Penn State Extension Service Newsletter for the Week of June 18, 2018 Poison Hemlock Becomes More Abundant in Pennsylvania

Poison Hemlock, Conium Maculatum, is becoming more abundant around the Pennsylvania countryside. The plant is extremely poisonous to humans and livestock. Photo by John Cardina, Tim Abbey, Penn State Extension, Horticulture, Green Industry Poison hemlock (Conium maculatum) appears to have become more abundant over the past few years. It is typically seen along roadsides, fallow areas, fence rows, pastures, and creeks. Touching this plant has caused skin irritation for some people, and is also toxic if ingested by livestock and humans. Therefore, it is important to be able to identify and control this weed.

Poison hemlock is closely related to wild carrot (also called Queen Anne’s lace). It has white flowers and lacy leaves similar to wild carrot. However, it is a larger plant, growing to 4 to 6 feet tall when mature. The stems of poison hemlock have purple spots and are hollow and hairless. The whole plant has a musty smell.

This plant is a biennial, which means the first year of growth ends with a low growing (basal) rosette of foliage. During the second year, the stem, branches and flowers are produced. Poison hemlock can reach up to six feet in height. The white flowers are produced throughout the summer from June into August. Individual flowers are small but clustered in an umbrella-like grouping, which makes them noticeable. The plants overall appearance resembles carrot and parsley.

As the plant puts on vertical growth, the stem develops purple spots, which are very distinctive. This plant is not only a landscape weed, and sometimes along the banks of water bodies and in meadows. It also has some health issues that should be kept in mind. All parts of poison hemlock are toxic to humans and other animals. The roots and seeds contain the highest concentration of alkaloids.

Poison hemlock has a long tap root (10 inches) and extensive fibrous roots. Hand removal is difficult because of the tough root system and the fact that the plant sap is, along with being toxic, a skin irritant. Even the use of weed trimmers needs to be conducted using precautions so that plant material doesn't come into contact with the body. There are no pre-emergent herbicides to use against poison hemlock in ornamental settings. Post-emergents include: diquat, pelargonic acid, glyphosate (all are non-selective), and 2,4-D. The most effective approach is to treat the first year rosettes and not the larger, mature plant.

If the poison hemlock plants are more mature and in their second year of growth, the best option is to mow when the plant is in late flower. This will set the plant back, prevent seed production, and possibly control it. (The preceeding article has been carried over as a reference for those concerned about this noxious plant species; the following is the Penn State Extension Service newsletter for the week of June 18, 2018)

Penn State Franklin County Extension Master Gardener Program Accepting Applications - The 2018-2019 Training Class will meet on Wednesday evenings from 6:00-8:30 p.m. beginning September 5, 2018 through February 27, 2019. There is a $225 program fee to cover the cost of training materials and expenses. Applications are being accepted through July 31, 2018. For more information or to obtain an application, please email Donna Scherer, Franklin County Master Gardener Coordinator, at or call 717-263-9226. Information can also be found online at the Penn State Extension website:

Margin Protection Program (MPP) for Dairy – The deadline to apply for federal funding has been extended until June 22, 2018. The new and improved program protects participating dairy producers when the margin – the difference between the price of milk and feed costs – falls below levels of protection selected by the applicant. To learn more about the Margin Protection Program for dairy, contact your local USDA Farm Service Agency county office at or call 717-264-8074.

Debunking Myths Related to Mosquito Control

Donna Scherer, Penn State Extension Educator

Mosquito Borne Disease Control Coordinator, Franklin County

Most people agree with the statement that mosquitos are a pest. However, many different opinions exist about how to control those pests, mainly because not everyone is basing their opinion on fact. Social media is full of suggestions for preventing mosquitos from becoming a pest at your next outdoor event, but few ideas are actually effective. Knowing a few facts about mosquitos will aid in debunking some of these myths being circulated.

Mosquito Biology

Mosquitos have four stages of development: egg, larva, pupa and adult. The egg, larva and pupa all require a water source to complete this life cycle. Both female and male mosquitos feed on pollen and nectar. However, only females bite as they need protein to lay eggs. Adult female mosquitos lay eggs on the water surface or edge of containers with nutrient rich water. One female can lay as many as 300 eggs at a time. These eggs can dry out and, when rehydrated, can complete their lifecycle in as little as four days. There are 29 known species of mosquitos in Franklin County, Pennsylvania. However, only a few of these species actually bite humans and have the potential to carry mosquito-borne diseases to humans.

Mosquito Habitat

Mosquito eggs need warm temperatures to hatch into larva. These larva feed on debris in standing water. They breathe through a syphon and need oxygen. Artificial water sources don’t support an ecosystem and are perfect for breeding mosquitos. Areas to check in your backyard are trash cans, recycling containers, corrugated drain pipe, gutters, tarps, kiddie pools, tires, bird baths, rain barrels, fountains and any item that collects water. Dumping the water every four days will keep the larva from developing into pupa and then adult mosquitos. Water that can’t be dumped can be treated with Mosquito Dunks that have the active ingredient BTi- Bacillus Thuringiensis. 

Prevent Mosquitos from Biting

Female mosquitos seeking a blood meal are searching for carbon dioxide, scent, and heat to find you. Aedes alpobictus are mainly daytime biters and will be out early in the day while most Culex mosquitos are evening biters. Both have the potential to carry mosquito-borne diseases to humans. Wear insect repellent with the active ingredient of DEET, Picardin, Icardin or Oil of Eucalyptus. These are registered with the EPA and FDA. Treating clothing with Permethrin is another way to prevent mosquitos from landing on you and biting.

Mosquitos are not strong flyers at outdoor events, so place a fan to create a cross breeze where you are sitting. Citronella candles, mosquito lamps and butane devices also repel mosquitos in small areas only where the vapor from these items reaches.

Debunking Myths

The amount of misinformation about preventing mosquitos in the media is disheartening as mosquitos have the potential to carry diseases and should be taken seriously. The following are the top seven myths that many in mosquito control hear and see on social media.

Myth One: Plants will repel mosquitos

Planting herbs into your landscape will not repel mosquitos. The list usually includes mints, rosemary, basil and lemon balm. Unfortunately, these plants do not provide any repellent. Essential oils could be distilled from these plants and made into an herbal repellent but that requires distilling the oils from large quantities of plant material on a commercial scale.

Myth 2: Bats control mosquitos

Evidence from stomach and feces samples show that bats feed on beetles, wasp, ants, flies, stoneflies, mayflies, moths, and grasshoppers. Less than 1% of a bat’s diet contains mosquitos.

Myth 3: Purple Martins control mosquitos

A study taken out of context postulated that a purple martin would need to eat its body weight in mosquitos to survive. That totals about 14,000 insects every day. Like bats, purple martins prefer other insects including dragon flies. Less than 3% of a purple martin’s diet contains mosquitos.

Myth 4: Bug Zappers control mosquitos

The American Entomological Society states: “Our survey of insects electrocuted during routine use of electric insect traps revealed only 31 mosquitos of the 13,789 total insects counted…The heavy toll on non-target insects and the near absence of mosquitos in catches suggests that electric insect traps are worthless for mosquito reduction and probably are counterproductive.”

Myth 5: Listerine concoctions repel or kill mosquitos

Leaving out containers of Listerine mixtures will not attract and kill mosquitos. The confusion comes from the ingredient eucalyptol. In repellents, the percentage of eucalyptol is 75%. However, in mouth wash, only 1% eucalyptol is an ingredient.

Myth 6: Ultrasonic Devices control mosquitos

The selling claim to these products is that they mimic the wing beat of a male mosquito or of dragonflies causing the female mosquito to flee. Unfortunately, female mosquitos did not respond to these ultrasonic devices in lab tests.

Myth 7: Dryer Sheets repel mosquitos

There are no studies that prove that dryer sheets repel mosquitos. A study conducted in 2010 and recently published on social media was actually carried out on fungal gnats[1]. The researchers tested the repellency of the dryer sheets in a very controlled situation and were successful at reducing the number of fungus gnats in test chambers containing a dryer sheet. However, there is a very large difference between fungal gnats and mosquitos. Fungal gnats do not bite; they are generally just an annoyance. On the other hand, mosquitos do bite and can carry harmful human diseases.

In summary, it pays to be diligent in researching the facts. The World Health Organization reports that the mosquito is the deadliest animal in the world, responsible for approximately 725,000 human deaths per year worldwide. Methods used to protect ourselves from this threat should be based on fact, not fiction. To protect yourself and your family, remember these three points:

  • Dump all standing water.
  • Treat any standing water that cannot be dumped, with a BTi product.
  • Wear insect repellent that has been tested and proven effective.


For more information about mosquitos and the diseases they carry, check the Center for Disease Control website,


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