If you’re growing potatoes in Norfolk County then you’ve likely come across some Colorado potato beetles
(CPB). These annoying insects are difficult to control and can cause significant feeding damage leading to yield loss. Colorado Potato Beetles taken from some Norfolk County fields over the last few years have been sent to Agriculture and Agri-food Canada (AAFC) for analysis. Dr. Ian Scott’s group has been testing to see if these beetles are becoming resistant to the common insecticides we’re using in potatoes.
As it turns out, CPB in Norfolk are following a similar trend to the rest of Canada; the insects are developing tolerance to some of our main chemicals. They found a growing tolerance to Group 4A neonicitinoids like Admire, Titan, Actara, Cruiser Maxx and Alias. This is in addition to the groups we already know have resistance in Ontario like pyrethroid (Group 3A), carbamate (Group 1A) and organophosphate (Group 1B) insecticides. With this information, plans can be adapted to get a better handle on this pest. It will become increasingly important to monitoring your CPB levels throughout the growing season as early season neonic treatments become less effective and for shorter amounts of time.
Colorado potato beetles are more susceptible early in their life cycle, so scouting is critical. CPB larvae have 4 instar stages, getting bigger every time until they pupate and emerge as an adult beetle. Scouting should begin as potatoes start to emerge to monitor the efficacy of the seed, in-furrow or early season insecticide. If you do have high levels of CPB in your potato field (>75 large or small larvae/50 plants; or >25 adults/50 plants), it is important to consider the timing and chemical group for your insecticide spray. Rimon, for example, only prevents the larvae from moving on to the next growth stage and does nothing on adults, so early application is needed. The 4th instar (largest larvae) of CPB causes the most defoliation, which can greatly reduce yield, so spraying at the 3rd instar (5mm long) or earlier is ideal. A lot of times earlier in the season CPB may be confined to the edges of fields which may be the only areas that need to be treated, but this can be determined through scouting.
There are many different effective insecticide groups registered for potatoes that do not have documented tolerance or resistance. These include:
Two newer products in the diamide group, Harvanta and Vayego, have also shown to be quite effective as a foliar spray in controlling CPB if you have not used them before. Each of these listed insecticides would be effective if included in your CPB spray program, but be sure to rotate between different chemical groups and spray when CPB threshold levels are reached. If you’re curious about all the registered products on potatoes, you can check out the Ontario Crop Protection Hub at www.Ontario.ca/CropProtection. There you can filter and search by crop, pest, efficacy, application type and much more.
One critical piece of the puzzle is if you use a neonic insecticide early in the season as a seed or in-furrow treatment, do not follow up with a foliar spray of a neonic in the same season. This slows resistance development since not every generation gets exposed to the chemical and increases the likelihood the application in the next season will kill them.
Although there are many insecticides that are currently effective for CPB, it is also important to know which registered products you should avoid as CPB have developed resistance to them. The list of these pyrethroid, carbamate and organophosphate insecticides is lengthy and although they may be effective on other potato pests, using them against CPB has proven to be ineffective over the years.
If you notice poor control after applying an insecticide, particularly after a neonic, you can still get samples tested for resistance. Just contact Dennis (519-766-5337, dennis.vandyk@ontario.ca) if you’re interested. The situation is not as bleak as it was in the ‘90s where 4-way tank mixes were still not killing CPB. Thankfully now we have a decent toolbox of products that are effective. With a little bit of scouting along with mixing and matching products we can ensure control of these tough insect pests well into the future.