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April 9, 1999 Vol. 99.2

IN THIS ISSUE:

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Production

Pest Management

Production:

PELLETIZED LIME

Limestone is applied to agricultural soils to reduce the soil acidity, as indicated by increasing soil pH. Because we use calcium and magnesium carbonates as liming materials to neutralize the acidity in the soil, limestone is also the primary source of the essential plant nutrients Ca and Mg. The quality of a limestone is determined by the amount of acidity it can potentially neutralize as given by its calcium carbonate equivalent (CCE) and by how fast it will react as given by it's fineness. You can compensate for a material with a low CCE by applying more. For example, a material with a CCE of 50% would require 2 times as much of this limestone be applied as recommended on the soil test. Guidelines for making this adjustment are included with each soil test from Penn State. Generally, if a limestone meets the minimum fineness standards for fine-sized limestone (95% through 20 mesh, 60% through 60 mesh, and 50% through 100 mesh) the fineness will be adequate for agricultural liming purposes. If it is coarser than this it may take too long to react to be beneficial. If it is finer than this, it may react faster but little practical benefit is usually observed from this faster reaction in most situations. The recommendation is that you should use a limestone that at least meets these fineness standards but there is little benefit from paying more for a finer material.

There have been a number of questions lately about using pelletized limestone. Pelletized limestone is a very finely ground limestone that has been formed into water-soluble pellets to make it easy to handle. When this pelletized limestone is spread in the field the pellets break down and you have the effect of applying a very fine limestone. Which means it will react very rapidly. Pelletized limestone is an excellent product but it is usually costs 3 to 4 times as much as regular pulverized limestone. Also, as noted above there is generally little practical benefit to using a material that is finer than the fine-sized standard. Therefore, while it's an excellent liming material, little return can be expected from the added expense.

Often claims have been made that pelletized limestone can be applied at low rates (20 to 25% of recommended rates), to adjust the Ca levels and raise the pH in the soil in place of normal rates of limestone application. The main reason that we need to lime soils is to reduce the soil acidity. Liming recommendations are based on the simple chemical principle that one molecule of calcium or magnesium carbonate will neutralize two molecules of acidity. On a per acre basis this means that to completely neutralize the acidity in the soil (ie. raise the pH to 7) 1000 pounds of CCE are required for each unit of acidity in the soil as measured by the soil test. It doesn't matter how fine the material is ground, and thus how fast it will react, it still takes 1000 pound of CCE for every unit of acidity. Therefore, if less than the recommended amount of limestone is applied, regardless of fineness, not all of the acidity will be neutralized. There may be a short term increase in pH due to the rapid reaction of the very fine material, but most of the acidity will still be there and can still have potentially negative effects on crop production. Also, it has been found that if either calcitic or dolomitic limestone is applied at a rate to achieve an optimum pH, the Ca levels will be adequate for agronomic crops. Thus, there is little value to applying any material just to adjust Ca.

The bottom line is that while pelletized limestone is an excellent liming material, that will react very rapidly, the same amount is required as with regular limestone. Also, except in emergency situations where very rapid reaction is needed, the extra expense for the pelletized limestone does not usually result in any greater crop response than regular limestone.

Doug Beegle, Agronomy, Soils

MY CORN'S NOT COMING UP !

After all of the investment that is made in land, equipment, labor and other inputs, it's frustrating when corn doesn't emerge as well as it should. Diagnosing emergence problems early helps to identify solutions and develop replanting plans. Corn should begin emerging after about 100 to 125 GDDs have accumulated following planting. This can be anywhere from one to three weeks after planting depending on the temperature. Here's a list of a few common things to look for if you encounter an emergence problem in corn this spring.

1) No seed present. May be due to planter malfunction or bird or rodent damage. The latter often will leave some evidence such as digging or seed or plant parts on the ground.

2) Coleoptile (shoot) unfurled underground. Could be due to premature exposure to light in cloddy soil, planting too deep, compaction or soil crusting, extended exposure to acetanilide herbicides under cool wet conditions, or may be due to extended cool wet conditions alone.

3) Seed with poorly developed radicle (root) or coleptile. Coleoptile tip brown or yellow. Could be seed rots or seed with low vigor.

4) Seed swelled but not sprouted. Often poor seed-to-soil contact or shallow planting- seed swelled then dried out. Check seed furrow closure in no-till. Seed may also not be viable.

5) Skips associated with discolored and malformed seedlings. May be herbicide damage. Note depth of planting and herbicides applied compared with injury symptoms such as twisted roots, club roots, or purple plants.

6) Seeds hollowed out. Seed corn maggot or wireworm. Look for evidence of the pest to confirm.

Note the patterns of poor emergence. At times they are associated with a particular row, spray width, hybrid, field or residue that may provide some additional clues to the cause. Often two or more stress factors interact to reduce emergence where the crop would have emerged well with just one present. Also, note the population and the variability of the seed spacing. This information will be valuable in the future.

Greg Roth, Agronomy, Corn & Sorghum Management



EARLY HARVEST MEANS HIGHER QUALITY FORAGE

The production of high quality forage "on farm" means the purchase of less "off farm" feeds to meet the nutritional requirement of your livestock. Data collected from the Pennsylvania Forage and Grassland Council's Hay Show at Ag Progress Days indicates that harvesting earlier, when the plants are less mature, can result in higher quality.

Exhibitors in the Hay Show were asked to identify at what stage of maturity their hay samples were harvested. This information was compared with quality analysis to determine what effect plant maturity had on quality. There were 142 samples in the Hay Show and all of them were uses in the comparison.

Crude protein decreased as plants matured (Figure 1). Delaying harvest from midbud until the plants were more than 1/10 bloom caused a decrease of 6% units in crude protein. Fiber content as measured by ADF increased as harvest was delayed (Figure 2). Fiber content increased by more than 8 % units between harvest at midbud and harvest later than 1/10 bloom.

Figure 1


Figure 2


Harvesting when the plants are less mature places greater stress on the plants and will probably cause earlier stand thinning. Using a multiple disease resistant variety on well drained and high fertility fields will improve stand persistence when harvesting before first flower. Considerations that should be made prior to implementing a harvest strategy that includes harvesting during the bud stage are: the value of higher quality forage to your operation (nutritional needs of your animal type and class); disease resistance of existing stands; soil fertility and drainage; and the cost and difficulty of establishing a new stand.

EARLY HARVEST IS ESSENTIAL IN MAKING DAIRY-QUALITY GRASS HAY

The use of perennial grasses for high-quality dairy feed throughout much of Pennsylvania is common. Unfortunately, the quality of the harvested forage is generally less than dairy-quality. The key factor in harvesting dairy-quality forage is harvest management. Recent research conducted by Dr. Jerry Cherney at Cornell University showed that plant development varies with grass species, but forage quality decline was consistent across all species. In other words, the forage species is not as important as timely harvest in obtaining high quality forage.

Reed canarygrass, bromegrass, tall fescue, and timothy were harvested at various stages of development and tested for quality. According to Dr. Cherney, the research showed that fiber digestion and other quality parameters decline with increased maturity. The magnitude and rate of quality decline with maturity are much more important than quality differences between individual species. Cherney also suggested that producers should consider harvesting their pure grass stands in the spring for dairy feed before they harvest alfalfa, in order to produce acceptable grass quality.

In other research, presented at the recent American Society of Agronomy meetings, results indicate that spring harvest of later maturing varieties of cool-season grass species are lower in quality than early maturing varieties. When an early and late maturing variety of orchardgrass were harvested at the same stage of maturity, the early maturing variety had greater quality than the late maturing variety. The research suggested that the lower quality was the result of higher temperatures during the growth of the late maturing variety relative to the temperatures in which the earlier maturing variety grew. However, the difference in quality between late and earlier maturing grasses was minor compared to the drop in quality associated with delaying the first harvest of either variety. In summary, the use of cool-season grasses for dairy-quality feed requires harvesting the grasses earlier than normal. Delay in grass harvest and not grass species is the major factor in producing low quality grass hay or silage. Consider harvesting grasses before you would normally harvest alfalfa to obtain high quality forage that is suitable for dairy animals.

Marvin Hall, Agronomy, Forages

Pest Management:

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 found on the worldwidewebpage, http:/www.fra.cas.psu.edu/. This site provides links to important websites at other universities.

Corn
Seed corn maggot
Soybeans
Seed corn maggot
Alfalfa
Alfalfa weevil
Small grains
Aphids

Seed corn maggots - This pest can attack corn and soybean seed and young seedlings causing significant damage when spring conditions delay plant emergence and development. Adult flies over-winter in puparia in the soil and begin to emerge during late April and early May. These flies, which are about 1/2 the size of a housefly and are similar in appearance, move to areas of high organic matter to deposit their eggs. Eggs are laid on the surface near seed and the maggots work their way into the soil in search of food. Any moist organic matter will work as a food source, but they prefer decaying material. This pest is associated with old pastures or hay field that has been plowed under or with fields that have had heavy manure applications. In rare situations, even fields with low or moderate levels of organic matter can suffer from the pest, if populations in the area are high and cool damp condition persist. In corn, a planter box treatment that contains diazinon or diazinon and lindane provide the best protection for field corn. Because of the high plant populations of soybeans and their ability to compensate when stand levels are reduced, it is rarely economical to use a planter box treatment. It fields that have had a history of economic soybean stand reductions, a planter box treatment can be used, but make sure the planter box treatment does not kill the inoculum.

Economic Threshold Values

None exists for the pest. Because a planter box treatment is very cheap, it is recommended as insurance for all corn fields, particularly if they have high organic matter levels. Without this insurance, the only recourse is to replant the field if significant stand reductions occur.

For soybeans, only use a planter box treatment if a field has a long history of damage from seed corn maggot.

When a soil insecticide is used, a seed treatment is not needed if the material has activity against the pest and part of the material is applied in-furrow with the seed.

Alfalfa Weevil - This pest overwinters in both the adult and egg stage in Pennsylvania. In an average year, about 10% of the spring population is the result of larvae hatching from eggs laid during the previous fall. These larvae hatch during early spring (early to mid April); at about the same time that spring growth of alfalfa begins. In some years, early damage symptoms are seen, but the plants soon outgrow this feeding as temperature increase. It is rare that an insecticide application will provide an economic return. It is the larvae that result from the eggs deposited in the spring by overwintering adults that can cause economic losses. In an average year only 5 to 10% of alfalfa fields need to be treated. This is due to the release of several parasites by the USDA in the 1970's and a naturally occurring fungi, which help regulate the weevil populations. Prior to these releases, it was not uncommon for 80 to 100% of fields to require an insecticide application.

After hatching, the small larvae move to the stem tips and begin feeding. About 3 weeks after hatching these larvae have reached the last instar (1/4 to 3/8 inches long). It is during this period, usually mid to late May, that significant defoliation is seen.

Economic Threshold Values

See the publication. "A Pest Management Program for Alfalfa in Pennsylvania", for economic threshold values and scouting procedures. General ranges are:

For 12 to 18 inch high alfalfa - 34 to 225 larvae per 30 stems
For 18 to 24 inch high alfalfa - 37 to 240 larvae per 30 stems
For 24 to 30 inch high alfalfa - 39 to 260 larvae per 30 stems

Aphids - In Pennsylvania several aphid species can be found attacking small grain fields: corn leaf aphid, English grain aphids, and oat bird-cherry aphid. Occasional the greenbug also can be found in small grain fields. All species can transmit the barley yellow dwarf mozaic virus. It is the transmission of this virus that is primarily responsible for injury caused by the aphids. In rare situations, aphid population levels are high enough to justify an insecticide application in the absence of disease transmission.

Aphids are small insects (1/8 inch long or smaller) that have a pair of tailpipe like appendages on the abdomen called cornicles. The English grain aphid has long, black cornicles extending from the rare of its abdomen. The oat bird-cherry aphid is yellowish green and characterized by a prominent reddish-orange spot at the base of its cornicles. The corn leaf aphid is bluish green and has a dark area at the base of the cornicles. Greenbugs are pale green with a dark green stripe running down the back of its body.

Economic Threshold Values

Spring - 20 aphids per stem in the seedling stage and 50 per stem in the boot stage. After heading 100 or more per stem and the flag leaf is beginning to turn yellow. If grain is in the dough stage, treatment is not recommended.

Predicting the Timing of Insect Occurrence
Knowledge of when insect species will be active during the growing season is important for timing scouting and management activities. This can be accomplished by two means: 1) establishment of a wide window of activity through observations across years and locations in the state and 2) the use of degree-day models. The first method is useful because it gives a general idea of when a specific pest should show up in the general area; but is limited, because timing of pest occurrence at a given location in a specific year can vary by as much as three to five weeks. This variation in timing is what makes insect management difficult. Improper timing of a control tactic can result in a control failure and increased production costs. A common example occurs when a soil insecticide is applied for corn rootworm control during late April or early May, but larval hatch is delayed until mid-June. Since the soil insecticide only lasts for 6 to 8 weeks, the product concentration has decayed to a level that will not provide adequate protection by the time the larval hatch period begins.

To deal with the variation in timing of key insect life stages, researchers have developed degree-day models for several key pests. These models are based on mathematical relationships between temperature and the number of days required to complete each life stage. In general insects develop slower under cool temperatures and faster under warm temperatures. Therefore, a key life stage for monitoring or control tactic implementation will be reached later in the season during a cool year and earlier in a warm year. A common method of expressing the effect of temperature on insect developmental rate is the use of degree-days. A degree-day is an index of the relative amount of heat available in a day for insect development. It is calculated by measuring the highest and lowest temperature during each 24-hour period and then using the following equation:

Daily degree-days = (maximum daily temperature + minimum daily temperature)/2) - Bt; where Bt = the base threshold of development for a specific species.

The base threshold of development is the temperature at which insect developmental rate is zero.

For example, on July 5, 1999 the maximum and minimum temperature for the day were 89 and 60°F. Adding 89 and 60 together and then dividing by 2 gives an average temperature for the day of 74.5°F. If the base threshold of development is 50°F, then the number of degree days accumulated is 74.5 - 50 °F = 24.5. By adding each day's contribution of degree-days together, we can accumulate a total number of degree-days for the season. This accumulation is a measure of the relative amount of heat for insect development over the season up to a given date.

For instance, the first generation European corn borer flight (egg laying period) will occur between 378 and 918 degree days, with peak flight occurring at about 558 DD. Scouting for signs of first generation injury symptoms should begin at 648 DD (when 50% of larvae have reached the second instar). To time a Furadan 4F post-emergence application or other material applied post-emergence, 380 (WCRW) to 474 DD (NCRW) should have accumulated since January 1. This is the predicted point of 5% larval hatch in the spring. A farmer or applicator has a recommended 1 week window on either side of this date for optimal effectiveness of the product.

When degree-day models are not available, refer to the "Field Crop IPM Training and Reference Manual" for estimated windows of insect activity.

Dennis Calvin, Entomology

WEED SEEDLING GROWTH AND GROWING DEGREE DAYS (GDD)

Over the past several years we have had questions regarding the relationship between weed seedling emergence/growth, GDD (heat units) and herbicide application timing. Unfortunately, this is not a simple question to answer and there is not a table or book to simply reference. Too many factors (e.g., species type, minimum and maximum day temperatures, soil type, water capacity, previous crop and tillage system, etc.) are involved to just make a general statement as to when and how weeds will emerge and develop.

However, research is being conducted on this relationship and a computer program called WeedCast has been developed that forecasts percent weed seedling emergence over time. WeedCast was developed to assist farmers, consultants, industry personnel, and students to easily forecast seedling emergence and growth of common annual weeds of crops in the North Central region of the US. It can be used as a guide or rule-of-thumb in situations where knowledge of weed biology is necessary for making weed management decisions. WeedCast can currently forecast emergence potential for 17 annual weeds such as foxtails, pigweed, lambsquarters, smartweed, velvetleaf, ragweed, and others. As research continues, it will continually be updated with more species and likely will include some information on perennials.

WeedCast is a PC program that runs on Window 3.1 or 95 and is available to download from the web. The address is http://www.mrsars.usda.gov , then select User Products; Weed Ecology and Management; and finally Download WeedCast Model. Data such as daily minimum/maximum temperatures and rainfall, will need to be entered into the program in order for it to predict emergence potentials for the selected weed species. If you try this software, please let us or the creators of this program know what you think of it!

DISTINCT HERBICIDE: WHAT IS IT AND WHERE DOES IT FIT?

What is it?: Distinct is a postemergence corn herbicide from BASF and has received EPA registration for use in Pennsylvania. Distinct is dry formulated as a 70% WG and is a mixture of diflufenzopyr and the sodium salt of dicamba. (Other forms of dicamba are the dimethylamine salt in Banvel and the diglycolamine salt in Clarity.) Diflufenzopyr is a growth regulator in the semicarbazone herbicide family and is an auxin transport inhibitor. It acts as a synergist when mixed with dicamba. Since diflufenzopyr concentrates the activity of dicamba in the growing points (meristems) of the plant, approximately one-half the normal rate of dicamba can be applied with no loss in weed control activity. The 4 oz/acre rate of Distinct contains about the equivalent amount of dicamba as 4 fl oz of Banvel/Clarity. Also, due to the lower use rates of dicamba, Distinct may have greater corn safety as compared to Banvel/Clarity.

Where does it fit?: Distinct's broadleaf weed control spectrum is similar to Banvel/Clarity but also has some annual grass suppression (referred to as "herbistatic" effects). Distinct can be applied at 6 oz/acre on 4 to 10" tall corn and 4 oz/acre to 10 to 24" tall corn. Include 1 qt nonionic surfactant and 5 qt UAN per 100 gallons of water (AMS at 17 lb/100 gallons may be substituted for UAN). Do not use crop oil concentrates or methylated seed oils since crop injury may result.

In studies conducted at Penn State and other Universities, Distinct provided very good control of many common annual broadleaf species (lambsquarters, pigweed, velvetleaf, ragweed) including triazine-resistant species. Small weeds, 2-4 inches tall, were easily controlled with the 4 oz rate of Distinct. Distinct provided suppression on the perennial species (Canada thistle and mugwort) that were evaluated in Penn State studies. But in weed trials conducted at the University of Maryland, Distinct provided excellent control of Canada thistle and burdock and poor control of hemp dogbane and dewberry. However, poor control of perennial weeds is likely due to improper application timing with respect to the biology of the perennial weeds (early summer is not the best time to control perennials no matter what herbicide is applied). In most situations, Distinct will need to be used in combination with a grass herbicide. Common programs could include a pre-grass herbicide such as Frontier, Dual, Harness, Bicep, Guardsman, etc. followed by Distinct or a post program which includes Accent (or Poast in SR corn) tank-mixed with Distinct. Despite good weed control ratings, the slightly higher cost of Distinct, as compared to some of the "standards", may be a limiting factor.

General precautions include: Allow a minimum of 15 days between sequential applications of Distinct. Do not apply within 32 days of forage harvest or within 72 days of corn grain or stover harvest. As with Banvel/Clarity be concerned with drift, tank cleaning, etc. when using Distinct.

HERBICIDE ROTATIONAL CROP RESTRICTIONS

Below are selected corn and soybean herbicides that have the potential to cause problems in rotational crops. Keep in mind that the some of the newer products as well as the older herbicides such as the triazines (e.g., atrazine, Bladex, Princep, Sencor) and chloroacetamides (e.g., Dual, Micro-Tech, Frontier, Harness, Surpass) can have long rotational restrictions for certain crops. The information listed in this table is our interpretation of label statements or a "best-guess" estimate. Consult the product labels if two or more herbicides are applied during the same season. Before applying any herbicide, consult the most recent label, since some labeling may have changed.

Rotational crops following corn (months after application)a
Herbicide Alfalfa Clover Field Corn Grain Sorghum Soybeans Sweet Corn Winter Barley Winter Rye Winter Wheat Spring Oats
Accent 12 12 NR 10 0.5 10 4 4 4 8
Aim 1 1 1 1 1 1 AH AH AH AH
Atrazine SY SY NR NR NY NR NY NY NY SY
Axiom NY NY NR NY NR NY NY NY NY NY
Basis 10 18 NR 10 0.5 10 18 18 4 8
Basis Gold 18 18 NR 10 10 18 10 10 10 18
Bicep II Magnum SY SY NR NRe NY NY NY NY NY SY
Bicep Magnum TR SY SY NR 12 NY 18 NY NY NY SY
Celebrity 12 12c NR 10 1 10 4 4 4 8
Distinct 4 4 7 days 4 4 4 AH AH AH AH
Exceed 18 18 1g 10 18d 3 3 3 3 3
Harness Xtra SY SY NR NY NY NY SY SY NY SY
Hornet 10.5 26b NR 12 10.5 18 4 4 4 4
LeadOff SY SY NR NRe NY NY NY NY NY SY
Liberty f 4 4 NR 2.5 NR 4 2.5 2.5 2.5 2.5
Lightning 9.5 40b 8.5g 18 9 18 9.5 4 4 18
NorthStar 8 18 0.5g 8 8 8 3 3 3 8
Prowl NY NY NRh NY NR NY 4 NY 4 NY
Python 4 26b NR 12 NR 18 4 4 4 4
Roundup Ultra NR NR NR NR NR NR NR NR NR NR
Spirit 18 18 1g 10 10 8 3 3 3 3
a AH = after harvest; NY = next year; NR = no restrictions.
b Plus successful field bioassay.
c Red clover is 12 months, other clovers are 10 mo. If soil pH is £6.5 and 18 mo. if >6.5
d 10 months if STS soybeans are planted
e use safener with seed
f for use on Liberty Link/GR varieties only
g NR for IMI corn hybrids
h plant below herbicide zone
i for use on Roundup Ready hybrids only

Rotational crops following soybeans (months after application)
Herbicide Alfalfa Clover Field Corn Grain Sorghum Soybeans Sweet Corn Winter Barley Winter Rye Winter Wheat Spring Oats
Authority 12 18 10 10 NR 18 4 4 4 30
Axiom NY NY NR NY NR NY NY NY NY NY
Broadstrike + Dual 4 26 c NR 12 NR 18 4.5 4.5 4.5 4.5
Canopy a 10 12 10 12 NR 18 4 18 4 18
Canopy XL 12 18 10 12 NR 18 4 4 4 30
Classic a 12 12 9 9 NR 18 3 3 3 3
Command 16 16 9 9 NR 9 16 16 12 16
First Rate 9 30 c 9 9 NR 9 30 c 30 c 3 30 c
Pursuit 4 40 c 8.5 18 NR 18 9.5 4 4 18
Pursuit Plus 9.5 40 c 8.5 b 18 NR 18 9.5 9.5 4 18
Raptor 9 18 9 18 NR 9 4 4 3 9
Reflex 18 18 10 18 NR 10 4 4 4 4
Roundup Ultra d NR NR NR NR NR NR NR NR NR NR
Scepter 18 18 9.5 b 11 NR 18 11 18 3 11
Steel a 18 40 9.5 18 NR 18 11 40 4 18
Squadron a 18 18 9.5 b 11 NR 18 11 18 4 11
Synchrony STS a 12 12 9 9 NR 18 3 3 3 3

QUICK NOTES - UPDATES

Bladex and Extrazine II Use Rates for 1999
For 1999, Bladex 90DF can be still be applied at a maximum of 3.3 lb product/acre (3 lb ai cyanazine/acre) and Extrazine II 90DF can be applied up to 4.4 lb product/acre. Both require the operator to be in an enclosed cab while applying these products.

Touchdown Herbicide on Roundup Ready crops
Zeneca and Monsanto have signed an agreement to allow Touchdown 5L (sulfosate) herbicide to be applied over-the-top of all Roundup Ready soybean varieties. However, EPA registration is still pending but is expected in time for the 1999 growing season. Over time, pending EPA approval, other Roundup Ready crops may be added to the Touchdown label.

No Liberty Link Soybeans for 1999
AgrEvo is not releasing Liberty Link soybean varieties for the 1999 growing season due to concerns with export and reluctance from Europe and Japan.

Dwight Lingenfelter, Agronomy, Weed Science

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

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