Wheat Midge Population on the Rise
 | Author:
Allison Kosto, MSU Broadwater County Extension Agent
MSU Broadwater County Extension Agent |
Wheat Midge Population on the Rise
Allison Kosto
MSU Broadwater County Extension Agent
It’s hard to imagine that a tiny insect can cause so much damage. However, this is the case with the Wheat Midge. The pest has slowly been spreading across the state. MSU Extension in Broadwater County conducts a monitoring program every summer to monitor population changes. It was confirmed in Broadwater County and Gallatin County in 2016. At that time, this was the furthest south it had been detected in the state. Until recent years only a few midges were caught in traps and there was little concern. However, that is now changing.
The first major outbreak of the wheat midge in Montana occurred in 2006 in the Flathead Valley. A conservative estimate put the economic loss at over 1.5 million dollars in Flathead County. It has only recently become a major problem in Montana but has been a key pest in Canada since the 1980s. North Dakota and Minnesota reported significant losses to the midge in the 1990s. It was first found in northwest Montana during the 1990s but was only in low numbers. It was not until 2006 that it started causing major economic losses. The midge is now found in the golden triangle, the hi-line and northeast Montana. And since 2016, it’s been found in the southern half of the state. Numbers have been increasing rapidly in the last few years.
In 2021, there was a significant spike in the midge population in Broadwater County with a trap off of Riley Road on the backside of the lake catching over 300 midges. However, that pales compared to this year. A trap near Lower Dry Gulch Road caught over 1,700 midges in a single trap. These traps catch male midge, but it’s the females that do the damage. Therefore, additional scouting took place to look for the female midge. It was determined that the female midge population was still under the economic threshold. However, this was the first year that additional scouting needed to take place. The good news is though, the high midge counts seem isolated to this pocket of the county. Counts at traps placed in other areas of the county remain low.
Spring wheat is the primary host of the midge. It is particularly fond of irrigated spring wheat. It can also be found on durum wheat and barley. The wheat midge looks like a tiny orange mosquito. The adult lays eggs on the developing wheat head. The larvae feed inside the wheat head causing significant damage. The damage is not visible from the outside and can only be seen by threshing and inspecting the heads. Larvae are capable of reducing grain size by 30 to 50% with several larva feeding on one kernel. Kernels may abort entirely, not fully develop or develop slightly. In the Flathead Valley, wheat fields that would normally yield 80 to 90 bushels/acre produced less than 2 during major outbreak years. Additionally, adults can function as a vector for diseases such as scab or glume blotch.
Crop rotation and diversification are the best ways to reduce the long-term economic impact of the midge. The same holds true for many other pests and diseases. There has also been good success in some areas of the state with biological control. There is a small parasitic wasp that will attack the wheat midge larvae and help regulate populations. If wheat midge populations get high enough, then insecticide treatment may be necessary. However, timing is critical, and it can often kill beneficial parasitic wasps as well.
It's critical to continue to monitor midge populations, especially on the backside of the lake. Farmers in this part of the county are highly encouraged to start participating in the monitoring program. If you have any questions about the wheat midge or would like to participate in the monitoring program, contact the MSU Extension Office in Broadwater County at 406-266-9242 or allison.kosto@montana.edu
