Website Address: http://fcn.agronomy.psu.edu/
Vol. 96:4
May 3, 1996
Elwood Hatley, CCA
The use of seed treatment for disease control in soybeans has not been a common practice in Pennsylvania. Soybeans tend to emerge rapidly when planted in warm moist soils encountered during late May and early June. With the trend for earlier planting, or when planting into cold wet soils, it may be necessary to consider a fungicide seed treatment. Cool or wet soils increase emergence time and allow disease organisms more opportunity to attack the seed. Seed treatments typically offer the greatest benefit when the seed or seedling is under stress during the first two weeks after planting. Examples of stress are heavy rains, soil compaction, surface crusting, cool soils, deep planting, reduced seed quality, and dry soils.
The most common seed and seedling diseases are caused by species of the following fungus organisms; Phytophthora, Pythium, Rhizoctonia and Fusarium . Phytophthora sp. and Pythium sp. are prevalent under wet soil conditions and produce a soft rotting of the seed or seedling before or after emergence. This is often referred to as damping-off since it occurs under damp soil conditions. With damping-off, a dark brown or black rot girdles the seedling stems, and the plant dies.
Rhizoctonia sp. and Fusarium sp. occur under drier soil conditions. Rhizoctonia sp. produce reddish lesions along one side of the stem and do not girdle the stem. Plant growth is reduced but death is not common. Dry rotting of the roots can be observed with Fusarium sp., as well as some reddening of the roots.
Dr. H. W. Kirby, extension plant pathologist at the University of Illinois, provided the following information on seed treatments for soybeans. This list is not complete and was given for illustrative purposes only. Check with your local dealer to determine what products are available in your area.
Nitrogen fixing bacteria, found in inoculants, are sensitive to chemical seed treatments. If a seed treatment is required and an inoculant is being used, apply the seed treatment first and several days in advance of the inoculant if possible. It is best not to use a seed treatment on fields that do not have a history of soybeans. Successful production in these fields requires introduction of a high population of viable nitrogen fixing bacteria. Under these conditions, it is best to plant quality seed and delay planting until the soil is warm.
John Ayers, Dept. of Plant Pathology
&
Elwood Hatley, CCA, Dept. of Agronomy
Zeneca Ag Products recently received a federal label for Touchdown herbicide (glyphosate-trimesium or sulfosate) for burndown use in front of corn or soybeans. Touchdown has been in the market place for several years, but was limited for use in non-crop and non-bearing crops until recently. Touchdown is a 6 lb per gallon formulation. The typical rate range is from 0.66 to 2.66 pints per acre. The 1 lb/A rate is 1.33 pints. A surfactant is required with Touchdown at 0.5% v/v or 2 quarts/100 gal. Pound for pound, Touchdown will perform the same as Roundup.
A number of restrictions exist with certain corn herbicides following the of or tank-mixing with insecticides. Most of these restriction are limited to "ALS" type herbicides which include the sulfonylureas, imidazolinones, and sulfonamides. Here is a quick summary of what's on the labels. For more detail, see the most recent label.
Bill Curran
True Armyworm. True armyworms consume leaf tissue, usually around the leaf margins, but in serious infestations they can strip the plant entirely of leaf tissue. As long as the growing tip has not been damaged, the plant generally recovers. Armyworms prefer grassy host plants, so corn fields most likely damaged are those near grasses, such as small grains, grass fields or grass cover crops. The larvae can inflict heavy damage when grass plants are killed by herbicide or cultivation, or when corn is no-tilled into wheat or rye. Typically, the longer the period between killing of the prior grass host and the planting of the corn, the lower likelihood there is of damage from this insect. A rule of thumb is to wait at least one week after plants have died from burndown until planting, to allow the insects to starve. The same principal can be applied for black cutworm. To scout, examine 20 plants at 5 locations in the field. During early growth stages, a treatment is warranted if 25% of the plants are injured. Several effective materials for larvae control are listed in the Agronomy Guide.
Black Cutworm. Black cutworm moths begins their flights in April, and search for places to lay eggs. Their preferred egg-laying sites are field with high weed populations, particularly broadleaves such as chickweed. Thus, because late-planted fields generally have higher weed levels, these fields are more likely to get damaged. Also, damage is more likely to occur in fields with low-lying areas. Larvae feed on leaf edges, eat holes into leaves, and feed on the stem near or slightly below the soil surface. However, the most serious damage they create is to clip the plant off at ground level. Because this type of feeding completely removes the growing point, the plant will die. To scout for larval damage, examine at least 250 plants in the field. A treatment is warranted when more than 3% of the plants show damage. Three percent may not seem like an economic problem, but with cutworm, damage can become severe in a short time period. Several effective materials are listed in your Agronomy Guide to control the larvae. However, the larvae may hide under soil clods and cracks during hotter and drier conditions, so the most effective time to treat is early evening.
Corn Flea Beetle. Corn flea beetles are very small black beetles which tend to jump away when disturbed. Damage appears as long white "scratches" in the leaves, usually parallel to the veins. To scout, examine about 100 plants and record the number of beetles per plant. Control may be justified when there is an average of 5 or more beetles per plant up to the 5-leaf stage. Most of our corn hybrids are resistant to flea beetles. If you are growing a susceptible hybrid, control may be justified at much lower levels. Several effective materials are listed in the Agronomy Guide.
Stalk Borer. Common stalk borer larvae migrate from grasses and other weeds and tunnel into the whorl of the corn plant. Edges of damaged leaves appear ragged and irregular, and a sawdust-like frass can be seen on the leaf surface. Risk of damage from this insect is generally higher in no-till situations, because grass hosts may be more common. However, damage can also be sometimes seen near field edges in conventionally-plowed fields, where grass hosts may be along field edges. No threshold guidelines exist for stalk borer. Control of the larvae is difficult, because it needs to be applied when the larvae are moving from the weeds to the corn plants, but prior to them entering the whorl of the corn plant. Perhaps the most effective management approach is to control the grass hosts.
Sod Webworm. Sod webworms overwinter as partially grown larvae and start feeding in April. Moths leave their eggs in grassy areas. Larvae are dirty white with numerous small brown to black spots. The body is sparsely covered with numerous pale hairs. Webworms are very active. They are approximately 3/4 inch long when fully grown. The larvae spin silk threads and web the soil particles together as they feed near the soil surface. Most of their damage occurs at or slightly below the soil surface. No thresholds exist for their control. Like stalk borer, fields with perennial grasses are more likely to sustain damage.
Slugs. Slugs feed on corn shortly after germination by severing the young sprout or shredding the tender young leaves. Plant stand reductions are greatest when moist soil conditions prevent the seed slot from closing during planting, allowing the slugs to feed directly below the soil surface. Corn plants can generally outgrow slug feeding if conditions are favorable. Monitoring for slugs is not easy. One way is to search the soil surface at night; more than 5 slugs/square foot may indicate economically-damaging populations. However, these estimates do not provide information on egg density. Heavily infested fields can also be identified by pulling up the plant and examining the brace roots. Cultural management is very important in managing slugs. No-till fields, which provides cool and moist conditions, are most susceptible to slug damage. Switching back to tillage for just one season can noticeably reduce slug populations. Where reduced tillage is used, delayed plantings may help reduce slug injury, because the increased temperatures will favor rapid plant growth. Some researchers also mention that using trash wheels to push corn stalks and other residue away from the plant has reduced damage by 20-30%.
Starter fertilizer, which helps promote more rapid growth, may help the plant outgrow slug damage. Despite the increasing importance of slugs, little progress has been made in chemical control. The one registered material is that of metaldehyde baits (Deadline Bullets, from Valent). However, these materials are fairly expensive, inconvenient to apply, and sometimes inconsistent. Application of 10 lbs/acre can be effective when banded over the plants. Valent is also working on a new formulation which can be applied through the insecticide boxes. Some researchers have also had some success in applying a urea-based nitrogen at night, as an irritant to slugs.
Sulfur, Kerosene, Turpentine and Molasses for Rootworm Control? There have been numerous reports from the midwest on "non-traditional" rootworm control materials, such as sulfur, kerosene, turpentine, and molasses. In short , the tests done to date indicate that they simply do not work. University of Wisconsin tests compared these materials to standards such as Counter, Force, and Lorsban. With these latter three materials, root ratings were maintained under an average of 3.0, or below the economic injury level. Plots using sulfur, kerosene, turpentine, and molasses, however, had root ratings of 5.25, 4.65, 4.85, and 4.60, respectively. The untreated plots had a root rating of 5.10. These plots using non-traditional materials were no better than doing nothing at all.
Although the next Agronomy Guide will not be available until the fall, the changes are relevant for 1996. Here in a nutshell are some of the changes (additions, new formulations, and deletions) for insecticides in soybeans and small grains. In future issues, we'll have changes for corn and alfalfa. Please refer to the label for full details.
Steve Spangler and Dennis Calvin
We can name that tune in three notes...wet, cold, and late! Last issue I submitted that some early plowing had revealed drier than normal soil moisture and the spring rains hadn't really arrived yet. Soil temperatures were even hovering around the 50 degree mark. Well forget all that. By my rain gauge, we received in excess of our normal amount of rainfall (3.2 inches for April) during the last week of the month. Total for the month is about 5.4 inches. We received precipitation 19 days during April. Needless to say field activities have stopped in their tracks. I started counting GDD(40)s on the 20th and have accumulated only about 117 at months end. Nicer hay fields have a few inches of growth but no stem elongation yet. Evidence of frost heaving in alfalfa, clover, and winter grains is rather considerable. For now its just hurry up and wait while watching the grain markets for entertainment.
Joel Hunter
Greg Hostetter
Most corn should be planted by May 7 in Lebanon. Some producers had corn planted the week of April 22 when field conditions and weather allowed planting. Most new seedings of alfalfa/oats are well on there way to producing a healthy crop if all goes well. Currently (5/1/96), there are no reports of alfalfa weevils and the fields I have scouted show no signs of activity. All winter crops are responding to a 2 inch rainfall on April 29 and the weeds have also taken advantage of the rain. Lambsquarters and pigweed are up and should be taken out with a burn down treatment or tillage. Winter annuals are flowering with yellow rocket in full bloom. Cattle have been let out to pasture. Most pastures got a shot of urea that missed timely rainfall and probably will need an additional application. Also most should be sprayed for weeds shortly. At this time, we need some wind and clear days to dry our soils to allow for soybean and corn planting. We had four good working days and need at least five more to finish planting and to let things settle and get equipment ready for hay harvest. Most rye has been taken off for ryelage or sprayed before seeding.
As a side note, the Mid Atlantic Tillage Conference has changed its thrust to Precision Farming and an organizational meeting will be held on May 30, 1996. If you are interested in directing/helping in some way please show up at the Embers in Carlisle around 9 a.m. We really need some new "blood" to ensure that producers are receiving timely information.
Del Voight
William S. Curran
Associate Professor Weed Science
email: wsc2@psu.edu
Website Address: http://fcn.agronomy.psu.edu/