July 25, 1997 Vol. 97.9

IN THIS ISSUE:

Calendar

• 1997 Ag Progress Days, Rock Springs, PA - August 12-14, 1997
• NCRS Program on Soil Conservation postponed until September 23 & 24, 1997

Production

• Training for Pesticide and Fertilizer Applicators
• Fall Fertilization of Forage Crops
• Using Small Grains and Soybean for Forage Under Drought Conditions
• Pollination and the 1997 Corn Crop

Pest Management

• Corn Herbicide Grazing, Foraging and Grain Harvest Restrictions
• Corn Herbicide Rotation Restrictions
• Insect Alert
• Potato Leafhoppers Threaten Alfalfa and Other Crops
• Drought and Heat Favor Spider Mites

Degree Day Accumulations

Production:

Training for Pesticide and Fertilizer Applicators

Back in the mid 80's I conducted several training sessions for operators of spray and fertilizer rigs. They were well attended, well received, and got excellent reviews. Some were conducted as workshops, and others as winter classroom sessions. The ultimate objective was to make these folks more professional in the way they conducted the companies business. These folks interfaced with many crop acres and a lot of farmers. If they were more professional, fewer mistakes occurred, better PR was practiced, agriculture gained and so did the dealership.

The 64 Dollar Questions

Do we need this type training today?

If yes (1) should it be classroom oriented or field oriented? (2) What time of the year? (3) Should it be held in conjunction with: (a) Crop Diagnostic Clinics, (b) Lime/Fertilizer/Pesticide Conference, (c) Other?, or (d) a completely separate event?

Please respond to:

Lynn Hoffman
116 ASI
University Park, PA 16802
Phone: (814) 692-7955
Email: ldh3@psu.edu
FAX: (814) 692-2152

If no ignore the question!

Lynn D. Hoffman

Fall Fertilization of Forage Crops

The question of fall fertilization of forage crops is most often related to concerns about winter survival of perennial forages. While fall fertilization can have an impact on winter survival there are many other factors that influence winter survival, including the overall nutritional management of the crop, harvest practices throughout the year, weather conditions, and varieties just to name a few. Here I will focus only on the nutritional factors.

For new seedings the key to winter survival is to have a healthy, well established plant going into the first winter. Having soil test levels at least in the optimum range for pH, phosphorus, and potassium before establishment is critical. While all of these fertility factors are important, it has been shown that good levels of phosphorus will promote vigorous root growth in the new seeding. A larger, more well established root system will be more resistant to heaving, which is a major cause of winter stand loss, especially in new seedings. A fall application of fertilizer to a new seeding cannot make up for the lack of good fertility at planting and resulting small root system.

Once a forage crop is established, the fertility program should focus on maintenance of good fertility levels in the soil for the life of the forage stand. The most important part of the maintenance program is regular soil testing to determine the need for lime, phosphorus, or potassium to replace the large amount of nutrients removed in the forage. On grasses nitrogen will also be an important part of the maintenance fertility program. For legumes and grasses, potassium seems to be the most critical nutrient for winter survival. Potassium, being a salt, lowers the freezing point of cells just like applying salt to a road lowers the temperature where the water on the road will freeze. Also, potassium influences the levels of soluble sugars in the cell sap. These sugars act as an antifreeze in the plant cells enabling them to withstand lower temperatures without freezing.

The timing of phosphorus and potassium applications for forages will depend on the situation. When the soil test levels are in the optimum range and the recommendations are low, the timing of fertilizer application is not critical. These low recommendations on an optimum testing soil are only to replace what the crop will remove so that the test level is still in the optimum range going into the following season. Fertilizer can be applied after one of the cuttings or in the fall. There will be no advantage to splitting the fertilizer application in this situation. Given a choice between applying the fertilizer during the season or in the fall, fall application may provide a very slight insurance effect, but this is not a major consideration.

Where high rates of fertilizer are recommended there may be an advantage to splitting the application some after first cutting and the balance in the fall. Many plants will take up potassium whether they need it or not. This is called luxury consumption. If all of the fertilizer is applied at one time, the next cutting may take up more than it needs leaving the crop short later on. By splitting the applications the efficiency of potassium use will be improved because there will be less luxury consumption. Also, as noted before, if the soil test levels are low enough to result in a large recommendation, particularly for potassium, applying some of the fertilizer in the fall before the plants are dormant may improve winter survival.

On forage grasses nitrogen is another consideration. Nitrogen should be applied to grasses in the spring and after each cutting, except the last cutting in the fall. The rate should be based on the expected yield of the following cutting. Applying nitrogen in the fall for use by the crop the following spring is not recommended. Another important consideration for nitrogen fertilization of grasses is the balance between nitrogen and potassium. Nitrogen applied in the fall on soils with low potassium levels can increase winter kill of grasses over where no fertilizer is applied. Thus, soil testing and applying a balanced fertility program is important.

There are no special considerations for nutrient sources used for fall fertilization of forages. All of the standard fertilizer materials are acceptable. Manure is also a source of nutrients. The phosphorus and potassium in manure can be considered equivalent to fertilizer phosphorus and potassium in their effect for building soil fertility. The availability of nitrogen will range from 20 to 50% depending on how soon after application it is soaked into the soil by rain fall. The sooner it gets rain the better. Manure is not generally recommended for legumes because the nitrogen in the manure is wasted and there is the potential for some adverse effects from manure application to legumes. If manure must be applied to a legume, fall is probably the best time to apply it to minimize the potential negative effects.

While having good fertility levels for a forage crop in the fall is critical for optimum production, fall fertilization is only one part of the management system to achieve this. Optimum soil test levels should be established prior to seeding and a maintenance fertilization program based on regular soil testing are the foundation of good nutrient management of forages.

Douglas Beegle

Using Small Grains and Soybean for Forage Under Drought Conditions

Most of Pennsylvania is under a drought watch with many areas experiencing severe drought conditions. This means many producers are going to need supplemental feed. Small grains and soybean can provide additional forage. The following is a discussion on possible ways to use these crops to produce supplemental forage.

Spring oat can be used for fall grazing or silage. It can be seeded during August and early September at about three bushels per acre. In most cases no additional inputs are required. We have not been able to obtain significant yield increases from added nitrogen especially when planted following drought stressed corn.

Winter small grains can be used for forage this fall (for grazing) or next spring (for grazing or silage). Winter grains can be grazed in the fall and early spring without greatly affecting grain yield if they are allowed to go into the winter with approximately two to three inches of growth and the cattle are removed in the spring prior to growth stage 6 or stem elongation.

Winter grains are difficult to harvest for silage in the fall because they are leafy and lack stem material. Harvest can be improved by seeding a mixture of spring oat and winter grain at 2.0 bushels and 1.0 to 1.5 bushels per acre respectively. The winter grain can also be harvested next spring for silage or grain.

All winter grain species can be harvested for forage. Winter rye has traditionally been the major small grain used for forage. It has the most winter hardiness and can be planted the latest for both erosion control and forage. It does, however, drop in quality faster then the other small grains. Therefore, it must be harvested prior to head emergence(boot stage). Other small grains can be harvested later, however, most are harvested at about head emergence to allow earlier planting of corn or sorghum for silage. Seeding other winter grains with rye (rye-wheat; rye-triticale) has helped maintain quality if rye harvest is delayed past head emergence.

Which winter grain is best for silage production? This depends on when it is most convenient for producers to harvest in the spring. Tonnage and quality will be very similar when harvested at the appropriate stage of growth. Normal harvest dates (boot to head emerged stages) are as follows:

These dates will vary with location and year, however they will have the same relative maturity (rye earliest and triticale latest).

Management of small grains for forage is similar to the practices used for grain production. Seeding rates should be increased as the seeding date is delayed. Consult the latest edition of the Agronomy Guide for this information. Timing of spring nitrogen application does differ slightly for forage production. For forage do not delay applying spring nitrogen. Apply the required amount at green-up in early spring. Early applied nitrogen can stimulate additional tillering which may contribute to dry matter production but not to grain production.

Soybean tends to be more drought tolerant then other grain crops because they flower over a long period and can take advantage of late rains. However, with severe prolonged drought, plants may start dying. Under these conditions, harvesting as silage is an option. Soybean silage tends to be higher in protein and fiber then corn and lower in protein and higher in fiber then alfalfa.

Soybean can also be seeded for silage until early August. They will continue growing until the temperatures approach freezing this fall. In some areas this could provide sizable tonnage, in other areas the yield would be low. Limited data indicates that soybean planted in mid-July at State College could yield approximately 1.5 ton of dry matter per acre when harvested in mid-September. Planted this late, they should be seeded with a grain drill at a seeding rate close to 300, 000 seed per acre. They should be harvested prior to a killing frost to maintain as much leaf material as possible.

Elwood Hatley, CCA

Pollination and the 1997 Corn Crop

The prevailing drought conditions throughout much of the state may adversely affect the pollination of the 1997 corn crop. Under normal conditions, tassel emergence begins in some fields about July 15 and continues in others until about August 15. Ideally, pollination should occur in most areas by August 1 since about 60 days are required to mature the crop following pollination. This year crop maturity has been delayed- on a recent trip through Franklin, York and Lancaster Counties on July 16, I did not see one field in tassel. This delayed maturity is due primarily to drought stress but also to the cool spring weather conditions. Our estimates of crop maturity based on current crop development at Rock Springs suggest that early May planted corn may not mature before mid October.

Drought stress will also affect ear development and pollination. In most plants there is an internal competition for vegetative development, tassel development, and ear shoot development. With severe drought stress prior to tasseling, ear shoot development can be delayed. This can result in barrenness or delayed silk emergence. If silk emergence is delayed significantly following pollen shed by the tassels, then incomplete pollination can occur.

Silk elongation normally begins 7 to 10 days prior to silk emergence from the husk. Complete silk emergence from an ear generally occurs within two to seven days. Silks from the basal portion of the ear typically emerge first, while the tip silks generally emerge last. Pollen shed normally coincides with silk emergence and lasts for up to 7 days on an individual tassel. Because of plant variability in typical fields, pollen is sometimes available for up to 14 days.

Pollination can also be limited if emerging silks are clipped by rootworm beetles. Generally at least a half inch of emerged silk is required for successful fertilization to occur. The recent high temperatures have caused high corn rootworm beetle populations in some fields. In some situations this year, control of the rootworm beetles may be necessary to prevent serious silk clipping. The threshold for corn rootworm beetles is 5 per plant before an insecticide should be considered.

Pollination can be assessed by gently pulling the husks off of an ear once the silks have turned brown and then gently shaking the ear. Those silks that remain attached to the ear were not pollinated. Often these will be the late emerging silks from the ear tip but they can be scattered throughout the ear.

Once the pollination process is complete, a rough yield estimate can be made by determining the average number of kernels per ear and multiplying it by the plant population. Multiply the number of rows by the number of kernels per row to get the number of kernels per ear. Then multiply this number by the plant population to get the kernels/acre. Divide the kernels/acre by 90,000 to get the yield estimate in bushels/acre.

Example: 16 rows x 20 kernels/row x 23000 plants/acre = 7.36 million kernels/acre

7.4 million/90,000 = 82 bushels/acre

Yield estimates can be useful to make marketing decisions. Row numbers and especially kernels per row will likely be reduced in many fields because of the drought stress that occurred while these yield components were being determined.

Greg Roth

Pest Management:

Corn Herbicide Grazing, Foraging and Grain Harvest Restrictions

If early harvest of corn is necessary because of drought conditions, a number of corn herbicide restrict the length of time necessary for safe harvest.

The following products restrict grazing and/or foraging (silage) following their use in corn. If a corn herbicide product is not listed in the following table, no grazing/feeding restrictions were listed on the product label. For additional information, contact the product manufacturer.

¹For use only with IMI (IR/IT) corn hybrids.

²For use only with SR Sethoxydim-resistant corn hybrids.

Corn Herbicide Rotation Restrictions

With the drought in much of the commonwealth, many producers may consider trying to establish a late summer crop for additional forage or feed. Herbicide recrop restrictions are based on susceptibility of potential rotation crops to herbicide residues or are based on limits set by EPA for potential residue in feed or food crops. In drought conditions, several herbicides have the potential to persist longer in the soil and injure susceptible follow crops. Pay particular attention to atrazine and simazine which can cause problems in a more "normal" year. Most of the other herbicides with a few "exceptions" should not limit the ability to establish a fall forage crop if necessary. Below is a list of the restrictions for commonly used corn herbicides and some potential forage crop options under consideration. The information listed in this rotation restriction table is our interpretation of label statements or a "best-guess" estimate. Consult the label if two or more of these materials are applied during the same season.

^aAH = after harvest; NY = next year; SY = second year following application; NR = no restrictions.
^bRestrictions should be similar for sorghum-sudan grass.
^c20 days per pint.
^dUse safener with seed.
^eAllow 30 days before replanting sorghum.
^fPlus successful field bioassay.

Bill Curran

Insect Alert

Corn Rootworm Injury - The 1997 growing season may prove to be one of the worst in recent years for stalk lodging and yield reductions from corn rootworm injury. Everything possible has come together to enhance the impact of corn rootworm on field corn. Mild winter conditions provided a excellent climate for high egg survival and good larval hatch. Warm, dry conditions during April allowed farmers to plant a higher percentage of corn fields early. The warm and dry April conditions were then followed by an extended cool period that delayed corn emergence. Many of the early planted fields took 3 to 5 weeks for corn to emerge. This delay in emergence led to corn being at a developmental stage similar to corn planted from mid to late May. In these early planted corn fields, the soil insecticide broke down to a level too low to control hatching corn rootworm larvae by the time larvae were hatching (the beginning of larval hatch varied between mid to late June in most areas of the state and continued over four to six weeks). Because the soil insecticides did not last long enough to protect the plants, rootworm larvae were able to feed on the corn roots. Compounding the amount of injury to the plants was the effect of delayed emergence, which resulted in corn plants with less developed root systems that were more susceptible and sensitive to injury. During the period when CRW larvae were feeding, drought conditions developed which prevented the plant from regenerating new roots to compensate for those lost. The impact of this combination of factors is a number of corn fields that will lodge and suffer economic yield reductions from CRW.

Adult Corn Rootworm Emergence - Adults of the corn rootworm are beginning to emerge in central Pennsylvania. Emergence begin about 10 days ago in the southwest, southeast, and south central areas of the state. Expect emergence to begin in the more northern and highland areas around the first of August. Adult numbers appear to be very high this year. Because of the drought conditions, there is a chance that some fields may benefit from sprays to control adults and prevent silk clipping which leads to poor pollination.

Counts from corn rootworm scouting can be used to determine whether adult control in the current year is advisable or whether larval control during the next cropping year is warranted. If beetle numbers exceed the economic threshold, a corn grower may decide to rotate to a crop other than corn next year, apply an insecticide at-planting time or control adult populations to prevent egg laying in the field. Depending on whether adult control is aimed at preventing silk clipping or to eliminate adults before eggs are laid in the field, different economic thresholds are used. Five beetles per plant is enough to warrant control to avoid economic levels of silk clipping, which can interfere with pollination of the ear. If an adult control program is desired to prevent economic populations for next, the economic thresholds are the same as for a at-planting time application: 1.0 beetle per plant in first year corn fields and 1.5 beetles per plant in field that have been in corn for two or more years. Adult control should be implemented when the economic threshold is exceeded. For prevention of silk clipping, an insecticide should be applied just prior to silk emergence or when an economic infestation is noted. Note: Once at least 50% of the plants have brown silks, an indication that pollination is complete, treatment is no longer justified. Sevin, Lorsban, dimethoate, Asana, Warrior, malathion, Lannate, Penncap-M, Ambush, and Pounce are registered for adult corn rootworm control. With the exception of Sevin and malathion, the insecticides should provide at least 7 to 10 days of silk protection. If beetle numbers begin to increase to economic levels before 50% brown silk, a second application may be necessary. It is important not to get over anxious and apply insecticides to whorl stage corn when number get high. Too early an application will kill beetles in the field at that time, but may not provide protection once corn begins to shed pollen. At that time new beetles will be attracted in the field that may cause economic silk clipping.

Potato leafhopper - Numbers of this pest continue to be extremely high across the state. The third and fourth cutting will very vulnerable to severe stunting and injury by the pest. New seedings are particularly vulnerable to feeding by this pest. In some areas of the state, reports of dimethoate (Cygon) and chloropyrifos (Lorsban) not holding up are coming in. Maryland is reporting similar problems. It is not clear why these failures are occurring. However, Dr. Galen Dively of the University of Maryland has offered a possible explanation (See attached article).

Two-spotted Spider Mites - The dry, hot conditions in recent weeks are perfect for population explosions of mites in soybeans. Soybean fields should be watched closely over the next few weeks for the development of the pest. Several fields in the Landisville, Pa area are already showing evidence of injury. The recent rains will help reduce numbers, but if the hot temperature return mite numbers will rapidly increase. See the article by Dr. Galen Dively for more specific information on management of the pest.

Grasshoppers - So far there has not been many report of grasshopper injury to field crops. However, the dry, hot conditions are ideal for the development of localized outbreaks. If the dry, hot conditions continue, keep your eyes open for the development of high populations and crop injury. Sevin 4-Oil, Furadan 4F, dimethoate, Asana, malathion, and Penncap-M are registered for grasshopper control. See the Agronomy Guide for rate information.

Japanese Beetle - This pest is now attacking corn and soybean fields in the state. As corn fields begin to silk, keep an eye out for significant silk clipping. If an average of two to three beetle per ear are seen feeding on silks before pollination, then an insecticide application may be warranted. Several formulations of carbaryl (Sevin), methoxychlor, and Penncap-M are registered to control this pest. Carbaryl and Penncap-M are also registered for corn rootworm beetle control. See the Agronomy Guide for rate information.

The following is an article written by Dr. Galen Dively on potato leafhopper management. This article is very comprehensive and informative. Rather then write a similar article, I felt the information provide is excellent and pertinent to Pennsylvania conditions. The article has been annotated for our needs.

Dennis Calvin

Potato Leafhoppers Threaten Alfalfa and Other Crops

Alfalfa

Every year there seems to be one insect pest that stands out. Well, this year it is the potato leafhopper. Populations of these pale-lime green, wedge shaped, 1/8-inch long insects are exploding in numbers throughout the mid-Atlantic area on a wide range of crops and wild plants.

On alfalfa, the tender regrowth is highly susceptible to leafhopper feeding injury. These sucking insects remove plant juices and in the process of feeding block the normal movement of fluids within the plant. This blockage results in a V-shaped yellowing on the leaves, commonly referred to as "hopperburn". Leaves showing hopperburn do not recover after the insects have been killed with an insecticide. When feeding is intense, yield losses within the regrowth period occur as a result of reduced stem height. Damaged plants are severely stunted, often to the point of providing opportunities for increased weed growth.

Losses in harvest tonnage are usually attributed to this stem-shortening. However, if hopperburn injury occurs over several cuttings, the potential yields of future cuttings and the winter survival (stand viability) of the crop may be reduced. The effect of leafhopper feeding on foliage quality is seen in the leaves. The blockage of fluid results in leaves that have about half the normal amount of crude protein. Digestibility and energy availability are not significantly reduced in damaged leaves. In most cases, even damaged leaves have enough protein to fulfill nutritional needs of ruminants. However, in dairy production, where crude protein may be limiting, control of hopperburn is necessary. An additional impact of leafhopper feeding is the delay in maturity of the crop. In some cases, the delay may be extreme enough to eliminate a final harvest in the fall.

Recommended insecticides include: Sevin XLR Plus (2 pts), Furadan 4F (1pt), Lorsban 4E (1-2 pts), dimethoate 4 EC (0.5-1 pt), Guthion 3 (0.66-1.33 pt), Penncap-M (2-3 pts), or permethrin (Pounce 3.2EC at 4-8 oz or Ambush 2E at 3.2-12.8 oz). Baythroid is also registered for control of potato leafhopper at rates of 0.8-1.6 fl. ounces per acre. Because this new pyrethroid is more resistant to UV breakdown and does not wash off foliage easily, it may control leafhoppers for as long as 28 days depending on a rate (harvest interval = 7 days). Most insecticides are effective in providing 90-100% control but some (i.e. Baythroid, Furadan and permethrin) have longer residual action than others. Compare costs, follow all label directions, and pay particular attention to restrictions. Getting initial control is usually not a problem, however, the population pressure is so great this season that reinvasion of adults may occur within days after treatment. Also, under dry conditions, the absorption rate of foliar systemics (Furadan or dimethoate) may be slowed if plants are moisture-stressed, and high temperatures may affect the efficacy of permethrin. Note that none of the insecticides carry over after cutting to the next crop so control decisions must be made independent of each crop. Another management option that should be considered for future plantings is host plant resistance. Leafhopper-resistant varieties of alfalfa have come on the market in recent years and many of these are competitive agronomically if one considers the control costs and monetary losses in alfalfa quality due to leafhoppers annually.

Soybeans

The soybean plant is much more tolerant to leafhopper feeding than the previous host crops. Usually one can wait until symptoms of leafhopper injury appear before a decision is made to treat. Symptoms include localized stippling, yellowish to reddish-yellow discoloration of leaves, plus leaf crinkling and cupping. This crinkling and cupping looks similar to herbicide damage. Soybean varieties with sparse or very short leaf pubescence are more susceptible. Stressed plants also are more susceptible to injury than healthy, vigorous plants. Treatment on soybean is suggested if populations exceed 4 adults/nymphs per sweep in stressed beans or 8 per sweep in normal growing fields. Excellent control can be achieved by air with all the registered products.

Comments by Dennis Calvin -

In narrow row soybeans, the lost of soybean plants from tractor tires versus savings in yield must be compared before making a treatment decision. Also, it is important that ground equipment allows good penetration into the foliage.

Older soybean plants (R1 and older) typically will not benefit from treatment, because PLH has less effect on these plants. Older plants are hairier and more lignified, making it difficult for leafhopper to get their beaks into the plant.

Dr. Galen Dively, University of Maryland

Drought and Heat Favor Spider Mites

Mite infestations have increased significantly during the past 2 weeks in soybeans, as well as other crops (i.e. watermelons, tomatoes, corn, garden beans, clover, and alfalfa) because of the hot, dry weather. Many infestations are showing the typical pattern of invasion along the edges of fields associated with grassy border areas. However, mite-infested hot spots' also have been observed scattered throughout fields, apparently blown in by "ballooning", a process by which young mites extrude a strand of webbing that catches the wind and carries them into the field interior. These scattered infestations are more difficult to spot-treat and often the entire field must be treated.

Spider mites thrive in hot, dry weather simply because they lay more eggs, and survive and develop at a higher rates. The time required to complete their life cycle can be as short as 10 days. High temperatures and low field moisture also favor spider mite populations by nullifying effects of fungal diseases and other natural control agents. Also, mites suck out more nutritious fluids from drought-stressed plants.

Spider mites injure soybeans by using their needle-like mouthparts to puncture leaf cells and consume the entire content, leaving empty and irreversibly damaged cells. The presence of empty cells results in the yellow or white stipples characteristic of mite-injured leaves. Generally, these feeding signs are first noticed at the base of the leaf associated with 20 or more mites on the underside. Extensive feeding by larger number of mites (300-600 per leaf) causes leaves to turn yellow or brown on the margins, and eventually die and drop from the plant.

Every soybean field should be scouted for mites, especially if hot, dry conditions continue. Pay particular attention to fields treated previously with insecticides and fields bordering grassy areas that have been cut recently. Fields showing what looks like dry weather injury, mineral deficiencies, and/or herbicide injury also should be examined carefully since these symptoms are similar to mite damage. Concentrate on the field borders and look for the early signs of white stippling at the base of the leaves.

On all crops, isolated spots of mite activity confined to the field edges can be spot-treated with a miticide using ground equipment to prevent further spread of mites into the field. When spot treating, sprays should overlap considerably into the unaffected beans adjacent to the damaged area. On soybeans, if the infestation is widespread, aerial application of the entire field may be justified if live mites are numerous (more than 20 per leaflet) and more than 50% of the plants show stippling, yellowing or defoliation over more than one-third of the leaves.

The options of mite control on soybeans are limited. Dimethoate 4EC is still the preferred material. It is a systemic chemical absorbed by the plant and thus is active on young mites for a week or possibly 10 days at best. However, control failures with dimethoate applied by air are common, mainly because drought-stressed plants do not absorb enough of the chemical to provide control. Lorsban 4E does a fairly good job of killing active mites on contact, but is not systemic. A second spray 3 to 5 days later is necessary to kill newly hatched mites; thus, this option is more expensive. Warrior is also labeled but its control efficacy by aerial application against heavy mite infestations is questionable. This product may provide adequate control of hot spots along field edges if applied by ground at higher spray volumes.

Parathion 8E used alone or in combination with dimethoate has provided good control in the past but this material can only be applied by air with special closed systems and according to certain set back restrictions. This product is not recommended in field situations close to homes and livestock buildings. Penncap-M 2F is also registered for mites on soybean but does work as well as parathion and should not be used if bees are foraging in the area. Regardless of the miticide used, control efficacy by aerial application can be enhanced significantly by the addition of a crop oil or organosilicone (which is more expensive), especially under the current high temperatures.

As long as hot, dry weather persists, there may be no relief from mite pressure. Thunderstorms can be forceful enough to cause significant direct mortality, while scattered and infrequent showers will not alleviate a heavy mite infestation. Rains can improve the overall condition of soybeans so that plants are better able to withstand injury. To check if rainfall has slowed mite development, examine the new leaves emerging from the growing tip. If these leaves are green and they remain green for several days, control may not be needed.

Dr. Galen Dively, University of Maryland

William S. Curran
Associate Professor Weed Science

1997 DEGREE DAY ACCUMULATIONS:

To track corn and insect development, compare the 1997 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 comparison.

The cumulative degree day value given is for the number of degree days needed after tillage of manure or green surface vegetation before it is recommended to plant corn in a field to avoid injury from seed corn maggot.

Dennis Calvin

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

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