Roots, Shoots, Fruits & Flowers: Corn Earworms, Leaf Smut, Live Oak Leaves, Systemic Insecticides, & Tree-of-Heaven

E. Lavone Boyd, Hawkins, Keith

Corn earworm.

Figure 1 Corn earworm. photo University of Florida

Susie in Vernon Parish is having problems with corn borers and ear worms on her corn. The seed packet suggests using Bacillus thuringiensis, but she doesn’t know what that is.

Bacillus thuringiensisis a pathogen of caterpillars and considered an organic treatment for these pests. Bacillus thuringiensis is the active ingredient of products like Dipel, Thuricide and other similar organic insecticides. The reason it is safe for people and pets is because the stomach chemistry of people and pets is acidic, and Bacillus thuringiensis would not survive. However, the stomach chemistry of caterpillars is alkaline, ideal for Bacillus thuringiensis to thrive. Bacillus thuringiensis will also treat other caterpillars on other vegetables and on ornamental plants.

Leaf smut on grass.

Figure 2 Leaf smut on grass. Photo Ryland Dunnehoo

Ryland sent in a question and was straight to the point, “What is this please, sir?”

Ryland has the spores of leaf smut . The good news is that a water hosepipe can rinse the spores off. According to the Texas Plant Disease Diagnostic Clinic, “Smut diseases are favored by high nitrogen fertility. Reducing drought stress through proper irrigation practices will help to reduce smut injury. Proper and consistent mowing practices will also reduce incidences of smut, particularly on loose smut that affects the inflorescence. A healthy and vigorous lawn is less likely to get the disease. Chemical treatment is not warranted but there are homeowner [fungicides] available. Please refer to the label for precautions and proper usage.”

Live oak.

Figure 3 Live oak. photo LSU School of Renewable Natural Resources

Margie shares a concern about her landscape trees, “I’m just wondering if you have an answer to why our live oak trees are losing brown leaves now? It looks like what they usually do in January.... I need to rake leaves...!”

A blogger with Davey Tree Expert Company wrote a narrative explaining leaf drop, “Find out what type of oak tree you have. Live oaks naturally shed leaves in summer, so if the leaves are green and healthy, there's no need to worry!

But if the fallen leaves are discolored or look unhealthy, that could mean a pest or disease. Oak wilt is a common one. First, leaves turn yellow, then brown right before they fall off starting at the top of the tree. These symptoms call for an arborist.

If there are no disease symptoms on your oak, investigate other possible causes, like the tree's moisture level.”

Honeybee collecting pollen from a pink rose.

Figure 4 Honeybee collecting pollen from a pink rose. Photo

Joe, a Master Gardener, sent this question about a specific pesticide, “This product is for roses, [and] it has systemic insecticide in it. Also, there are systemic insecticides that I use for flowering plants, will this stuff affect bees and other pollinators? They don’t eat the plant but [ is it safe for them?]”. A systemic insecticide goes into the plant through its roots. For example, a dry granular insecticide must be watered to enable plant roots to take up the insecticide. Another method for treating systemically is to apply a liquid soil drench poured around the base of the plant.

Area Horticulture Agentdid a little research about the product in question and replied, “The active ingredient in this product is highly toxic to bees by direct exposure.

However, the exposure by pollen is 6 parts per billion of that active ingredient. Here are some analogies for parts per billion:

1 silver dollar in a roll stretching from Detroit to Salt Lake City;

1 sheet in a roll of toilet paper stretching from New York to London;

1 second in nearly 32 years.

The bottom line is that it’s ok use this product without lethal concern for the pollinators.” However, there are unanswered questions about sub-lethal effects of systemic insecticides on pollinators, and those questions are under examination by various universities and agencies. The good news is that if honeybees survived the bad old days of Dichlorodiphenyltrichloroethane, commonly known as DDT,then they will probably adapt to our modern conditions today.

Tree-of-heaven, a noxious tree

Figure 5 Tree-of-heaven, a noxious tree. Photo Justin Landrum.

Justin, a beekeeper from Anacoco, emailed Area Horticulture Agentwith this question, “Can you help me identify this tree? It’s about 10’ and had a few pollinators on it today. [This is the] first time that I have noticed it. It’s in a wild area and not planted.”

The easy answer is “tree-of-heaven”, and it is a noxious weedy tree. This tree is also a prolific seed producer and can make dense stands that displace desirable vegetation. For beekeepers, the honey from tree-of-heaven is “skunky”.

Area Horticulture Agenthad first-hand experience with these fast-growing trees at his parents’ home in Virginia. Area Horticulture Agentused an old US Army forklift and chains to yank these trees out of the ground, and this treatment was largely successful. Cutting the stems tends to be an exercise in futility, and the stump sprouts again readily. Herbicides can be successful if applications are timely and persistent.

If you want to contact Roots, Shoots, Fruits and Flowers, please send your questions and pictures to Keith Hawkins, Area Horticulture Agent (AHA), 337-463-7006 or Also, you can be on the “green thumbs” email list by emailing your request to the address above.

“This work has been supported, in part, by the USDA National Institute of Food and Agriculture, Renewable Resources Extension Act Award, Accession Number 1011417.”

9/13/2019 3:14:59 PM
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