Fighting the parasite known as mistletoe

Published 12:00 pm Sunday, February 16, 2014

Last week I made it easy on myself by giving this week’s topic in advance. I said I’d share information about a chemical that can be used to help control mistletoe. Being forthright and upfront here, rare would be the case where using the stuff on mistletoe is doable, practical and successful. But I have used it myself on young ash trees for three years running and my jury is still out.
The chemical is ethephon. It is not an herbicide, but rather a plant growth regulator that works like an artificial hormone. Ethephon has several uses and the mistletoe gig is just an add-on minor one first toyed with at Texas A&M. But it is labeled for mistletoe, meaning it is legal. Its main uses include preventing unwanted fruit on ornamental trees such as flowering peach, Bradford pear and others raised for pretty blooms but not edible fruit. In the commercial apple business, ethephon is sometimes applied at just the right time and right rate to thin out an overcrowded fruit set, but just on certain varieties. It is also sometimes useful on tomatoes to hurry ripening before a hard freeze. In our corner of the world, ethephon is applied to cotton late in the season to get a uniform maturing and opening of bolls so the crop can be harvested in just one trip with super expensive equipment.
In its numerous normal uses, ethephon works by producing ethylene within the plants. Ethylene is naturally produced when plants are under a severe stress such as drought. The ethylene signals plants to get in the survival mode and quit spending energy on the slow reproductive mode. So blooms fall off and existing fruit, such as tomatoes and cotton, ripen faster.
Researchers at A&M found that ethephon causes abscission of the stem of mistletoe. That means the correct concentration, amount and timing can cause mistletoe to fall from a tree. However, it does not kill the mistletoe roots inside tree limbs. Keeping the mistletoe out long enough would cause those roots to eventually starve. I’ve noted that my February treatments results in greenish-blackish mistletoe falling to the ground in late spring and summer.
The most common trade name for ethephon for home use is Florel Fruit Eliminator. For mistletoe on deciduous trees, spray the mistletoe only when leaves are off the tree but only when the temperature is 65 degrees or higher. That means watching the weather forecast for those few opportunities in early winter or now through late March. As for plants underneath trees to be treated, I used to spread plastic over the ground, but not anymore. My only plants subject to dripping solution are dormant bermudagrass and late winter liriope, also known as big monkey grass. Neither seems to care about wintertime hormones.
Trying to treat mistletoe in large trees with ethephon is just not practical. For young front yard trees like mine, I’m okay with going up the ladder with the pump-up sprayer on one sunny winter day per year for several years.

Terry Rector writes for the Warren County Soil and Water Conservation District, 601-636-7679 ext. 3.

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