Homegrown: Deer damage
Our four mugo pines at the entry to our home in Battlement Mesa (elevation 5,500 feet) for the past year are showing progressive browning off of needles partly because of deer damage, particularly this past season. I have tried a number of changes in watering and insect control to no avail. Your advice would be appreciated.
There are several possibilities that come to mind that might be causing the browning you’re seeing. You’ve mentioned two of them: watering and deer damage.
Watering issues are probably the most common reason for what you’re seeing. Either too much or too little can cause problems in any plant.
You’ve probably covered all the bases, but I’ll mention it just for the record that the best thing to do is some digging down and checking the soil moisture to make sure that things are OK there. We make lots of assumptions about how much water a plant does or doesn’t get but until you get into the soil, you really can’t be sure.
Make sure that the soil is soaked deeply and completely when you do water. I like to see saturated soil 12- to 18-inches deep after watering.
Then, you need to allow the soil to dry out just a bit before soaking it again. You see, the roots of plants need two things: water, which we all know about, and oxygen.
Obviously, not watering often enough will hurt the plant but watering too much is just as harmful because the roots in a constantly wet soil can’t breathe.
One thing to add about watering is that plants, especially conifers, are “slow movers.” What I mean by that is, if you do discover a problem with the watering the plant received and correct it, the plant will take several months, even a year or two before it starts to look better. Just be patient.
The second thing that may be going on is the deer feeding you mentioned.
The browning isn’t directly due to their feeding. It has more to do with how pines grow. Pines rarely form buds along their stems. Almost all of their buds are at the tips of the branches.
When deer feed, they’ll eat the stem part of the way, removing all of the terminal growth and buds. The stub they leave has green needles on it but eventually, those needles will naturally brown and fall off as time goes by and that stub will die.
Repeated feeding in time will result in a portion of the plant that’s bare of any green growth.
I’m afraid I don’t have any miracle cures for keeping deer away. There are repellents that work most of the time. The best ones have “putrefied egg solids” as their main ingredient.
You’ll have to reapply them occasionally depending on the weather and any sprinkler water that gets on them. Other than that, the only sure-fire way to keep deer away from your plants is to install an 8-foot fence, which probably isn’t much of an option for you.
The last thing that may be causing problems is a little insect called needle scale. If your plant has this pest, when you look closely at the needles, you’ll see small black (occasionally white or gray) dots on them.
This insect sucks sap from the plant and their numbers can build up to a point where the needles start to brown and fall off. We’ve always had this little critter around here, but it’s been a bigger problem the past three or four years.
If you’re not sure needle scale is there, bring a sample by the nursery the next time you’re in town, and we can take a look.
There are insecticide treatments to control needle scale. The most effective is a couple of summer oil sprays in mid-May and early June.
Finally, it’s also possible that you have more than one thing going on, so check on all of these things.