Volume 5, No. 5 , August 2002

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Index


Dear Reader,

Unfortunately, the drought in Virginia, like many other states, is continuing. From the soybean standpoint, the southern Piedmont seems to be the hardest hit. I've heard of some growers giving up on a seed crop and harvesting soybean for hay, But other areas are suffering as well. The Ag Expo site typifies the current conditions, but also shows the potential that our crops have under irrigated conditions. At Camden Farm, the double-crop soybean under irrigation is waist-high (this is what we've experienced over the past two years on the better soils), but the non-irrigated portions of the field are barely 1 foot tall. Lack of canopy development will surely hurt our yields this year, but don't give up on the double-crop plantingst yet. Late August rains can still make a good crop. Let's just continuing praying for raithis month.

On the bright side, prices of soybean have jumped. USDA production figures have the crop pegged at only 2.6 billion bushels and carryover at 155 million. The result is Nov. future prices hovering around $5.50. Rainfall in the mid-west may change this, but at this point, the prospect of decent prices look good.

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Corn Earworm Moving in Early to Soybean

Ames Herbert, Extension Entomologist

2002 Survey Results: Percent corn earworm infestation in corn was much higher compared with the previous year throughout most of eastern Virginia. Infestation levels increased from an average of about 8.2% on Eastern Shore in 2001 to about 48%; increased from 15.3% to 50.6% in the mid-eastern counties; increased from about 4.5% to 45 % in the Northern Neck; and increased from about 0.2% to 55.4% in the Northern counties surveyed. These 2002 levels were the highest we have seen in several years. In additional, many of the worms had already exited the ears at the time of sampling, which indicated earlier movement from corn than normal. Moths moved earlier from drought stressed corn fields, but may be held longer in those fields that did receive rain or irrigation and are progressing at a more normal rate. This could mean two flights of moths and an extended period of potential damage.

Survey Predictions: Based on the survey results, we expected heavy and relatively early infestations in many soybean fields. Early infestations caused some growers to make applications to beans that were in the late flowering to early pod formation stage, which could mean having to make second applications during pod fill stages if fields are re-invaded.

The insect situation is hectic in all of the row crops (cotton, peanuts and soybeans). As far as soybeans are concerned, I understand that many fields are being sprayed. Our predictions have proven correct for corn earworm - early and heavy infestations. These early sprays seem justified as worms are feeding on flower stems and young pods. Again, this could mean that fields will need a second treatment if moths continue to move into fields. We may see a second 'flight' out of those corn fields where the crop was not drought stressed and earworms developed at a more normal rate. Therefore, we must keep scouting fields.

Blacklight Trap Catch: Moth catches have been steadily increasing since June. The relatively high nightly averages are confirming the high numbers in corn. Moths are moving and field scouting should continue. The earworm moth flights decreased in the last few nights due to the cooler weather experience the first week of Aug. Moths are still active in fields and weedy areas however, and the catch may go back up as the weather warms. The problem is not over yet. Weekly moth trap catch summaries will be available at all Virginia Cooperative Extension county offices through mid September. Call your local office for weekly updates, or access my home page at http://www.vaes.vt.edu/tidewater/faculty/herbert/advise.html, or contact Linda Byrd-Masters at 1-757-657-6450, ext. 126 for assistance.

Results of 2002 Blacklight Trap Catch Data (Corn Earworm Moths)
Nightly trap catch average for week ending:
Location (county) 6/20 6/28 7/3 7/11 7/18 7/25 8/1 8/8
Southeast/Eastern Shore
Accomack 0.7 0.4 1.4 2.0 4.6 9.0 27.4 23.0
Chesapeake n/a 0.4 0.8 0.4 n/a 5.1 96.6 93.6
Dinwiddie South n/a 1.7 n/a 1.9 1.1 1.0 10.0 16.1
Dinwiddie Central 0.0 0.6 1.8 1.4 1.7 1.7 62.1 41.6
Dinwiddie North 0.0 1.0 1.0 1.5 (Trap relocated to Prince George 2)
Greensville 1 0.0 0.4 0.4 0.3 0.0 0.3 2.6 n/a
Greensville 2 -- -- -- -- -- -- 20.7 21.4
Northampton 1 0.0 0.1 0.4 0.7 0.4 3.1 31.1 31.4
Northampton 2 0.4 0.1 1.0 1.9 1.4 2.4 19.1 25.0
Petersburg 1.0 0.4 22.0 30.0 6.6 5.7 159.0 215.0
Prince George 1 0.0 1.7 7.0 3.6 0.7 3.4 65.0 51.0
Prince George 2 -- -- -- -- 1.7 0.9 11.6 11.6
Southampton 1 n/a 0.0 0.5 0.5 1.1 18.7 47.8 51.7
Southampton 2 n/a n/a n/a 0.0 0.9 10.7 2.6 26.4
Suffolk 0.1 0.0 1.6 4.0 3.6 27.1 111.6 68.1
Sussex 12.0 5.5 n/a 2.6 4.3 4.1 5.6 13.7
North of James River
King William n/a n/a n/a n/a n/a 6.7 19.7 32.0
King and Queen n/a n/a n/a 1.0 n/a 0.3 1.6 5.0
Lancaster n/a n/a n/a 6.0 4.6 7.0 26.6 61.7
Middlesex n/a n/a n/a 0.0 2.3 6.8 37.9 30.1
New Kent n/a n/a n/a 5.0 7.0 n/a n/a n/a
Richmond Co. n/a n/a n/a 11.0 3.0 8.0 31.6 189.0
n/a = report not available

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Beet Armyworm Advisory

Ames Herbert

Beet armyworm has moved into Virginia. Moths migrated up from the south where this pest has been a problem most of the summer. It is a very unusual pest for Virginia. I have only seen it one time, and that was on pigweed in the fall of the year. It does not overwinter here, so has to work its way north. I have never seen it as a pest on our crops. But it is here now and what do we do? First, don't panic. Just because they are in a field does not mean you have to treat automatically. Like any other pest, the numbers have to be there to justify the expense of treatment.

To date, most of the beet armyworm complaints are coming from peanuts, with a few reported in both soybean and cotton. In cotton, they seem to be most common in fields with pigweed in or nearby the field. They are also more common in fields that are not cut out. We are most likely going to see worm infestations with mixed species including beet armyworm, corn earworm (cotton bollworm) and even some fall armyworm. Identifying these and making the right insecticide choice will be a challenge.

In soybeans the worm infestation could also include all three species. What are the thresholds for beets? None that I know of. It is such an unusual problem that no one, to my knowledge, has developed a threshold. They can do a lot of damage if populations are large. They are capable of completely destroying plants. In small numbers they should mostly act like leaf feeders and may not present a threat. We recommend defoliation thresholds in a full season crop of 40% pre-bloom and 15% during pod fill, and for double-crop with poor growth (due to drought or late planting) 20% pre-bloom and 10% during pod fill. However, keep in mind that percent defoliation is not the best way to address the problem. The amount of leaf area remaining on the crop determines whether or not yield reductions will occur. If a leaf area index (LAI), which is an index that indicates the square footage of leaf area per square footage of ground area, remains above 3.5 to 4.0, then no yield loss will occur. Most full-season soybean easily reach LAIs of greater than 5.0; therefore, the above thresholds should apply. However, most double-crop fields in Virginia have not come close to approaching this level; therefore reduce the defoliation thresholds to: 20% defoliation pre-bloom; 10% defoliation pod fill; and 15% defoliation full-developed seed. For more information on identifying soybean fields at risk to leaf-feeding insects, refer to Virginia Cooperative Extension Publication 444-203. This publication can be found on the web at: http://www.ext.vt.edu/pubs/entomology/444-203/444-203.html

If it is a mixed worm population, Steward would be the best choice at 9 oz. Asana, Karate or Lannate have not proven effective against beet armyworm in other states. Steward will also provide good control of earworm and fall armyworm.

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Keep Watch for Soybean Aphid

Soybean aphid is a new pest that invaded the U.S. in 2000. In Virginia, the pest was discovered in soybean fields in the summer (Sept.) of 2001. A native of Asia, the soybean aphid feeds by sucking plant sap, which can cause leaf curling and plant stunting. Early populations feed developing leaves, stems, and petioles in plant terminals. As the plant grows, populations can expand to the mid-level canopy and feed on the undersides of leaves. Early season infestations that peak in the early soybean reproductive growth stages (R1-R2) can cause yield loss of up to 52%. Loss from last-season feeding is minor-to-undetectable, unless virus is present. The aphid can transmit several viruses.

In Virginia, aphids were found in 24 of 25 counties surveyed in 2001, but infestations were low to moderate. Because infestations did not occur until Sept., no yield loss was reported. Do soybean aphid pose a threat to Virginia soybean? Only time will tell, but the relative scarcity of buckthorn species, the pest's overwintering host, it is not likely that we will experience early-season infestations. However, we must continue to scout our fields and recognize this pest. Also, just because a few aphids are found in soybean do not necessarily mean that it is soybean aphid. Stray aphids will occasionally find there way into soybean fields. Only soybean aphid will colonize the crop; therefore, it colonies are found, corrective action may be needed. For more information on the soybean aphid, refer to Virginia Cooperative Extension Publication 444-202. This publication can be found on the web at: http://www.ext.vt.edu/pubs/entomology/444-202/444-202.html

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Soybean Rust

Soybean rust is a serious disease that has potential for causing serious losses in the U.S. First, let me make it clear that this disease has not yet been detected in the continental U.S. However, it has been reported in Australia, China, Korea, India, Japan, Nepal, Taiwan, Thailand, the Philippines, several African countries, Brazil, Argentina, and Paraguay. Because windborne spores can spread it, it is possible that it may eventually reach Virginia. I will not go into detail on the disease in this newsletter, but will instead refer you to an excellent web site that describes the disease, its biology, and rust symptoms. This USDA web site can be found at: http://www.aphis.usda.gov/ppq/ep/pestdetection/soybean_rust/soybeanrust.html

Soybean rust is caused by two fungal species, Phakopsora pachyrhizi and Phakopsora meibomiae. The first detection of rust in the U.S. was in Puerto Rico in 1976 and was determined to be the weaker of the 2 pathogens, P. meibomiae. In 1995, the more aggressive P. pachyrhizi was discovered in Hawaii. This pathogen spread rapidly in Zimbabwe, South Africa, Paraguay, and Brazil, where yield losses were reported from 10 to 80%. In addition to soybean, over 30 species of legumes can harbor the disease and include: kudzu, sweet clover, vetch, medic, lupine, green, kidney, lima, and butter bean, blackeyed pea, and cowpea.

The following page shows some of the symptoms of soybean rust.

Source: http://www.aphis.usda.gov/ppq/ep/pestdetection/soybean_rust/detection.htmlK

Figure 1. The earliest stages of soybean rust are found on the undersides of the first leaves in plants near the flowering stage. Photo courtesy of Clive Levy, Commercial Farmers Union of Zimbabwe
Figure 2. Chlorosis, or yellowing of infected leaves, progresses in different degrees, usually not completely until the infection is well advanced. Asian Vegetable Research and Development Center (AVRDC), courtesy of Arnold Tschanz, USDA, APHIS, PPQ, Riverdale, MD.

Figure 3. Soybean rust damage that appears on upper leaves of soybean plants when advanced.
Figure 4. Spots with chlorosis characteristic of more advanced infection.
Reid Frederick, USDA, ARS, Ft. Detrick, MD

Soybean rust forms two types of lesions on leaves, tan and reddish brown. The tan lesions (Figures 5 and 6) when mature, consist of small pustules with masses of tan colored urediniospores on the surface. Reddish brown lesions (Figures 7and 8) appear different with reddish brown necrotic areas surrounding the pustules.

Figure 5. Tan lesion of soybean rust on a soybean leaf.
Reid Frederick, USDA, ARS, Ft. Detrick, MD
Figure 6. Close up of tan lesions of soybean rust on a soybean leaf.
AVRDC, courtesy of Arnold Tschanz, USDA, APHIS, PPQ, Riverdale, MD

Figure 7. Soybean rust tan lesions with reddish brown lesions in the center.
Joe Hennen, Botanical Research Institute, Ft. Worth, TX
Figure 8. Close up of reddish-brown lesion.
AVRDC, courtesy of Arnold Tschanz, USDA, APHIS, PPQ, Riverdale, MD

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Sincerely,

David L. Holshouser


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