Snow-on-the-Mountain and Cucumbers

If you’ve driven around the countryside the past few weeks you may have noticed the green of many pastures broken up by bright white patches.  The plant that is catching your eye is probably a species that is common across the area, but has really exploded in grazed areas this year, snow-on-the-mountain.  Snow-on-the-mountain is actually a native plant, first noted on the Lewis and Clark Expedition by William Clark while in Montana. 


The plant has light green, oval leaves and is fairly inconspicuous most of the year.  In late summer flower stocks begin to show up.  Flower stocks are often branched, with multiple flower clusters per stem.  Up to 3 feet tall, these stocks begin to grow leaves with a broad white boarder around the edge, sometimes entirely white.    These leaves are often a bit narrower and lanceolate in shape when compared to the rounder, ovate, lower leaves. Eventually stalks are capped with small white flowers in a cluster above the showy leaves. 


Snow-on-the-mountain is a member of the Spurge family, so if you’re still not sure you have the right plant, break off a leaf or piece of stem.  The broken stem should produce a milky sap, similar to milk weed.  Try not to touch the sap however.  The sap, as well as the rest of the plant, contain diterpenoid esters that can cause skin irritation.  In animals snow-on-the-mountain may cause irritation of the mouth and intestinal tract, diarrhea, weight loss, and in extreme cases death.  The good thing is that animals will usually avoid eating the plant.  Caution does need to be taken in heavily grazed pastures where all other forage may be utilized and animals are less selective as well any hay that may contain Snow. In a bale, animals may not be able to distinguish toxic plants from the good hay and accidently ingest enough to cause symptoms. 


Because the plant is an annual and native to the area, you don’t really have to worry about control.  In most well managed pastures, established grass will out compete seedlings and keep numbers to a minimum.  This year’s rains and temperatures must have come at the right time creating the flush we are now seeing.  Control methods are mostly focused on preventing the plant from producing seed.  Spraying, mowing, chopping, or manual seed removal are all options. This year’s plants may have already produced viable seed, so before you decide to buy some herbicide go out and check.  If so, treating now won’t do anything but kill an already dyeing plant.  If you do want to some control, torodon plus 2,4-D or metsulfuron plus 2,4-D applied next year before bloom should do the trick. 


Two other plants that you may have noticed growing out of control this year in fence lines and shelter belts are bur and wild cucumber.   Both vines can quickly dominate the area they grow, covering grass, shrubs, and trees with no problem.  While not doing any direct damage to the plant they cover, the cucumbers place themselves in the best position to capture sunlight without regard for the host’s needs.  In trees especially, this can cause loss of leaves and undue stress to species, especially evergreens that often require full sunlight.


While coming from two different species (Sicyos angulatus – Bur Cucumber and Echinocystis lobata - Wild Cucumber), both plants are fairly similar.  Both are vines, both have clusters of white flowers, star shaped leaves, and spine covered fruits.  There are a few differences to note if you’re curious.  Bur cucumber will grow up to 10 feet in length.  Its leaves will have 3-5 lobes and the vine may be slightly fuzzy.  Wild on the other hand can grow to lengths of 25 feet with 5-7 lobed leaves and a smooth stem.  The biggest and easiest way to tell the two apart this time of year is the fruit.  While both produce spine covered fruits, Bur’s fruit is oblong in clusters, while Wild is round to oval, each growing separately.


The good thing is that both of these plants are annuals, so mechanical control (cutting or pulling) before the fruit ripens and produces new seed is a very effective control technique. Herbicides can be used, but be very careful if using on plants entangled in trees.  If you want to go this route, glyphosate is your best option.  Paint or carefully apply to the base of the vines making sure not to get any on desirable plants.  Torodon or Dicamba products should not be used if desired species are present.  The longer residual on these products risks movement into the soil and absorption by other plants that we don’t intend to harm. If you can get to the plants before seeds are produced, control this year may help reduce next year’s population.  If not, control may still be an option for ascetics alone.  In both cases, marking the location of heavy infestations and coming back next year to treat any new plants before they get out of control is a great idea.


One plant that may look similar to Bur and Wild cucumber is Honeyvine Milkweed. Milkweed is a perennial and should be controlled differently, but is easy to tell apart by its heart shaped leaves and the characteristic milkweed pods and seeds.  If you have any questions about these or any other plant that you may have encountered feel free to contact myself or your local extension office.  Bring in a sample (if you can get it in without it getting too dried out) or take some photos of the leaves, stem, fruit/flowers, and entire plant for perspective.  We’d be happy to help you with identification and control options.

 -Ben Beckman is a beef systems Extension Educator serving the counties of Antelope, Cedar, Knox, Madison and Pierce.