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Category: Lawn and Garden

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Healthy Douglas FirChristmas Tree Planting Tips

The lifting, storage, and transport involved in shipments of evergreen planting stock can have long lasting effects. Planting stress affects root quality, and those effects can last beyond planting and can cause plants to not recover completely. Water is probably the most important factor. The system can be thought of as keeping a checkbook. Each stress subtracts from the quality balance remaining for tree health. Some tree nurseries allow for freezer storage of seedlings that may help preserve moisture in the plants and plant roots. Plugs need different care than bare root stock. Proper planting and care to have roots set properly can avoid J root which will cause long term stress on trees.

Christmas Trees

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Symptoms of ash rust on the lower surface of leaves. Note orange sporulation of the fungus.
Symptoms of ash rust on the lower surface of leaves. Note orange sporulation of the fungus.

We see ash rust almost every year, but this year there seems to be quite a bit of it. The fungal rust disease is very dependent on the spores produced by the alternate host (Spartina marsh grass). In cool, humid seasons with a bit of wind, infections are numerous on ash leaves as they expand. There is no control at this time. Rake up and remove leaves that fall, as they will produce spores that go back to the marsh grass. The ash trees can tolerate some infection year after year, but it does look unsightly. There is usually no need for chemical control, but fungicides would need to be applied preventatively, so mark your calendar for next year during the second week of May, to check your trees. At that time, a fungicide such as myclobutanil could be applied to specimen trees, according to the label.

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Please see the following link for the 2013 Plant Pathology Clinic, Survey, and Research Reports Bulletin:

Delaware Plant Pathology Clinic Reports, Research Results, and Bulletins

Click on the downloadable pdf for all of the reports and results from 2013 compiled into one easy to read document! Information is included on plant samples, nematode samples, USDA surveys, and research.

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This message is an alert for growers and retail bedding plant sellers that some petunia seedlings have been detected in the U. S. that are infected with tobacco mosaic virus (TMV). TMV is very common and has a wide host range, but infection in flats of seedlings could be problematic. Purchase your plants from reputable suppliers. Anything with a chlorotic yellow mottle should be sent to your county office or the UD Plant Diagnostic Clinic and be tested for TMV.

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Frost Cracking Maple. Image courtesy of B. Johnson
Frost Cracking Maple. Image courtesy of B. Johnson

The Clinic recently received an inquiry via our Ask an Expert feature, about the bark splitting on a red maple tree. A key piece of information was the south west exposure of the tree. The maple is suffering from what we call winter cracking or frost cracking in trees. What happens during very cold weather is that the side of the tree that faces south in the sunny location has temperature changes that are more pronounced than on the rest of the tree. The freezing and thawing of the bark and side of the tree facing that sunny area during the day, but re-freezing overall or at night, will lead to cracking of the bark. Many times the tree can heal or compensate for the crack in the bark on that side. You will want to watch that area closely for signs of insect damage or disease as time progresses, though. Do not paint or cover the area. The tree should begin to form a callus or thickened area around the split. Avoid fertilizing trees in the late fall, as that encourages new growth and new growth is more susceptible to splitting. Thin barked trees such as maple and cherry are more prone to frost cracking. Keep the tree watered next summer if we experience times of drought, and water once a week, deeply.

nfg 1/31/14

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Mulberry Weed (Fatoua villosa)

Description and Geographic Distribution

Mulberry Weed or hairy crabweed (Fatoua villosa) (Thunberg) Nakai is an invasive exotic Asian species from the Mulberry family (Moraceae).  First reported in Louisiana in 1964 by J.W. Thieret and possibly present as much as twenty years earlier, it has since spread to much of the Eastern United States, appearing throughout the Southern states and as far north as Michigan and Delaware. In Delaware, it is a recent arrival, with specimens reported in 2013.  It is also present on the West Coast, with documented occurrences in Washington and California.  Appearing much like a nettle (Urticaceae), it is an herbaceous erect annual. It is characterized by papery, heart-shaped, alternate leaves. The plant has densely pubescent (hairy) stems. The flowers are dense, light green cymes (clusters) with no true petals, and seeds that are forcibly expelled. It flowers in the mid-summer and fall.

Much of the spread of Fatuoa villosa can be attributed to its frequent appearance in horticultural material and nursery stock.  It is also likely to spread through purchased top soil that contains its abundantly produced and explosively projected seeds.  It favors disturbed areas and is an especially problematic weed in agricultural fields, greenhouses and gardens.

Control

Suspected mulberry weed should be removed from garden beds or pots and be discarded in the trash, not composted nearby.  The plant produces abundant numbers of seeds, so it should be treated with herbicide or rogued out before it sets seed.  A two to three inch layer of mulch can prevent most seed germination, as can pre-emergent herbicides.  Post-emergent herbicides would also be effective.  Reference to commercial products or trade names does not imply endorsement by University of Delaware Cooperative Extension.

Image, N. Gregory University of Delaware
Image, N. Gregory University of Delaware

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MANAGEMENT OF BOXWOOD BLIGHT (caused by the fungal pathogen Cylindrocladium  pseudonaviculatum) will be important in our area over the next few years, after detections in MD, DE, and PA. Be cautious when bringing new boxwood plants into a site with established boxwood. A nursery quarantine or watch area may be a wise thing for landscapers to set up, putting plants on a watch for 4 to 5 weeks before installing in a landscape planting.

Black streaks on twigs of boxwood with boxwood blight
Black streaks on twigs of boxwood with boxwood blight

Dr. Karen Rane, diagnostician with University of MD, spoke with Dr. Jim LaMondia from the Connecticut Ag Experiment Station and Dr. Kelly Ivors from North Carolina State University recently, regarding management in a landscape with mature boxwoods. They emphasized that, if all infected boxwoods are not going to be completely removed and destroyed, then pruning out and destruction on-site of all infected branches is necessary to reduce inoculum.  Just a few fallen leaves will serve as an important inoculum source.  Dr. Ivors said that nurseries in NC use a flamer (used for weed management in organic systems) to destroy fallen leaves on the soil surface after plants have been removed.  Vacuuming hard surfaces using a shopvac can also help to remove fallen leaves.  Drip irrigation system instead of overhead can be important in management.  Wetting of foliage promotes splash dispersal of spores as well as providing the optimum environment for spore germination and infection. Sanitation and fungicide applications will be extremely important for a few years to control boxwood blight. One year of management will not be enough, because microsclerotia in fallen leaves can survive for several years, and serve as a source to cause infections if new growth is not protected.

Dr. LaMondia and Dr. Ivors emphasized the use of protectant and systemic fungicides in combination to help protect new growth from disease and to reduce sporulation.  A spray that includes chlorothalonil should be applied a day or two prior to pruning out diseased material in order to kill spores on the surface of the infected tissue, or soon after pruning.  Both researchers recommended using combination sprays containing both a protectant and a systemic fungicide either as a tank mix of two products with different modes of action or using a pre-mixed product that contains two active ingredients. Both suggested chlorothalonil as the best protectant product.  Fungicides sprays should be alternated every 2 weeks when conditions are favorable for disease, as one or two sprays in a growing season will not control boxwood blight. Dr. LaMondia suggested starting with a tank mix of thiophanate-methyl +chlorothalonil, followed two weeks later with a propiconazole + fludiozinil (Medallion) spray.  Dr. Ivors suggested alternating Palladium (fludioxinil and cyprodinil) and Spectro (thiophanate methyl and chlorothalonil).  The addition of a spreader sticker may be necessary to improve coverage but check individual product labels. Products should be applied by a certified professional with the proper equipment for coverage of large plants, according to the fungicide label. Please see the following web site for some chemical recommendations and rates: http://www.anla.org/docs/government%20relations/boxwood%20blight/7.22.13-BB.pdf

NFG 9/3/13

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FUNGI AND SLIME MOLDS grow in mulch composed of organic debris and wood chips. Fungi and fungus-like organisms such as slime molds are decomposers, and they do it very well to the benefit of our ecosystem. Without fungi, we would be deep in organic debris and fallen leaves. With adequate moisture, fungi will break down mulch into simple sugars they use to grow and survive. Most wood decomposers are harmless to people and animals. Fungal fruiting bodies and patches of slime mold are 95% water. They may be raked lightly to break them up, or they can be removed with a shallow shovel and the material discarded. On playgrounds, curious children can get very close, and breathe or eat this material. We consider these organisms harmless, however, people are very different and their immune systems are different.  There are allergies, asthma, and breathing related conditions that may affect individuals in our populations.  Children and their families should be made aware that there may be organisms on playgrounds and in yards that may be producing microscopic spores that may become air-borne. Air-borne spores may cause reactions in sensitive or immuno-compromised individuals.  Individuals (or their guardians) with health conditions should make judgment decisions about how much exposure can be tolerated. With our recent wet weather pattern, there will be an increased number of fungal spores in many environments. Raking will disrupt slime molds and they will dissipate naturally, or they can be scooped up and removed. Replacing mulch each year will bring in new organic material and organisms that colonize the material, so older mulch may not have as much visible fungal or slime mold growth. See the fact sheet for more info: http://extension.udel.edu/factsheet/artillery-fungus-and-other-things-that-grow-in-mulch/

NFG 7/2013

Slim Mold on Mulch Next to Bricks
Slim Mold on Mulch Next to Bricks

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Phytophthora root rot, a soil borne disease caused by a fungus-like organism, is a widespread problem which can affect many of our woody and herbaceous landscape plants. Azaleas, hollies, and rhododendron are probably the most frequently affected plant group in the landscape, especially in wet soils. Submit a sample including roots to the Plant Diagnostic Clinic and we can confirm what the problem is. Don't continue replanting with susceptible hosts. Increase drainage and plant a more resistant shrub or tree.  The best control for Phytophthora is to avoid getting it started in the first place. Phytophthora is favored by planting susceptible species and cultivars in poorly drained soils, or by overwatering even in sites with adequate drainage. Once a Phytophthora problem is established in a landscape site, the best option is probably to remove the affected plants and replace with resistant species. Some possibilities include Ilex glabra (inkberry holly), Clethra alnifolia (summersweet), Itea sp (sweetspire), Physocarpus opufoliius (Eastern ninebark), and Leucothoe fontanesiana.  Examples suggested by extension agents in North Carolina include nandina, Chinese holly (cultivars including 'Rotunda', 'Dwarf Burford' and 'Carissa'), liriope, Indian hawthorn, and Camellia sasanqua cultivars (Camellia japonica is susceptible). The rhododendron hybrids: Caroline, Martha Isaacson, Professor Hugo de Vries and Red Head are considered resistant.  In addition, the azalea cultivars 'Formosa', 'Fred Cochran', 'Fakir' and 'Corrine Murrah' are considered highly resistant.  Other resistant azalea cultivars include Rhododendron poukhanese, Formosa, Fakir and Corrine Murrah, 'Merlin', 'Hampton Beauty', 'Higasa', 'Pink Gumpo' and 'Delaware Valley'.  Susceptible cultivars include 'White Gumpo', 'Hinodegiri', 'Hershey Red', 'Coral Bells', 'Pink Pearl' and 'Hino Crimson'.  Susceptible cultivars are also among the most widely planted. Camellia sasanqua is resistant to root rot while C. japonica is highly susceptible. Keep in mind that resistant hybrids are not immune. Chemical control is generally not practical for the homeowner, and involves a drench or injection by a certified applicator.

NFG 7/1/2013

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Flooding
Flooding

SATURATED SOIL can lead to problems with roots of trees and shrubs, and ultimately contribute to death or uprooting of trees. When soil becomes saturated through over-watering or heavy rains, plants cannot develop new fine feeder roots that are responsible for uptake of nutrients. A good root system also anchors a plant well into the planting site. Development of a good root system can take time, and over-watering can prevent root growth and establishment. Plants with an under-developed root system are more prone to stress and root disease. Subsequent stress from drought that may occur later in the season can lead to death of plants that do not have a good root system. Trees and shrubs without a good root system are more prone to upheaval and toppling during storms with wind. Proper planting and soil preparation with good drainage may prevent problems in the future.

Saturated soil can also lead to problems in row crops, field crops, vegetables and turf. Good drainage can help  to avoid problems with root rot that may move in following flooding and saturated soil.

Flooding in a corn field
Flooding in a corn field - image courtesy of Daren Mueller