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Preparing trees for winter checklist

A great summary of the steps needed to minimize winter injury to trees and decrease disease pressure, ensuring a great start to next year's growing season.

The following article was written by Aaron Bergdahl, Forest Health Specialist with the NDSU/North Dakota Forest Service.  It first appeared in the NDSU Extension Crop and Pest Report, September 12, 2013.

White ash - NDSU 2013

With the coming of fall it is important to remember to prepare your trees for the tough North Dakota winter. The following checklist serves as a reminder of the most important considerations for fall tree care and proper tree winterization.

  • Water trees weekly in late fall until freeze-up. Two gallons per inch of stem diameter is recommended, if the soil is dry at a depth of six inches. This will help minimize winter injury.
  • Rake up and remove/destroy fallen leaves. This is the best thing you can do to reduce the amount of fungal leaf disease next year because many fungal leaf diseases overwinter on leaf litter.
  • Prune dead wood to decrease overwintering sites for tree diseases and insect pests.
  • Wait until the tree is dormant (at least November) to prune living branches, always using proper technique.
  • Wrap the lower main stem of trees that have not developed thick bark to protect them from sunscald and rodent feeding damage.
  • Wrap burlap around smaller, high-value (landscape) conifers or set up a burlap sun/wind shield to help minimize the chances of winter burn.
  • Throughout winter, use caution when applying deicing products near trees and shrubs. Salts and other chemicals contained in some products may cause harm.

By completing this checklist you will be doing your part to maximize the chances that your trees will make it through the winter in good health and will be ready for a productive growing season.

For more information, please contact: Aaron Bergdahl, Forest Health Specialist, NDSU/North Dakota Forest Service. aaron.d.bergdahl@ndsu.edu (701) 231-5138

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Frosted apples

Apples will freeze at approximately 28°F. Use frosted apples quickly.

Frosted applesVery cold temperatures will sweep across the state tonight. Most apple cultivars freeze at approximately 28°F but can tolerate temperatures down to 25°F before suffering major damage.

If apples freeze on the tree, wait until they thaw before picking. Frozen fruits will bruise easily.

Frozen apples are edible, but will not store long. Eat or process the fruit quickly.  

Harvested apples should be kept cool (32–40°F is ideal). For small amounts, keep in perforated plastic bags in the refrigerator. For large amounts, the fruits can be stored in cardboard boxes.

Written by Tom Kalb, Extension Horticulturist. Photo was made available under a Creative Commons license specified by the photographer: Fredrik Alpstedt.

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Time to plant garlic

Plant garlic now and enjoy some amazing meals next summer!

Garlic clovesMost gardens in North Dakota have been struck by frost. The natural tendency for gardeners may be to slow down, but there is still some great gardening weather ahead of us!

Think about growing garlic. It can add amazing flavors to your meals next summer.

Garlic types include hardneck, softneck and elephant. Hardneck types are hardiest and most suitable for us in North Dakota.

Get your cloves from a local garden center or an online seed company. There are robust varieties from all over the world, including Europe, the Middle East and Asia. The bulbs come in an attractive array of colors from pearl white to royal purple.

Garlic scapesGarlic grows best in a rich, well-drained soil. Add an inch of compost to the site and up to 3 pounds of 10-10-10 per 100 square feet. Work this into the soil.

Separate cloves from the bulbs a day before planting. Set cloves upright in the furrow, 4–6 inches apart and 2 inches deep. Space rows 18–30 inches apart.

Water deeply to activate the bulbs. The bulbs will push out roots and underground shoots this fall. Mulch with 4 inches of straw in November. This straw will insulate the soil and protect the sprouted bulbs.

The flower buds, called scapes, can be harvested in June (see bottom photo). They are mild in flavor and great in stir fries.

Harvest the bulbs in July. Then get ready for some of the most delicious meals you have ever eaten!

Written by Tom Kalb, Extension Horticulturist, North Dakota State University. Photos were made available under Creative Commons licenses specified by the photographers: Felix and danbruell.

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Kill weeds now; feed lawn later

This is a great time to kill weeds but a bad time to feed the lawn.

Field bindweed in lawnNow is the best time of year to kill broadleaf weeds in lawns. This includes dandelions, thistles, clovers, black medic and field bindweed (shown). As days get shorter, these perennial weeds begin channeling their nutrients down into their roots to prepare for winter. This is great, because a herbicide sprayed on a weed at this time will be channeled down into the weed’s root system, killing the entire plant.

The most effective products include a combination of herbicides. Trimec formulations will include a combination of 2,4-D, mecoprop and dicamba. Dicamba is especially powerful, but the chemical can build up in the soil and damage trees, shrubs and perennials. Limit yourself to one application of dicamba per year; and now is the best time for it.

Now is not a good time to feed your lawn. The grass plants want to prepare themselves for winter. A fertilizer application now prevents this by promoting blade growth and delaying hardening. This makes the lawn more susceptible to winter injury.

It is better to wait until mid to late October to feed the lawn. This is after the grass blades stop growing and after you have stopped mowing. This application in October is the single most valuable time to fertilize the lawn—any lawn.

You will not see any immediate effects of this dormant application, but the fertilizer will develop a stronger root system this fall and generate new buds for blade growth next spring. Turf roots grow until the ground freezes in mid November.

Written by Tom Kalb, Extension Horticulturist, North Dakota State University. The photo was made available under a Creative Commons license specified by the photographer: Colin Jacobs.

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Normal fall needle drop in conifers

Conifers - pines, spruces and others - sometimes lose older needles during the fall. This is normal, and does not indicate a pest problem.

During autumn, deciduous trees like green ash and linden change color and lose their leaves. This is normal and expected. It happens every year and people are used to it. When evergreen needles turn brown and die, it’s definitely unexpected, but not necessarily abnormal. 

There are several species of evergreens or conifers that grow in North Dakota. Pines and spruces are most common. Pines have relatively long needles (two to nine inches), which are held in clusters called fascicles. These needles live for two to seven years and then die and drop during the fall. These are the older needles toward the center of the tree. Needles that are going to drop start turning yellow as early as late August. By mid-September these needles turn brown and begin falling from the tree.

Another common group of conifers are the spruces such as Colorado blue spruce and Black Hills spruce. These trees have shorter needles, about three-quarter to an inch long, and are attached to the stem individually, not in bundles. Spruce needles usually live longer than pine needles and may persist for up to 10 years. Just like pines, those spruce needles which are older and more shaded, will turn color and drop during autumn. In the photo, the ponderosa pine (background) is showing normal fall coloration, while the Colorado blue spruce (foreground) is not shedding any of its needles.

Ponderosa pine tree (background) that is showing normal fall needle drop.  Colorado blue spruce (foreground) is not shedding needles in this photo.

Some needle drop by conifers during the fall is normal. The exception occurs with larch trees (also called tamarack). Larch trees lose all of their needles every year because they are deciduous evergreens. Larch needles are one to two inches long and borne in clusters on short shoots or individually on long shoots. The needles are also very soft. Some larch trees are native to the swamps and bogs of northern Minnesota. A common larch that has been widely planted in North Dakota is the Siberian larch. Larch needles turn bright yellow and provide a golden rain during autumn.

Evergreen needles don’t last forever. Some needle loss toward the center of the tree during autumn is normal. Needle loss at other times of the year is not normal and may be due to an insect or fungal pest or the result of severe environmental stress. Larch trees, the exception to the rule, lose all of their needles every year. Enjoy the colors this fall.

-Joe Zeleznik

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Frost warning

The first frost may strike tonight. Be prepared!

Frozen tomato. Photo by Joshua Heyer.Frost may strike parts of our state on Friday morning. This is terrible news—it’s way too early!

This frost might be the end of a disappointing year for many crops. The season started poorly this year due to a cold spring. Most gardens were planted later than usual and never caught up.

As of today, crops in most of our state are a week or two behind. The last thing we need is an early frost.

We cannot stop Jack Frost from coming, but we can be ready for him.

Our first frost is usually a light one (29–32°F). In this case, we can protect our sensitive plants with a blanket or tarp. This will provide a few degrees of protection, which is all we need.

Keep in mind that cold air sinks. Gardens in low spots (frost pockets) are most vulnerable to damage from early frosts.

Cover your most sensitive plants. Tomato, pepper, cucumber, squash and melons are very sensitive to freezing temperatures.

Broccoli, cabbage, carrot and radish can tolerate light frosts and do not require protection. The cool temperatures of fall will actually improve the flavor of these vegetables.

The frost may kill potato vines, but their underground tubers will be safe.

Impatiens, zinnia, celosia, geranium and coleus are among the most sensitive of flowers.

Among the most frost-tolerant flowers are petunia, marigold, cosmos and pansy.

If tonight’s first frost is a light one, we will likely get two or more weeks of gardening season before a hard frost (28°F or colder) strikes. When that killing frost is expected, you need to harvest whatever tender vegetables you can. This includes peppers, cucumbers and squash. Blemish-free tomatoes with a pink blush can ripen off the vine.

Apples on trees tolerate temperatures down to 25°F before suffering damage.

Reprinted from the NDSU Yard & Garden Report for September 8, 2014. Blog entry written by Tom Kalb, Extension Horticulturist, North Dakota State University. Photo was made available under a Creative Commons license by the photographer: Joshua Heyer.

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Iron chlorosis - brief overview

This articles touches on iron chlorosis in trees, including its causes and potential cures. Everything works some of the time, nothing works all the time.

(The following appeared in the ND Forest Service’s ‘Prairie Forester’ publication in 2009.)

-Joe Zeleznik 

Life is tough on trees in North Dakota. They face bitter cold winters, spring floods and summer droughts. One thing they don’t face is nutrient deficiency … usually. Iron chlorosis is the exception. It affects trees throughout the state and it is sometimes fatal.

Autumn Blaze maple, iron chlorosis, close-up of leaf, NDSU campus

The main symptom of iron chlorosis is yellow leaves with green veins. Iron is used by the trees to make chlorophyll, the green pigment that traps sunlight for photosynthesis. There is no predicting if or when a tree will be affected by iron chlorosis; a tree can be healthy for many years, then suddenly become chlorotic. Iron chlorosis can be the first step in a decline spiral that eventually kills the tree.

Some species are more susceptible than others to reduced iron. Silver maple trees are especially vulnerable. Silver maple is one of the parents of the Freeman maples such as Autumn Blaze® or Sienna Glen®; these hybrids are slightly susceptible to iron chlorosis, but not as much as silver maple. River birch and red oak are less sensitive than silver maple, but more sensitive than most other tree species.

Most of North Dakota’s soils have enough iron in them to support healthy plant growth. But sometimes the iron is in a form that’s not available to plants. The culprit is usually high soil pH. The soil is not acidic enough to keep iron in the available form. Low soil oxygen can also cause iron to be unavailable. Trees are more susceptible to iron chlorosis if they are growing in flooded or compacted soils. Even low temperatures can reduce iron availability.

Can chlorotic trees be “fixed” or “saved”? As with most things, the answer is “it depends.” In the case of iron chlorosis, prevention is more effective than after-the-fact treatment.

Determining the cause of the low iron availability is critical to developing a treatment approach. Obviously, we can’t change the weather – low-temperature induced chlorosis can’t be prevented. However, flooding and compaction – and therefore low soil oxygen – can be mitigated by improving drainage or aerating the soil.

Autumn Blaze maple, NDSU, iron chlorosis

For chemical treatment products, there are a lot of manufacturers’ claims. What does the science say? It’s not conclusive. Everything works some of the time, but nothing works all of the time.

If the cause of the chlorosis is high soil pH, then there are two options – lower the pH or add iron in an available form. Soil pH can be lowered by adding elemental sulfur or by adding acid-forming fertilizers. Some experts recommend combining these approaches by applying iron sulfate to the soil. Treatments must be repeated every two-to-three years. Iron can also be added as a chelate. Chelated iron comes in many formulations, so ask your local garden center what formulations are on hand.

Iron can also be added directly to the tree, either as a foliar spray or as a trunk injection into the vascular system. Iron chelate sprayed onto the leaves offers a quick fix to the problem, but the effects are often short-lived. Trunk injections have shown mixed results. Sometimes, injections are effective and trees regain their health and vigor. However, if the damage is too severe, then trees will not recover.

Iron chlorosis can be found in trees throughout the state. But with proper management, it can be prevented, and sometimes, cured.

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A leaf of a different color

Most leaves are green during the growing season. Leaves that are off-color are often showing signs of some type of stress. However, that's not always the case, as seen in these photos.

Leaves normally change color in the fall – we all know this.  If leaves begin to change color in the summer, that’s usually not a good sign.  Insects, diseases, nutrient deficiencies, environmental stresses – or some combination of these – can all cause leaves to turn yellow, brown or other colors during the growing season.

However, some trees and shrubs are supposed to have two-toned leaves during the growing season.  On other trees, you may see individual leaves of one color, and other (individual) leaves of a different color.  In some cases, that’s okay!  See the pics below.

-Joe Zeleznik

09.AUG.13

‘Schubert’ chokecherry – ‘Schubert’ chokecherry (a.k.a. ‘Canada Red’ chokecherry) is valued for its purple foliage during the growing season and bright red fall color.  The bright green leaves at the tip of this branch are a new flush of growth appearing in mid-season, and they will turn purple in one to two weeks.  This variety of chokecherry is native to North Dakota and is extremely hardy.  Suckering from the roots may cause problems.

Newly formed Schubert chokecherry leaves, showing green color, before changing to a purple tone.

Poplars –This hybrid poplar produces leaves that start off with a purple hue which then change to green – just the opposite of the Schubert chokecherry.  There are many poplar trees that are either native to North Dakota or adapted to the environment here.  Most poplars grow quickly but die young – especially the hybrids.  This can be handy when establishing a windbreak, as the poplars can provide immediate protection while the more-permanent trees establish slowly.

Newly formed leaves of a hybrid poplar show a purple hue, changing later to green.

Ivory Halo dogwood – This species has variegated leaves.  That is, the leaves are naturally two-toned.  There are many other trees and shrubs that are variegated, but finding ones that are tough enough to handle the North Dakota environment can be difficult.  Ivory Halo is hardy to Zone 3, and it does best in protected areas with good soil moisture. 

Two-toned, variegated leaves of Ivory Halo dogwood.

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NDSU Horticulture Field Day Set for July 22

July 22nd from 9:00 a.m. to noon
NDSU Horticulture Field Day Set for July 22

Daylilies

NDSU-Plant Sciences Department will host a horticulture field day on July 22, 2014 from 9:00 a.m. to noon. Festivities will begin at the NDSU Horticulture Research and Demonstration Gardens located at the corner of 12th Avenue North and 18th Street in Fargo. Tours will be conducted of the various gardens and of horticulture faculty research plots.

The NDSU Daylily Garden is an official display garden of the American Hemerocallis Society and features over 1400 daylily cultivars. “This is the largest public daylily collection in the nation,” says Esther McGinnis, Extension Service horticulturist and assistant professor. “The collection is truly a hidden treasure for our state.”

The field day will also feature the All-America Selections bedding plant display garden. “Walking through the gardens is an education and you can see which flowers perform well in our challenging North Dakota climate,” McGinnis says.

New this year, NDSU horticulture faculty will be on hand to offer tours of their campus plots demonstrating their research on raspberries, chokecherries, blackberries, grapes, vegetables, and turfgrass.

Light refreshments will be served.

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Ash anthracnose recently observed.

Ash anthracnose is a recurring problem. This year (2014), it was a little later than normal, but has finally arrived.

Some ash trees have recently lost their leaves because of a problem called ash anthracnose.  We see this in spring, especially following wet weather, as we’ve experienced lately.  Additional symptoms can include black blotches on leaf margins, causing leaf distortion, and small purple-to-brown spots in the middle of leaves. The leaf symptoms may not necessarily be visible on fallen leaves, since the infection that triggered leaf drop is likely on a petiole or other inconspicuous location.ash anthracnose.  Notice the dead leaflet margins, and the curved growth of the leaflet(s).

Treatment with fungicides is usually not warranted. Fungicides are only effective as a preventative treatment, usually as leaves are expanding.  Treating trees now can prevent mid-season infections, but infection is more common in the wet spring, rather than the drier summer.  For most large trees, fungicide applications aren’t very practical.  However, there are cultural practices you can implement now, such as a light fertilization, to help reduce recurring stress on ash. “Light” fertilization would be 1-3 pounds of nitrogen per 1,000 square feet of soil surface around the tree.  If you already fertilize your lawn, then there should be more than enough to meet the tree’s nutritional needs.

The fungus that causes ash anthracnose overwinters in the upper parts of trees on seeds, on twig cankers, and on any other plant part that remains attached to twigs, so raking and destroying fallen leaves and twigs may only help reduce inoculum rather than completely eliminate it. As a result, ash anthracnose is a recurring problem on ash as long as we have wet, cool weather in the spring. Disease severity varies from one year to the next, and among individual trees.

-Joe Zeleznik

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