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External feeding on leaves by the first-instar and second-instar larvae of A. segetum results in the presence of very tiny round 'windowpanes' where the larvae have eaten away the upper epidermis and the green tissue, but left the lower epidermis. External feeding on leaves, stalks and stems results in falling leaves, small holes in the stems or cut stems. External feeding on tubers and roots results in a variety of holes, ranging from those that are small and superficial to very large deep ones.
The activity of the third-instar and fourth-instar larvae is easier to recognize because whole leaves may fall off the plant after being cut through at the base of the stalk. Alternatively, small holes may be found on the stems and roots at the soil surface. A further sign of activity is the presence of leaf pieces partly pulled down into the soil.
The activity of the fifth and sixth instars is very obvious. Whole plants (e.g. lettuces, leeks, maize, cotton or small spruce seedlings) fall over, and on root crops (e.g. beetroots) deep holes become visible at and above the soil surface. Damage to underground tubers (e.g. potatoes) may be difficult to recognize before harvest.
Damage is far more severe under very dry conditions (Thygesen, 1971; Esbjerg, 1990) and occurs deeper below the surface.
Little information is available on host-plant resistance in A. segetum. Methanol extracts of potato tubers and wheat germ deterred oviposition (Anderson and Löfquist, 1996) and in Denmark careful weeding of onion fields is recommended as a preventive measure because the first-instar larvae cannot survive on onion plants (Esbjerg et al., 1995). For an insect as polyphagous as A. segetum, it is unlikely that host-plant resistance will be developed.
Due to the variable regulations around (de-)registration of pesticides, we are for the moment not including any specific chemical control recommendations. For further information, we recommend you visit the following resources:
The crop losses caused by A. segetum larvae are relatively easy to assess by sampling to determine the percentage of lost plants or the percentage of non-marketable stems, roots or tubers. In some cases, the larval densities have been estimated.
In Jiangsu, China, cutworms destroyed 3-37% of cotton seedlings (Hu, 1982), and in Kazakstan, 17.5% of young maize plants were destroyed at a density of 5.2 larvae/m² (Shek and Bulavskaya, 1978). Neupane and Bhimsen (1971), in Nepal, estimated a loss of 33% of potatoes and a 24% weight loss caused by 7.8 larvae/m². Kay and Wheatley (1979), in the UK, found 34% of beetroots were damaged at a density of 14 larvae/m² and 17% of young lettuces were destroyed at a density of 3.5 larvae/m². However, Kay and Wheatley also found that 34 larvae/m² had no economic impact on mature lettuces. In Denmark, damage levels of 10-25% for carrots and 3-68% for beetroots are common if the larval period of A. segetum coincides with three to four dry, warm weeks (Esbjerg, 1985). In Germany, Cruger (1978) could find hardly any undamaged potatoes at a larval density of 200 larvae/m². Barbulescu (1973) described damage to a variety of crops in Iran as very severe at a density of 90 larvae/m². There are also numerous reports of severe attacks of cutworms from the former Soviet Union.
In field experiments, damage levels of up to two carrots per larva or about 50% damaged carrots at a larval density of 30-35 larvae/m² were found under very dry conditions; however, the damage level is about half of this under normal conditions (Esbjerg, 1989a).