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Wireworms in Florida Sugarcane 1
D. G. Hall, R. H. Cherry, R. S. Lentini, and R. A. Gilbert2Wireworms, the larval stage of the click beetle, often cause severe damage to numerous crops in Florida. At least twelve species of wireworms have been found in southern Florida, but only the corn wireworm, Melanotus communis, is considered to cause significant economic damage to sugarcane. Since Melanotus communis is the important wireworm species, the rest of this document will pertain to this species. Melanotus communis has traditionally been a more important pest in Florida sugarcane grown on muck soil than on sandy soil.
Biology
Adult click beetles may be collected during all months of the year, but they are most numerous during May, June, and July and are scarce from September to March. The beetles are brown and about 5/8" long ( Figure 1 ).
The larvae of click beetles are called wireworms because they resemble a jointed piece of stiff, bright, brownish-yellow wire. Melanotus communis wireworms are approximately 1-1/4" in length when fully grown ( Figure 2 ). They are soil pests and attack the underground portions of the sugarcane plant.
Figure 1. Adult beetle.
Figure 2. Wireworm larva. Damage
Generally, wireworms are a pest of newly planted sugarcane and only rarely a pest in ratoon sugarcane. Wireworms feed on the buds and root primordia during germination of sugarcane seed pieces, and on shoots and roots after germination. Most of the injury to young shoots is near the point where the shoots join the seed piece or stubble. Wireworm injury can generally be identified as relatively large, ragged holes cut into seedpieces and buds, or into young shoots ( Figure 4 ). The death of buds or young shoots leads to stand reductions. Wireworm injury has been reported as facilitating the entrance of the fungus that causes sugarcane red rot disease.
Field studies have shown that significant stand reductions during early plant growth may occur at infestation levels of fewer than 4 wireworms per 5 feet of row. One recent study showed that one wireworm per 5 row feet could cause 6.2-7.8% stand reduction at twelve weeks after planting. Tillering may compensate for some of the early stand losses, but, at harvest, stalks from infested sugarcane fields tend to weigh less.
Figure 3. Wireworm damage. In a large plot study, the weight of cane harvested was reduced by 3.8% per wireworm per 5 feet of row. Stand reductions in plant cane caused by 8 to 12 wireworms per 5 feet of row carried over into the first ratoon crop and resulted in lower ratoon crop yield.
Control
Biological
Although there are a small number of insect parasites that attack wireworms, biological control of wireworms in south Florida by beneficial insects and diseases has generally been considered to be insignificant. Birds such as the cattle egret may sometimes be of value in reducing wireworm levels because they may consume wireworms that are exposed at the surface of the soil when a field is disked or cultivated.Cultural Practices
Flooding for wireworm control can be effective but is a slow process and may not be practical. More studies are needed, but the current information suggests a minimum of six weeks of continuous flooding is needed during the summer to obtain wireworm control. Longer flooding durations are needed during colder months.Flooding during late spring and summer will kill the wireworms and also prevent egg-laying by the adult click beetles. Fallow field flooding or growing rice as a rotation crop may eliminate the need to use a soil insecticide at sugarcane planting the following fall. Growing a ratoon rice crop may offer slightly increased control during years when click beetle activity extends into July and August.
Chemical
The following table lists the insecticides presently labelled for the control of wireworms in Florida sugarcane (Table 1 ).
Tables
Table 1. Chemical control for wireworms in Florida sugarcane.
COMMERCIAL INSECTICIDE ACTIVE INGREDIENT(ai)
RATE PER ACRE
COMMENTS
Mocap 20G ethoprop 19.5 lb Apply in furrow at planting and cover.
Thimet 20G
phorate
19.5 lb Apply in furrow at planting and cover. As with all agricultural chemicals the user must read and understand all the label instructions prior to use. Use all pesticides only as directed by the label. Insect populations and crop response to insecticide applications should be monitored closely in order to develop the most efficient and effective insect pest control program for each particular situation.
Footnotes
1. This document is ENY-665, one of a series of the Entomology and Nematology Department, Florida Cooperative Extension Service, Institute of Food and Agricultural Sciences, University of Florida. First printed October 1991. Revised May 2002. This publication is also a part of the Florida Sugarcane Handbook, an electronic publication of the Agronomy Department. For more information you may contact the editor of the Sugarcane Handbook, R. A. Gilbert (ragilbert@gnv.ifas.ufl.edu). Please visit the EDIS Web site at http://edis.ifas.ufl.edu.2. D. G. Hall, U. S. Sugar Corp., Clewiston, FL; R. H. Cherry, professor, Everglades Research and Education Center; R. S. Lentini, former senior biological scientist, Everglades Research and Education Center, Belle Glade; and R. A. Gilbert, assistant professor, Everglades Research and Education Center, Florida Agricultural Experiment Stations, Institute of Food and Agricultural Sciences, University of Florida. The use of trade names in this publication is solely for the purpose of providing specific information. It is not a guarantee or warranty of the products named and does not signify that they are approved to the exclusion of others of suitable composition.
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U.S. Department of Agriculture, Cooperative Extension Service, University of Florida, IFAS, Florida A. & M. University Cooperative Extension Program, and Boards of County Commissioners Cooperating. Larry Arrington, Dean.
Copyright Information
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