Make sure dwarf mistletoe doesn’t kiss tree goodbye

Love your column! The other day my husband and I noticed some mistletoe-looking stuff on our pinyon. Very unattractive stuff — did not inspire any kissing. I know it’s not mistletoe because it’s too dry here, but it was that same texture in a very bronzy green. Is this harmful to the pinyon tree?

— Bess

Actually, I think you have another kind of mistletoe called dwarf mistletoe in your pinyon. Mistletoe is a parasitic plant that derives the nutrients and/or water it needs from a host plant. The seeds are ejected from the plant onto other plants or spread by birds. The seed germinates and it sends root-like structures into the stem of the host plant where it can suck up the necessities it needs from the host.

There are two types of mistletoe: dwarf mistletoe and leafy mistletoe. Leafy mistletoe is what people put up at Christmas time. It has thick, leathery, olive green leaves. These types of mistletoe generally only occur on deciduous trees. There’s only one that occurs in Colorado and that’s only down in the southwest corner of the state and down into New Mexico. Leafy type mistletoe generally steals only water from the host, and though there can be some stunting or distortion of growth, there’s usually no significant damage to the host.

Unfortunately, dwarf mistletoe is a different critter. This type of mistletoe usually only occurs on conifers. Not only does it take water from the host, but also all the nutrients it needs. Dwarf mistletoe is usually yellow, brown or orange in color and cannot photosynthesize. It therefore cannot make the “stuff” it needs the way most plants do (including leafy mistletoe) and instead steals them from the host. There is more stunting of growth and even die-back of the host in severe cases. Though it can take some years, left alone, dwarf mistletoe will usually significantly disfigure a plant and make it susceptible to attack by bark beetles and other problems that can kill the tree.

The best treatment is to prune out any branches that have mistletoe growing on them. Try to cut 12 inches below where the mistletoe is sprouting out of the branch. Obviously, this treatment is best early on when the mistletoe is small. The larger it is and the more of them, the more you have to cut out of your pinyon. Not only does it make the tree look bad, but it’s stressful as well. The general recommendation is that you never want to remove more than 50 or 60 percent of the canopy when pruning. I’m even a little uncomfortable with that amount of pruning, but if it’s necessary, do it. Keep an eye on the tree and cut out any mistletoe you see sprouting as soon as possible.

Sometimes people just cut off the mistletoe where it’s sprouting from the stem. You can do that, but it will grow back. If there is no other alternative (especially in cases where the mistletoe is sprouting from the trunk of the tree), it helps slow down the problem. This is kind of a band-aid approach in that it will not cure the problem, just slow it down. If the tree is just riddled with mistletoe or is showing some significant die-back, I’d consider removing the tree.

An alternative to pruning is to spray the mistletoe with a product called Florel. We sell this product primarily to reduce unwanted fruit in trees but it can help to contain mistletoe. You want to spray only the individual bunches of mistletoe, not the entire tree. This product will not completely kill the mistletoe, just slow it down, but it should be about four years before you will have to treat the tree again. For dwarf mistletoe, apply it in early summer prior to seed dispersal.

The only good news in this is that dwarf mistletoe tends to be pretty host specific. That means that this species you have on your pinyon will pretty much only parasitize other pinyon. If you have other conifer evergreens in your yard, even other species of pine, they are probably not at risk. Hope this all helps.

Dennis Hill is the nursery manager at Bookcliff Gardens, bookcliffgardens.com. Send questions to Bookcliff Gardens, 755 26 Road, Grand Junction 81506; or email .(JavaScript must be enabled to view this email address).


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