C.O.R.N. Newsletter: 2014-16

Cressleaf groundsel has been abundant throughout parts of Ohio for a while, but every year a few additional hay producers get to experience it for the first time apparently.  We have some resources available online about the biology and control of this weed, and its toxicity to animals.  A fact sheet is available in the “Other Weeds’ category on our website, http://u.osu.edu/osuweeds, and a brief video by OSU Extension Educator Jeff McCutcheon also covers this -https://www.youtube.com/watch?v=pvEQXAouvQA.  A web search will no doubt provide some additional resources.

Cressleaf groundel (Senecio glabellus) is a winter annual weed that emerges in the fall, and flowers in May.  It is a problem in no-tillage corn and soybean production, but not that difficult to control.  Most fall herbicide programs are effective, and it can be adequately controlled in the spring with mixtures of glyphosate and 2,4-D when still relatively small.  Cressleaf groundsel is more of a concern in pastures and hayfields, due to its toxicity and the risk to animals that ingest it.  The following information on toxicity comes directly from our fact sheet, and was provided by Dr. William P. Shulaw, OSU Extension Veterinarian:

Nearly all species of Senecio are considered potentially toxic plants because they contain compounds called pyrrolizidine alkaloids (PAs). These are metabolized in the liver to other compounds that are toxic, primarily to the liver cells. Senecio glabellus is considered nearly as toxic as some of the more troublesome plants in this genus, but fortunately, it does not appear to be very palatable to grazing livestock. The PAs are found in the plant throughout the growing season but appear to be at their highest levels when the plant is in the bud to flower stage. The flowering portions of the plant and the youngest tissues generally contain the highest concentrations. PAs are not destroyed by the hay-making and curing process. Ensiling of forages may reduce the concentration of PAs, but will not entirely eliminate them. Sheep are considered more resistant to the effects of PAs than cattle and horses, and have been used in some areas to control the plant.  However, sheep are susceptible to poisoning if they consume sufficient amounts.

Under typical grazing conditions in Ohio, it is unlikely that animals will consume significant quantities of the S. glabellus because of the availability of higher quality, more palatable forages. Poisoning could result under unusual conditions, such as drought, where good quality forage is not available. Hay containing significant amounts of the plant may pose a greater risk. Poisoning usually occurs as a result of consumption of the plants over several days to several months. Because the effect on the liver is cumulative, signs of poisoning can occur weeks to months after consumption of the plant ceases. The signs are directly attributable to liver degeneration and failure. Affected animals usually show depression and loss of appetite initially, and progress to neurological signs with head pressing, aimless walking, incoordination, and rectal straining. At post mortem examination, the liver will usually be shrunken and fibrotic with grayish blue to yellowish discoloration. Treatment is only symptomatic and not usually successful once signs appear.

As soybean planting wraps up, it’s time to consider evaluating soybean stands.  Planting conditions were not always ideal this year.  Soil conditions were a little wet when planting started and now have turned fairly dry in most areas.  Here are some points to keep in mind when evaluating soybean stand.

1.)    Uneven stand.  I evaluated a soybean stand last week in west central Ohio.  Similar to last year, soybean emergence is a little uneven.  Last year, we observed soybeans at the VE stage (emergence) and the VC stage (unifoliates open) while some soybean plants were not yet emerged (but the seed was viable).  Initially, this was not a pretty stand, but more plants emerged, the stand evened out, and yields were good.  Keep in mind soybean plants may be at different stages, but if the seed is viable (i.e., not damaged from disease or insects), the field should be fine.

2.)    Reduced stand.  Dig around in areas where there are no plants.  If you find seed that is healthy and germinated but not broken through the soil, a little moisture should help the plants emerge.  (Soils were dry in many areas late last week.)  In 2012, it took six weeks before plants received enough moisture to germinate.  If you find dead seedlings (disease) or no seed or seedlings (insects), then take a stand count.

3.)    Stand counts.  I briefly discussed how to take a stand count in last week’s article.  If you missed it, you can find it here toward the end of the article: http://corn.osu.edu/newsletters/2014/2014-15-1/early-season-soybean-damage-frost-ppo-or-disease

4.)    Replanting.  Replanting decisions should be made very carefully and only after conducting a stand count.  If all plants in a field are lost, it is beneficial to replant because there is still adequate time left in the growing season.  (I have seen a field that lost all plants due to a flooding river that was flowing through a field.)  If only areas of fields were affected, replant the affected areas while leaving the rest of the field as is. 

If the entire stand is reduced, the field can be inter-planted to fill in the reduced stand.  Keep in mind, however, we estimate a soybean yield reduction of 0.5 bushel/day when planting later than mid-May.  Additionally, previous research conducted by the AgCrops Team indicates that a stand of approximately 50,000 plants/acre (at harvest) results in a 15% yield reduction compared to 116,000 plants/acre (when planting in May).