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Field and Forage Crops |
The one weather event that would essentially eliminate further significant beet armyworm outbreaks has occurred, that is cooler weather and a lot of rainfall. The hot, dry weather that has plagued much of our cotton acreage in North Carolina for most of the growing season also helped create favorable conditions for beet armyworm outbreaks. If hot dry weather returns, beet armyworms would likely reappear late to catch our rapidly-maturing cotton crop. A scattering of beet armyworms on the anticipated regrowth on our early opening cotton crop is expected, however.
Early returns from our statewide damaged boll survey confirm that growers have been through a rough year for bollworms on conventional cotton. Stink bug damage to bolls, however, was much lighter than the previous two years, reversing what was considered by some a trend of increasing stink bug damage to conventional and Bollgard cotton. With the exception of a few very late-maturing cotton fields, bollworms and stink bugs should no longer be an economic problem in 2002.
Fall armyworm damage should now be limited to small, second stage larvae feeding in the space between bracts and the surface of variously-sized bolls. Without blooms and squares present for early growth, fall armyworms generally do not become established in late August or in September in North Carolina. During a damaged boll inspection of 30 cotton fields (300 bolls) conducted on August 26, six small, second stage fall armyworms were found without a single larger armyworm and no bolls damaged by this species.
Cotton aphids also appear to have declined sharply, and are typically down for the count once cotton is defoliated, although at times aphids can make minor comebacks on regrowth in opening cotton.
With the insect season drawing to a close, let's hope for the warm, dry weather harvest conditions experienced during 2000 and 2001.
This has been a hit or miss dry year in pastures across the state. In some places, we think green June beetle populations have been lower due to hard dry soils. However, if your pastures are on relatively high organic matter soil and you have seen many adults this year, you may be at risk for green June beetle damage. Though grubs and adults are more noticeable during late-spring and early summer, now would be the best time for treatment. If you have received any of the recent rainfall, a good time for chemical treatment would be after this rainy period when a few days of dry weather are expected.
Green June beetle grubs feed on organic matter in the root zone exposing roots and allowing grass to be uprooted during grazing. Problems with beetle grubs are often greater where poultry litter or other high organic matter fertilizers have been used. Heavy feeding can dislodge or damage roots of plants. Periods of drought can magnify the effects, resulting in brown and dying patches. At night, large larvae may leave the soil and crawl. Holes with small earthen turrets about the diameter of a finger are sometimes evident in late spring.
Treat infested areas based on scouting. In pastures, examine sod samples about 1 square foot and four inches deep for grubs. There is no precise threshold, but if 4 or more larvae per square foot of sod are detected, treatment may be considered. Your decision should be based on the extent of damage being caused and if winter overseeding is to take place. Treatment is hard to justify in pastures, but, if needed, is most effective in August and September. Sevin insecticide is the normal chemical recommendation. The best time of day to treat is in late afternoon when temperatures are above 70 degrees F. Also examine areas for dark blue scolyiid wasp activity. These wasps prey on grubs and indicate grub presence. Pulverized soil is an indicator of surface grub activity and broadleaf weed encroachment indicates places where grass has died, possibly from grubs or cattle exposing grass roots. Be sure to use adequate water and observe the 14-day grazing interval. For some additional information and photos, see the Auburn publication by K.L. Flanders on the World Wide Web at: http://www.aces.edu/department/extcomm/publications/anr/anr-991/anr-991.htm.
This week has been decision time for pasture growers. Late instar larvae are developing in pastures and poised to do major damage. Hot, dry weather has discouraged caterpillar pathogens, increased the pressure by the armyworm complex and intensified the damage to fields. Specific control recommendations are difficult to relay in this note. When reading a label, armyworm refers to the true armyworm. There are also fall armyworms, yellowstriped armyworms and beet armyworms. It is suspected that most of the populations creating problems are fall armyworm, but the other species are also being reported. Fall armyworms have the inverted Y on the head and four dots on the tail segments. Help in determining the species may be found in the field crops manual (North Carolina Cooperative Service Publication AG-271). A rough threshold is 5 worms per square foot, but 3 worms per square foot may be enough at this point. Sample 10 to 12 times in different places in a field. Field edges are often more heavily infested.
Labels are tricky for these pests and pasture. Consult the North Carolina Agricultural Chemicals Manual (page 69) for help. There is some rumored dissatisfaction with using Sevin 80S, but I am not convinced that failures are not entirely due to applicator technique or weather. Sevin ground applications must use about 30 gallons of water to ensure adequate coverage. Applications are best made toward the evening, while plants are not wet, and when rain is not expected within 48 hours. Sevin has a 14-day grazing interval. In Bermudagrass, Lannate is labeled and works very quickly and is a restricted use chemical. Malathion is also labeled in grass pasture and Warrior might be a choice in alfalfa or wheat hay.
It is frustrating in that the dry weather has created this problem and now rain is interfering with control. My fear is that most of you seeing any of the armyworm species will probably need to treat now, or soon. Consult the North Carolina Agricultural Chemicals Manual for choices, and then read the label. Large larvae (1 inch in length and above) mean you do not have much time to make a decision. Make your decision based on scouting, larval size, grazing interval, expense, pasture composition, and weather.
See the following information on the World Wide Web:
http://ipmwww.ncsu.edu/AG271/small_grains/fall_armyworm.html
http://ipmwww.ncsu.edu/AG271/corn_sorghum/armyworm.html
Fury is labeled for armyworm control on alfalfa.
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Last modified on September 3, 2002 by Stephen J. Toth, Jr.