The convenience and effectiveness of the insecticide imidacloprid, the active ingredient in the products Admire 2F and Provado 1.6E make it appear to be the proverbial ‘magic bullet’ for Colorado potato beetle (CPB) control. In just four or five years, this chemical has reduced the regional population of this menacing vegetable pest to a fraction of what it once was. A single application can be so effective and convenient when compared to continuous scouting and multiple applications with other materials that even at $612/gallon (1998 price from a Connecticut supplier), it now dominates the market and has driven several other CPB products out of production.
However, let us not forget the hard lessons this pest has taught us in the past. This beetle can become resistant to any chemical it is exposed to continuously for six generations. At two generations per year since imidacloprid’s release, we may start to see resistance problems in 1999. This material is already starting to lose its effectiveness in some potato fields on Long Island. (See the photo of CPB feeding on eggplant.) To preserve the effectiveness of this tool, we are going to have to practice resistance management. Another lesson has been learned. In the long run, multiple control techniques, Integrated Pest Management or IPM, will always outperform a strict reliance on a single tactic. Finally, we have learned to minimize the amount of pesticide used, to lower the risk from both obvious and hidden side effects (e.g. high price tag, pollution, toxicity, secondary pest outbreaks, etc.).
MINIMIZE THE AMOUNT OF PESTICIDE USED (COST ANALYSIS)
The in-tray or in-flat transplant drench technique is described on the Admire 2F label for tobacco and has been tested on and recommended for eggplant and tomato by Extension specialists and researchers at the University of Maryland and Rutgers University. It seems to be legal based on the general directions for use under chemigation that calls for applying Admire 2F “only through low-pressure irrigation systems.”
Soil application at low label rate
The lowest dose that is recommended on the Admire 2F label for eggplant and tomato via various types of soil applications is 16 ounces per acre. This low rate has been shown to control 99.9% of the pests in an experiment where untreated eggplant had more than 27 beetles per plant. The cost of applying 16 ounces per acre is $76.48 at $4.78/ounce ($612/gallon).
Transplant drench at 1/2 ounce per 1000 plants
At a 42-inch row spacing and plant density of 6,270, it would take approximately 3.15 ounces per acre, at a cost of $15.06 to apply Admire with a standard watering can to transplant trays. Larger eggplant varieties such as ‘Florida Highbush’ may be planted at a density of 3,500 to 3,700 plants per acre so the costs would be proportionally less (around 1.75 ounces = $8.36/acre). Dr. Gerry Ghidia at Rutgers recommends applying the material in one pint of water per flat (1.7 to 2.6 gallons water/1000 plants, 72 or 48 cells per tray) after allowing the plants to harden off properly. He has experienced a slight problem with phytotoxicity in some years, but not others, when plants were not acclimated to outside conditions. Transplants should be rinsed with straight water after application to wash the material from the foliage into the root zone and avoid delay of chemical uptake.
How long can you go? Maryland researchers maintained control (98%) and yields with a rate of just one ounce per acre after applying the diluted solution to individual transplant tray cells (plants) with a pipette (Dively et al. 1996). But wait, can we go lower?
Transplant drench at 1/2 ounce per 1,000 plants only in 10 border rows surrounding 10-acre field
You would have to treat 4,090 plants with 4.1 ounces of material to surround the perimeter of a 10-acre field with a barrier of protection (4.1 ounces per 10 acres = 0.41 ounces per acre at a cost of $1.96 per acre). Now your biggest problem may be that it may take you half a lifetime to use up a gallon of this stuff, especially if you do not have 10 acres of eggplant and tomatoes! This ‘perimeter’ treatment strategy has been successfully used in large potato, tomato and eggplant fields in Maryland and New Jersey for the past few years.
- After one or two seasons, you absolutely must rest the chemical by switching to other available foliar-applied materials and tactics to preserve the effectiveness of imidacloprid. Think about it, wouldn’t you rather combat this terrible pest with less effective materials when its population is low after one or two years of imidacloprid use, than when its population is finally resistant to this chemical, out of control and you are practically knee deep in beetles! Other selective products that are effective for controlling CPB but do not kill most beneficial predators and parasites include Kryocide*, SpinTor and Neemix. Agri-Mek is also registered but for tomatoes only. Some non-selective insecticides that are registered and possibly still effective for CPB control include Asana, Thionex, and Vydate.
- Limit the beetles’ exposure to imidacloprid to a single generation per season. That way you are non-continuously selecting for the survival of that one beetle in 1,000 that can detoxify imidacloprid. Otherwise, that one in a thousand individual is the only beetle that survives to reproduce, and has a strong possibility of passing on the gene that can detoxify the chemical to its offspring. This results in replacing a susceptible population with a resistant super race; Admire no longer works.
- Do not use the foliar applied product Provado at all. There are rotational restrictions on the Provado label that limits follow up crops during the next 12 months to cole crops and lettuce (minor acreage for most New England vegetable producers), or cucurbits and solanaceous crops (both plant families are preferred host for Phytophthora). In short, the use of Provado may limit your rotations to such an extent that it may lead to disease problems which you cannot control. Provado applications would also be much more expensive than a low dose Admire drench and, if used on second-generation CPB or for other pests, may increase the selection pressure toward a resistant beetle population. The low dose of Admire is supposed to be gone by July when the second generation typically appears, so that the few beetles present then will not be exposed to a “second helping.”
USE MULTIPLE CONTROL TECHNIQUES (IPM)
- Rotation. Beetle populations build up on solanaceous weeds and crops (e.g. potatoes, eggplant, tomatoes and horse nettle). They spend the winter as adult beetles in the soil of these fields and, especially, in the drip zone under adjacent trees. In May when adult beetles emerge from the soil, their flight muscles are slow to develop and they often walk to nearby host crops. Rotation away from last year’s site delays infestation in the spring, reduces the number of beetles that find the new field and lowers the number of eggs laid per beetle. Delaying infestation also allows plants to become larger and capable of withstanding more feeding without having an effect on yield. The further the distance from the previous season’s host sites, the fewer the number of beetles that ultimately find the new field. Often fields rotated to more than half a mile away do not require treatment the next year. Even an Admire transplant drench is probably not justified in fields rotated greater than 1/2 mile with no other beetle source around.
- Trap Crops. If you can only rotate less than 1/2 mile or within the same field (but on a different piece of ground than last year’s crop), you can use the outer 10 rows of your eggplant or tomato planting as a trap crop. Most growers have noticed that the edge of the planting closest to last year’s solanaceous crop tends to suffer earlier and more severe damage than the rest of the planting. That is because most of the colonizing beetles are walking from last year’s crop or landing to feed and lay eggs within the first few rows once arriving in the new site. By using the Admire transplant drench only on plants in the 10 rows closest to the previous year’s host crop (or in the “perimeter strategy”), you eliminate most of this year’s beetle population before it migrates further into the planting or lays eggs. Another possibility is to leave a cereal cover crop on last year’s solanaceous planting until mid-June. This inhibits beetle flight (take-off) and, thus, exposes more of them to natural mortality by predators and parasites or starvation.
- Natural Enemies and Selective Insecticides. There are many natural occurring enemies that help control CPB populations. The 12-spotted lady beetle (Coleomegilla maculata) and the nocturnal ground beetle (Lebia grandis) have been shown to be very effective predators of CPB eggs and often consume over 50% of those laid. This ground beetle larvae also parasitizes the CPB larvae. The 12-spotted lady beetle builds up and overwinters in and around cornfields, which makes last year’s sweet corn field a good choice for this year’s tomato planting. Lacewings (Chrysopoids), stink (Podisus maculiventris), damsel (Nabis sp.) and assassin (Reduviids) bugs feed both on CPB eggs and larvae. These brown stinkbugs can be commonly seen feeding upon and controlling low levels of second generation CPB larvae within fields. The technid fly, Myiopharus aberrans, has been shown to kill up to 30% and 80% of first and second-generation CPB larvae, respectively, in some New England locations (Ferro and Hazzard, 1990). There is also a fungus (Beauveria bassiana) which attacks and kills adult and larval CPB in moist environmental conditions. Using rotation and/or the selective insecticides mentioned above while eliminating unnecessary early season fungicide applications allows these beneficial agents to maintain control of CPB population and keeps defoliation below the 20% threshold.
- Use Action Thresholds. Do not try to kill every CPB in the field. Remember that your objective is to run the most cost-effective operation over the long term by maintaining yields and minimizing costs. Rotation without application, spot treatments using selective insecticides and the low dose use of Admire in some years, may be the cheapest way to keep defoliation below 20% on your farm.
- Natural Mulch. Straw and other natural mulches on the soil surface have been shown to drastically reduce the number of CPB that inhabit a planting and the damage they cause. The idea of manually applying straw mulch may not be practical or cost effective, but no-till or strip-till systems may offer an opportunity to reduce insect, weed and disease problems using far fewer man-hours. For example, no-till tomato production with a correctly applied post-emergence herbicide requires far less labor for weed control.
The bottom line. Use IPM, lower rates and resistance management and save money or return to the bad old days when nothing seemed to control this beast!
* Kryocide works only on larvae. Best results are achieved when applied just after egg hatch during warm temperatures.
SELECTED READINGS AND REFERENCES
- Dively, D.; J. Linduska; \ M.Ross;D. Baumann; C. Cain and M. Boltz. 1997. Colorado potato beetle control with transplant drench treatments of Admire to bedding trays of eggplant. 1996; Arthropod Management Tests. Vol. 22. p. 132.
- Ferro, D. and R. Hazzard. 1990. Managing the Colorado Potato Beetle inNew England. Unpublished. pp.3.
- Ghidia, G. 1998. Insecticide Resistance Management of the Colorado Potato Beetle on Eggplant in New Jersey. Rutgers Cooperative Extension. F5842. pp.4.
- Olkowski, W.; N. Saiki and S. Daar. 1992. IPM options for Colorado potato beetle. The IPM Practitioner. Vol. XIV, No. 9. Sept. pp. 1-21.
By: T. Jude Boucher, Vegetable Crops IPM Program Coordinator, University of Connecticut Cooperative Extension System. Reviewed 2012.
Originally published: Yankee Grower, University of Connecticut Journal for Profitable Horticulture. Volume 1, Number 2 March/April 1999, p.7-9.
This information was developed for conditions in the Northeast. Use in other geographical areas may be inappropriate.
The information in this document is for educational purposes only. The recommendations contained are based on the best available knowledge at the time of publication. Any reference to commercial products, trade or brand names is for information only, and no endorsement or approval is intended. The Cooperative Extension System does not guarantee or warrant the standard of any product referenced or imply approval of the product to the exclusion of others which also may be available. The University of Connecticut, Cooperative Extension System, College of Agriculture and Natural Resources is an equal opportunity program provider and employer.