Q&A With Seth Nagy: Mosquito Larvae, Weeds, Fertilizer

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This week I want to share three questions we received at the N.C. Cooperative Extension, Caldwell County Center. I hope you find these questions and their answers helpful.

Question: Is there something I can use to control mosquito larvae? I have a wet area in my backyard that is about 5 feet by 15 feet. The area is about 2 feet deep and full of frogs & tadpoles.

Answer: There is a product called Mosquito Dunks. They are round donut-shaped tablets that have the spores of the bacteria Bacillus thuringiensis subspecies israelensis as the active ingredient. This is a naturally occurring bacterium that is toxic to larvae of mosquitoes, blackflies, and fungus gnats.

Although Mosquito Dunks will control mosquito larvae, I would check to be sure there are actually mosquito larvae in your wet area. Tadpoles are very good predators of mosquito larvae as long as the tadpoles can catch the larvae. Trash or debris in the water gives the mosquito larvae a hiding place.

Also, check around your home for stopped up rain gutters, flowerpot saucers, old tires, which are all great places to hold water. Anything that holds water is a potential habitat for mosquitoes to develop. Drain or empty the water, and mosquitoes will not develop.

Certainly, Mosquito Dunks are a very unique and effective product. This product is very safe for humans, the environment, and companion animals. However, it is best to always read and follow the labeled directions.

Question: What is this weed? It’s growing in my pasture near the creek.



Pennsylvania smartweed can grow in crop fields, gardens, and pastures. It likes wetter areas. Cattle typically graze this weed when it is in the pasture and they can get to it. (credit John Cothren)

Answer: This is Pennsylvania smartweed. This weed can be found growing in landscapes,  agronomic crops, and nurseries. It loves wet areas. In pastures, cattle will readily graze it as long as they can get to it. If control is needed, any of the common broadleaf pasture herbicides,  such as WeedMaster, 2,4-D, or Banvel, will control it.

Question: How much fertilizer should I put on my pasture this fall?

Answer: Allison Brown, Alexander County Livestock Extension Agent, wrote a great answer to this question about fall fertilization on tall fescue pastures. I have included it below.

Recently, studies have been done to see how efficient fertilizer applications are on fescue fields that have been set aside to stockpile for winter grazing. In the past, recommendations have been between 60 and 80 lbs of nitrogen. In 2018 – 2019, Dr. Alan Franzluebbers conducted 30 trials across NC in known fescue areas to see if this was an accurate and cost-effective recommendation.

One of those trials was conducted on my farm in Hiddenite. Forage was collected, weighed, and sampled. A comprehensive soil test was completed, as well as a complete nutritional analysis on the forage.

The results showed that the forage yield responded to a small dose of nitrogen fertilizer. The break-even price ratio was assumed from $200/ton of hay and $.50/lb of N fertilizer. My bulk cost of urea this year averaged around $.45/lb of N fertilizer or $21.00 / acre. Of course, this does not include costs of application or labor. Essentially, applying 40 lbs N/ acre in the fall would be sufficient and economical enough to provide growth for stockpiling fescue for winter grazing.

This study also analyzed Total Organic Carbon and Soil Microbial Biomass Carbon. The hopes are that through, rotational grazing and better soil management, we can greatly reduce the total amounts of fertilizer needed in the future by improving our organic matter in the soils.

We still have some work to do on our land, but it is improving. In the beef business, we have to look at all input costs, and fertilizer can be a major one. Overgrazed and continuously grazed pastures will likely not have adequate amounts of organic matter to provide the forage growth you need for your cattle.

Cattle grazing stockpiled fescue. Farmers that have soils with higher organic matter can likely reduce nitrogen applications and still produce high yields in the fall.

Cattle grazing stockpiled fescue. Farmers that have soils with higher organic matter can likely reduce nitrogen applications and still produce high yields in the fall.

For answers to your agricultural questions, call the N.C. Cooperative Extension, Caldwell County Center at 828-757-1290, or visit us online. Cooperative Extension is open to everyone. We strive to provide research-based and unbiased information.