Determining the need for a soil insecticide, and which insecticide best suits the problem, is often a challenge for the corn grower. There is no exact way of determining the need for soil insecticide in corn, but some general characterizations can be made and used as guidelines. By considering the previous insect histories on a field by field basis and reviewing agronomic situations, categories of need may be established. Soil and soil surface dwelling insects are influenced by:
These ecological characteristics do not guarantee that insects will or will not be a threat to corn seedlings, but are often associated with the probability of damaging insect populations. Research over several years on poorly drained mineral soils in the Tidewater area of NC (13 sites over 4 years) showed, in typical corn growing conditions, an average yield benefit of 5.7 bu/A for soil insecticide use. In situations that are more favorable to insects, a greater benefit would be expected, whereas in less favorable conditions, a dollar loss may be anticipated with soil insecticide use.
If there is not a reasonable assurance of stand-reducing insect populations, an at-planting insecticide should not be used because of cost and possible negative environmental impact. Also, when using these products, great care should be exercised to prevent a human safety or wildlife hazard.
"Situations" Describing the Need for At-Planting Soil Insecticide Use..
The five "Situations" presented below describe most North Carolina corn acres and may be used as general guidelines for determining the need for soil insecticide. The "Situations" represent typical conditions, which may affect the probability of pest insect occurrence and are applicable in many instances. However, conditions on every farm are unique and using these guidelines should be done in conjunction with the farmer's personal experience ( see North Carolina Agricultural Chemicals Manual) .
Cutworms were not considered in the categories, other than for no-till, since most at-planting insecticides will not control high populations of these caterpillars. Scouting and post emergence treatment with an effective insecticide is most often recommended for cutworms, however, if these pests are a chronic problem Lorsban granules may be used (banded) as an at-planting treatment since, they are moderately effective.
Situation #1, No Insecticide Needed. This situation is characterized by conventionally planted corn with at least a yearly rotation; is on well drained soils low in organic matter that are not prone to cool, water soaked conditions; is on sites not excessively weedy in the previous year; and has little or no history of seedling loss due to insects. This situation exists in many Coastal Plain and Piedmont fields and insecticide use has a very low probability of being profitable. If no soil insecticide is used some minor pests, such as thrips, may make the crop look unthrifty in the early seedling stages but will not reduce yield. Untreated fields should be scouted for cutworms or other seedling insects and treated with a postemergence insecticide if warranted.
Situation #2, Low Cost Insecticide Treatment. If corn is conventionally planted, with yearly rotation, but with a history of general seedling loss (5%+) due to insects; is planted on high organic or cool, wet natured soils; and/or has had excessive weed growth the previous season (e.g. set-aside fields or taken-in pasture), then a general preventative soil insecticide program is suggested. In this case the lowest effective rate of the cheapest soil insecticide, which can be applied correctly, should be used. Counter, Furadan, Force, Lorsban, Phorate, and Thimet are choices that the grower can consider. Use Phorate and Thimet only as a "T" banded treatment since in-furrow application will likely reduce stands. Price should be the primary factor in making the insecticide choice. Tests under average farm conditions have produced a yield increase of about 5.7 bu/A with soil insecticide under this situation. Where wireworms are an anticipated problem, soil insecticide which can be placed into the seed furrow (Counter, Furadan 4F, Force, or Pounce G or EC) will give superior results.
Situation #3, Fields with Billbug Problems. In this case do not plant corn (corn after corn) if damage has been severe (25%+). Treat with Counter 15G (prefered) or 20CR in a T-band, or Lorsban 15G in a T-banded at labeled rates if damage has been moderate or less. High Counter or Lorsban rates (10-13 lbs of product/acre) should be applied in fields where billbug pressure is high and where long lasting control is needed (e.g. in non-rotated fields or fields next to last years corn). Rates can be reduced after approximately 160 rows from the previous years corn. Scout fields soon after emergence. Do not use Lorsban on 8%+ O.M. soils. All efforts to promote rapid seedling growth will be beneficial, especially the use of starter fertilizer. Plant early if possible. In severe billbug situations exist in an area, control may be less than desired, especially if plant growth is slow. Working with neighbors to synchronize rotations may be necessary to enhance the effectiveness of rotation. Correcting pH, drainage, and other problems will help reduce billbug problems. Billbug problems are enhanced by no-tillage culture.
Situation #4, Non-Rotated Corn. The lack of rotation tends to build-up pests, including insects and nematodes. These fields often respond positively to a soil insecticide-nematicide. Unless information from field histories or nematode sampling (preferred) suggests otherwise, an at-planting soil insecticide may be beneficial. Not rotating should be avoided since rotation gives substantial, low cost benefits. In the Piedmont, there has been a long history of growing non-rotated corn with little damage from insects. However, in recent years the western and northern corn rootworms have become firmly established in the Piedmont. Rootworm damage is best avoided by rotation, but in non-rotated fields where rootworm has become a problem, a soil insecticide is suggested.
Situation #5, No-Tillage Corn. In no-tillage corn, soil insects and armyworms tend to be more abundant and seedlings typically grow-off more slowly (leading to more insect damage). Thus, a soil insecticide is suggested in this case. Often only an in-furrow treatment can be applied due to equipment limitations and only non-phytotoxic chemicals should be used (Counter, Furadan, Force, or Lorsban). Cutworms can be serious in no-till and several soil insecticides will give some control of cutworms when used as a banded treatment (Counter, and Lorsban). Tests under average farm conditions in the NE Coastal Plain with no-till corn following double crop soybeans have shown an average yield increase of 11.9 bu/A with soil insecticide under this situation. The use of insecticide plus starter or pop-up fertilizer often gives positive results (e.g. Furadan 4F + 10-34-0).
This page (http://www.ces.ncsu.edu/plymouth/pubs/ent/crsoil.html) was created by John W. Van Duyn Ph D. Extension Entomologist, Wayne Modlin, Res. Tech. III.
Date Created 1/30/01.
Last revised on 01/29/04.
Distributed in furtherance of the Acts of Congress of May 8 and June 30, 1914. Employment and program opportunities are offered to all people regardless of race, color, national origin, sex, age, or disability. North Carolina State University at Raleigh, North Carolina A&T State University, U.S. Department of Agriculture, and local governments cooperating.