One of the most important components of an IPM program is the use of good scouting methods. In order to carry out a sound scouting program, a pest management practitioner must know:

• when to scout,
• the proper methods for scouting, and
• what tools to use.

When to scout can be determined by past experience with a pest, crop growth stage, or using models that predict the timing of pest occurrence (See the section on, "Understanding Pest Biology and Key Pest Activity Periods"). Proper scouting methods must be statistically valid, so that they provide a reliable estimate of the pest population density. Driving by a field and looking out the windshield or walking a few steps into the field and looking at a couple of plants will not provide a good estimate of a pest's density. Accurately estimating pest density is important because your estimate will be compared with the economic threshold for the pest. If you use inadequate sampling procedures, you run the risk of reaching an improper management decision that can cost money. A good scouting method will require randomly or systematically sampling the field to get a representation sample and taking enough samples to accurately estimate the pest's population density. Because each pest species distributes itself differently in a field, the number of samples required to accurately measure the population varies.

The frequency of scouting will also vary for each pest. For instance, insects can migrate into a field rapidly requiring frequent sampling. Insects can also grow from a small to large size within a short period of time. Weed populations on the other hand are relatively stable. Weeds that were in the field last year will more than likely be there this year as well. Therefore, a weed survey in the fall and another in the spring may provide all the information that is needed for an IPM program. In field crops, few diseases are managed during the growing season. For this reason, scouting is usually limited to disease identification so the farmer can implement cultural or genetic methods to manage the disease.

Tables 24 and 25 provide information on the relative timing of IPM scouting for insects, weeds, and diseases for each field crop species and other scouting activities. Beginning on page 46, scouting procedures are provided for each crop species divided by specific periods in the crop's growth or crop production cycle. General information about the plant's growth and development, pest species of interest during the period, equipment needed and field monitoring procedures is provided. Before beginning an IPM program this material should be reviewed.

The scouting procedures have been modified to integrate insect, disease, and weed scouting into one process for each crop growth period. A field scout cannot use a different scouting procedure for each pest due to time and cost limitation. He or she will need to collect as much information as possible during each visit to the field. With experience, a scout will be able to reduce the time spent in a field and still make reliable pest management decisions.

General Comments

Although pest activity relative to crop production is minimal during this time period, it is a period when the potential for pest problems in the coming year can be assessed. Many insect, mite, and mollusk pest species are attracted to specific habitats for shelter and/or food, or build-up their populations under certain field conditions. By walking through a corn field between harvest and planting, information can be acquired that will give you insights into which of these pests are likely to occur in the field during the upcoming cropping season. This is also a good time to assess potential weed problems in a field and map their location. Crop residue may reveal diseases that are prevalent in the field. Using this information plus information on the fields cropping history and pest history in the surrounding area, the complex of insect, weed, and disease pests likely to occur in a field can be determined. By knowing which pest problems may potentially develop in a field, remedial actions can be taken to minimize the possibility of a pest or the field can be designated as a high priority for scouting. Conversely, fields with a low risk of pest problems can be scouted less frequently or not at all. Based on a fall weed survey, the most efficacious and cost effective weed management program can be developed for a field.

Record keeping:

Because this information will be collected up to six months before it is used, it is best to record the information in a record keeping system. The value of a good record keeping system is underestimated by many farmers. Quality records and the knowledge of how to use them can save dollars and frustrations caused by unexpected pest problems. For insect, weed, and disease management, field specific records are needed. Ideally, a farmer should maintain records on crop sequence in a field, the type of weeds in the field, diseases, tillage practices, herbicide program, crops in adjacent fields and ground cover around the crop, as well as within the crop, past insect history in the field, the stage of the crop relative to other corn fields in the area during the previous year, insect and disease pressure in surrounding corn fields the previous year, soil characteristics (organic matter, moisture, etc.), typical spring weather conditions, winter conditions and manure applications. This information can be useful in assessing the potential insect, weed, and disease complex that may occur in the field and to plan IPM activities.

Field Monitoring Procedures:

Immediately After Harvest - There is no fixed method of collecting information at this time except for the fall weed survey. For insects and diseases, all that is needed is a short visit to each field that will be in corn the following year. Much of the information can be acquired while harvesting the field. Simply note the types of weeds in the field and the relative amount of the field that is infested, the amount and type of crop residue on the surface, the ground cover around the field, the presence and degree of lodged corn from earlier rootworm or European corn borer injury, and any areas bare of crop. In addition, time should be taken to look under crop residue and grass clumps for slugs. During this visit, evidence of key diseases should be noted. Where corn is lodged, it is important to diagnose the cause of lodging. Lodging can occur due to stalk rot, ECB damage, corn rootworm damage or root lodging. Identifying the correct cause is important in avoidance of the problem in future years.

Within a Month of Planting - Return to each field and evaluate the degree of winter annual weeds and green plant material in the field. Green plant material in the field at this time is attractive to black cutworm and true armyworm moths as sites to deposit their eggs. In addition, make a note of any manure applications to a field. Decaying organic matter is attractive to seedcorn maggots. In old pastures or sod fields that will be planted in corn, monitor for wireworm and white grub infestations. Look under sod and grass clumps for slugs and sod webworm larvae.

A. Wireworm Monitoring Procedures:

Materials and Equipment Needed - To monitor for wireworm you will need a shovel or trowel, large mesh netting (about the size of a wedding veil), and some corn or small grain. The mesh netting should be small enough to prevent the grain from passing through.

Monitoring Procedures - Monitoring can be initiated when the soil temperature reaches 45^oF at a soil depth of four inches. At ten locations in the field dig a hole four to six inches deep and place one small bag made of the mesh netting, containing the grain, into the hole (Table 26). Tie the bag at the top with a rubber band or string. Bury the bag and leave it for one to two weeks. Mark each location with a flag or other device that is easy to relocate. After the one to two week period is over, return to the bags and dig them up. Open the bags and count the number of wireworms in each bag. See Table 12 for information on economic thresholds.

About the monitoring procedure - This method is based on the wireworms' attraction to carbon dioxide. As grain absorbs water from the air and soil, it begins to respire giving off carbon dioxide. Wireworms in the soil move toward a carbon dioxide source to locate roots and seeds. The seeds in the bag serve as a carbon dioxide source. If wireworm populations are in the field, they will be attracted to the bags of germinating seed.

B. White Grub Monitoring Procedures:

Materials and Equipment Needed - To monitor for white grub you will need a shovel and a dark cloth about one yard square.

Monitoring Procedures - When the soil warms up in the spring (> 45 ^oF at a four inch depth), grubs move up and begin to feed on the roots of grasses. In old sod fields, dig up a one square foot area about four inches deep (root zone of grasses) and place it on the dark cloth. Shake the soil off the roots. Then break the sod apart and look for grubs that are close to the surface. Shift through the soil on the cloth. Count the total number of grubs per one square foot area. Repeat the process in at least 9 more locations, in the field (Table 26). See Table 12 for information on economic thresholds.

Other Information to Record - Record the winter weather conditions (mild, average, severe) and soil and field condition, any herbicide applications and the date of application, and any tillage that has been done to the field.

General Comments:

When scouting for corn pests and making management decisions, it is important to understand the crop's growth and development. Understanding how a pest injures the plant and the plant's ability to respond to injury is useful when determining the significance of a pest infestation. The following is a brief description of plant growth and development relative to pest occurrence.

During the period from planting to emergence, the seed is imbibing water from the soil, germinating, and beginning its growth. Insects that attack during this period are seed feeders and can cause substantial stand reductions. Several seedling diseases attack the seed and developing seedlings during this time. Usually the first sign that something is wrong, is delayed crop emergence or spotty emergence in the field. To diagnosis and assess the extent of the problem, the seed must be dug up and observed. There is no corrective action that can be taken to prevent further injury from these pests.

The period from emergence until the plant has five fully expanded leaves (V5) is one of the most critical times in the crop's development. During this period, the corn plant is establishing its root system and vegetative structures and it is still dependent on the energy stored in the seed for growth and development. The plant's growing point is still below ground level and therefore, protected from above ground feeding insects and frost. Because the plant is small, it can be seriously injured by insect feeding, disease, or weed competition. For this reason, it is extremely important that pest infestations be monitored on a timely basis to minimize their impact on the crop.

By the fifth leaf stage, the plant is autotrophic (able to generate its own food) and its rate of vegetative growth is more rapid. To support this rapid growth, the plant is developing a strong secondary root system. From the fifth to nine leaf stage, the plant's primary goal is to acquire as many resources (nutrients, light, carbon dioxide, and water) as possible to maximize its growth and development. Almost all of the energy produced during this time is used in the development and maintenance of plant tissues; very little energy is put into storage. Therefore, the plant has little energy reserves to remobilize when under stress from pests. Insects attacking the plant during this period fall into two major groups: 1) leaf feeders and 2) root feeders. It is during this period that corn rootworm larvae are hatching and beginning to feed on the roots. A large part of the nutrients needed by the plant are taken up during this period. Root pruning by rootworms or other root feeding insects interferes with the plants ability to obtain the nutrients and water needed for maximum plant growth. Stem feeding insects can have a similar affect on the plant. Although the impact can severely effect plant growth and development, very little can be done about root feeding insects at this time. However, foliage and stem feeding can be prevented by timely scouting and an appropriate insecticide application. Diseases that attack a plant from emergence through the fifth leaf stage also can damage a plant up to the 9th leaf stage.

Field monitoring during this period involves several measures of crop health. A scout will want to observe crop emergence; stand density; weed infestations; crop injury from insects, diseases, mammals and birds; nutrient deficiencies and toxicities; and herbicide injury. The monitoring procedures presented is this section are designed to allow a scout to monitor for all pests and crop abnormalities.

Equipment Needed:

• trowel or pocket knife
• a measuring device (tape measure)
• pencil and paper to record pest infestation and crop health information
• small scissors and larger bags for collecting diseased leaf tissue

Additional Information:

Planting to emergence - Insects, slugs, and seed/seedling rot diseases are usually not a problem under good growing conditions. Only when the seed sits in the ground for three to four weeks because of wet, cool conditions do many of the problems develop. An exception is damage by wireworms. These insects, however, are primarily a problem in fields that were in sod pasture within the last three years. Excessive soil compaction can result in increased levels of preemergence diseases.

Emergence to ninth leaf stage - When scouting for insects, it is important to note their size. If most black cutworms in the field are longer than 1 1/2 inches, then they have already done most the their feeding and will pupate soon. Therefore, control efforts at this time are of no value. Similarly, if most true armyworm larvae in a field are 1 1/4 inches long, they have completed most of their feeding and will be pupating soon. Sod webworms that are 3/4 inch long have also caused most of the damage they will cause to the crop. In the case of stalk borer larvae, if the larvae are longer than 3/4 inch long and inside the corn plant you will not be able to kill them with an insecticide application. If damage from European corn borer is visible, but no larvae can be found or the larvae have entered the stalk, do not attempt to control. Once inside the stem, larvae are protected from an insecticide application.

Most of the pathogens that contribute to seed rot and the resulting emergence problems, can also cause damping-off and seedling blight diseases. If these problems are suspected, be sure to carefully scout areas of the field where there may have been excessive moisture and where compaction may have been a problem.

Some leaf blight diseases may appear at this time; the most common in the mid-Atlantic region is anthracnose. Usually, the disease is restricted to the lower leaves. In most instances, these leaves dry up and disappear. Once rapid growth of the plant begins, the plants seem to "outgrow" the disease, and after a few weeks very little anthracnose can be found. However, fields with anthracnose should be noted and carefully monitored later in the season (Monitoring period: Green Silk to Physiological Maturity and Physiological Maturity to Harvest) for the presence of anthracnose leaf blight and stalk rot.

Field Monitoring Procedures:

Two to three weeks after planting (ca. 125 growing degree days), it is a good idea to check the crop's progress. If the corn has not emerged by 125 GDD, then scout to determine if a problem exists and if replanting is needed. At three to five locations in the field, dig up about 3 feet of row and observe the seed. If the seed is swollen and the coleoptile is elongating but has not reached the soil surface, the seed will emerge within the next few days. If the seed has not swollen after one to two weeks but there is no evidence of insect feeding, then most likely the soil has been too dry in the seed zone or the seed is not viable. If the entire seed content has been eaten out inside, then most likely seed corn maggots have been at work. If only the germ of the seed has been eaten, most likely wireworms are active in the field. Slugs may eat seed or seedlings that are exposed in an open planter slit in a no-till field. If the root shoot and/or coleoptile are discolored (usually dark-brown or black), seedling disease may be the problem.

Once the young seedlings have emerged, a field should be monitored at seven to ten day intervals. If time is constrained by other activities, then scouting should be concentrated on fields that are at high risk of developing an insect problem (See the exercise on "Preseason Planning" to assess the risk of each field). Those fields at high risk of developing black cutworm, true armyworm, stalk borer, slugs, flea beetle, European corn borer, and sod webworm should be given the highest priority. It is these fields that remedial action can be taken to prevent further crop damage. Fields at risk of developing seed corn maggot, wireworm, white grub, corn rootworm, seed corn beetle, and/or garden symphylan are past the point of preventing injury to the crop. Management of these pests should have taken place at or before planting. If stand reductions are severe because of these pests, then the economics of replanting should be evaluated (See the Penn State Agronomy Guide). If corn rootworm hatch has not occurred, a properly timed postemergence insecticide application can still protect the crop from injury.

During this time it is important to look closely for plants that may have been completely eaten or cut off. Plants cut off or consumed early in their development may not be visible without digging up the root system. Many times, insects such as the black cutworm cut plants off and then the plants dry up and blow away leaving no evidence of insect feeding. Typically, however, if an insect is active in the field there will be evidence of fresh injury.

Damage by leaf feeding insects is obvious during this period. Therefore, a visual inspection will give you a quick assessment of the field. Note the percentage of plants that show symptoms of insect feeding and the insect species responsible for the injury. Before making a control decision make sure live insects are present.

Unless you are interested in a postemergence program to control rootworm, there is no need to dig roots. If you do want to control rootworms post-emergence, either rely on adult beetle counts from last year or dig up five roots at each location and shake the soil off onto a dark cloth. Observe root injury and count the number of large larvae seen. If injury is obvious and several large larvae can be seen, then apply a soil insecticide and incorporate with the cultivator. If the majority of larvae are large (1/2 inch or longer), it is too late to prevent economic injury to the crop.

Weed scouting is best done one to two weeks after crop emergence. Check for evidence of herbicide injury by observing the leaf color and shape, and the roots for abnormalities.

Planting to Emergence - At each location (I) dig up a 3 foot length of row to check seed or seedlings for emergence problems Emergence to Ninth Leaf Stage - At each location observe 10 consecutive plants in a row.

Monitoring procedures (emergence to ninth leaf stage) - Upon entering the field make a quick visual examination of the field. Look for areas where the stand looks thin, weeds or clumps of grass are present, there is variation in crop height, there are variety differences, or waterways exist. After visually assessing the general condition and lay of the field, lay out an efficient sampling path for the field in your mind. In a square field a "W" or "U" shaped sampling path should give a representative sample of the field. In a long narrow field, a "zig-zag" sampling path should work. Along the sampling path, stop at 5 location and observe 10 consecutive plants in a row at each location (for fields less than 20 acres). For fields larger than 20 acres, check 10 consecutive plants at 10 locations. Fields over forty acres should be broken down into 20 to 40 acre sections and scouted separately. Count the number of plants injured by insects or disease and record the amount of injury and the pest species responsible for the injury. Count the number of weeds per 100 feet of row. Compare with economic thresholds for the pest species responsible for the crop injury to make a management decision (See Tables 12, 21 and 23 for economic thresholds). When sampling, try to sample bad spots in the field relative to the amount of the field they represent. For instance, if there is a weedy area in the field that is approximately 1/10 of the field, then 1/10 of your samples should come from that area. Always avoid sampling within the first 10 rows of the field's edge. Also, if a field contains more than one variety of the crop or planting date, scout each area separately. This is important because corn varieties can differ in their susceptibility to a particular pest and a plant's stage of development can make it more or less prone to injury or attractive to colonizing insects. Sometimes it is best to sample problem areas separately and compare values to the good areas in the field. Plant population estimates, soil testing, plant tissue testing, and herbicide injury are all examples where this approach is of value.

General Comments:

During this period the plant is continuing its rapid accumulation of vegetation and the reproductive structures are established. The plant's primary goal is to acquire as many resources (nutrients, light, carbon dioxide, and water) as possible to maximize its growth and development. Almost all of the energy produced is used in development and maintenance of plant tissues; very little energy is put into storage during this period. Therefore, the plant has little energy reserves to remobilize when under stress from insect feeding or other stresses. Insects attacking the plant during this period fall into three major groups: 1) leaf feeders, 2) root feeders, and 3) stem feeders.

Corn rootworm larvae are actively feeding on corn roots during this period. A large part of the nutrients needed by the plant are taken up during this period. For this reason, root pruning from rootworms or other root feeding insects can interfere with the plant's ability to obtain the nutrients and water needed for proper plant growth. Stem feeding also inhibits proper nutrient and water uptake and movement of sugars in the plant.

Very little can be done about root feeding insects at this time. However, foliage and stem feeding can be prevented by timely scouting and an appropriate insecticide application. The beginning of corn rootworm adult and Japanese beetle activity occurs during these stages of crop growth. Insect monitoring at this time is to evaluate European corn borer and true armyworm pressure, assess adult corn rootworm numbers and observe any stalk lodging from root feeding of corn rootworm larvae.

Leaf blight diseases, such as northern leaf blight and northern leaf spot, may appear during this period. In areas where gray leaf spot has been a problem (continuous no-till corn, fields along streams or rivers, fields where drainage is poor), it may be seen during this period. Usually, the number of lesions will be small and somewhat difficult to find. Proper identification is important.

This is the last chance for weed control in a field before the crop gets too tall. Check for weeds and determine the need for a postemergence application.

Equipment needed:

• trowel or shovel
• knife or pocket knife
• pencil and paper to record information (optional - dark cloth)

• small scissors and larger bags for collecting diseased leaf tissue

Additional Information:

If true armyworm larvae in a field are 1 1/4 inches long, they have completed most of their feeding and will be pupating soon. In the case of stalk borer larvae, if the larvae are longer than 3/4 inch long and inside the corn plant, you will not be able to kill them with an insecticide application. If damage from European corn borer is visible, but no larvae can be found or the larvae have entered the stalk, do not attempt to control. Once inside the stem, larvae are protected from an insecticide application.

Monitoring Procedures:

At seven to ten day intervals check each corn field on your farm. If time is constrained by other activities, then scout the fields that are at highest risk of developing an insect problem (See the exercise on "Preseason Planning" to assess the risk of each field). Those fields at high risk of developing true armyworm or European corn borer should be given the highest priority. It is these fields that remedial action can be taken to prevent further crop damage. Fields at high risk of developing a European corn borer infestation during this period are the earliest planted corn fields (or tallest) in the area, particularly those beginning to silk when adults are flying and laying eggs. Second generation European corn borer moths begin laying eggs in corn when it reaches vegetative growth stages just prior to tassel emergence (VT).

Damage by leaf feeding insects is obvious during this period. Therefore, a visual inspection will give you a quick assessment of the field. Note the percentage of plants that show symptoms of insect feeding and the insect species responsible for the injury. Before making a control decision make sure live insects are present. By this time it is too late to replant a corn field.

Upon entering the field make a quick visual examination of the field. Look for areas where the stand looks thin, weeds or clumps of grass are present, there is variation in crop height, there are variety differences, or waterways exist. After visually assessing the general condition and lay of the field, lay out an efficient sampling path for the field in your mind. In a square field a "W" or "U" shaped sampling path should provide a representative sample of the field. In a long narrow field, a "zig-zag" sampling path should work. Along the sampling path, stop at 5 locations and observe 10 consecutive plants in a row at each location (for less than 20 acre fields) (Table 27). For fields larger than 20 acres, check 10 consecutive plants at 10 locations. Fields over forty acres should be broken down into 20 to 40 acre sections and scouted separately. Count the number of plants injured by insects or disease and record the amount of injury and the pest species responsible for the injury.

When sampling, try to sample bad spots in the field relative to the amount of the field they represent. For instance, if there is a weedy area in the field that is approximately 1/10 of the field, then 1/10 of your samples should come from that area. Always avoid sampling within the first 10 rows of the field's edge. Also, if a field contains more than one variety of the crop or planting date, scout each area separately. This is important because corn varieties can differ in their susceptibility to a particular pest and a plant's stage of development can make it more or less prone to injury or attractive to colonizing insects.

Monitor those areas of the field where leaf diseases have been seen in previous years. Carefully, look in areas where air drainage is poor. Unless lesions are relatively mature and the scout is experienced in disease identification, lesion samples should be collected for proper identification.

General Comments:

Just prior to green silk, when the tassel has fully emerged and elongated, the plant has reached its maximum vegetative growth. During this period the plant is undergoing the pollination process. The plant's primary goal is to maximize the number of kernels pollinated. Energy that has been stored and that is produced during this period is used for maintenance of plant organs and for pollen production and silk elongation. Stress on the plant will result in reduced pollination or kernel fill. Insects attacking the plant during this period fall into three major groups:

     1) leaf feeders
     2) root feeders
     3) stem feeders

Corn rootworm larvae have completed the majority of their feeding by this time. If the plant has had adequate soil moisture and good nutrition, it will have begun to regenerate its root system. However, if soil moisture has been limited the plant will continue to suffer from the earlier root injury and experience a reduced yield. Any additional stresses to the plant will compound the overall yield reduction.

The major insect pests of consequence during this period are the adult corn rootworm, European corn borer, Japanese beetle, fall armyworm, and corn leaf aphid. Adult corn rootworm and Japanese beetles are attracted to corn fields when plants are in the green silk stage. Chemicals given off by the silks can be detected by both insects and convey the message that pollen, a high protein substance, is present in the field. The nutrients provided by the silk tissue and pollen are needed by female corn rootworms for egg development. If the corn rootworm or Japanese beetle population is high enough to prevent the silks from extending one to two inches beyond the tip of the husk, then kernel pollination will be reduced resulting in an economic yield reduction. In addition, corn rootworm females attracted to the field during this time will lay eggs in the soil that contribute to larval populations the following year.

The corn leaf aphid is a sucking insect that feeds on the plant sap. Unless numbers are extremely high, they do not cause economic damage to the plant. However, if densities are high enough, the honeydew produced by their feeding falls onto the silks and interferes with pollination.

The European corn borer larvae is both a leaf and stem feeding insect. However, it is the stem tunneling that leads to its most important impact on the plant. Stem tunneling in the stalk cuts off the veins (xylem and phloem) in the plant that transport water, nutrients, and photosynthate (sugars) throughout the plant. In addition, the tunneling weakens the stem causing the plant to lodge. If the insect tunnels in the ear shank, it can cause the ear to drop off the plant.

As with the corn rootworm the green silks attract female European corn borer moths to the field to deposit their eggs. Research has shown that 85 to 90% of all eggs deposited in a cornfield during the silking period are laid on the ear leaf and two leaves above and below the ear leaf. Larvae hatching from these eggs then feed primarily in the ear zone. To prevent economic injury from the pest, it is imperative that the crop be scouted when egg laying is occurring. Once small larvae reach the shelter of the leaf collar or ear, they can no longer be killed with an insecticide application.

Beginning at approximately brown silk, the plant begins the grain-filling period. From this point to physiological maturity, the plant is primarily concerned with developing the fullest ear possible. Energy that has been stored and that is produced during this period is used for maintenance of plant organs and for grain fill. Stress during this period can have a negative effect on the ear weight. In fact, the plant will take resources from the lower leaves and use them to develop the ear under periods of stress. Insects attacking the plant during this period fall into two major groups: 1) leaf feeders and 2) stem feeders. By this time in the plant's growth and development, leaf blight diseases such as gray leaf spot, are likely to occur. Because crop value is relatively low, few fungicides are labeled and treatment is difficult. Fungicides are seldom used for disease control.

The major pest of consequence during this period is the European corn borer. By this time most European corn borer larvae will have entered the stem and are not accessible for control using insecticides. The pest's impact on yield is much less than in earlier stages because part of the grain weight has already been established. ECB larvae feeding during this period may cause increased stalk lodging and ear droppage, so early harvest can help minimize losses. Silk feeding by adult corn rootworm and Japanese beetles after brown silk has no effect on yield. Scouting only provides information on the degree of injury by European corn borer.

Equipment Needed:

• shovel
• knife or pocket knife
• pencil and paper to record information
• your eyes (most scouting during this period is a visual assessment of insect numbers)
• small scissors and paper bags for collecting diseased leaf tissue

Additional Information:

Fields with leaf diseases should be monitored carefully. Although it will often be too late to prevent losses from diseases, they do add stress to the plants and can contribute to increased amounts of stalk rot. Knowing which diseases are present now will also aid in field and variety selection for the next year's corn crop.

Monitoring Procedures:

At seven to ten day intervals check each corn field on your farm. If time is constrained by other activities, then scout the fields that are at highest risk of developing an insect problem (See the exercise on "Preseason Planning" to assess the risk of each field). Those fields at high risk of developing European corn borer and corn rootworm infestations should be given the highest priority. It is in these fields that remedial action can be taken to prevent further crop damage. Fields at high risk of developing a European corn borer and corn rootworm infestation during this period are the latest planted corn fields in the area.

During this period you can scout for all pests simultaneously. Unless there is reason to believe European corn borer is of economic concern, there is no need to take the time to scout for the pest. European corn borer scouting is very time consuming and economic control is difficult in most areas of the state using insecticides. The scouting protocol for this pest, however, is included at the end of this section.

A. Corn rootworm adults, Japanese Beetle adults, corn leaf aphid, and fall armyworm monitoring.

Scouting during this plant growth stage is mainly concerned with the corn rootworm. The other pests are minor in comparison and their densities can be noted when scouting for rootworm. Do not scout along the outer rows of the field because insects tend to be at higher numbers along the edge of fields. Walk at least 10 rows into the field before selecting the first plants to be sampled.

There are two scouting methods that can be used for corn rootworm: fixed and sequential sampling. A fixed sampling procedure uses the same number of plants in a field regardless of infestation level. Sequential sampling allows the number of plants sampled to vary depending of infestation level. If insect numbers are high or low relative to the economic threshold, then fewer samples are required to decide on a control action. If numbers are close to the economic threshold, then it is more difficult to determine the appropriate management alternative.

Scouting for corn rootworm should begin when adult activity is first noticed or predicted by computer based developmental models. This can vary from the first of July to late July in Pennsylvania. In warmer areas of the United States adult activity may begin in late June. When the first adult beetles are seen, scouting does not need to be a complete sample of the field, but a check to see if females are actively laying eggs. Newly emerging females do not have mature eggs. It is about 10 to 14 days after a female emerges before her eggs are ready to be laid. During this egg maturation period, females tend to migrate between fields. Therefore, scouting during this period can lead to an improper measure of numbers of corn rootworm in the field. Once a female begins to deposit eggs in a field, she tends to stay in the field. It is at this time that intensive scouting should begin. To assess whether females are actively laying eggs, squeeze the abdomen of the female. If eggs can be forced out, then the eggs are ready for deposition in the field. The female can be distinguished from the male by the abdomen extending beyond the wings. In western corn rootworm, the female beetles have three stripes and most males have nearly black wings.

1. Fixed Sampling Procedures:

a. Walk into the field at least 10 rows and randomly select two consecutive plants, being careful not to disturb the insects. Fast movement can scare beetles off the plant.

b. Carefully reach out and grab the silks in your hand. Do not shake the plant. Visually inspect the plant for beetles, starting with the tassel and working your way down the plant.

c. After visually inspecting the plant, count the number of beetles in the silk.

d. Finally, pull the leaves back away from the stem and count any beetles in the leaf axils.

e. Record the number of beetles per plant and repeat the procedure on the second plant.

f. Next, randomly select a second set of plants. Because the corn will be over your head at this time, try to follow a "U" pattern around the field when scouting. However, the pattern is not important as long as the plants are selected at random and represent the entire field.

g. Two sets of plants should be observed at 40 locations in the field. If the field is less than 10 acres, then two sets of plants at 20 locations should be adequate. However, if the insect density is near the economic threshold, then you may want to take several more samples.

h. Calculate the average number of beetles per plant for the field and compare with the economic threshold (Table 12).

i. If a decision to control is not reached, return to the field in 7 to 10 days and rescout. Continue scouting until a management decision is reached. Once the numbers of beetles per plant begin to decline stop scouting. Note: It is usually a good idea to scout a field at least twice.

2. Sequential Sampling Procedures:

A substantial savings in time can be realized by using a sequential sampling procedure. The assumptions underlying this approach are: 1) that reaching a decision falls into three categories, treat, do not treat, and continue sampling, 2) when insect numbers are high and low relative to the economic threshold, fewer samples are needed to reach the appropriate management decision, and 3) when insect numbers are near the economic threshold, a greater number of samples are needed to be sure that the appropriate management decision is reached. Sequential sampling can provide up to a 50% savings in time over the fixed sampling procedure.

The procedure for sequential sampling is similar to the approach used for fixed sampling, but typically requires fewer stops in the field:

a. Walk into the field at least 10 rows and randomly select a plant, being careful not to disturb the beetles on the plant. Fast movement can scare the beetles off the plant.

b. Carefully reach out and grab the silks in your hand. Do not shake the plant. Visually inspect the plant for beetles, starting with the tassel and working your way down the plant.

c. After visually inspecting the plant, count the number of beetles in the silk.

d. Finally, pull the leaves back away from the stem and count any beetles in the leaf axils.

e. Record the number of beetles per plant and repeat the procedure on the second plant.

f. Randomly select a second plant. Because the corn will be over your head at this time, try to follow a "U" pattern around the field when scouting. However, the pattern is not important as long as the plants are selected at random and represent the entire field.

g. Add the number of beetles observed on the second plant with those observed on the first plant.

h. Continue this procedure until eight plants have been sampled. Compare the number of total beetles observed with the decision lines on the sequential sampling table (Tables 28 - 31) for the appropriate economic threshold value.

i. If the total number of beetles observed on the eight plants falls within the "continue sampling" range, then sample one more plant.

j. Repeat the process after each new plant is sampled until the total number of beetles counted in the field for a given number of plants is outside the upper or lower limit (See sequential sampling Tables 28 to 31).

k. If the total number of beetles is below the lower value of the "continue sampling" column, then no control is needed or scouting can be terminated. If the total number of beetles is above the upper value of the "continue sampling" column, then control is recommended for the field in the next growing season.

l. If a decision to control is not reached after sampling 50 plants, calculate the average number of beetles per plant and return to the field in 7 to 10 days to rescout. Continue scouting until a management decision is reached. If after two visits to the field you cannot reach a management decision, use the highest average count of beetles per plant per visit as you would with the fixed sampling procedure to make a management decision. Once the number of beetles per plant begins to decline stop scouting. Note: It is usually a good idea to scout a field at least twice.

B. Disease Monitoring:

Disease monitoring can be done while scouting for corn rootworm and European corn borer using the above monitoring procedures. Monitoring methods for diseases are the same as in earlier monitoring periods. If lesions are seen on leaves as high as the ear leaf, there is a good chance that disease development will be enough to result in yield losses. Growers in high risk areas might consider a fungicide application at this time. However, the economics of fungicide applications must be carefully evaluated. Fungicides applied more than a week to 10 days after pollination will probably not be economically effective.

Fields with high levels of disease must be noted and carefully monitored for the remainder of the growing season.

Northern leaf blight, northern leaf spot, and gray leaf spot are the most common fungal leaf disease observed in this region. Under certain conditions, such as high humidity, extended moisture periods, warm nights, etc. spread of these diseases can be rapid.

Scouts must be aware that the disease bacterial leaf blight displays symptoms that are often confused with northern leaf blight. A good way to tell the difference is to look for feeding scars of the corn flea beetle within the lesions. The flea beetle transmits the causal agent, a bacterium, and consequently, bacterial leaf blight lesions will have one or more feeding scars within them. Fields where anthracnose was noted earlier should be examined for the reappearance of that disease. Again, it will probably first appear on lower leaves, but can rapidly spread up the plant.

C. European Corn Borer Sampling Procedures For Management of the Second Generation:

1. Walk into the field at least 10 rows and randomly select five consecutive plants.

2. Beginning with the first plant, check both sides of the two leaves immediately above and below the ear leaf for European corn borer egg masses. An egg mass can range in size from a pinhead to a dime. Most egg masses, however, will be about the size of an eraser head. An individual egg in the egg mass is about the size of a pinhead. Egg masses are typically laid on the underside of the leaf along the midrib within one foot of the stem. However, some eggs will be laid on the top side of the leaf, usually in hairless areas. An egg mass is opaque white to orange and looks like fish scales or roofing shingles. Egg masses that are ready to hatch have a black speck in the middle of each egg, which is the head capsule of the larva.

3. Count and record the number of egg masses found on the plant.

4. Repeat the process for the remaining four plants.

5. Next, following a "U" or "W" path in square fields and a "zig-zag" path in long narrow fields, randomly select a second set of five plants and count the number of egg masses.

6. Sample 20 sets of 5 plants in the field.

7. Calculate the total number of egg masses found on the 100 plant samples.

8. Now divide the total count by 0.91 to estimate the total number of egg masses per 100 plants. Remember, the five leaves per plant sampled only accounted for 91% of the egg masses.

9. Compare the number of egg masses observed with the economic threshold for your field. See Table 15 to calculate an economic threshold.

Note: The time to initiate second generation European corn borer scouting can be determined in several ways:

a. A blacklight trap can be monitored to determine when adult moths are active in the area. Egg laying is directly related to adult capture in the trap.

b. A European corn borer phenology model (see below) can be used to predict the period of egg laying in the field. The model is accurate within 3 days of the actual egg laying period.

c. Scouting can be initiated when the field begins to silk. This method, however, is the least accurate because the stage of plant development between fields corresponds differently with the activity period of adult European corn borer.

D. Collecting Stage Structure Information to Initialize the Second Generation ECB Phenology Model:

1. Locate three corn fields that represent the range of maturities in the general area.

2. In each field search for corn plants where ECB leaf or stem feeding is evident.

3. Dissect each plant and locate live first generation ECB larvae.

4. After locating a larva, either determine and record its instar or collect the larva in a 70% isopropol alcohol solution for later instar determination (contact your state extension specialist for help).

5. Try to collect between 20 to 40 larvae in each field. This should give a total of 60 to 120 individuals to establish the population's stage structure.

6. Record the number of larvae in each instar for input into the computer model.

7. A good stage structure data set should have the greatest number of larvae in the fourth instar, with few pupae present in the field. If most larvae are first to third instar, then return to the field in a week and collect a new sample.

Scouting at this time can be useful in assessing the potential for rootworm injury in the coming year and whether the corn should be harvested immediately to avoid losses caused by ear droppage and stalk lodging from European corn borer. This is the period to look for stalk rot and to make harvest decisions.

Take a walk through the field and observe the condition of the plants. Plants that appear to be "goosenecked" and stunted are an indication of old corn rootworm injury. Stalks that are broken at a node or between nodes are an indication of European corn borer feeding or stalk rot organisms. European corn borer injury can be distinguished from stalk rot by a ragged break in the stalk and brown sawdust like material at the point of the break. Many times the gray, 3/4 inch long larva can be seen. Carefully monitor those fields where leaf diseases were present. Using sampling patterns described earlier for insects, squeeze several stalks in the lower two or three internodes. If the stalk crushes easily, stalk rot is occurring. If 10-15% of the stalks show stalk rot symptoms, consider harvesting the crop as soon as possible. Splitting stalks (admittedly, this is destructive sampling) can give an indication of the causal fungus, but this information is not all that important. If stalk rot is present, it most likely will continue to develop. Shiny, black lesions on the stalk are an indication of anthracnose stalk rot. Stalk rots usually break smoothly, as fibers of the vascular system break down and separate. In many cases a pinkish color will be seen around the area where the stalk has broken off. Leaf feeding is of no concern at this time, but is an indication of old insect damage. If substantial lodging is observed, it is wise to harvest the crop as soon as possible.