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Ornamental Crops IPM E-newsletter, 2010

For December 2010

In this Issue:

  1. New Greenhouse Insect Pest
  2. Weeds in Nursery and Christmas Tree Plantings: Beating the Competition
  3. Suggestions for Managing Insecticide Resistance in the Greenhouse


Cornell IPM Team for Production Ornamentals

New Greenhouse Insect Pest

Daniel Gilrein, Extension Entomologist, Cornell Cooperative Extension of Suffolk County

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Duponchelia fovealis, which has no common name, is a Mediterranean moth that has spread around the world. A relative of the European corn borer, Duponchelia caterpillars will feed on leaves, buds and flowers. In addition they may chew on or bore into stems; sometimes they feed on decaying plant debris.

The moths are relatively easy to identify. With a wingspan of about ¾", the grayish-brown moth has front wings with a yellowish lines in a distinctive pattern. The moths often rest with the end of their abdomen pointing upwards.

Duponchelia fovealis late instar of Duponchelia fovealis
Adult Duponchelia fovealis moth
The later instar larvae can feed on the main stem.


Mature caterpillars vary from brown to white with a dark head and dark spots on the body and are sometimes found around the base of plants covered in webbing, in which they may include some surrounding soil material that helps provide camouflage.

The insect was first found in North America in 2004. Since then it has been detected in at least 13 states. Currently surveys are being conducted to determine its US distribution.

Duponchelia has a very wide host range, and besides many outdoor fruit and vegetable crops, it has been found on the following greenhouse crops:

Daisy (Bellis spp.)
Geranium (Pelargonium)


Although it is not likely to overwinter outdoors in our northern climate, it has potential to become an important greenhouse pest. And while some insecticides show promise for control, this insect's habits, and the way crops are grown – closely spaced and with dense foliage, may make control a challenge.

A full version of this article appears in the November 2010 edition of the Long Island Horticulture News from Cornell Cooperative Extension of Suffolk County

Photo Credits: James A. Bethke, University of California Cooperative Extension & Tracy Ellis, San Diego County Ag Weights and Measures

Weeds in Nursery and Christmas Tree Plantings:
Beating the Competition

Brian Eshenaur, NYS IPM Program

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From the moment a nursery crop or Christmas tree field is planted the competition is on! It's plant vs. plant in a race to capture water, fertility and light. If the weeds get there first and aren't controlled, a significant reduction in growth of the young woody crop plants is to be expected.

In this plant growth competition weeds have some characteristics that can give them a competitive edge. Weeds have a great plasticity, or ability to adjust to variable conditions and resources. For example many weeds can produce seed on a very small plant or even on a seedling. Weeds can also adjust to the conditions better than crops, so when the water and nutrient levels are low weeds often produce larger root systems to extract as much as possible. On the other hand when water and nutrient levels are high, weed roots will be small and the shoots will be tall. Weeds are also better consumers of nutrients and often can use nutrients beyond what are necessary for growth, at luxury levels where crops often can't use excess fertilizer. Research has shown that in the competition for nutrients, weeds normally win, so fertilizer will likely go to the weeds and not the crop.

Light is another area of competition between weeds and nursery plants. Timing is critical on this issue. If the nursery plants are given the time to form a canopy and the weeds come in later, in the shade of the nursery plants, there will be little if any impact on the growth. On the other hand, if weeds develop early and grow beyond the crop, then the quality of the tree and shrub stock will be sacrificed.

Weeds are formidable foes-- so what's a grower to do? Steps growers can take to gain the edge!

  • Have a game plan. Use techniques to get the crop established first providing optimal conditions. Emphasize weed control in the first season or two when it is needed the most. Consider fertilizer placement to benefit your nursery stock and not weeds.
  • They're here, now what? If weeds are present in a crop it might seem logical to add supplemental fertilizer to make up for what the weeds are using. However this extra fertilizer almost always goes to the weeds. So if weeds are competing, don't fertilize the weeds, remove the weeds. This will do more for the crop than fertilizer.
  • When to stop. Weed control should begin before weeds start to interfere with the crop plant. Stop weed control when the crop plants you are growing have covered all bare soil. However, allowing the weeds to go to seed will mean the battle will continue. So remove flowers or seed heads before they mature.

Suggestions for Managing Insecticide Resistance in the Greenhouse

J.P. Sanderson, Dept. of Entomology, Cornell University

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Most growers have been controlling pests long enough to have experienced the frustration of using an insecticide that was once very effective only to find it is not working well any more.  Conserve insecticide and thrips is a recent example of this occurrence.  Insecticide resistance is a major concern for chemical control of almost all of the important greenhouse insect and mite pests.  A combination of the biology of the pests, the intensity of chemical use in the past and present, and several aspects of the greenhouse environment and commercial production practices, has led to insecticide resistance problems.  The following suggestions should be considered as a part of any chemical control program.

  1. Minimize Insecticide Use.  If pest control relies exclusively on synthetic insecticides, then resistance can only be delayed, not avoided.  Therefore, the use of non-chemical control tactics (sanitation, eliminate weeds, soil sterilization, screening vents, natural enemies, etc.) should be maximized.  The decision to apply insecticides should primarily be based on pest scouting reports, not a calendar schedule.
  2. Avoid persistent applications.  Ideally, an effective insecticide should be applied at a concentration high enough (within legal limits) to kill all individuals in a population, then quickly disappear from the environment, so that the insecticide residues do not degrade over time to a concentration that will kill only susceptible individuals.  For example, aerosol formulations that apply a short "burst" of a high insecticide concentration and do not leave much residue may select for resistance more slowly than full-coverage or systemic applications of the same insecticide, as long as resistance to the insecticide has not already developed in the population.
  3. Avoid "Tank Mixes."  A mixture of two insecticides may provide superior short-term control than either insecticide used alone, but there is a danger in the long-term use of insecticide mixtures.  The assumption behind the use of tank mixes is that if individuals which are resistant to one or the other pesticide in the tank mix are rare in the population, there is little chance that resistance mechanisms to both pesticides would occur together in any one individual.   However, if by chance individuals do exist with resistance mechanisms to both chemicals, then continued use of the tank mix will begin to select for these multiply-resistant pests.  Chemical control would then become much more difficult, because the pests would be resistant to multiple classes of insecticides.      
  4. Use Long-term Insecticide Rotations.  The pesticides used in a rotation scheme should have different modes of action against the pest and resistance to the chemicals should be at a low (undetectable) level at the start.  Organophosphate and carbamate insecticides have similar modes of action and should not be alternated in an insecticide rotation scheme.  Use each effective insecticide for at least the duration of one generation of the pest before rotating to a different insecticide.  If two insecticides are used within the same pest generation, the selection effect will be essentially the same as using a tank mix.  This is because the same individuals would be contacted with both insecticides, although at slightly different times.  To minimize the problems of overlapping generations and persistent insecticide residues, it might be wise to use the same insecticide for two or even three generations prior to rotating, if allowed by the label.   
  5. Use Pesticides with Non-specific Modes of Action.  Insecticidal soaps and horticultural oils both have broad modes of action, and it is therefore unlikely that resistance will occur to either of these.  In addition, tank mixes of these materials with effective synthetic organic insecticides might delay resistance to the synthetic insecticide, because the soap or oil will kill many individuals that are resistant.  However, some tank mixes that include oil or soap may be toxic to certain plants.
  6. Integrate Chemical and Biological Control.  Many of the newer insecticides are compatible with the use of many kinds of natural enemies.  The effective use of natural enemies can add an additional mortality factor that does not select for resistance, and may conserve the effectiveness of insecticides. Effective natural enemies may include predators, parasitoids, and/or insect pathogens.  Many extension entomologists and commercial insectaries have information on pesticides that are compatible with various natural enemies.  Growers can learn from these sources and their own experience. 

Searchable ‘side effects’ lists of compatible pesticides can be found at Koppert biological control natural pollination and at the Biobest side-effects manual.

Cornell IPM Team for Production Ornamentals
Betsy Lamb
State Coordinator for Ornamental Crops IPM
Ithaca, NY,
Brian Eshenaur
Western New York Specialist
Rochester NY
Disclaimer: Pesticide recommendations are for informational purposes only and manufacturers' recommendations change. Read the manufacturers' instructions carefully before use. Cornell Cooperative Extension and Cornell University assume no responsibility for the use of any pesticide or chemicals.
Some of the links provided are not maintained by Cornell Cooperative Extension and Cornell University. Cornell Cooperative Extension and Cornell University are not responsible for information on these websites. They are included for information purposes only and no endorsement by Cornell Cooperative Extension or Cornell University is implied.
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