Have you noticed a different looking plant out in your pasture or right of way? Does it look like a white, fuzzy thing, maybe a bud? It is the Russian Knapweed Gall. It was released in 2012 in the San Luis Valley as a biocontrol to Russian Knapweed. We are seeing a great increase in the galls at this time. Russian knapweed is an aggressive, non-native, deep rooted, noxious weed. The galls on the plant are caused by tiny fly larvae (midge) (Jaapiella ivannikovi) that feed on the stem and cause a rosette gall of fused leaves. This activity causes the stem to stop growing.
Highly grazed and mowed areas are preferred by the by the gall flies. When gall midges are established in an area and mowing is applied Russian Knapweed can be suppressed. Fresh galls will have adult flies in two or three weeks. Four or Five generations of gall midges can infest per season. This is a good thing. Suppression of a noxious weed is the goal. Any mowing or grazing schedule will increase the occurrence of the galls. You can mow after bird ground nesting season where that is a concern. The gall midge will spread or you can move the fresh galls around to another area to establish them. Just snip off the fresh galls and place in another field of knapweed as soon as possible. Place the galls in a paper cup with a moist paper towel so the midge fly can complete the larval stage. Then put the cup and all out in the field.
The Colorado Department of Agriculture has an excellent description on their website for Russian Knapweed Biocontrol.