Home & Garden: Battling Grand Valley’s goatheads to protect pets
Free Press Gardening Columnist
There are places I will not take my dog, Rusty, due to the abundance of puncturevine (aka goat head) seeds. When Rusty does pick up one of these pointed seeds in his paw he will limp toward me to have it removed. He doesn’t cry, but I know it hurts.
This weed — Tribulus terrestris — got its genus name from the Latin tribulus meaning spiky weapon. It consisted of spikes that, no matter how it was thrown, when it landed it always had one spike pointing up. This is very appropriate name for the seeds of this weed. You cannot always tell when an area is covered with puncture vine seeds as they are the same color as the soil in most of the fields around our area. They blend in and I often don’t know there are puncturevine seeds until I get home and take off my shoes.
Puncturevine — called goathead, devil’s thorn and cat’s head — is an annual weed in our area, but a perennial in tropical regions; it’s easily killed with 2,4-D. Glyphosate is also a very effective chemical used to kill these vining puncture plants. In order to prevent seed formation you need to kill the plants early before they start setting seed. Even when the plants are dead the seeds continue to develop and may germinate the following year. And even if they are not viable (won’t germinate), the seeds can still be picked up in the paws of our pets and on the soles of our shoes. Due to the lack of humidity, these seeds can lay dormant for many years before they germinate and develop their thorny seeds.
There are no preemergent herbicides I know of which will prevent the germination of these spiny seeds. Preemergent herbicides work by creating a chemical barrier through which seedlings cannot emerge. In other words, the seed has to be buried in the soil, not on the surface, for these chemicals to be effective. Large seed such as those produced by puncturevine plants germinate above the preemergent barrier, reducing the effectiveness of the chemical. Spot spraying young puncture vine with either 2,4-D or glyphosate will eliminate the plants the spray hits, but it takes many years to rid the soil of its supply of seed.
When you are using herbicides to control this weed be cautious and know what you are applying. I looked at a series of trees and shrubs the other day that had the classic symptoms of herbicide injury. The owner had three containers — one containing 2,4-D amine, one of glyphosate, and the third containing dicamba. The first two are not root active; in other words, they are not absorbed by roots. Dicamba (aka Banvel) is absorbed by roots and moves to actively growing tissue where it causes distortion and can cause plant death. Some plants are more sensitive to dicamba than other plants resulting in greater injury. With the roots of trees and shrubs and flowers extending well beyond their drip line, uptake of this chemical often occurs.
I recently ran into a problem I had not seen for a number of years, that being blossom blast and limb dieback of Bradford pear caused by the bacterium Pseudomonas. Blossom blast is described as the blackening and death of the flower cluster and fruiting spur. This condition can be caused by fire blight caused by Erwinia amylovora. Both of these are bacterial organisms spread by insects, pruning tools, wind, or rain. Typically when hot weather arrives, the spread of the fire blight organism stops. Pseudomonas however is known to go systemic and as a result branch dieback continues.
Several of the pear orchards in this area have the classical symptoms of Pseudomonas. Homeowners with ornamental and fruiting pears are also losing branches due to this bacterial disease. Some bacterial organisms can be stopped by injecting the tree with tetracycline; Pseudomonas however has no known curative agent once it goes systemic. When a twig branch with Pseudomonas is cut from a tree you will discover the inner woody portion of the branch has a dark wet appearance. If this was fire blight, the cambium area just below the bark would be black, and the woody part of the branch would have its normal white appearance. If you have a pear tree with Pseudomonas, you most likely will lose the tree.
GJ Free Press columnist Dr. Curtis E. Swift is a retired horticulture agent with the Colorado State University Extension. Reach him at Curtis.Swift@alumni.colostate.edu, 970-778-7866 or check out his blog at http://SwiftsGardeningBlog.blogspot.com. He owns Swift Horticultural Consulting and High Altitude Lavender.
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