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Hort Update Feb. 16, 2017

Single leaf with symptoms of Peach leaf curl
Single leaf with symptoms of Peach leaf curl. Photo by Paul Bachi, University of Kentucky Research and Education Center,

Knotweed Turf iNfoIt's not too early to think about control

Prostrate knotweed is a summer annual weed; however, its seed breaks cold dormancy and germinates much earlier than other summer annual weeds. It is estimated that germination begins when soil temperatures are consistently 35 to 50 degrees F for approximately two months, and stops when soil temperatures exceed 50 degrees F. During most years in Nebraska, germination likely begins between late February and early March. With pre-emergence herbicides being the preferred chemical control method, application may need to begin soon in turf areas with knotweed issues. To help manage knotweed, core aerate to relieve compaction and improve drainage. For herbicide information, see link below.

It’s Not Too Early to Think About Knotweed Control, Nebraska Extension Turf iNfo

Vole Damage/SymptomsFeeding runs beneath snow

Prairie and meadow voles scar lawns by constructing surface runways (one to two inches wide) and clipping grass very close to the roots. Runways are most visible after snow melts. Small holes lead to underground runways or nesting areas. Vole damage to lawns will repair itself during spring growth. Voles are small, mouse-like rodents that exist throughout Nebraska. Their short, one inch, tails, stocky build and small eyes distinguish them from true mice.

Controlling Vole Damage, Nebraska Extension

Trees & Shrubs

How to identify ashSee Nebraska Forest Service pictorial guide

Many customers have questions about protecting their trees from emerald ash borer. But before talking about treatments, they first need to determine if their tree really is an ash. The Nebraska Forest Service has developed an excellent pictorial guide to aid the industry and clients in identifying ash.

EAB was confirmed in Omaha, NE 6/8/16 and Greenwood, NE 6/17/16. Remember, treatment is not recommended until EAB is confirmed within 15 miles of a customer's location.

Ash Tree Identification Guide, Nebraska Forest Service

Oak Wilt & MulchRisk of spreading wilt in mulch is extremely low to zero

With oak wilt currently found in counties along the Missouri river, questions have been asked if wood mulch from chipped oak trees placed around oak trees could spread the disease. A similar question relates to the use of compost in which infected oak wood was placed. The answer is the risk is extremely low to almost zero. The only disease known to possibly spread via wood mulch is verticillium wilt.

Squirrel DamageBark stripping and twig clipping

Squirrels may damage trees during winter and spring by stripping bark or clipping off twigs to access sap for moisture. They may also feed on tree buds. Occasionally, tree squirrels gnaw on decks, porches, fences, and other objects; most likely for marking territory. While trees can withstand quite a bit of squirrel damage, the wounds may lead to other issues or stress. If a tree needs protection, metal collars can be installed around the trunks of shade trees; or polybutene-based repellents may be applied to help reduce squirrel damage. To prevent tree damage from the repellent itself, be sure to follow label directions for application. For structural gnawing, use a physical barrier such as metal flashing. If this is not an option, commercial repellents may be effective. Apply the repellent on the marks and to a 12-inch radius around the gnawed area; and repeat as necessary.

Winter Evergreen InjuryRisk increases as temperatures warm in late winter

Winter desiccation injury on evergreens occurs when green foliage loses moisture faster than it can be replaced by roots from frozen soil. Injury is typical on the south or southwest sides of a tree or shrub and fairly uniform, i.e. one inch of the tip of every needle has turned brown. Plants growing near pavement or the south side of light colored or brick homes are often most susceptible. Correct summer and fall watering is most important to preventing winter dessication. If needed, winter watering can be used. Only water when the soil is not frozen and air temperatures are above 40 degrees F. Apply water at mid-day so it has time to percolate into soil before colder nighttime temperatures and freezing may occur. The application of anti-transpirants, like Wilt-pruf, when air temperatures are above 45 degrees F. can help reduce dessication damage. Label directions need to be followed closely.

Winter WateringBeneficial if needed and done correctly

Winter watering of trees and shrubs will be beneficial this year if warm winter temperatures and a lack of precipitation continue. The priority for watering is young plants first - those planted in the last year and especially those planted this past fall, and then evergreens, especially those growing in exposed locations and near the south sides of buildings. When watering, the soil should not be frozen and air temperatures need to be above 45 degrees. Irrigation should take place early enough in the day for moisture to soak into the soil to avoid ice forming over or around plants overnight. Water just enough to moisten the soil six to eight inches deep. One or two irrigations during winter should suffice. If conditions remain warm and dry through winter and into spring, it will be critical to begin irrigation as soon as soils thaw this spring.

Pruning TipsAvoid structural issues with correct pruning of young trees

With late February through March being the ideal time to prune shade trees, look at corrective pruning on younger trees, those planted in the last 3 to 10 years, to help avoid long term structural issues. Hire a certified arborist to prune larger trees. Corrective pruning includes removal of:

  • a double leader,
  • branches that are crisscrossing and rubbing against another branch or one that will eventually rub if left to grow larger,
  • closely parallel branches that may eventually grow into one another,
  • branches with very narrow forks that can lead to included bark and weakened branch attachment.
Landscape Ornamentals

When to Cut Back Shrub RosesSee Nebraska Forest Service pictorial guide

To remove any winter injury, pruning should be done in mid to late April as new growth begins. After eliminating any winter injury, remove up to one third of the oldest, woodiest stems each year, cutting them back to the plant's crown. This encourages the growth of new, vigorous stems from the plant crown and eliminates the development of many old, woody branches with poor flower production. It also increases air circulation through the plant, reducing potential for disease problems.

Powdery Mildew PreventionSee Nebraska Forest Service pictorial guide

The last two years many landscapes have experienced moderate to severe powdery mildew infestations on a variety of plants. Peonies and a variety of other plants were commonly affected. Powdery mildew infections are favored by extended periods of cool, wet spring conditions which increases humidity around plant's foliage. Fungal spores overwinter on dead pieces of last year's infected leaves.

Areas in landscapes that are shaded and have moderate temperatures are ideal for powdery mildew development. Avoid planting highly susceptible plants in these areas. Try to increase air circulation in these locations by pruning shrubs and trees. Limit nitrogen fertilizer applications to plants in these areas, too, since faster succulent plant growth is more easily infected by the powdery mildew fungi. Consider moving plants with a history of powdery mildew to locations with more sun and better air movement.

If good garden cleanup was not done in fall, then this spring before plants begin to grow rake and remove any plant debris from last season. This will reduce the number of fungal spores present to infect this year's plants. In woody plants that are frequently infected, like roses, prune out the disease growing points periodically during the growing season.

Severe powdery mildew infections, or landscapes with a frequent history of infection, will require the use of preventative fungicide applications to minimize the disease. Refer to the publication below for recommended products. Repeated applications will be necessary for season-long control, whenever weather conditions are favorable for infection.

Powdery Mildew on Landscape Plants, Nebraska Extension

Fruits & Vegetables

Pruning Fruit TreesBest done from late February through March

Pruning fruit trees is best done from late February through March, before trees begin to break bud. This minimizes the potential for cold injury and trees heal wounds fastest when pruned at this time of year. Start with those trees that have higher levels of winter hardiness, including apple, pear, tart cherry and plum. Save sweet cherry, peach and apricot for last. Prune heavily on neglected trees and vigorous cultivars. The main purpose of fruit tree pruning is to 1) increase sunlight penetration of the tree's canopy, 2) remove less productive wood and 3) shape the crown into a strong efficient structure. Pruning increases fruit size, promotes uniform ripening, increases fruit sugar content and decreases pest problems due to better spray coverage and faster drying of the foliage after rain.

Occasional summer and fall pruning may be needed, but keep it to a minimum to avoid spreading fireblight and creating wounds that can be invaded by other diseases.

Make proper pruning cuts and use sharp pruning tools. Do not use pruning paints or wound dressings on pruning wounds. If a fruit tree sustains storm damage, consider removing the tree if over 50% of the trees branches need to be removed due to breakage.

Midwest Home Fruit Production Guide, Ohio State University Extension

Peach Leaf Curl & Plum Pockets PreventionDormant sprays must be applied before leaves begin to expand

Peach leaf curl & plum pockets are caused by Taphrina fungus. The most characteristic symptoms in peach are curling and crinkling of the leaves as they unfurl in spring. Usually, the entire leaf is affected, but sometimes only small areas are involved. In addition to curling, diseased leaves are thickened and often turn red or pink. As the season progresses, diseased leaves turn gray and appear powdery. This is the result of the fungal pathogen producing spores on the leaf surface. Eventually, the leaves turn yellow or brown and are prematurely cast. This disease may also occur on fruit, blossoms, and young twigs. Diseased fruits are distorted, swollen, and exhibit discolored surface areas. These areas are usually wrinkled and lack the normal peach fuzz. Infected fruits seldom remain on the tree until harvest. A severely disease tree does not yield well and is subject to winter injury.

Plum pockets, a disease caused by Taphrina communis, causes similar symptoms on plum leaves, while the plums become distorted and puffy. This disease is not considered a serious problem in most cultivated plums. Wild plums, however, are highly susceptible. If necessary, the same control procedures used to prevent peach leaf curl may be used to minimize plum pockets.

Dormant sprays of fungicides are effective controls if applied in late winter before buds begin to swell and when temperatures are above 40° F. These diseases cannot be controlled once leaves have started to expand. Use the fungicides ferbam, chlorothalonil (Daconil), Bordeaux or liquid lime-sulfur. Do not add oil to lime-sulfur or spray oil treatments for three weeks after application of lime-sulfur. Lime-sulfur should not be applied to trees when temperatures are below 45 or above 80 F. Follow recommended label rates for all commercial fungicides.

Peach Leaf Curl, Nebraska Extension

Peach Leaf Curl, Cornell University

Starting Garden Transplants at HomeGarden center references for customer questions

Recommendations for starting garden transplants at home - Garden centers will be getting customer questions about how to start transplants at home. Depending on the plant species, most transplants should be started about 6 weeks prior to the expected outdoor planting date. To grow quality transplants, use a soilless potting mix and provide fairly high humidity, cool temperatures (60 to 70 degrees F.) and 14 to 16 hours of bright light per day. Use a grow light or one cool white and one warm white fluorescent light, placed one to two inches from the plants. A little air movement, such as with a fan, can also lead to sturdier transplants.


Nuisance Insects IndoorsPesticides not recommended; exclusion is the best control

Nuisance insects - With warmer than normal temperatures recently, common nuisance insects may becoming active indoors. Garden centers will be getting calls on controlling pests like boxelder bugs, millipedes, spiders and Asian lady beetles. These insects are harmless and don't warrant pesticide usage indoors. Recommend clientele simply vacuum up the insects and make note of the problem areas in the home. This summer homeowners should focus on caulking cracks, crevices and other conduits into the home to prevent future problems in spring or fall. Repair window screens and check that doors are tight fitting.

Pest Proofing, Nebraska Extension