Canada thistle galls have been spotted in some areas this summer. These wood-like galls are a product of thistle stem gall fly (Urophora cardui) attacking Canada thistle plants (see photo). Doesn’t sound all bad, right? Canada thistle developing a pest issue? Tell me more!

Adult gall flies lay eggs in the thistle plant early in the summer season. The thistle stem gall fly prefers wet environments, so galls are more likely spotted in parts of the region that have stayed wet this year. Gals interrupt normal plant functions and reproduction as well as divert nutrients from vegetative growth and sometimes cause deformed seed heads that decrease seed production.

Don’t get your hopes too high as the gall fly will not eradicate Canada thistle alone; however, it can reduce stands. Any management tactic that is implemented to reduce vegetative thistle growth early in the season (before gall flies lay eggs) will likely cause gall flies to leave and find a different site. Most noxious weed plans aim to stop vegetative growth. The advantage of stem gall flies is their ability to travel to isolated stands of thistle that are hard to access. When combined with competition from other, desirable vegetation, the effect of both the galls and the competition can help with suppression. Thistle stem gall fly will not effectively manage Canada thistle alone, but keep in mind that integrated pest management involves utilizing every tool available to you! For more detailed information on this topic, go here.

Late alfalfa

As fall approaches and many start thinking about silage and grain harvest, don’t forget about alfalfa cutting management as well. Every year many growers find themselves struggling to determine when to take that last cutting of hay. Fall harvest should be determined by a few factors.

• The first thing to consider is that alfalfa needs 500 alfalfa growing degree days (GDDs) after cutting and before a hard freeze to get enough root reserves to survive most Midwest winters (calculate your GDDs here). This equates to about six weeks in the Upper Midwest. By determining your long-term average hard frost (24°F) date (see here) and working backwards six weeks, you should have a pretty good idea of last suggested cutting date.

• If you have a newly established stand of spring seeded alfalfa that experienced favorable weather conditions and looks well established, an October cutting may be appropriate as long as ~500 GDDs have accumulated since your last cutting. Remember that late fall cuttings can result in a lower first spring cutting yield. If your young alfalfa stand did not experience a favorable growing season or was not established until late summer, avoid the last, late cutting.

• Keep in mind that it’s not ideal to let more than 200 alfalfa growing degree days accumulate after you make the last cutting. After this much growth occurs, root reserves are fairly depleted and plants become more susceptible to winterkill.

• If you plan to terminate your stand in the spring, a later harvest is fine; however, terminating alfalfa with herbicides is best at 4-plus inches of regrowth.

• If it gets late and you’re concerned about forage supply, consider harvesting after the winterization period; technically, it should be safe to take a cutting at this time.

This correlates to cutting after a killing freeze (23-24°F for several hours) after the plant is dormant. This is not as stressful to the plants as cutting during winterization, and can be a viable option for those who need feed and do not want to risk next year’s stand.

Remember in any scenario, it’s ideal to leave 5-plus inches of stubble, which leaves some plant tissue and helps to reduce erosion. Leaving soils bare over winter is a recipe for erosion and will likely result in less snow cover with little plant residue on the soil surface.

The more stress an alfalfa stand sees during the growing season, the more apt it is to experience winter-kill after a late cutting. If a field was cut multiple times (4-plus), it is more likely to have winter-kill issues than a field cut fewer times. Younger, well-established, winter hardy/ disease-resistant varieties may tolerate a late season cutting better than older stands or those that experienced heavy pest pressure over the growing season.