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May 15, 1998 Vol. 98.5

IN THIS ISSUE:

Production:

PLANTING CONDITIONS

Due to the weather problems, many farmers will choose to no-till their corn and soybeans. Remember if it's too wet to plow, it's too wet to plant. Poor stands occur when the soil slit has not been properly closed. If you are planting in too wet soils and the seed is covered and the slit is closed soil shrinkage as the soil dries out often causes the slit to reopen and expose the seed. The ONLY way to keep this from happening is to WAIT until the soil dries. If you are not seeing loose soil flowing around and dropping behind the seed openers-quit-and wait for drier soil conditions.

It may pay a no-tiller to switch to 8 or 13 wave fluted coulters instead of the more common bubble coulters. I usually don't favor one over the other in ideal conditions, but the fluted coulter will cause less sidewall compaction in the seed zone in higher moisture planting conditions. PATIENCE! Corn and beans planted right will make more money than those same crops "mudded in" a few days earlier.

Lynn Hoffman, Agronomy
Extension Tillage Specialist



CORN PLANTING PRIORITIES AND HYBRIDS

Given the wet spring, many fields will be planted substantially later than normal. Generally, adapted "medium season" hybrids that will usually mature in an area can be planted through May 20-25. After that they risk frost before maturity and some consideration should be given to switching to earlier hybrids. "Full season" hybrids that may have some risk of frost before maturity in any season should probably only be planted through May 15 or so except perhaps for silage. For a more scientific approach, estimate the growing degree days necessary to mature a particular hybrid and compare that to those available during the rest of the season. Growing degree data for a few representative locations around the state are available on our Corn and Soybean Management web page at http://cornandsoybeans.psu.edu/gddhybrids.cfm. Use this in conjunction with hybrid data to estimate the potential for hybrids to mature. You can also consult with the publication "Latest Planting Dates for Corn Hybrids in Pennsylvania" available from county extension office and the PSU Publications Distributions Center (814-865-6713). If you don't have one of these in your file, you should.

Yield penalties for delaying planting corn will be about 1 bu/acre during late May. Grain moisture at harvest will also increase, or harvest will be delayed. On the bright side, there is not a high correlation between early planting dates statewide and high state average yields. This is because many other factors besides planting date, like August temperatures and rainfall, contribute to corn yield potential. In fact, in the last high yielding year of 1996, corn planting was behind normal in late May.

Greg Roth, Agronomy,
Corn and Sorghum Management

Pest Management:

QUICK NOTES - UPDATE

Select 2EC has received EPA registration for use in alfalfa. Select is a post-grass herbicide and may be applied to seedling or established alfalfa (including sainfoin, holy clover, and birdsfoot trefoil). It can be tank-mixed with 2,4-DB for control of broadleaf weeds. Apply 6 to 8 fl. oz./A Select for control of annual and suppression of perennial grasses. Include a crop oil concentrate at 1% v/v in the spray mixture. Check with your supplier about labeling and availability in Pennsylvania.

Dwight Lingenfelter, Agronomy



WET WEATHER WOES! - WHAT TO DO ABOUT WEED CONTROL

In southeastern, southcentral, and other parts of Pennsylvania, many corn acres were planted from April 25 to May 1 and then it routinely rained. Despite the extremely moist conditions, soil temperatures were relatively warm (58° F at 3 inches at 8 a.m.) and most corn emerged after about 14 days. Because of the wet conditions some weed management complications have arisen. Below are some problems and possible solutions.

Problem 1: Some of the planted acres did not receive preemergence herbicides before corn emergence.

Solution: Most of the commonly used pre herbicides can be applied as "delayed-pre" applications. (Refer to the last issue of Field Crop News (May 1 1998; Vol. 98:4) for a table listing maximum corn heights and weed stages for delayed-pre applications or refer to the herbicide label.) However, you may need to tank-mix with post products to control any emerged weeds. Another option would be to apply an early post herbicide such as Basis, Basis Gold or another Accent-containing product.

Problem 2: No-till corn that has emerged and no burndown/residual herbicides have been applied yet.

Solution: Unless Roundup Ready corn is planted, traditional post herbicide programs will have to suffice. Depending on the severity of the weed problems, possible herbicide options include Basis, Basis Gold, Marksman, Extrazine II, or Beacon/Exceed/Accent plus Banvel combinations. Include a pre herbicide, such as Bicep II, Harness Xtra, FulTime, or Prowl for residual control. However, be cautious of corn sensitivity to some of these products as well as to crop oil concentrates (see Problem 4 below).

Problem 3: Some corn is emerging and has not yet received nitrogen and a preemergence herbicide application.

Solution: Unfortunately, according to their labels, none of the commonly used preemergence herbicides can be applied in liquid fertilizer once the corn has emerged due to crop injury concerns. (Only the Zeneca product labels (e.g., Surpass 100, Top Notch, FulTime) do not directly state not to use with a liquid fertilizer carrier as a delayed-pre treatment. We do not recommend applying any herbicides in liquid fertilizer after corn emergence. Check with your Zeneca representative for additional information about this matter. In most cases, two operations will be necessary to accomplish these tasks.

Problem 4: Due to the prolonged low light conditions and wet conditions, corn seedlings will be extremely sensitive (because of a thin cuticle layer) to many herbicides.

Solution: Post herbicides such as Banvel, 2,4-D, and Bladex, may cause above normal injury to corn under these conditions, therefore it would be best to wait until several days of sunlight have occurred before applying these types of herbicides. Also, with the saturated soils, herbicides like Banvel can quickly move through the soil and into corn roots causing plant injury. Wait a few days for soils to dry.

Problem 5: Expect weed control to break sooner this year. If pre herbicides were applied prior to the heavy rains, in many cases, the length of residual weed control will be reduced.

Solution: Post rescue treatments will likely be necessary this year to control new weed flushes before crop canopy closure. If weeds are sprayed when relatively small, reduced rates may provide sufficient control and help save some additional herbicide costs.

Dwight Lingenfelter and John Yocum, Agronomy



POSTEMERGENCE HERBICIDE APPLICATION TO CORN

Herbicide labels that refer to corn height in inches are ambiguous. The labels do not specify what the measurement boundaries are on the corn plant (e.g., ground surface to tallest, free-standing, point; ground surface to whorl; base of stalk to fully extended leaf; etc.). The leaf number method generally begins by counting the first rounded leaf or coleoptile (this first leaf sometimes rapidly matures and falls off), continues up past the last visible leaf collar to the uppermost leaf that is 40 to 50 percent exposed. This leaf typically has its leaf tip pointing downward. This method usually results in the addition of one or two leaves more that the leaf collars method. The number of visible leaves and height does not always give a true indication of the crop stage. The more exact method of growth staging is to use a method that corresponds to the number of leaf collars. This system describes the growth of young corn by counting the number of leaves that have exposed leaf collars, beginning with the first or rounded leaf. The collar is a light colored band that appears where the leaf attaches to the stalk or sheath. A plant with four leaves with visible collars would be called a four-leaf or a V4 plant.

Exact growth staging can be important, since some postemergent herbicide applications applied after the labeled stage may cause a decrease in the reproductive capacity (yield) of the crop. In general, applications made prior to the V3 stage provide the greatest crop safety. Some labels, especially those on newer products, provide several ways of determining growth stage. Until there becomes a universal rule throughout the crop protection industry for staging crop growth, we will have to continue to use a number of methods. Table 1 provides the restrictions for common post corn herbicides.

Bill Curran and Dwight Lingenfelter, Agronomy



ADJUVANTS AND HERBICIDE APPLICATIONS

Adjuvants are a key component of many postemergence herbicide applications. With the wet weather we have been experiencing, I suspect that post applications will be even more common in the next few weeks than in a more "normal" year. In deciding what the appropriate adjuvants are for post herbicides applications, keep a few things in mind.
1.) Examine the herbicide label for adjuvant recommendations. Most products that were introduced in the last 10 years have adjuvant information on the label. Even some of the older products have adjuvant recommendations. Some manufacturers commit a fair amount of R&D to determining the best adjuvant system for their products. This is the place to start.
2.) Examine other literature sources such as our Penn State Agronomy Guide/Weed Control Guide or similar publications from other public institutions. The publications usually have recommendations boiled down for most commonly used herbicide products.
3.) Consider the current environmental conditions when selecting adjuvants. What is the temperature, humidity, and soil moisture? Are the weeds drought stressed or are they lush and succulent? How big are the weeds and the crop? These factors are all important for predicting how active the herbicide application will be and what the potential is for good control of the weeds and crop injury (e.g., If the weeds are small and succulent and the crop is sensitive, you may want to avoid any oil based adjuvants or fertilizer solutions and stick with a nonionic surfactant).
4.) Once you have selected the appropriate type of adjuvant (i.e. crop oil concentrate, nonionic surfactant, etc.), use a brand that has a history and proven track record. Avoid adjuvants from sources you have never heard of or that do not have reliable unbiased data to support their claims.

Table 1. Postemergence Herbicide Application Restrictions for Corn
Herbicide Over the top application Use of drop nozzles Comments
Accent 24" tall (free-standing) or
<6 collars (V6 stage) 		24" - 36" tall or
V6 - V10 stage 		 
Accent Gold up to 12" tall   Do not apply to corn >12" tall or exhibiting 6 collars.
Atrazine 12" tall    
Banvel 1 pt - 8" tall or 5 leaves
1/2 pt - 8"-36" tall or
15 days before tassel emergence 		  Do not apply Banvel near soybeans if corn is >24" tall, soybeans are >10" tall, or have begun to bloom.
Basagran No restrictions    
Basis Spike to 4 leaves (2 collars) or
1/2" to 6" tall		   Do not apply to corn having 3 collars or >6"
Basis Gold up to 12" tall   Do not apply to corn >12" tall or exhibiting 6 collars.
Beacon 4" - 20" tall (free-standing) For splits, 20" tall to before tassel emergence  
Bladex 90DF Emergence to 4 leaf stage   Do not apply if 5th leaf is visible
Buctril 1 pt - emergence to tassel
1 1/2 pt - 4 leaves to tassel 		  Post application before 3 leaf stage may result in corn leaf burn.
Buctril + atraz. 1 1/2-2 pt - emergence to 12" tall
3 pt - 4 leaf to <12" tall 		  Post application before 3 leaf stage may result in corn leaf burn.
Clarity 16 fl oz - emergence to 8" tall When tank mixed with Accent or Beacon - 8"-12" tall If tank mixed with atrazine and oil apply before 5" tall corn.
Exceed 4" to 20" tall or 6 collars >20" to 30" tall  
ExtrazineII DF Before 5th leaf is visible or 8" tall   For best results, apply from emergence to 2 leaf stage.
Hornet Emergence up to 24" tall    
Laddok S-12 Spike to 7 leaves or up to 12" tall    
Lightning Up to 12" tall   Apply to IMI corn hybrids only
Liberty Emergence to 24" tall or
seven collars (whichever comes first)		   Apply to Liberty-Link or GR corn hybrids only
Marksman Emergence to 5 leaf stage or up to 8" tall    
Permit Spike to 48" tall When necessary If tank mixed: with 2,4-D, apply up to 8" tall corn; with Banvel apply up to 36" tall corn.
Poast Plus or Poast Emergence to onset of pollen shed When necessary, as dictated by corn canopy and weed height Apply to Poast Protected corn hybrids only
Pursuit No restrictions on label When necessary Apply to IMI corn hybrids only. If tank mixed, use most restrictive application timing.
Resource 2-leaf to 10-leaf stage (collars must be visible) When necessary, to direct below corn leaves  
Roundup Ultra Up to 24" tall   Apply to Roundup-Ready hybrids only
Sencor Emergence to pretassel When necessary See tank-mix partner
Scorpion III Up to 8" tall >8" (prevent contact with corn)  
Shotgun Spike to 4 leaf or up to 8" tall 5 leaf or 8"-12" tall  
Spirit 4" to 20" tall or 6 collars >20" to 24" tall  
2,4-D <8" tall 1/2 pt - 8" to 36" tall  
Tough No restrictions on label When necessary Best to apply before 4-leaf stage of weeds but can vary with tank-mix partner.



HARD WATER AND SOLUTION PH - DO THEY AFFECT HERBICIDE PERFORMANCE?

Hard water. It seems that more and more questions are popping up on hard water and solution pH and how this might affect herbicide performance. The hard water issue usually involves calcium (Ca), magnesium (Mg), or iron (Fe) salts in the water carrier that could potentially interfere with the performance of some herbicides. This is generally independent of solution pH although a number of products sold in the market place contain both a water softening agent and a buffering or acidifying agent. A good example of a herbicide potentially affected by hard water is glyphosate (Roundup and Touchdown). Other weak acid herbicides (i.e., sulfonylureas, imidazolinones, 2,4-D, dicamba, and the post grass herbicides such as Assure, Fusilade, Select, Poast,) can also interact negatively with hard water. The degree of hardness necessary for reduced herbicide activity is not well documented and depends on the herbicide, the water source and mineral content, weed species, and environmental conditions during application. Ammonium sulfate is often recommended as an adjuvant to reduce the potential for hard water problems. Urea containing fertilizers do not provide the same benefit. Monsanto recommends the addition of Ammonium sulfate to Roundup Ultra if greater than 500 ppm of Ca, Mg, and/or Fe are present in the water source. This may be a good rule of thumb for any of the weak acid herbicides, although the exact degree of water hardness necessary for this benefit is not known. A number of products are sold commercially that contain ammonium sulfate or some other softening agent that ties up mineral ions.

Solution pH. The solution pH topic actually deals with two related issues; one is with pesticide stability and half-life, while the other involves herbicide performance as it relates to herbicide penetration. The stability of most herbicides in water solutions is very good, as long as they are sprayed within a day or two of mixing. The exception can be some of the sulfonylurea herbicides which degrade by chemical hydolysis when in water solution. Many of the Dupont products (e.g. Classic, Harmony Extra, etc.) state that the herbicide solution should be sprayed within 24 hours to avoid herbicide degradation. Novartis's Exceed label states that the product should remain active for at least 36 hours. The degradation rate by chemical hydrolysis of the sulfonylureas increases as the pH of the solution decreases (pH less than 5, in particular). Therefore, acidifying spray solutions may increase the rate of sulfonylurea degradation. Other pesticides and in particular some fungicides and insecticides degrade more rapidly in alkaline solutions (pH greater then 8). In terms of herbicides, Gramoxone Extra and Buctril are both reported to be unstable under alkaline conditions. However, the half-life of most herbicides in water solution is generally adequate as long as they are not held for a prolonged time in the spray tank.

The effect of solution pH on herbicide uptake by plants has not been well documented, particularly under field conditions. In theory, weak acid herbicides may better penetrate plant leaves in their neutral form. As the pH of the spray solution increases, more of the weak acid herbicide molecules become ionized or charged potentially reducing plant uptake. This of course assumes that the parent acid is present in the spray solution or on the leaf surface and is capable of changing ionization state. In reality, many weak acid herbicides are formulated as salts (e.g. isopropylamine salt of glyphosate = Roundup Ultra) and may not undergo these reactions when spray solution pH could be a factor. The activity of foliar applied herbicides that are neutral (most other post applied products) are not influenced by solution pH, while the activity of basic herbicides (i.e. triazines) could even be reduced in acid solutions.

The pesticide manufacturer should be able to provide you with sound advice on solution pH and the performance of their product. The best advice is to test your water for both water hardness and pH before you add anything to the spray tank that may or may not be necessary.

Bill Curran, Agronomy, Weed Science



TANK-MIXING ALFALFA HERBICIDES AND INSECTICIDES

Every so often we get questions about tank-mixing alfalfa herbicides and insecticides. Often, this type of tank mixture is used in seedling-year stands. Unfortunately, in most cases, neither the herbicide nor the insecticide labels explicitly state what products can be tank-mixed. However, most labels do not forbid tank-mixing herbicides and insecticides, but they strongly recommend compatibility tests. The first test of compatibility is physical compatibility. To test for physical compatibility, mix both the insecticide and herbicide together with their carrier at the recommended or desired application rate in a jar. Let the material set for 24 hours and check to see if any precipitate has formed or major changes in the consistency. If the materials past the physical compatibility test, then you may need to test for chemical compatibility. To test for chemical compatibility, spray the materials in a small area of a field and allow adequate time for the materials to work (5-7 days). Has any change in color or health of the crop occurred. Are the appropriate weeds and insects being killed? Chemical incompatibility can cause the compounds to lose effectiveness or can lead to phytotoxic effects on the crop. Before mixing an insecticide and herbicide that the pesticide label does not list, it is a good idea to first check with the company to see if they have any information that can help. Table 2 lists some commonly used alfalfa products and their label statements concerning tank-mixing.

Table 2. Tank-mix statements for some common alfalfa herbicides and insecticides.
PRODUCT TANK-MIX LABEL STATEMENT
Herbicides  
2,4-DB 200, (Butyrac 200)
  • No statement on label.
Buctril
  • Insecticides listed on label: Dimethoate, Furadan, Lorsban, Malathion, Pounce, Sevin.
  • Other products may be tank-mixed with Buctril, but "jar test" first to determine compatibility.
Poast/Poast Plus
  • Physical incompatibility, reduced weed control, or crop injury may result from mixing Poast/Poast Plus with other pesticides (fungicides, herbicides, insecticides, insecticides, or miticides), additives, or fertilizers.
  • Check with local agricultural authorities before tank mixing.
Pursuit
  • When organophosphate or carbamate insecticides are tank-mixed with Pursuit, temporary injury may result to the treated crop.
Select
  • No statement on supplemental label.
Insecticides  
Dimethoate 400 or 4 EC or Dimate 4E (formerly know as Cygon)
  • This product should not be tank-mixed with other pesticides, surfactants, or fertilizers unless prior use has shown the combination is noninjurious under your conditions of use.
  • Follow precautionary statements and directions for all tank-mixed products.
Lorsban
  • Should not be tank-mixed with pesticides, surfactants, or fertilizer formulations unless prior use has shown the combination is noninjurious under your current conditions.
Permethrin (Ambush, Pounce)
  • No statement on label.

Dwight Lingenfelter, Agronomy and Dennis Calvin, Entomology


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 world wide webpage, http://www.cas.fra.psu.edu/.

Corn Soybeans Alfalfa Small Grains
  • seed corn maggot
  • flea beetle
  • garden symphylan
  • thrips
  • wireworm
  • black cutworm
  • grape colaspis
  • corn root aphid
  • white grub
  • sod webworm
  • slugs
  • seed corn maggot
  • thrips
  • alfalfa weevil larvae
  • spotted alfalfa aphid
  • meadow spittlebug
  • clover root curculio
  • English grain aphid
  • corn leaf aphid
  • cereal leaf beetle

Black cutworm - Black cutworm larvae have been reported in sweet corn grown under plastic. According to degree day accumulations, some cutworm larvae have reached or will shortly be reaching the stages of development that can clip off small seedlings (see table 3 and 5). The warm spring temperatures have accelerated the insect's development, so they are about two weeks ahead of normal in reaching damaging stages. Spring rains have prevented many farmers from planting corn, which will result in delayed development of the crop. This combination could mean increased injury by the pest. 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 apply a protective insecticide at-planting or preemergence. See the Agronomy Guide for effective materials and rates.

Economic Threshold Values:
Seed leaf stage - 2% of plants cut
Two leaf stage - 3% of plants cut
Three leaf stage - 5% of plants cut
Four leaf stage - 7% of plants cut
Five leaf stage - Seldom a problem at this stage

Alfalfa Weevil Larvae - As with the black cutworm, alfalfa weevil development is ahead this year. Reports of fields showing injury have been coming in, but so far I have not heard of a large number of fields requiring an insecticide treatment. In many areas of the state, we are just entering the period when maximum injury from the pest will occur. Watch alfalfa fields closely over the next couple of weeks. Concern about how early injury is being observed has lead to speculation that a longer residual insecticide material will be needed to protect the crop until harvest, if alfalfa weevil populations reach the economic threshold. A longer residual material should not be needed. Egg laying by adults is over and no new individuals are being added to the population. The warm spring has accelerated development of the pest. Typically when development is accelerated, the spread in weevil age is reduced. This means that normal alfalfa weevil insecticides will adequately protect the crop. 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, and Ambush formulations. See the Agronomy Guide for specific rates and application methods.

Economic Thresholds - 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 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 -
One or more spittle masses per stem in mid-May

Clover root curculio - This insect causes economic losses in Pennsylvania alfalfa fields but cannot be effectively controlled. Fields injured by the pest will have areas where most of the alfalfa plants have died and/or plants appear stunted. This is typically in an area of the field that is droughty or excessively wet. When roots are dug up, they have dark brown jagged areas on the surface of the root where the larvae have been feeding. Death of the plant is the result of root scaring during feeding that allows plant pathogens to enter the stem. Prevention of this injury would require an adult control program. Although this could be done, implemention would result in valuable parasitoids that control alfalfa weevil populations being killed. This would result in major outbreaks of alfalfa weevil and a significant increase in the need for insecticide applications. Researchers are currently working on new control strategies that will not affect alfalfa weevil integrated pest management programs.

Potato leafhopper - Although I have not yet received any report of the pest in Pennsylvania alfalfa fields, I expect the pest to arrive in the state early this year. The abundance and frequency of storm systems that have been originating in the Gulf of Mexico and moving into the state should bring migrating adults into the state. Also, storms moving up the Atlantic coast can bring the pest into Pennsylvania. 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.

Dennis Calvin, Entomology

Precision Vision:

PESTICIDE SPRAY DRIFT AND YOUR ANGRY NEIGHBORS!

Seems like just a week ago but actually it has been five weeks since I returned from the North American Conference on Pesticide Spray Drift Management in Portland, Maine. The weeks have been going by fast with the planting season here. I thought that the conference, at least from the name, would be another boring presentation of facts about pesticide labels. Was I ever wrong! Even working in precision application, I had my eyes opened to the impact of pesticide drift.

The USDA- Agricultural Research Services estimates that pesticide use on major field crops in the United States is 482 million pounds of active ingredient and about 90 percent of that amount is applied by sprayers. That is 241,000 tons of active ingredient! That number doesn't include the carrier water or other components such as adjuvants or other chemicals that are used to increase the effectiveness of the application.

I have been talking in previous columns about sprayer calibration and nozzle selection. Spray drift is one major reason for applicators to pay attention to sprayer condition and spray application. I spoke about some other reasons in previous columns. This time, I want to focus your attention on the impact of drift of pesticides. Many Pennsylvania farmers and custom applicators are applying chemicals to fields near populated areas or schools. Since the days of Rachael Carson's book, Silent Spring, the U.S. public has been aware of the dangers to humans. Whether correctly informed or not, the public can make life difficult for applicators to do their work. Besides danger to human health, pesticides can damage nearby crops, orchards and livestock. Of course it would be pleasant if all of the applied chemicals could be put on the target crop, but in reality, this rarely happens. Pesticide drift happens.

So, what exactly is "drift?" One definition, commonly accepted: "Pesticide drift," means the physical movement of pesticide through the air at the time of pesticide application or soon thereafter from the target site to any non-or off-target site. Pesticide drift shall not include movement of pesticides to non-or off-target sites caused by erosion, migration, volatility, or windblown soil particles that occurs after application unless specifically addressed on the pesticide product label with respect to drift control requirements. (Spray Drift Coalition)

Now, in this column, I cannot cover all of the details of spray drift. Nevertheless, since it does happen and we cannot eliminate it totally, to protect sensitive areas, buffer zones are usually used. buffer zone is defined by the Spray Drift Coalition as: an area where pesticide is not directly applied, thereby providing protection to a defined area. Buffer zone designations are contingent on: 1) state regulation, 2) pesticide product labels, 3) prevailing weather conditions, and 4) sensitive/protected areas. Buffer zones are usually next to a protected area.

Since we are not, by definition, having to consider volatilization of pesticide as a drift problem, we can concentrate on the major factors to consider: 1) spray droplet size, 2) wind and 3) weather conditions. We can control usually, the droplet size through the selection of spray pressure and nozzle type, but the wind and weather we have to live with.

I recommend for those of you who can surf the Internet, do a web search on "spray drift" or type in some of the following web sites for excellent manuals and details on spray drift control: http://www.ianr.unl.edu/pubs/pesticides/g1001.htm (University of Nebraska), or http://ohioline.ag.ohio-state.edu/b816/ (The Ohio State University), or our Penn State University website at http://server.age.psu.edu/dept/extension/Factsheets/b/ . These web sites offer excellent detailed brochures.

The basic principle to remember is that smaller spray droplets are more likely to drift and the smaller they are, the farther they will drift depending on the wind speed and the weather conditions. Many people try to describe the size of spray drops. The size or diameter of spray droplets are commonly measured in units of microns or one millionth of a meter. Human hairs are often described as being about 75 microns in width. A 150 micron drop is about the same diameter as the thickness of two sheets of paper. There is a range of sizes to put droplets in:
Very fine droplets - median diameters less than 120 microns (dry fog to misty rain)
Fine and medium size droplets - median diameters from 120 to 350 microns (misty to light rain)
Coarse and very coarse droplets - median diameters over 350 microns (light rain to heavy rain)

The impact of spray drift becomes insignificant at droplet sizes over 150 - 200 microns. The goal of controlling spray drift is to select nozzles that minimize the number and total volume of spray in droplets smaller than 150 microns. These are the sizes that drift the greatest distance. The drift distance is the width of the buffer zone if you want to protect a specific area, such as a schoolyard or a residential neighborhood. Don't forget if you are spraying Roundup on a resistant crop and the drift gets to a Roundup sensitive crop, you have done damage. Different nozzle selection guides provide a droplet size called the volume median diameter (VMD). That term means that the diameter of drop or the VMD is the size of drop at which one half of the total spray liquid (volume) is contained in drops smaller than the VMD. Another guide to nozzle selection is to use spray pressure and nozzle sizes to reduce the amount of spray volume in drops smaller than 150 microns to a minimum. Nozzles can be selected to discharge as low as one percent of spray volume in droplets smaller than 150 microns. The point I also want to make is that in general, you can't see spray drift from any distance. The droplets are too small for the human eye to discern.

Here are some ways to reduce drift - (University of Illinois - The Cutting Edge)
-Select a nozzle that produces coarser droplets
-Use the lower end of the pressure range
-Lower boom height
-Increase nozzle size
-Spray when wind speeds are less than 10 mph
-Spray when wind is moving away from sensitive crops
-Do not spray when the air is very calm (or when there is an inversion). Inversions typically happen early in the morning or near bodies of water. Use a drift control additive when needed.

David Wagner, Ag & Bio Engineering, Precision Ag


Agents Corner:


ADAMS COUNTY

Rain, or chance of showers today. That has been our forecast for the last month here in Adams County. From April 1 through May 15, we had received 9.7 inches of rainfall. This has delayed corn planting and first cutting of haylage, due to excessive soil moisture.

With the mild winter and warmer spring, crop growth was about two weeks ahead of normal during April and early May. Rye was cut beginning on April 18 and barley reached growth stage 10 around April 20. The barley is currently in the early stages of maturity. Wheat heads have emerged on most of the crop with the flag leaf present on the later plantings. The warm moist weather has promoted some powdery mildew, and septoria in the wheat.

Corn planting began in our area around April 23. The early corn has emerged and has reached the first true leaf stage. Much of the planting has been delayed due to rainfall.

Orchardgrass heads have emerged and the crop is fast approaching maturity. Alfalfa is in the bud stage with some early blooms. Below threshold levels of alfalfa weevil have been seen in some fields, however, with the current maturity level, mowing will be our best option. A small amount of hay has been harvested between rain showers. Currently, we are waiting for the proper field conditions to continue planting and hay harvesting, without causing soil compaction.

Larry Swartz, Adams County

CENTRE & CLINTON COUNTIES

As with the rest of the state, field work in these two counties has been "on hold" for the last two weeks, waiting for the rains to cease. Very little corn has been planted, although fields that got planted in April have emerged and look good. Oats and spring seeded alfalfa both look very good. Established alfalfa fields were heavily infested with dandelion, and could be harvested most any day. However, corn planting will likely take priority over hay harvesting.

Some rust has been reported on wheat and barley fields. No major insect or diseases have been reported yet, but too few crops have been planted to note much insect or disease pressure.

Gary Dauberman
Centre/Clinton Counties

LAWRENCE COUNTY

Short of the week ending April 25, little corn planting has taken place here in the northwest. At one point, producers were ahead of schedule, but this advantage was short-lived. Corn that was planted in April emerged in good time and some producers will need to adjust spray programs as a result.

The hay crop seems to be ahead of schedule this spring, like most other plants and insects. This in conjunction with delayed corn planting could translate to a poor quality hay crop. Remember, there is no replacement for a high quality forage in a ration. Graziers were on pasture earlier this spring and for the most part, pastures have been producing well. This may be the year to encourage nitrogen application on grass fields following 1st cut. Should weather conditions continue we should have a good second and possibly third cutting.

Alfalfa weevil have emerged earlier this year, and have reached threshold levels in some fields. Producers are encouraged to scout fields and treat or cut early, those fields with high populations of weevil.

A couple of notes on fall seedings: we finally had a good winter from a soil heaving standpoint, but some fields will be lost to winter annual weed pressure. On a positive note, fields treated with Gramoxone for chickweed in early spring have shown excellent results. In addition to weed problems, we also saw a higher incidence of sclerotinia in fall seedings this spring.

The wheat crop has continued to progress well, but the oat crop will be variable. In some cases fields were never seeded, and many that were showed poor establishment due to the wet conditions. Many of these fields will be planted to corn.

Ryan Hockensmith.
Lawrence County

SCHUYLKILL COUNTY

Schuylkill County had a dark and gloomy beginning to the planting season. Showers and rain storms abounded. Two ducks were seen building an ark. Some folks are speculating that the wet spring will certainly be followed by a dry summer. But I can't put much stock in that prediction because the weather (temperature and rainfall) in April 1998 is very similar to that in April 1996 and that was a rather good crop production year. At any rate we will just have to take what we get and make the best of it. A few farmers jumped the gun and managed to get some corn planted during the last week of April and it seems to be emerging well. Not all of that corn was sprayed for weed control so the post-emergence products may be put to the test.

Several corn trial plots are planned for the western end of the county. One is a comparison of population rates with planting drops ranging from 24,00 to 34,500 plants per acre. A second trial involves comparing silage corn planted in 30 inch rows to corn at the same population but using split rows of alternating 10 inch and 20 inch spacings. This row spacing configuration should allow the use of a conventional four row 30" harvester. Both of the trials will be under a center pivot irrigation system so lack of water should not pose a problem. Now if we could only figure out how to shift the irrigation system into reverse, maybe we could pump enough water off the fields to get started.

J. Allan Shoener
Schuylkill County

SUSQUEHANNA/BRADFORD

Now that 40 days and 40 nights have passed, we in the northeast expect to dock anytime soon and get the rest of this spring underway. I understand it's not much different elsewhere in the state. Fortunately, the warmer temperatures have treated previously-planted crops quite favorably.

The spell of dryer weather we're facing now has a few producers wondering whether to harvest alfalfa- or grass-based forages or plant corn. Clearly, the forages are about 10+ days ahead of normal and most are anxious to get started on something.

Spring-seeded oats and forage seedings have emerged quickly and are growing well. Established forages are growing as expected with the warm rains, although, inadequate fertility is painfully obvious on some fields this year. Herbage growth in one mixed grass/clover pasture in Susquehanna County accumulated at a rate of about 70#/acre/day.

There is corn planted but very few acres at this time and it will be interesting to watch this corn use this "fuller" season. I anticipate many producers will be able to accomplish several field tasks over the next week.

Mark Madden
Susquehanna/Bradford Counties

Degree Day Accumulations:

1998 DEGREE DAY ACCUMULATIONS

To track corn and insect development, compare the 1998 cumulative degree-days shown in Table 3 to the required values in Tables 4 and 5. Choose a location that is closest to your site when making a comparison.

Table 3. Cumulative Degree Days for Corn and Insects for the Period Ending May 11, 1998
Corn Insects
County Location 1998 30-year ave. CSB AW BCW CRW ECB
50F 50F Diff 40F 48F 50F 53F 55F
Erie Waterford 89 82 7 618 284 223 149 110
Crawford Meadville 97 89 8 675 313 248 168 125
Mercer Mercer 96 90 6 690 319 253 171 128
Bradford Towanda 701 87 14 695 324 258 176 131
Lycoming Montoursville 110 95 15 770 360 289 198 150
Tioga Mansfield 90 82 8 634 292 231 155 115
Susquehanna Montrose 80 74 6 584 266 208 139 103
Butler Butler 104 96 8 755 352 281 192 145
Indiana Indiana 103 95 7 761 355 282 193 146
Lawrence Lawrence Jct 99 89 10 672 313 248 168 125
Blair Martinsburg 97 92 4 742 346 274 187 141
Centre State College 98 91 7 726 337 267 182 137
Columbia Bloomsburg 111 96 15 797 372 299 207 156
Clearfield Curwensville 97 90 7 708 328 260 177 133
Dauphin Elizabethville 115 100 15 844 396 319 221 168
Bedford Bedford 107 99 7 820 386 308 212 161
Mifflin Belleville 109 97 11 798 373 299 206 156
Northumberland Sunbury 117 100 17 838 392 316 220 167
Lehigh Trexlertown 120 102 18 882 413 334 234 178
Schuylkill Hegins 110 97 13 806 376 302 208 158
Westmoreland Greensburg 101 96 5 767 359 285 195 147
Somerset Somerset 84 84 0 669 308 242 162 121
Washington Washington 110 102 8 828 390 312 215 163
Franklin Chambersburg 120 106 14 913 432 349 243 186
York York 127 109 18 964 456 369 260 200
Lancaster Ephrata 118 102 15 888 418 337 235 179
Berks Hamburg 122 103 19 892 419 338 237 181
Corn degree-days based on a May 1 starting date. Insect degree-days based on a January 1 starting date.


Table 4. 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 5. 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

Living Mulch Tour in Schuylkill County

When: June 25, 1998
Meet at: The Mahantongo Fire Co. in Pitman, PA SE of Sunbury
and Shamokin just over county line in Schuylkill Co.
Place: Carl Riedler Farm
R.D.#1
Klingerstown, PA 17921-0127
Purpose: To show the benefits of a crownvetch and birdsfoot trefoil living mulch.

Erosion control; A perennial crownvetch living mulch reduces water runoff, soil loss, and pesticide loss from sloping land. It provides a permanent cover for intercepting the force of falling raindrops, which would otherwise detach soil particles and make them prone to erosion. It also slows the rate of runoff, thus improving moisture infiltration into the soil. By increasing the amount of water that penetrates the soil, a crownvetch living mulch often improves the moisture availability for crops.

Improved fertility; A crownvetch living mulch aids soil fertility by stopping nutrient loss in surface runoff. In addition, because crownvetch is a legume, it fixes nitrogen from the air. Research at The Pennsylvania State University indicates that yields of 178 bushels per acre are possible for corn planted into crownvetch that is 5 to 7 years old with only 125 lb/A of added nitrogen. Some growers of crownvetch seed have planted their fields to corn to clean out the weeds and use up the excess nitrogen.

Cover crop seeding and management; Crownvetch and birdsfoot trefoil can be seeded into IR or IMI corn with the use of Pursuit + Basis for weed control. After the seeding year, there are a whole host of herbicide treatments that can be used to control weeds and suppress the living mulch without killing it. A dozen of these treatments will be shown on the tour.

Background: Crownvetch and birdsfoot trefoil are perennial legumes adapted to the temperate climates of the northern two-thirds of the United States. They are native to central and southern Europe, North Africa, and the Near East. These are hardy, deep-rooted plants that have already proven their value in soil stabilization and erosion control for roadsides, steep banks, and other noncropland areas. Their potential as a perennial "living mulch" for no-tillage crop production is now possible. As a living mulch, crownvetch and birdsfoot trefoil provide a permanent, living ground cover. Other crops such as corn, small grains, and alfalfa can be seeded into it, as if it weren't there. The use of a living mulch will solve some of the age-old soil erosion problems of farmers without the need for putting a large percentage of the farm in sod crops.

Tour: June 25, 1998; 10:00 to 2:30 p.m. - We will start with a tour of some of field scale corn planted into crownvetch. Then we will follow with an examination of a dozen of the recommended herbicide treatments that may be used for weed control and crownvetch and birdsfoot trefoil living mulch suppression after the first year. Over lunch we will have a discussion of the benefits and problems of using a living mulch. Both CCA and pesticide update credits will be given.

Registration: No charge but please register anyway. Bring your own lunch for lunch in the park.

Further Dr. Nathan Hartwig J. Allan Shoener
Information: Penn State University Schuylkill Co. Coop. Ext.
  116 A.S.I. Bldg. 1202 Ag. Center Dr.
  Univ. Park, PA 16802 Pottsville, PA 17901
  Ph: 814-865-1906 Ph: 717-622-4225
  email: nlh@psu.edu email: schuylkillext@psu.edu
William S. Curran
Associate Professor Weed Science
email: wsc2@psu.edu

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