May 16, 1997 Vol. 97.4

IN THIS ISSUE:

Calendar

• Weed Field Days - Landisville, July 10 and Rock Springs, July 11, 1997
• Northeast Branch American Society of Agronomy - College Park, MD - July 13 to 16, 1997
• Penn State Crops Clinic - Rock Springs Agronomy Farm - July 22 and 24, 1997
• NCRS Program on Soil Conservation - Rock Springs Agronomy Farm - July 23, 1997
• CCA Exam - PDA Building in Harrisburg - August 1, 1997

Production

• Using Plant Analysis to Diagnose Nutrient Deficiency Problems
• Replanting Prospects

Pest Management

• New Herbicide Resistant Weeds Reported
• Herbicide Performance and Rainfall
• Delayed Pre Herbicide Applications in Corn
• Herbicide Drift Management
• Postemergence Herbicide Application and Corn Growth Stages
• Insect Alerts
• Scouting for Early Season Corn Insects
• Early Season Corn Insect Management

Agent's Corner

• Fayette

Degree Day Accumulations

Calendar

The 1997 Penn State Crops Clinic is approaching. This year it will be held on Tuesday, July 22 and repeated on Thursday, July 24 from 9:00 am to 4:00 pm at the Agronomy Farm of Penn State's Russell E. Larson Ag Research Center near Rock Springs. As in the past, the participants will choose from a variety of hands-on topics. Topics this year include: growth and development of corn; corn rootworm biology as relates to corn plant's growth stage; soil quality assessment; soybean diseases; silage and hay making problems; herbicide & crop/weed screen; weed ID; and planter adjustments and attachments. CCA and pesticide applicator credits will be available. The registration fee will be $35. Look for your registration form - coming soon. Hope to see you there!

Dwight Lingenfelter

Production:

USING PLANT ANALYSIS TO DIAGNOSE NUTRIENT DEFICIENCY PROBLEMS

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

The problem with this method is that book values are only available for the few specific stages of growth given in the table below. For annual crops the recommended sampling times are often not for the stage of growth when the problem is observed and usually they are too late to take corrective action. For example, most nutritional problems with corn are observed when the corn is short and you can look out over the field. This is also early enough that corrective action could be taken for some problems. Thus waiting until silking to take samples of problem corn plants for plant analysis is of questionable value except as a postmortem. For perennial crops, corrective action can often be taken during the next season or next cutting. A final problem with this method is that there are many environmental and cultural factors that can influence the level of a nutrient in plant tissue. Thus, book values are only ball park estimates of sufficiency for nutrients and actual sufficiency levels can vary significantly depending on the specific conditions.

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

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

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

Douglas Beegle

REPLANTING PROSPECTS

The abnormally cool April and early May conditions this year may result in some reduced stands and the need for replanting corn. Dry soil conditions have helped to reduce the potential for seed rots and most fields will emerge with few problems, but there likely will be a few that need replanting. Corn emergence takes about 125 GDDs under normal conditions and slightly more under early planted, no-till or deeper planted corn. Some of the first corn planted at Rock Springs on April 23 still had not emerged on May 15, over three weeks later, with just about 125 GDDs accumulated since then.

To make replant decisions, consider the following factors:

• Original target plant population/Intended plant stand
• Plant stand after emergence/damage
• Uniformity of plant stand after emergence/damage
• Original planting date
• Possible replanting date
• Likely replanting pest control and seed costs

Estimate the potential yield from the original stand and a new planting, at a higher plant population and later date, from the chart below. Then estimate the cost and the potential gain of replanting. Consider the use of additional inputs carefully. There is generally no need for starter fertilizer on late May replantings. If weed control is reasonable, and the field can be no-tilled, plant and use a post-emergent herbicide program if necessary. If Prowl herbicide has been used, herbicide injury is generally not a problem if the field is no-tilled with a seed depth of 1.5 to 2 inches, with good soil coverage. Row insecticides should be considered if the field is tilled before replanting or if insects were part of cause for reduced stands. Planting back into the original rows may help to get some benefit from the first insecticide application.

Based on several planting date studies we have conducted in the past few years, I feel the values in the chart below (Table 1) are reasonable. Under high yield conditions in southeastern PA, I might consider the use of a new chart developed by the University of Illinois (Table 2), that suggests a higher optimum plant population and earlier planting date. Consider replanting more if the stands are uneven in plant spacing or plant size. Also consider replanting if the field will be used for corn silage, since the crop is worth more.

Greg Roth

Pest Management:

NEW HERBICIDE RESISTANT WEEDS REPORTED

Populations of ALS (sulfonylurea, imidazolinone, and sulfonamide herbicide families) resistant shattercane in Nebraska and giant foxtail in Minnesota have been identified. Thirteen fields in central and south central Nebraska contain shattercane that is resistant to the herbicide Beacon. The fields were investigated after a weed control failure in 1996.

Most of the fields have been in continuous corn production; two were in a corn-soybean rotation. ALS herbicides have been applied to eight of the fields for at least two consecutive years. Several fields had Beacon applied for five consecutive years. Although one shattercane population was also resistant to Accent and Pursuit, the other Beacon resistant shattercane biotypes have not yet been thoroughly tested for cross resistance to other ALS herbicides.

In Minnesota, foxtail biotypes that are resistant to the ALS inhibiting herbicides Accent and Pursuit have been found in two southern Minnesota counties. The management practices that preceded the development of ALS resistance were quite similar. Since 1991, both sites were in a corn and soybean crop rotation with Accent plus a broadleaf herbicide in corn and Pursuit with or without Pinnacle in soybean being the sole weed management program. Cultivation was also absent from the weed management program. Confirmation of the foxtail resistant biotypes was done in the field and the greenhouse. Novartis confirmed the resistance of the giant foxtail to Accent, Pursuit, and Beacon herbicides. DuPont confirmed the resistance of robust white foxtail to Accent and Pursuit.

These are two more examples of the importance of diversifying a weed management program. Repeatedly using products from within the same herbicide family or with the same mode of action can lead to the failure of many useful herbicides.

In particular, herbicides within the triazine family (Atrazine, Bladex, Lexone, Sencor, Princep, etc.), the ALS herbicides (Accent, Basis, Beacon, Broadstrike, Canopy, Classic, Exceed, Lightning, Permit, Pinnacle, Pursuit, Scepter, etc.), and the ACCase herbicides (Assure, Fusion, Fusilade, Poast, and Select) have demonstrated their potential for selecting resistant weeds. So, keep herbicide rotation in mind as we move into a potentially busy postemergence weed control season.

HERBICIDE PERFORMANCE AND RAINFALL

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

If the 10 day limit has gone by and weeds are starting to break through, several options exist.

1. Rotary hoe - Although not many producers own rotary hoes in Pa., this is one time they may pay. This can be used to remove emerging weeds and help "lightly" incorporate the herbicide. The optimum time for hoeing is when the weeds are just emerging through the soil. Corn should be less than 5 inches tall and soybeans should be fully emerged (beyond crook stage). Rotary hoeing is not effective on large seeded weeds or on weeds that have fully emerged.
2. Herbicides - If grasses are emerging, Bladex or Bladex + Atrazine will control small emerged annual grasses (less than 1 1/2 inches tall) unless stress conditions prevail. Be sure to use the DF Bladex formulation if corn has emerged. Accent will control annual foxtails and fall panicum postemergence that are 2 to 6 inches tall. Basis and Basis Gold will also control small annual grasses. If you planted IR or SR corn, Pursuit or Poast Plus are options for grass control postemergence, respectively. With Liberty Link or Glufosinate Resistant corn hybrids, you have an additional backup with Liberty for both broadleaves and grasses. However, remember that stress conditions (e.g. dry and cool or hot) will reduce the effectiveness of post products, so make them in a timely fashion.
3. Cultivation - Again, although most Pa. producers do not routinely cultivate, row cultivation can also be an effective tool for controlling weeds. Row cultivators should be used while the weeds are small, however, cultivating too early may injure the small developing crop. In addition, cultivating too early in the season may redistribute the soil applied herbicide treatment potentially exposing areas of untreated soil.

Bill Curran

DELAYED PRE HERBICIDE APPLICATIONS IN CORN

With the cool windy spring we have had, delayed pre treatments may be a major option this year. A number of residual herbicides can be applied after planting up until corn and weeds reach a certain size or growth stage. The greatest risk of failure comes with trying to control annual grasses such as foxtail and panicum after they emerge.

Several products are now available to control emerged grasses (Accent, Basis, Pursuit on IMI-Corn only and now Poast Plus for SR Sethoxydim-Resistant Corn only.) Certain tank-mixes containing one of these grass herbicides will provide control of emerged grasses plus residual control. Because of their recent introduction, few residual herbicides are labeled with Basis or Poast Plus in tank-mixture. However, Frontier and Prowl are labeled with Accent and a number of residual products are labeled with Pursuit. For most products, do not apply in liquid fertilizer if corn has emerged. Some early-postemergence considerations are listed in the following table.

^a May use a reduced rate of Frontier and Accent under certain conditions.
^b Accent rate of 1/3 to 2/3 oz/acre and Beacon rate of 3/8 to 3/4 oz/acre.
^c May be tank-mixed with Accent, Atrazine (Harness), Banvel or Clarity, Marksman, Permit, or Pursuit (IMI-corn).
^d May be tank-mixed with a number of different products including Accent, Banvel or Clarity, Prowl, Pursuit (IMI-corn), etc. See a herbicide label for specific information.

Dwight Lingenfelter and Bill Curran

HERBICIDE DRIFT MANAGEMENT

With the windy spring weather, spray drift is certainly on many commercial operators minds. Herbicide drift is spray material that misses the target during application or moves off the target after application. There are two kinds of drift—droplet and vapor. Droplet drift is the movement of liquid spray droplets through the air during application. Vapor drift is the movement of spray material as a gas or vapor during or after application.

The applicator can control a large portion of potential drift. Research has shown that a majority of the potential drift can be controlled by adjusting spraying equipment and spraying during periods of low wind conditions. However, with our recent weather, this may not always be possible. The following are some tips to help reduce the potential of herbicide drift.

• Avoid spraying when there is strong wind (>10-12 mph).
• Use large orifice nozzles at relatively low pressures (i.e. <20 psi). Use nozzles that are designed to reduce drift such as, TeeJet DG (Drift Guard) flat fans or Turbo TeeJet nozzles.
• Use nozzles that produce large droplets. The larger the droplet the less likely the water carrier will evaporate.
• Adjust boom height as low as possible, but without interfering with necessary spray pattern. (i.e. 110° tips).
• Do not spray at high traveling speeds which causes turbulence behind the spray boom. 4 to 5 mph is a good traveling speed.
• Spray when soil temperature is cool and relative humidity is highest. It is best to spray before 9:00 am and after 6:00 pm. If possible, spray after a rainfall.
• Avoid volatile herbicides if windy.
• Use drift control additives to increase the viscosity of the spray solution, when permitted by the herbicide label. Products such as Chem-Trol, Nalco-Trol, Target, and Windbreak are common drift retardants.

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

Dwight Lingenfelter with reference—"Spray Drift Control", D.R. Daum and J.D. Keener, PSU, 1991.

POSTEMERGENCE HERBICIDE APPLICATION AND CORN GROWTH STAGES

When considering herbicide application timing and corn growth stage there is variability among herbicide manufacturers. Most herbicide labels refer to corn growth stage by height in inches, number of leaves, or number of leaf collars.

Herbicide labels that refer to corn height in inches are ambiguous. The labels do not specify what the measurement boundaries are on the corn plant (e.g., ground surface to tallest, free-standing, point; ground surface to whorl; base of stalk to fully extended leaf; etc.). The leaf number method generally begins by counting the first rounded leaf or coleoptile (this first leaf sometimes rapidly matures and falls off), continues up past the last visible leaf collar to the uppermost leaf that is 40 to 50 percent exposed. This leaf typically has its leaf tip pointing downward. This method usually results in the addition of one or two leaves more that the leaf collars method. The number of visible leaves and height does not always give a true indication of the crop stage. The more exact method of growth staging is to use a method that corresponds to the number of leaf collars. This system describes the growth of young corn by counting the number of leaves that have exposed leaf collars, beginning with the first or rounded leaf. The collar is a light colored band that appears where the leaf attaches to the stalk or sheath. A plant with four leaves with visible collars would be called a four-leaf or a V4 plant. Exact growth staging can be important, since some postemergent herbicide applications applied after the labeled stage may cause a decrease in the reproductive capacity (yield) of the crop. In general, applications made prior to the V3 stage provide the greatest crop safety. Some labels, especially those on newer products, provide several ways of determining growth stage. Until there becomes a universal rule throughout the crop protection industry for staging crop growth, we will have to continue to use a number of methods. Below is a list of herbicides (Table 3) and their post application restrictions.

Dwight Lingenfelter

INSECT ALERTS

This section of the newsletter is designed to alert pest management professionals to occurrence of specific pests and the need to initiate or terminate management activities.

• Begin Scouting Immediately. Degree day accumulations in the southeast, south central, and southwestern areas of Pennsylvania indicate that alfalfa weevil larvae should be entering the second instar and plant injury should become evident. If warmer temperatures begin, we may begin to see evidence of injury in a week to ten days in central Pa. Northern and highland areas of the state will probably begin to experience injury symptoms toward the end of May.
• Conditions Have Not Been Conducive for Seed Corn Maggot Injury. Seed corn maggot injury is primarily a problem in fields where manure or green vegetation has been plowed under and prolonged cool, wet conditions exist. Under dry warm conditions, corn and soybean seedlings quickly outgrow the pest's potential for injuring the plant. Under cool and dry conditions, the corn will germinate and grow slowly, but seed corn maggot larvae will not establish in the field (most conditions in Pa).
• Garden Symphylan. In fields where stands were reduced or stunted last season because of the presence of garden symphylan, at planting or prior to planting is a good time to spot treat the field for this pest. Make sure you treat at least 50 feet wider than the area where stand loss was observed last year. Lorsban 4E and 15G, Dyfonate 4E and II 15G, and Counter 15G and 20CR are registered in field corn for the pest. In soybeans, garden symphylan does not appear on any label. However, Lorsban 4E and 15G are registered for soybeans and black cutworm control.
• Aphids in Small Grains. Both English grain and corn leaf aphids feed on small grain plants. These aphids overwinter on the plants and are present at low numbers early in the spring. Both species transmit barley yellow dwarf virus. See Agronomy Guide for more on their Biology.

Dennis Calvin

SCOUTING FOR EARLY SEASON CORN INSECTS

At seven to ten day intervals check each corn field on a farm. If time is constrained by other activities, then scout the fields that are at highest risk of developing an insect problem according to preseason assessment of the field (see Agronomy Guide page 6 Table 1-6). Those fields at high risk of developing black cutworm, true armyworm, stalk borer, slugs, flea beetle, 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 wireworm, white grub, corn rootworm, seedcorn maggot, seedcorn beetle, and/or garden symphylan are past the point of preventing injury to the crop.

During this time period, it’s 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 like black cutworm, cut plants off and the plants dry up and blow away leaving no evidence of insect feeding. Typically, if an insect is active in the field there will be evidence of fresh injury. At ten locations in the field visually check 10 plants in a row for evidence of insect feeding. Count the number of plants injured by insects and record the amount of injury and the insect species responsible for the damage. Compare the number of injured plants with economic threshold values in Table 3. If the injury is higher than the economic threshold, implement appropriate management (See Agronomy Guide pages 81 to 95 for management information).

EARLY SEASON CORN INSECT MANAGEMENT Part II: From Plant Emergence to 5th Leaf Stage

This article (Part II) addresses insects, mollusks, and symphylans that attack corn from emergence to about the 5th leaf stage - black cutworm, sod webworm, wireworm, white grub, garden symphylan, slugs, stalk borer, true armyworm, billbugs, and flea beetles.

Black Cutworm - This pest is responsible for more insecticide applications then any other corn insect, with the exception of corn rootworm. Although less than 5% of corn acres are economically injured by the pest each year, damage comes on quickly and losses can be at great. A farmer who has experience unexpected losses from black cutworm typically elects to use a soil insecticide to protect the crop rather than experience loss again. An insurance approach as protection against the pest, however, does not have to be the rule. Unexpected damage by the pest is usually the result of time limitation on a farmer who cannot check his fields on a regular basis. Also, unless a farmer has had training in insect management techniques and knows the life cycle of the pest, he/she does not know when to look or what to look for. Given the need for specialize knowledge and the time demands of farming, it can be a good investment to hire a scout or assign scouting responsibilities to one partner or family member. With a good scouting program, economic losses from black cutworm can be prevented under most conditions.

The most effective approach to managing black cutworm is to implement a pheromone trapping system. Obviously, it is too late to use pheromone monitoring this year. Therefore, begin scouting for black cutworm injury in late May and continue until the plants have reach 18 inches in height. Most cutworm injury of corn is completed by the third week in June. To scout for black cutworm visit a field once a week from the time the plants emerge until plants are 18 inches tall (See section on scouting early season insects for details). If time is constrained only *scout those fields at high risk. No-till fields with many winter annual broadleaf weeds, such as common chickweed have the highest risk. Corn planted into soybean stubble is also at risk. If corn is not planted into the field until at least 10 days after plowdown or burndown of weeds with a herbicide, then the risk of developing black cutworm is very low. Also, fields with no weeds on the surface at planting have a low risk of black cutworm injury.

The presence of corn seedlings that have been cut off and laying on the surface is usually an indication of black cutworm injury. Under dry conditions, the insect may feed below ground causing the plants to appear wilted. Within a few days after clipping, the seedling plants dry up and may blow away leaving no evidence that they emerged.

Several effective foliar insecticides for control of black cutworm are listed in the Penn State Agronomy Guide. Since the larvae often hide under soil clods and plant residue during dry hot periods, the most effective time to treat is early evening.

Sod webworm - This insect primarily shows up in corn planted into a grass sod, such as an old pasture. Injury is very similar to black cutworm, except the insect pulls the cut plant into a silken cocoon that is covered with grass clippings of soil. Under dry soil conditions, the insect may feed below ground level causing plants to appear wilted or to be missing. Lorsban 4E is the primarily rescue treatment for this pest.

Wireworm and white grub - These two groups of insects tend to occur under the same general conditions. Both are associated with grass sods. Therefore, as with sod webworm, they are typically a problem when corn is planted into an old pasture or hay field with turf type grasses. The only management option at this time, if significant injury occurs, is to replant. See section on how to make a replant decision.

Garden symphylan - Very seldom a major problem. A few fields each year may be affected. Evidence of the pest is an area in the field that nothing grows and plants are stunted along the margin of this area. See Insect Alert section for management recommendations.

Slugs - Gray garden slug eggs typically hatch in early May. Therefore, evidence of injury will be seen by mid-May in most years. Slugs are mainly a problem in no-till fields near woodlots or following old alfalfa or a pasture.

Stalk Borer - Problems with stalk borer are associated with corn that is planted into an old hay field that contained orchardgrass. In the fall female moths lay their eggs on the orchardgrass. In the spring these eggs hatch and small larvae borer into the stem to feed. When the old hay field is killed with a herbicide, orchardgrass clumps sometimes survive and need to be killed with a herbicide. When the herbicide kills the orchardgrass, the small stalk borer larvae migrate to the corn seedlings and borer into the stem, stunting or killing the plants. Corn can also be injured by this pest when grasses along the field margin harbor the insect. Small larvae migrate from these plants at about 1,400 to 1,700 GDD (base 40). The grasses along the margin can be checked for stalk borer present at about 1,300 to 1,400 GDD (infested plants will have dead stems and larvae inside). Apply an insecticide at the first evidence of injury. An insecticide to prevent injury must be applied before the small larvae migrate from the orchardgrass into the corn plants.

True Armyworm - Problems with this pest are primarily associated with corn planted in a rye cover crop that is left in the field on the soil surface. Adult females lay eggs on the rye which hatch into larvae that feed on the developing rye. When the rye begins to dry down or is killed with a herbicide, the larvae migrate onto young corn plants and begin to feed. Burndown with a herbicide, plowing, or removal of the green vegetation from the field at least 10 days before planting will reduce the likelihood of problems with this pest. When problems occur treat with an registered insecticide (See Agronomy Guide).

Billbugs - Although evidence of feeding by this insect is seen in most fields, it is seldom an economic problem.

Flea Beetles - This insect is seldom seen as a problem in field corn except in the southern areas of the state. Most corn hybrids have resistance to Steward's wilt, a disease transmitted by the insect. Only if 50% or more of the leaf surface area has been removed by its feeding and corn plants are growing slowly, should you consider treating.

AGENT OBSERVATIONS

SW PA CROP PLANTING REPORT

SW PA was without significant moisture the whole month of April. Oats, seeded alone and underseeded with alfalfa, were easily planted during the week of April 6 - 12. Corn planters have been running in SW PA since about April 22. As of this date (5/13) the top managers are over 80% planted and others are just beginning. It appears that many producers who planted no-till last year have returned to some tillage this year. Most soybean producers have not really begun to seriously plant yet.

Temperatures have been unusually cool with frost occurring frequently in some areas of the region. Small grains and forages have been slow to grow which will mean reduced yields for first cutting. Barley is heading and wheat is finally beginning to elongate. Pastures are short due to grazing pressure and lack of moisture.

I also just returned from central Indiana (5/12) and Ohio where most of the corn is planted and farmers are rapidly planting soybeans. Only about 5 - 10% of the corn had emerged, but fields looked to be in great condition when compared to last year.

Don Fretts
Fayette County

1997 DEGREE DAY ACCUMULATIONS:

To track corn and insect development, compare the 1997 cumulative degree-days shown in Table 1 to the required values in Tables 6 and 7. 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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