Corn leaf aphid is very common in whorl stage corn, but rarely cause economic losses. Infestations become apparent when the tassels begin to emerge revealing colonies of aphids. Infestations are more common in late-panted corn. Corn is most susceptible to yield loss by aphids while in the whorl stage. If large numbers are present three weeks before tassel emergence, physiological damage and some yield loss may occur. Corn may be stunted or wilted, especially when plants are under drought or nutritional stress. However, infestations usually occur close to tassel emergence, and despite large numbers of aphids, don't cause economic losses. While infestations that cause physiological yield loss are uncommon, some producers feel that the large number of aphids and the honeydew they produce may interfere with pollination by gumming up the tassels. Excessive honeydew on the tassels may limit pollen shed and it has been associated with barren corn, although this is very uncommon. Silks that are covered in honeydew will continue to grow until they are pollinated. Excessive honeydew and the sooty mold it may cause can reduce the marketability of the ears.
Controls
Biological: Aphids are preyed on by lady beetles, green lacewings, and syrphid larvae, but these usually cannot control the rapid spring increase in populations.
Cultural: Early planting of the corn crop as well as proper tillage and fertilization to hasten its growth and maturing can help to prevent the damage caused by the corn leaf aphid.
Monitoring: Growers need to monitor for corn leaf aphid twice prior to tasseling. This should be done 3 weeks prior to tassel emergence and again one week later. Four consecutive plants should be randomly selected in each of five locations per field. Carefully pull the whorl leaves from these plants, unroll the leaves, and estimate the number of aphids. Do not include off-color aphids (those that are diseased or parasitized) in these estimates.
Growers should consider treating for corn leaf aphids if an average of 15 or more aphids (10 with stressed plants) per whorl are found 3 weeks before tassel emergence or 30 or more aphids (15 with stressed plants) per whorl
one week later. Closer to tassel emergence, greater numbers can be tolerated without loss of yield or ear contamination.
Application Alternatives:
Diazinon 50 WP (diazinon)- Apply as a foliar treatment at 1 to 2 lb per acre.
Endosulfan 3 EC (Thiodan, Phaser)- Apply as a foliar treatment at 1-1/3 qt per acre to a limit of 4 qt per acre per season.
Malathion (malathion)- Apply as a foliar treatment at 1 pint per acre.
Western Corn Rootworm
(Diabrotica virgifera virgifera)
The western corn rootworm is an infrequent pest in sweet corn in Kentucky and it is restricted only to fields are continuously kept in corn production for several years. As most sweet corn fields are regularly rotsted to other
crops, this is not a common pest. The larval stage of this pest is the most destructive, feeding on the roots of corn in late May and June. Above ground, infested plants may appear to be drought or nutrient stressed, making slow growth, and prone to fall over after heavy rains, making mechanical harvesting difficult. Small roots are chewed off and larger roots are tunneled by the narrow, white, ½ inch long larvae. The eggs western corn rootworm are laid in July and August in soil around the base of the corn plant. The rootworm spends the winter in the egg stage. The egg hatch begins in May and small larvae can be found in late May. The larvae grow through three instars and a prepupal stage and adults begin to emerge in late June and early July.
The adult western corn rootworm is and is yellow-brown with three prominent black stripes on the dorsum. The northern and southern corn rootworms also occur in Kentucky, but problems in sweet corn with these species is rare.
Controls
Biological
Biological control of western corn rootworm is not well understood in Kentucky.
Cultural: Crop rotation, alternating corn with vegetable or non-corn field crops in which the corn rootworm larvae cannot develop, is the most effective rootworm management practice in Kentucky. The more years that a field stays in continuous corn production, the more likely it will develop corn rootworm problems.
Monitoring: Adult rootworm beetles are monitored during the summer and a soil insecticide is used the following year if an average of more than one rootworm beetle is observed per plant at any time during July,
August or September if the field is planted with corn the following year.
Application Alternatives:
Aztec 2.1G (tebupirimphos+ cyfluthrin) soil applied in a band, T-band or infurrow at a rate of 6.7 oz per 1000 row feet.
Force 3 G (tefluthrin) soil applied in a T-band or infurrow at a rate of 4 to 5 ounces per 1000 row feet. Force will also control cutworms when applied as a T-band at planting.
Fortress 5 G (chlorethoxyfos) soil applied in a band, T-band or infurrow at a rate of 3 oz per 1000 row feet.
Lorsban 15G (chlorpyrifos) soil applied in a band, T-band or infurrow at a rate of 8 oz per 1000 row feet.
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