Musk Thistle

Musk Thistle Plant

Musk Thistle, Carduus nutans, is a biennial, noxious weed that occurs throughout the United States. EDDmaps reports it in Lyon county, where I took these photos. A rosette forms in the first year and the second year the plant will bolt and form a flower heads. The plant is solitary and does not spread vegetatively. The stems and leaves have spines. The flowers are white to pink or purple with spine tipped bracts at the covering the receptical, or base, of the flower. The flower heads often “nod” with the stem bending and the head tilting over to one side. Carduus species can hybridize, so morphological characteristics vary.

Musk Thistle Flower

Musk Thistle Flower

Musk Thistle

Musk Thistle Rosette

Confirm your identification prior to treating an area. Native thistles can appear very similar to musk thistle, but pose no environmental or economic threat in agricultural, grazing or natural areas.

To control musk thistle, it is best to remove the plant in the first year, when it is a rosette and has not flowered. The tufted seeds spread easily with wind. Thistles only reproduces from seed, so mechanical control can be very effective. Mechanical control is most effective when the tap root is disturbed and destroyed. Once the plant goes to seed, the area will need to be monitored every year and any rosettes destroyed. Seeds readily germinate in disturbed soil, so plan mechanical controls in the spring prior to flowering from June to September.

Musk Thistle with "Nodding" Flower Heads

Musk Thistle with “Nodding” Flower Heads

Biological control agents have been released for this weed in Nevada, but are no longer available for distribution and release. If you have a large contiguous patch, where other controls are not an option, you can monitor for the biological control agents by looking for the larvae in the root crown or seed heads. The spines and the detestable flavor of the plant prevent grazing by most animals, so control by grazing is not effective.

This time of year, the plants will have already gone to seed. If you notice the remainder of the plants, mark the location and plan to revisit the area in the spring to scout for rosettes. Prevention of further establishment is key to preventing this noxious weed from causing economic or environmental harm.

Peach leaf showing "shot hole" damage

Peach leaf showing “shot hole” damage

Advanced shot hole damage showing how the disease damage progresses

Advanced shot hole damage showing how the disease damage progresses

Our office has been buzzing with calls regarding problems with trees. These problems have been as varied as aphid infestations, browned leaves, holes in leaves and trees with 20-30% of their leaves turning yellow and falling off. All of these problems are caused by one thing: the unusually cool, wet weather followed by a couple of hot, dry weeks.

Fruit trees in our area have been hit the hardest. First, there were the series of frosts after several warm snaps this spring, leaving most people without any fruit on their trees. Next, it has been unusually wet – excessive rains have caused flooding and road wash outs throughout Lyon county. Cool, moist days have increased the incident of fugal and bacterial pathogens, especially in fruit trees. Normally, these pathogens are latent in our area and only appear when trees are irrigated

Leaf scorch on a redmond lindon tree leaves

Leaf scorch on a redmond lindon tree leaves

with a sprinkler system. All of the rain created the same situation.

We have seen many peach trees with shot-hole, a symptom of a fungal disease caused by Wilsonomyces carpophilus. Bacterial leaf scorch bacteria, Xylella fastidiosa, is very wide spread and can infect plants in many plant families. Non-bacterial leaf

Apricot leaf with mild leaf scorch damage that can appear to be similar to shot hole damage

Apricot leaf with mild leaf scorch damage that can appear to be similar to shot hole damage

scorch occurs when the plant cannot take up enough water to compensate for transpiration leaf drying/browning or leaf die-back. It can be caused by not enough water in leaves or soil, fungi or bacteria clogging the plants vascular system, or damage to the roots including rotting because of too much or not enough water. Sometimes there is sufficient water in the soil but the plant cannot take up enough because of salinity or clay in our soils which inhibits water absorption or if roots have not expanded sufficiently to compensate for the sudden new growth from additional moisture then unusually dry hot weather. Signs of root scorch include browning on the edges of leaf and the leaf surface between leaf veins. As long as it is not severe enough to cause significant leaf die-back and over watering does not occur, though unsightly, the plant usually recovers. At times, shot-hole signs can be confused with leaf scorch. If in doubt, email us pictures or bring samples to our office. Proper diagnosis of a plant problem is the first step to planning plant recovery. While there are some treatments for shot-hole, planting varieties which have natural resistance and properly watering are usually the best tools for the home orchards.

Young apricot tree with branch tips damaged by high aphid density and leaf scorch

Young apricot tree with branch tips damaged by high aphid density and leaf scorch

Aphids have also enjoyed this cool wet weather, which has created ideal environmental conditions for a longer period of time. New growth on trees is often the most susceptible. Aphids can vector plant viruses and cause the plant to be covered in sap, which can be unsightly or a nuisance. For the home gardener, most aphid problems will go away in a few weeks when the conditions are too hot or dry. Aphid populations can be decreased by spraying with a strong stream of water or by placing sticky tape around the base of the plant to trap the ants which herd aphids like tiny cows.

Robed locus canopy with yellow leaves caused by heat stress

Robed locus canopy with yellow leaves caused by heat stress

In my yard is a purple robed locust which responded well to all the rain, blossoming several times and putting out new growth. Then the heat wave hit. Almost 50% of the leaves on my tree turned yellow and fell off. Marcia has helped me resolve other problems with this tree, so I was afraid it was struggling from a split in the trunk it suffered 2 years ago. When I asked about it, we decided to go look in our water wise arboretum at the robed locust there. It was also shedding leaves, but only about 25%. The heat was much harder on my damaged tree than the healthy one at the office.

By Joy Paterson and Marcia Moffitt

Joy Paterson assists Ray Johnson in releasing bindweed mites into a patch of bindweed

Joy Paterson assists Ray Johnson in releasing bindweed mites into a patch of bindweed

Never heard of bindweed? It is a vining plant with white and pink flowers. Field Bindweed has an expansive rhizome network underground where the plant can reestablish after mechanical or chemical treatments. The weed is not a common weed problem to have in Nevada, however, it is a common contaminant in seed and can cause economic loss and out-compete desirable vegetation once established. Ray and Virginia Johnson with Custom Gardens understand this all too well.
They contacted the University of Nevada Cooperative Extension to obtain information about biological control of bindweed. We directed them to our recent update of “Biological Control Options for Invasive Weeds in Nevada”. Ray and Virginia contact Nevada Department of Agriculture, who did not currently have a program for biological control of bindweed.

Ray with marked releases of bindweed mite

Ray with marked releases of bindweed mite

After contacting USDA-APHIS and obtained the necessary permits, they have received two species, a moth and a mite, with two releases of mites and one release of moths.
I was able to come out and help them with one of the mite releases. Ray and Virginia understand that biological control efforts require years if effort to control, so this is a fight that they will continue over the next few years. We are working together to find additional agent sources and I will stop back by this fall to check for establishment.