 |
Field and Forage Crops |
In general, our cotton crop is still ragged and behind schedule, with this past month's weather taking a heavy toll on cotton stands and maturity. Although we have been plagued by additional rain in some areas, the recent predominance of sunny weather and warmer temperatures have greatly helped the cotton crop.
For cotyledon to three true leaf cotton that is not longer protected from thrips damage due to the limited persistence of seed treatments or Temik being washed out of the root zone, thrips can still cause moderate to heavy damage.
It appears that our cool, rainy weather has probably held adult thrips on their wild and cultivated hosts longer. Therefore, migrating thrips flights into cotton will likely last a little longer into June than normal. Hopefully, these flights will significantly decline around June 10 to 15.
In the meantime, 5-day inspection intervals for thrips on newly-emerging leaves and in buds are in order. In most cases, when plants reach about the 5 true leaf or node stage, they can be regarded as safe from thrips injury. As mentioned in last week's issue of North Carolina Pest News, if newly-opening leaves are shiny and relatively flat, they are not being damaged by thrips presently and a foliar insecticide application is not needed.
So far, reports of cotton aphids have been few, and the weather has not been favorable for spider mite buildups. Both cotton aphids and spider mites are far more damaging to plants under drought stress. And drought stress certainly has not been a factor so far this year. Fortunately, mite and cotton aphid levels must be very high before economic damage is possible, making outbreaks easier for scouts to detect than with other cotton pests, such as bollworms and stinks bugs.
A small ground beetle in the genus Amara has been especially common this year, particularly in reduced tillage cotton. Unlike its predator colleagues, this particular species (approximately 1/4 inch in length, fast-moving, and with bronze-colored wing covers) eats seeds and can also clip off cotton seedlings. Unlike cutworms, most of the seedling clipping has been above the soil line, midway up the plant stem. In two cases brought to my attention this past week, these beetles were threatening stands to the extent that a foliar insecticide treatment was made. Although I have seen these beetles in essentially all of the cotton fields I have visited in the past 10 days, stand reductions were limited. Little or nothing is known about remedial control of these ground beetles, but they should be susceptible to cotton-labeled insecticides with generally good beetle activity, such as the pyrethroids, Sevin, and Orthene.
Tobacco budworms and plant bugs are seldom damaging to cotton in North Carolina until squaring is underway. Budworm establishment on tobacco has been about average so far this season. We will have more information on these and other pests in the coming weeks.
Our Early Scouting School will be held at the County Government Center at 231 E. Cronly Street, Suite 800 in Laurinburg, North Carolina on June 19, beginning at 9:00 a.m. All summer scouts, industry personnel and consultants are welcome to attend. For directions or further details, please contact co-hosts David Morrison in Scotland County (e-mail: david_morrison@ncsu.edu; telephone: 910-277-2422), Georgia Love in Robeson County (e-mail: georgia_love@ncsu.edu; telephone: 910-671-3276), and Keith Walters in Hoke County (e-mail: keith_walters@ncsu.edu).
Bacterial blight of cotton is caused by a bacteria (Xanthomonas campestris pv. malvacearum). The disease is seedborne or can be transmitted from cotton debris from the previous cotton crop. The ability of the bacteria to overwinter in North Carolina is unknown. Symptoms on the cotyledons differ from those on true leaves (see Cotton Disease Information Note No. 3). Leaf spots from bacterial blight on cotyledons are round to elliptical, whereas the spots on true leaves have an angular appearance. Leaf spots on cotyledons caused by bacterial blight differ from those caused by the fungus Ascochyta (Phoma: see Cotton Disease Information Note No. 2) in that they will not have the black specs (pycnydia of the fungus) in the spot. Although stand loss as a result of this disease is rare, many plants received by the Plant Disease and Insect Clinic at North Carolina State University have a severe root rot. Growers with this disease may need to consider replanting cotton after destruction of infected plants by incorporating diseased tissue and rebedding. Provided there is an adequate stand, disease loss from bacterial blight typically is about 5 to 10 percent.
Growers should document the following information:
The following web site lists some susceptible and resistant varieties: http://lubbock.tamu.edu/cotton/docs/bactblightratings.html.
Early season for peanuts is always thrips season. The thrips are present, but their abundance and damage has been tolerable for growers so far. Even untreated peanuts do not seem to be suffering from the severe damage so often observed early in the year. The good soil moisture will promote rapid peanut plant growth with a few days of warmer temperatures and sunshine. Make certain to check peanuts carefully and note the potential for rapid plant growth before making the decision to apply any foliar insecticides for thrips management. The value of additional treatments for thrips and the potential impact on the level of tomato spotted wilt virus is questionable. Dr. Ames Herbert of Virginia Tech University and I have two large studies underway attempting to answer questions about multiple treatments and reduced insecticide rates. The incidence of virus in peanut fields at the present time is very low, but that is not unusual at this point in the season. The next couple of weeks will start to reveal the prospects for tomato spotted wilt virus in peanuts in 2003.
Employment and program opportunities are offered to all people regardless of race, color, national origin, sex, age or disability. North Carolina State University, North Carolina A&T State University, U.S. Department of Agriculture, and local governments cooperating.
Last modified on June 9, 2003 by Stephen J. Toth, Jr.