June 13, 1997 Vol. 97.6

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
• CCA Exam - PDA Building in Harrisburg - August 1, 1997
• NCRS Program on Soil Conservation postponed until September 23 & 24, 1997

Weed Tours Quickly Approaching

Certified Crop Advisor Corner

Production

• Harvesting Winter Wheat
• Corn Development Slow
• Early Season Chlorophyll Meter Nitrogen Test for Corn

Pest Management

• Insect Alert
• Corn Rootworm Biology and Management
• Some Weed Control Observations
• Watch Out for New Weed Species
• Waterhemp, A Weed to Watch For

Agent's Corner

• Lebanon
• York

Degree Day Accumulations

Weed Tours Quickly Approaching:

Don't forget to register for the 1997 Weed Tours on July 10 at Landisville and July 11 at Rock Springs. Call Lisa Crytser at 814-865-2543 for additional information.

Bill Curran

Certified Crop Advisor Corner:

Northeastern Branch of the American Society of Agronomy meetings will offer 3 continuing education units (CEU's) during its meeting at the University of Maryland. There will be one CEU in each of the following areas; Soil/Water, Soil Fertility, and Crop Production. The Certified Crop Adviser session will be held on July 16, 1997 in the Plant Science Building on the University of Maryland campus in College Park, Maryland. The campus is located between Baltimore and Washington. Advanced registration is not required. For additional information, call 301-405-1319. The following is an outline of the program:

Elwood Hatley, CCA

Production:

Harvesting Winter Wheat

Harvest time is quickly approaching. Both yield and quality can be affected by harvest management. It is usually suggested to start harvest when grain moisture reaches 14%. This eliminates the need to artificially dry the grain and eliminates a moisture dockage when selling directly from the combine. A wheat kernel is mature at 30% moisture. It will dry at a rate of 2.5% per day from 30 to 20%. From 20 to 14% it will dry at about 1 percentage point per day under good drying conditions, but may require 10 days to drop 1 percentage point under poor conditions. Research at Ohio State University indicates that during the time wheat is drying from 30 to 14%, yield will drop by 12 pounds per day and bushel weight by 0.25 pound per day. Therefore, each five days delay in harvest could potentially reduce yield one bushel and test weight 1.25 pounds. The yield losses result from increased lodging, shattering, and bird and rodent feeding. Drying and rewetting from rain and dew causes the reduction in test weight.

Wheat can be harvested, without damage to the kernel or affecting milling quality, once the moisture drops to 20% or lower. Harvesting between 20 and 14% moisture has the following advantages; increased yield and test weight, reduced combine harvest loss, maintaining good germination, and earlier seeding of soybean when double cropping. The disadvantage is the need to artificially dry the grain for proper storage. The cost of drying, either on the farm or at the elevator, must be compared with the advantages of early harvesting.

Elwood Hatley, CCA

Corn Development Slow

Corn planting occurred at a record pace this year with PDA reporting 88 percent of the crop planted by June 1. Cool temperatures in May, however, resulted in slow emergence and development of the crop. Growing degree day accumulations since May 1 have been about 100 GDD less than average. The cool weather resulted in sporadic reports of poor emergence, particularly under heavy corn residue or on corn planted deeper than 2 inches. I have seen several fields where the coleoptiles split under the soil surface and corn leafed-out under ground. Some fields emerged 3 to 5 weeks following planting and plants continued to emerge for about 3 weeks, resulting in uneven stands. These late emergers have reduced seedling vigor and will result in some yield loss. On the whole, I have seen a lot of good stands and am optimistic about the yield potential of this years crop. In 1994, we had a cool May as well and went on to have a record yielding crop that year.

The cool spring and windy and dry conditions in some areas could result in significant N losses from sprayed UAN applications. I would monitor these fields as they reach the V8 stage to detect any N deficiency symptoms, although I suspect most N deficiency, if any, might occur later in the season.

This should also be a good year to see responses to narrow rows, since canopy closure will be significantly delayed this year. This year has provided excellent growing conditions for perennial weed development in no-till fields and there appears to be the potential for considerable weed competition. Hopefully most fields will be treated accordingly to keep yield losses to a minimum.

I am not concerned much about late crop maturity yet. Many of the short season areas, where maturity is often a problem, had good conditions for timely planting in May. There is still much of the season left. Normally May contributes 300-400 GDDs to a season total of 2200-3000 GDDs, depending on location. We all know the weather can also change dramatically and we can make up the 100 GDDs we are behind later in the season. Rainfall and temperatures in late July and August will, as usual, be the primary factors in determining the yield potential of this years crop.

Greg W. Roth

Early Season Chlorophyll Meter Nitrogen Test for Corn

The chlorophyll meter is a portable, hand-held device that instantaneously measures the greenness (or chlorophyll content) of a plant in the field. Nitrogen (N) is closely associated with leaf chlorophyll; thus chlorophyll meter readings of corn leaves reveal the N status of the plants. The early-season chlorophyll meter test consists of taking meter readings of corn leaves when plants are between the six- and the eight-leaf stages (when plants are about 10 to 20 inches tall), which allows time to sidedress if necessary. Meter readings taken from plants in a field are compared to readings taken from high N reference plots that have been adequately fertilized with N fertilizer. Additional N is required for optimum corn yield if the average meter reading of the field is less than 95% of the high N reference value. An N fertilizer estimate can be calculated using meter readings and field factors.

Advantages of the early-season chlorophyll meter test:

• Chlorophyll meter readings are quick, easy, and provide instantaneous values.
• No samples need to be collected, processed, and sent to a laboratory for analysis.
• Cost of sampling involves only labor costs.
• N recommendations are accurate (comparable to the Pre-sidedress Soil Nitrate Test).

Disadvantages of the early-season chlorophyll meter test:

• Initial expense is high (the meter costs about $1400).
• Early-season corn leaf chlorophyll levels are affected by hybrid selection and environmental stresses; therefore, high N reference plots must be established.
• This test is not applicable to fields that have received a preplant or an at-plant N fertilizer application beyond starter N.

This test provides another option in addition to the already widely used presidedress soil nitrate test for corn (PSNT) for assessing nitrogen status of the corn crop and making economically and environmentally sound N recommendations. Both tests appear to give similar results. This test has been studied extensively in Dr. Richard Fox's research program here at Penn State and at other research centers. Also, we conducted an extensive three year field evaluation of the test involving county agents, crop consultants, and fertilizer dealers who used the test under actual farm conditions. On that basis, we are now recommending that the early season chlorophyll meter nitrogen test for corn can be used as a nitrogen management tool in Pennsylvania.

A new Agronomy Fact sheet #53 ÒThe Early-Season Chlorophyll Meter Test for CornÓ has been published which gives all of the details on this new test.

Doug Beegle and Dwight Lingenfelter

Pest Management:

Insect Alert

Cutworm - Larvae about 3/4 inch long have been found around the state cutting corn plants. In some fields, individuals have found larvae feeding internally in the stem of small plants. Both black and dingy cutworms may be responsible for this injury. These two species are difficult to distinguish without the aid of a microscope. Black cutworm larvae have bumpy skin, while dingy cutworm skin is smooth. Dingy cutworm larvae are foliar feeders, while black cutworm larvae cut the plants off and may feed underground on or in the stem. The peak period of cutworm activity should occur over the next two weeks, so keep a close eye on corn seedling; especially in corn fields that had significant broadleaf weed populations at planting or shortly before planting.

Potato leafhopper - Low numbers of adults have been observed in alfalfa fields in south and central Pennsylvania. The first reports followed a thunderstorm system that originated in the Gulf of Mexico and moved into Pennsylvania. So far this year, few rain storms have moved into the state from the Gulf. In general the more frequent that thunderstorms hit the state from the Gulf of Mexico, the higher the pressure from this pest. Also, when the pest arrives early in the spring population levels tend to be greater. As of now, it appears that leafhopper pressure will be low to moderate on the second cutting in most areas of the state.

Alfalfa weevil - In alfalfa fields that will be cut on a timely basis, it appears that this insect will cause little injury this year. Larvae range from first to fourth instar in fields in Centre Co. In fields with high numbers of late instar larvae at harvest, keep a close eye on regrowth. Slow regrowth can indicate that larvae are eating off the new shoots. Two larvae or more per alfalfa crown is enough to justify a stubble treatment.

Corn rootworm - A computer model projects that 5% hatch of rootworm larvae will occur over the next week in the southeast and southwest areas of the state. Rootworm hatch is predicted to begin the following week in most areas of central Pennsylvania. In higher elevations and northern counties, initiation of hatch is predicted for the first week of July. See Table 1 for more detail. Post-emergence applications of Furadan 4F should be timed to 5% egg hatch.

European corn borer - Emergence of overwintering adults occurs between 310 and 850 DD, with peak emergence at about 490 DD (base threshold = 55¡F). Therefore, light and pheromone traps should be in place by about 310 DD to capture the early part of the emergence period. Typically, adult females fly and are captured in light traps about three to five days after emergence. Adult males will be captured in pheromone traps shortly after emergence. York Co. had 251 DD accumulated as of June 7. Therefore, moths should be emerging and move to traps within the next week to ten days. In Centre Co. Pa., initiation of emergence should not be seen for about ten days to two weeks. The earliest any evidence of first generation ECB feeding should be seen is at about 468 DD. Scouting should be initiated at 648 DD.

Stalk Borer - Degree days accumulations for stalk borer indicate that larvae should begin to move from grasses to small corn plants within the next week in warmer areas of the state (York, Lancaster, Westmoreland Co., etc.). Cooler areas of the state are 10 days to two weeks from the time of movement from grasses into corn. Watch for early evidence of injury and treat with Lorsban, Pounce, or Asana if economic thresholds are exceeded. The following economic thresholds should be used: 1 leaf stage - 7%, 2 leaf stage - 8%, 3 leaf stage - 10%, 4 leaf stage - 11%, 5 leaf stage - 12%, 6 leaf stage - 23%, 7 leaf stage - 100% of plants infested. Leaf stages are based on the number of leaves with visible leaf collars. Fields with orchardgrass in or around the field or large stemmed broadleaf weed around the field should be watched closely.

Corn Rootworm Biology and Management

Corn rootworm is by far the most important complex of pest species that attack field corn in Pennsylvania. Three species can be found in the state, the western corn rootworm, the northern corn rootworm, and the southern corn rootworm. Of these, only the western and northern corn rootworm are significant pests of field corn. The southern corn rootworm is a major pest of curcubit crops (cucumbers, squash, pumpkin, etc.)

Both the northern and western corn rootworm have similar life cycles. Adults emerge in late summer, from early July to September depending on location and growing season, and lay their eggs in the soil of corn fields. In recent years, there has been some instances of western corn rootworm adults laying eggs in soybean fields, in areas of eastern Illinois and western Indiana, where a soybean/corn rotation is common. So far, in Pennsylvania, egg laying in soybeans and economic infestations of rootworm in first year corn have been extremely rare.

The eggs of corn rootworm overwinter in a condition known as diapause. Diapause is a physiological condition that insects enter to avoid harsh environmental conditions. Diapause is broken after a given number of cold days have passed. This typically occurs in January or February. Once diapause is broken, the eggs begin normal development as heat is absorbed from the insect's environment. Typically, temperatures are not high enough for rootworm egg development until sometime in March. From March until mid to late May, the amount of heat available for insect development is small.

For corn rootworm, the base DD temperature is 53¡F. Therefore, if the temperature never exceeds 53¡F, then no development takes place (i.e. the insect is in suspended animation). There are two key periods in corn rootworm development that need to be predicted for pest management: egg hatch in the spring and adult emergence in late summer. The initiation of spring egg hatch has been shown to occur between 583 and 684 DD (base threshold = 50¡F; note that this varies from the base threshold of 53¡F in Table 1), based on 10 to 15 years of data collected in Indiana. Adult emergence is predicted to occur between 1,645 and 2,336 DD. As of June 7, 1997, the number of DD accumulated across the state varied between 271 and 489 in Montrose, Susquehanna Co. and York, York, Co., (use DD values for Black cutworm). Based on this rate of DD accumulation, 312 to 413 DD and 94 to 195 DD more are needed before the beginning of egg hatch at Montrose and York, Pa., respectively.

Table 1 shows the predicted range of dates when 5% egg hatch (first instar larval emergence) is predicted for general regions in the state. For a more in-depth discussion of degree days, see the "Field Crop NewsÓ, Vol. 97:3, article on "Using Degree Days in an Insect IPM Program".

The predictions presented in Table 1 can be used to time post-emergence insecticide applications. For maximum effectiveness, insecticides should be applied at about 5% egg hatch. This timing provides enough time for the insecticide to move into the root zone to protect the roots from late instars of corn rootworm. It is the last two instars that cause 90 to 95% of the root injury. By applying the insecticide at 5% hatch, the large majority of the early instars (smaller larvae) will be killed. To increase effectiveness of post-emergence applications of the insecticide, the insecticide should be incorporated when possible. Because Furadan 4F is the primary insecticide that is applied post-emergence in Pennsylvania, timing is very critical. The product is water soluble and will be moved lower than the root zone if applied too early relative to egg hatch. If applied too late, the larvae will have reached a size large enough to cause injury before the insecticide reaches the root zone to provide protection. Larger larvae also require greater amounts of insecticide. One limitation to post-emergence applications is that rain or irrigation is needed to move the insecticide into the root zone. Proper timing increases the opportunity for a rain event to move the insecticide into the root zone.

Because the growing season has been extremely cool until this week, insect and crop development is considerably behind. In an average year, hatching events would be approximately two to three weeks earlier. Early planted corn (April planting) may loose any protection from corn rootworm injury if a soil insecticide was applied because to the late hatch. Most soil insecticides have a six to eight week period of concentration high enough to kill part of the rootworm population. Therefore, corn planted on April 15 with an soil insecticide should be protected until about June 17. According to Table 1, a field in Lancaster Co. planted on this date would at most only have reach 50% hatch by June 17. Therefore, 50% of the corn rootworm larvae would hatch after the insecticides period of protection had ended. In a field with extremely heavy rootworm pressure, stalk lodging may be seen and economic losses may occur depending on moisture levels. Another side affect of the cool spring is that even late plantings (after June 1 in most areas) of corn, which normally would avoid corn rootworm injury, may be at some risk of injury by the pest. A beneficial side effect of cool spring temperatures, however, is that the period of egg hatch is lengthened, reducing the number of larvae present to injure the plants at a given point in time. The result of this may be a reduction in the injury potential of a rootworm population within a field. This effect will be more important in cooler areas of the state (northern and higher elevations).

Dennis Calvin

Some Weed Control Observations

I am hearing about and seeing a lot of weed escapes following preemergence herbicide programs. With the dry weather we experienced during May in many areas of Pennsylvania, the larger seeded broadleaves in particular are now breaking through treatments that should have normally controlled them. Specifically, velvetleaf, ragweed, cocklebur and other larger seeded broadleaf weed control may be inadequate. I am also seeing grass breaks in some fields. Scout those fields now to determine the need for additional control measures.

I received a number of phone calls over the last week about herbicide injury to corn. Specifically, the type of injury taking place is a burning of the leaves from contact type herbicides. Herbicide applications have included atrazine-based products perhaps with Prowl and some of the post contact materials such as Basagran, Buctril and Resource. The systemic herbicides such as Banvel, 2,4-D or the sulfonylureas have not produced these results. With the cool cloudy weather we have experienced until just recently (finally summer has arrived), corn growth is slow and the leaf tissue is very tender, succulent and susceptible to this type of contact herbicide injury. Leaf cuticle (wax) development is reduced under cool cloudy conditions. Without sufficient cuticle development, young corn plants are more prone to contact-type injury. Hot humid weather can also be problem for post applied herbicides, although this is also associated with the systemic herbicides. Herbicide injury from the contact herbicides is usually superficial and both corn and soybeans generally fully recover without impacting yield. If you or a customer experienced some of this type of injury, the best solution is to revisit the field in 4 or 5 days and hopefully be impressed at the resiliency of the crop.

Watch Out For New Weed Species

Every season, one or two weeds seem to become more prevalent in certain fields, along roadsides, or in certain regions of Pennsylvania. For example, I have noticed more and more cocklebur, shattercane, johnsongrass, and Virginia copperleaf over the last two or three years. Certainly burcucumber and eastern black nightshade have been on the increase in many areas of Pennsylvania. I recently received several calls about bigroot morningglory, an aggressive perennial that can cause serious damage to both corn and soybeans. And last summer we found tropical soda apple, a relative of horsenettle, in an isolated area near Sunbury. This weed is on the federal noxious weed list and is considered a real threat to pasture and hay acreage throughout the southern U.S. The northern limit for tropical soda apple is currently unknown. With today's global economy which includes importing many different agricultural products to the U.S. and Pennsylvania, the threat of introducing new pests is always present. In addition, we already have over 500 important weed species in the U.S., some of which are native and others that were introduced during the last 100 years. Every year, there is still plenty of opportunity to introduce weed species we have up until now avoided. So, as you are scouting fields or solving various pest management problems this summer, try to make note of new or unusual weed species. Managing an isolated infestation is much easier than one that is already unstoppable.

Waterhemp, A Weed To Watch For

A number of different pigweed species belong to the genus Amaranthus. The pigweeds commonly found in the northeastern U.S. include smooth pigweed (A. hybridus), redroot pigweed (A. retroflexus), tumble pigweed (A. albus), prostrate pigweed (A. blitoides), spiny amaranth (A. spinosus), and Powell amaranth (A. Powellii). Smooth and redroot pigweed are the most common pigweed species of field crops in Pennsylvania. Over the last several years, two closely related species, tall and common waterhemp (A. tuberculatus and A. rudis), have exploded in prevalence in many areas of the midwest. This exponential increase in waterhemp throughout the midwest is related to the dramatic increase in use of ALS herbicides (Classic, Pinnacle, Pursuit and Scepter in soybeans and Accent and Beacon in corn). The ALS herbicides have been used extensively in soybeans for about 10 years. Their use in corn is more recent and typically still includes effective waterhemp and other pigweed herbicides like atrazine. The waterhemps would generally not be any more of a problem than other pigweed species, except for the fact that ALS resistance with these species is fairly common in many midwestern soybean fields.

Several weed distribution maps indicate that tall waterhemp populations extend into the Northeast as far north as Maine. In the Northeast, we have not experienced the same explosion of waterhemp problems that our neighbors to the West have. This is probably related to a lower incidence or even absence of waterhemp in the Northeast, the relatively low proportion of soybean acreage compared with other crops, and our more diverse cropping systems (i.e. hay, pasture, and small grains).

However, keep an eye out for waterhemp this summer. Pay particular attention to pigweed identification if you experience a weed control failure. This is especially true when relying on the ALS herbicides. Unlike smooth and redroot pigweed, waterhemp typically has no hairs on the stems or leaves, giving the plants a smooth texture. The leaves of waterhemp are typically glossy and more elongated or lanceolate than redroot and smooth pigweed (Photos 1, 2, and 3). Stem color of waterhemp can vary from light green to dark red. Unlike redroot and smooth pigweed where both male and female flowers are found on the same plant (monecious), waterhemp plants are either male or female (dioecious). It is often difficult to properly identify some pigweeds until late summer when they are flowering. The redroot pigweed flowering structure is branched, compact and thicker than a pencil. The smooth pigweed seed head is highly branched, more so than redroot and the branches on the flower are compact usually more than 1.5 inches in length and thinner than a pencil. At maturity, the entire plant and flowering structure are usually either green or purple. Waterhemp leaves are usually long and narrow without hairs, male plants shed pollen and female plants produce seed. Flowering structures are open and located near the top of the plant and at the tips of the branches. The branches are much thinner than a pencil and can vary in color from green to red. See photo 4 for examples of pigweed species seed head differences. Remember, not all pigweeds were created equal.

Photo 1. Redroot or smooth pigweed seedling

Photo 2. Tall waterhemp seedling

Photo 3. Maturing tall waterhemp plant

Photo 4. Mature pigweed seed heads. From left, Palmer amaranth,
Powell amaranth, redroot pigweed, smooth pigweed, and waterhemp.

Pictures taken from Pigweed Identification, 1994. Kansas State University CES. and Waterhemp Management in Agronomic Crops. College of Agricultural, Consumer, and Environmental Sciences, University of Illinois.

Bill Curran

AGENT'S CORNER

Lebanon County

Lebanon has 467 heat units since March 1, 1997 indicating the development of many insects and of course crops. The last few weeks have been cooler than normal and nights are really causing warm season crops to struggle. Peppers, tomatoes and melons all are developing slowly. Corn for the most part is moving with the northern part of Lebanon at V-2 and south at V-4 as of 6/9/97. Although the experts say this season was not a season for maggots, I was in numerous fields that had maggot damage and or large populations of the adult fly.

Populations of corn are suffering. Again in the northern part of the county, the average population is running around 20-22,000 ppa and in southern Lebanon Co., between 22-26,000 ppa. I am unsure whether the producers are shooting for this or there was some pest or condition affecting germination. Soybeans are at V-1 across the county. Soybean populations look good with most running around 160-180,000 ppa. Most established alfalfa has three inches of new growth following the first cutting. So far I have not observed any leaf hoppers.

New alfalfa seedings have struggled with the cooler weather. The stands are there, but not growing very quickly. Most tall grass was clipped this week. If stage of growth is the quality indicator than we will have some lower quality hay this year since much of it was cut with the heads almost fully developed. Hopefully we will get more rain and some warmer nights.

Aphids, weevils(adult), and flea beetles seem to be very active this spring as well as grubs. There are numerous weed escapes including yellow foxtail, velvetleaf, and lambsquarters. Burcucumber is quickly developing; I noted some with three true leaves. Many producers are respraying fields because of preemergence herbicide failure. Another good lesson to move toward split applications.

Del Voight
Lebanon County

York County

Corn is still struggling along trying to find some warmth. Corn planted around April 22 is barely 8-10 " high (as of 6/9). At least we've had ample rain since Memorial Day weekend. Soybeans are up in the first trifoliate on average. Stands of both corn and beans are good considering the cold soil conditions of this spring. Pre-emergence herbicides did well under the circumstances. Mildew has sprung up on the top leaves of wheat since the Memorial Day weekend rain. Grass hay cutting is beginning. First alfalfa cutting is done. There were some spots with alfalfa weevil damage. Oat growth was slow and uneven due to the earlier dry period.

John Rowehl
York County

1997 DEGREE DAY ACCUMULATIONS:

To track corn and insect development, compare the 1997 cumulative degree-days shown in Table 2 to the required values in Tables 3 and 4. 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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