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Unusual disease and insect problems in an oh so odd fall season

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By William Johnson

THE PREVAILING topics of horticulture-related e-mails and phone calls I receive in any given week are reliable barometers for issues that many gardeners across the county are likely to be dealing with.
Brown patch
disease in lawns
Over the past two weeks, I’ve received numerous inquiries about problems with lawns. Many concerned the appearance of small to large spots that were noticeably discolored.
One e-mail asked: “What are all of the brown dead spots in my lawn? I see them all over the neighborhood.”
While lawn grasses can suffer from several diseases, the most likely problem at this time of year is commonly known as brown patch, caused by a fungal pathogen known as rhizoctonia solani. Typically, homeowners do not start noticing the spots until they reach several inches in diameter.

Gardening Asp caterpillar                                                 William Johnson

Many county residents have reported higher than usual populations of asp caterpillars. While most caterpillars do not sting, several species that do, including asp caterpillars, are found in our region.

Diseased areas expand during the moderate temperatures of fall and can reach a diameter of eight feet or wider under favorable conditions.
Descriptions typically make reference to the blades of grass along the outer edge of such spots being yellow or yellowish orange in color. As the fungal pathogen grows outward, it colonizes healthy blades, which turn yellow. As the infection continues, blades are killed and turn brown – hence the common name given to the disease.
The combination of fairly warm temperatures and ample rainfall this fall has provided unusually favorable conditions for brown patch to thrive. It is most problematic on St Augustine lawns but it also occurs on Bermuda and zoysia lawns.
Homeowners generally want to know if they should apply a fungicide to treat brown patch. Although it does not usually kill the grass, it will cause the leaves to slough off and make for a thin area in the lawn where weeds can get a stronghold.
Infected spots will typically produce new growth in spring. Given the cool temperatures last weekend, lawn growth will slow down and so will development of the disease.
I recommend not spraying at this time of the year. However, if your grass has brown-patch disease, the probability is high that the disease will reappear next fall. I recommend delaying treatment for brown patch until late next summer after daytime temperatures first drop into the upper eighties.
At that time, apply a fungicide to the entire lawn before disease symptoms occur. Fungicides that have results against brown patch include the active ingredients myclobutanil (such as Spectracide’s Immunox lawn disease control), propiconazole (Ortho’s lawn disease control), thiophanate-methyl (Scotts’ lawn fungus control) or triadimeton (Bayer’s advanced fungus control for lawns). Follow the application rates provided on the fungicide label’s directions.
Asp caterpillars
Another common inquiry was about high local populations of insects commonly called asp caterpillars.
One e-mail said: “Why are asp caterpillars so abundant in Galveston this year? I have lived here for 25 years and this is the first that I’ve heard of them. I was recently stung by one and it was a nightmare. The pain kept me up all night.”
Coincidentally, I was surprised to find a small asp caterpillar on the sill of an entrance door to the AgriLife Extension office.
While most caterpillars encountered in the home landscape do not sting, several species that do, including asp caterpillars, are found in our region. Stinging caterpillars have stiff poisonous hairs or spines connected to poison glands. When a person comes into contact with the spines, they break and venom is released.
Reaction to this venom varies from mild to severe. Small children and the elderly can suffer severe reactions.
Injury from such caterpillars is most common among children playing in yards and trees. Asp caterpillars are also known as puss caterpillars because of their resemblance to cuddly house cats.
Insecticides that provide good control of asp caterpillars include spinosad as an active ingredient (such as Green Light’s lawn and garden spray or Monterey’s garden insect spray).
William Johnson is a horticulturist with the Galveston County office of Texas A&M AgriLife Extension Service. Visit his website at aggie-horticulture.tamu.edu/galveston/index.htm

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