July 25, 1997 Vol. 97.9

IN THIS ISSUE:

Calendar

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

Production

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

Pest Management

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

Agent's Corner

• Adams
• Dauphin
• Mifflin / Juniata / Perry Counties
• York

Degree Day Accumulations

Pest Management:

Poisonous Pasture Weeds

Scout your pastures for poisonous weeds such as White Snakeroot and others mentioned below

Calls and reports concerning livestock death due to poisonous weeds frequently increase during the next few weeks. During the hot and dry months of July and August, the condition of many pastures becomes poor and over-grazed. Cattle may be forced to graze on weeds that they normally wouldn't, or they may eat a weed out of curiosity. Scout your pastures and remove these weeds before they cause livestock health problems. Following are descriptions of some of the more common poisonous weeds:

White Snakeroot (Eupatorium rugosum).

Perennial. Leaves and stems are the dangerous parts of the plant. Has a fibrous root system. Leaves are opposite along stem, oval, toothed margins and with long petioles. Small white flowers in compound terminal clusters are conspicuous in late summer. Found in woods, damp and shady pastures, and occasionally in thickets and clearings. Newly cleared lots may also contain this weed.

Nightshades (Solanum sp.).

Several different nightshade species are close relatives (jimsonweed) have been known to be poisonous to livestock and pets when parts of the plant, particularly the berries, have been consumed. Common nightshade members include eastern black nightshade, bitter nightshade and horsenettle. Plant appearances vary between species, but most all produce small berry-like fruits.

Wild Black Cherry (Prunus serotina).

Perennial woody tree or shrub. Not necessarily a "pasture weed," but sometimes found in or bordering pastures. Damaged or wilted leaves or branches are the dangerous parts of the tree. Leaves are alternate, simple, elliptic-pointed, leathery in texture, and finely toothed on the margins. Flowers are showy, fragrant, and white, hang in drooping clusters, and produce dark-red to black cherry fruits.

Poison Hemlock (Conium maculatum).

Biennial. It looks very similar to wild carrot or wild dill. Leaves are alternate and have a lacy appearance, while the small white flowers are arranged in compound umbles. Stems are smooth and covered with purple blotches. All parts of the plant are poisonous, however, stems are less poisonous than the rest of plant. Generally, it is not palatable to livestock but ingestion of as little as 0.25 to 0.3% of body weight of poison hemlock is lethal. It grows in moist soils of pastures, ditches, roadsides, and disturbed sites.

Common Pokeweed (Phytolacca americana).

Perennial. Pokeweed can grow as tall as 10 feet with alternate oblong leaves, smooth reddish purple stems, and deep purple berries (mature) in clusters. The roots are the most poisonous part of the plant, while the berries are the least poisonous part. Poisoning is rare in animals since the large taproot is generally difficult for animals to forage and ingest. Found in pastures, no-till fields, shady roadsides, wasteplaces, woodlots, and fencerows.

Dan Childs (Purdue Pest & Crop Newsletter, 1996) and Dwight Lingenfelter

Potato Leafhopper Management in the Third Growth Cycle

Potato leafhopper populations PLH during the third growth cycle of alfalfa are influenced by local (field to field) movement. This is in contrast to the second growth cycle, when the pest moves into an area on storm fronts that originated in the Gulf of Mexico. While leafhoppers that arrive in the spring are about 70% female, those that move between fields during the third growth cycle are only 50% female. This may slightly affect economic threshold levels, but when variation in sampling is considered, the standard threshold values are accurate enough for making good treatment decisions.

The time from egg deposition to the adult stage of potato leafhopper is about 28 days under average temperatures. Eggs are laid in a field when the regrowth reaches a height of about 2 to 4 inches (7 to 10 days after cutting).

Therefore, about one generation can be completed during each alfalfa growth period (ca. 30 to 35 days). During the second growth cycle the overall population level of the pest increases, thereby increasing the likelihood of economic damage during the third growth cycle. It has been shown that fields which experienced economic levels of leafhopper during the second growth cycle have about a 70% chance of developing an economically damaging infestation during the third growth cycle.

Until recently, leafhopper pressure was low in alfalfa fields. Within the last week, their populations have exploded. Dr. Hower, Penn State Entomology Department, indicated that populations are the highest seen within the last ten years. Therefore, expect high leafhopper pressure on the third cutting of alfalfa. In fields that were cut early versus applying an insecticide in the second cutting, be ready to protect the third cutting once the regrowth reach two inches.

To determine whether a field can benefit from an insecticide treatment, it is best to scout the field on a seven to ten day cycle beginning when the regrowth reaches a height of 2 to 4 inches. Typically, a couple of visits to the field is enough to reach a management decision. See the "Field Crop News" article "Potato Leafhopper in Second Cutting Alfalfa" Vol. 97:5 for specific methods of scouting. Once third cutting alfalfa has reached 12 inches in height, it is recommended that the field be cut early verses applying an insecticide to control the pest. This prevents injury to the alfalfa from the tractor and spray equipment tires.

Potato Leafhopper Impacts on Seedling Alfalfa

A substantial amount of research literature is available on the impact of PLH on established stands of alfalfa. However, there is little information available on how PLH injures new seedings. The only information that I am aware of comes from Dr. Paul Flinn's Masters Thesis. The following is a summary of how seedling alfalfa recovered from PLH injury from his thesis. Plants exposed to four late instar nymphs produced an average of six new trifoliate leaves during the seven day recovery period. On the other hand, only 2 of 7 plants exposed to 4 adult females were able to produce new trifoliates, indicating that most plants would not survive. Densities of 4 or more females could thus translate into possible loss of a seedling stand under field conditions. Longer periods of infestation, or shorter height, at the time of exposure, would both increase stand damage. Since females are the most damaging class of PLH and migrant females arrive at a time when spring seeded alfalfa is very vulnerable, it is important to protect new seedling at this time.

Although alfalfa can be killed by four or more adult females per plant, this is an extremely high density of the pest. Dr. Hower feels that this level of infestation is uncommon, and even with this years record infestation levels, most fields are unlikely to have densities this high. Therefore, it is unlikely that new seeding will be lost to this pest, even when uncontrolled. What is not known is the impact on final stand density, the yield potential in future years, and how stand longevity will be affected. Because we lack a good understanding of the pest's long-term impact on an alfalfa stand, it is a good idea to protect the new seeding if possible.

Currently, no economic thresholds have been established for new seedings of alfalfa. Dr. Art Hower, Dr. Dennis Calvin, Ms. Jan Pruss, and the Crop Management Associations are currently conducting field research to evaluate the economic impact of PLH on seedings of alfalfa.

Insect Alert

Potato Leafhopper - Potato leafhopper numbers have sky rocketed off the Richter Scale since the last newsletter. It appears that high numbers of immigrants arrived in the state on major thunderstorms at the end of June and early this month. These populations are about 80 to 90% female. It is the females that do the majority of feeding and that are responsible for depositing eggs that lead to population growth. Yield and quality is falling off rapidly in the second cutting. Yellow alfalfa is common in both established and new seedings. New seedings seeded under a small grain crop are also being hit hard by the pest. Currently, there is little information available on the impact of leafhopper on new seedings. See the article on "Potato Leafhopper Impacts on Seedling Alfalfa". The product registered for control of leafhopper in a new seeding under a small grain is malathion. Although this product will kill leafhoppers in the field, it has a short residual; and if the small grain canopy is dense, it is almost impossible to get coverage. Therefore, getting the small grain off as soon as possible and then cutting the alfalfa is the best management strategy. After cutting, make sure the new regrowth is protected from leafhopper with a long residual insecticide (wait until at least two inches of regrowth to spray).

Corn Rootworm - If significant root feeding has occurred in a field, injury symptoms should become evident within the next few weeks. So far, I have heard no reports of corn lodging from rootworm injury. My feeling is that injury from this pest will be minor this year because of the cool early spring conditions and the relatively good growing conditions over the last month.

European Corn Borer - First generation flights are nearing completion for this year. In areas where a single generation type of corn borer occurs (northern and high elevations of the state) we should be entering the major period of its flight. Injury symptoms on the leaves emerging from the whorl should be evident over the next few weeks for first generation larvae.

Stalk Borer - Larvae of this pest should be migrating from grasses into corn and soybeans now in many areas of the state.

Black Cutworm - The period of injury from this pest should be past in most areas of the state.

Japanese Beetle - Adults of this pest typically begin emerging around the fourth of July. This year emergence may be a week or two late because of the cool spring temperatures. Once emergence begins, watch corn fields for silk clipping and soybeans for significant defoliation along the margins of fields.

Fall Armyworm - This pest typically begins migrating into Pennsylvania around the end of July. Watch whorl stage corn fields for evidence of its feeding. This pest, however, rarely causes economic injury in field corn.

True Armyworm - Watch wheat fields that are headed out for head clipping by the pest. This is not a common problem, but can cause significant yield losses if populations are high.

Dennis Calvin

AGENT'S CORNER

Adams County

Wheat harvest has finally begun. There was very little incidence of cereal disease, however, yield may be reduced approximately 20% this year. Second cutting alfalfa is almost complete. With the lack of moisture, there was excellent quality alfalfa harvested as both haylage and dry hay.

Leafhoppers have arrived and numbers warrant a control method on third cutting regrowth. Success of newly established alfalfa stands this spring has been variable. Harvesting of the mulch hay, used for mushroom compost, is almost complete.

The early corn is 3-4 feet tall and shading over nicely. Some corn is showing severe symptoms of drought stress. Soybeans have reached 6 inches. Some stands are thin due to the dry conditions during planting. Spider mites were present in some soybean fields this past week.

Larry A. Swartz
Adams County

Dauphin County

As I am writing, a scattering of thunderstorms is passing through the area. Unfortunately, these storms are widely distributed and any amounts of rainfall are very limited and will not provide adequate soil moisture to break the present mini-drought condition. Soil moisture levels across the area are limited, and much of the corn crop is showing stress by mid morning, most days, but recovering during the night.

Early planted soybeans are beginning to flower, but growth is limited. Later planted bean stands are reduced and development is severely limited due to moisture stress conditions. Groundhogs continue to be a major problem in many soybean fields. (Does anyone have a good method of control for groundhogs?)

Third cutting of alfalfa is heavily infested with potato leafhoppers. Where the large population levels came from so rapidly is a surprise. In many fields that had very low levels one week, the next week levels were as high as 2.5 PLH's per sweep. Application of control materials are being applied to give extra protection to drought stressed alfalfa stands.

Wheat harvest began on July 7. Yields range from 45 to 65 bu/acres. Test weights are good. Barley harvest is nearly complete with yields in the mid 70 bu/acre range. Marketing of barley has been the hard part this year as local mills are refusing to take grain.

Paul H. Craig
Dauphin County

Mifflin / Juniata / Perry Counties

Following a period of warm temperatures and adequate soil moisture, crop growth in Central PA has begun to slow considerably in the last week. Corn plants have begun to curl their leaves each afternoon and the soybeans are not gaining much height. One interesting side effect of the weather seems to be few reports of crop damage as a result of post-emergent herbicide applications. I have seen damage on corn and soybeans. While most situations have used labeled rates and additives, the most likely cause of damage seems to be high temperatures combined with surfactant and/or nitrogen in the spray mix. Fortunately the crops have been able to recover from most of the damage.

Harvest of second cutting alfalfa is well underway, the hot and dry weather has allowed producers to harvest excellent quality hay and haylage. Potato leafhopper populations are reaching levels where control measures are necessary. John Flanders, Head Technician for the West Branch CMA, reported he found leafhoppers over threshold levels in some third crop regrowth fields. Also, leafhoppers have been active in new seeding fields for at least two weeks.

Much of the barley has been harvested and the wheat crop will soon be ready. Most of the oats I have seen are loosing their green color. All of the small grains are standing extremely well. At this point, yields seem to be slightly better than average.

Greg Hostetter
Mifflin / Juniata / Perry Counties

York County

Crops are suffering from effects of extreme dryness and heat the last part of June. Some areas have received little or no rain since Memorial Day weekend. I expect we will have more weed intrusion later, due to poor crop canopy closure. We can see reduced growth from very few weeds already. Barley harvest is over, yields are down from average. Wheat harvest is about to start any time now. Oats are beginning to dry down.

Second cutting alfalfa produced well, if the first cutting was done in a timely manner. The producers on an early bird cutting schedule got it in before leafhoppers built up to threshold levels. Conditions the next week or two will make or break our growing season for corn.

John Rowehl
York 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 2 and 3. 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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