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Corn - Black Cutworm
Excerpt from Agronomy Guide for Field Crops Table of Contents
DescriptionLarvae are greyish-black with a paler underside and no distinct markings on their bodies. Mature larvae are about 3.5 cm (1 1/4 in.) long and hide in the soil during the day. They can be found near freshly cut plants, under soil clumps or along a poorly closed seed furrow. Adult moths are grey with a small black dagger marking on each forewing.
Plate 11. Black cutworm larvae are greyish-black with a paler underside. Mature larvae are about 3.5 cm (1.25") long. Corn plant has been cut at the soil level. | Top of Page | Life HistoryCutworm moths do not overwinter in Ontario but are carried in from the south on strong southerly weather systems. The heaviest immigration occurs from April to May but may occur as early as March. Cutworms are therefore more frequent in fields with green cover early in the spring before primary tillage. There are several generations per year, however, only the first generation causes economic damage in corn. Warm, clear, calm nights in early spring are ideal for moths to lay eggs. Eggs are laid on dense vegetation, low to the ground, and are usually laid before primary tillage in the spring. Feeding occurs from early May through to mid-June. | Top of Page | DamagePlants attacked by young larvae will have small holes or gouges in the leaves. Plants may suddenly wilt, because the stem has been hollowed out. Larger larvae cut off the plant at or just below ground level. Factors that favour cutworm outbreaks include a history of cutworm damage, presence of winter annual weeds such as chickweed and volunteer wheat before planting, no-till and heavy crop residue. | Top of Page | Scouting TechniqueStart scouting for cutworm once every 5 days as soon as your corn emerges. Pay particular attention to those areas where weeds were heavy just before tillage and planting this spring. Look for leaf-feeding (pinholes) by young climbing larvae as the first sign of damage. Also look for wilting plants, foliage-feeding or for plants being cut off at the ground. Dig around damaged plants and search through the soil, as cutworms like to hide in the soil during the day. Note the size of the cutworms found. | Top of Page | Action ThresholdsIf more than 10% of plants show leaf feeding, treating at this time will give nearly 100% control. Once corn reaches the 5-leaf stage and begins to produce roots at the base of the plant, the risk has passed. Cutworms that are nearly mature (over 2.5 cm long) are difficult to control and will stop feeding in a few days when they reach full size. | Top of Page | Management StrategiesInsecticide treatment is most effective when applied to the soil soon after cutworms have hatched. Cutworms are most active in the evening, therefore insecticides applied at this time of day are most effective. It is not necessary to treat the entire field, only those areas showing evidence of feeding. Refer to OMAFRA Publication 812, Field Crop Protection Guide, for recommended control products. Only a small acreage of Ontario corn has cutworm problems in any given year, therefore using granular insecticide at planting time is not recommended. Insecticide application to mature larvae is not recommended since most of the damage is done. In no-till corn fields, it is important to have no green vegetation that could attract the moths in early spring. Fall burndown of volunteer crops and other weeds is recommended. Fields should be bare for at least 2 weeks before planting.| Top of Page | Related Links| Top of Page | For more information:Toll Free: 1-877-424-1300 Local: (519) 826-4047 E-mail: ag.info.omafra@ontario.ca |
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