Bedford 319 253 67 1170 623 518 382 307
Mifflin Belleville 316 249 67 1142 605 503 371 297
Northumberland Sunbury 326 255 70 1183 626 522 386 309
Lehigh Trexlertown 329 259 69 1227 646 539 399 320
Schuylkill Hegins 313 247 65 1145 604 502 369 295
Westmoreland Greensburg 312 246 66 1116 595 493 364 292
Somerset Somerset 279 217 61 1000 528 433 315 252
Washington Washington 332 259 73 1187 638 531 394 317
Franklin Chambersburg 341 269 72 1271 677 566 420 338
York York 349 276 73 1322 703 588 439 353
Lancaster Ephrata 328 260 68 1235 653 544 402 323
Berks Hamburg 333 262 71 1239 654 546 405 325
Corn degree-days based on a May 1 starting date. Insect degree-days based on a January 1 starting date.


Table 6. Cumulative Degree-Days Required for Insects to Reach key Periods for Scouting or Management
  Maturity rating (days)
80 90 100 110 120
50% Silking 1100 1150 1250 1300 1400
Black Layer Formation 1900 2100 2300 2500 2800


Table 7. Cumulative Degree-Days Required for Insects to Reach key Periods for Scouting or Management
  Stalk Borer Alfalfa Weevil Black Cutworm* Corn Rootworm European Corn Borer Seed Corn Maggot
Adlt Emrg 5% Hatch 1st Gen 2nd Gen
SB AW BCW CRW ECB1 ECB2  
Initiation 1400 300 91 1283 380 WCRW** 558 1550 450***
Termination 1700 500 430 2253 478 NCRW** 1228 2045  

*Degree-day accumulation should begin at first moth capture in a black light or pheromone trap.
**These values represent degree day accumulations for optimal timing of Furadan 4F post emergence applications. WCRW-Western Corn Rootworm, NCRW-Northern Corn Rootworm
***This number of degree days represents the number of degree days required from plowdown of green vegetation until it is safe to plant corn or soybeans and avoid seed corn maggot injury.

Dennis Calvin, Entomology

William S. Curran
Associate Professor Weed Science
email: wsc2@psu.edu

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Website Address: http://fcn.agronomy.psu.edu/