Good care of trees and shrubs will prevent many troubles. Because trees and shrubs live for many years, their susceptibility to disease is influenced not only by current climatic and environmental conditions but also by conditions and care during previous years. Maltreatment and lack of care favor many diseases. Conversely, many troubles in nurseries and outplantings can be minimized by selection of proper planting sites, avoidance of unnecessary wounding, routine care including fertilization and timely watering and pruning, and preventive measures such as those described below.

Trees and shrubs on sites subject to deep soil freezing should be mulched to prevent root injury. Evergreens susceptible to unusual winter drying, such as those planted in exposed areas, should be treated with an antidesiccant.

Disinfect your tools regularly when pruning to control diseases. An easy, effective way to do this is to swab the cutting blades with an aqueous solution of denatured alcohol prepared by mixing 7 parts alcohol with 3 parts water. A vial or other pocket-size container will hold a saturated cotton swab.

Discoloration and decay following pruning are minimized if exposed tissues are allowed to close of their own accord. Applications of shellac or another wound dressing can be used for control purposes or where wound invasion by canker-causing fungi or bacteria is likely to occur.

For new plantings, choose pest-resistant plants where available. Named cultivars propagated in nurseries and offered for landscape use in the last 15 years have usually been monitored for insect and disease susceptibility in the nursery, and most highly susceptible individuals have been eliminated from production. Table 3.5.1 lists some disease-resistant selections.

3.2 Nursery Hygiene

Do not let sloppy nursery hygiene ruin your investment in clean plants and soil fumigation. Soilborne pathogenic fungi, bacteria, and nematodes are carried into the nursery and spread within it by dirty feet, implements, and machines; moving surface water; blowing soil; and infested or infected plants.

1. Insist on clean stock. Do not order or accept stock likely to be infested with nematodes, crown gall bacteria, the Verticillium wilt pathogen, or similar organisms.

2. Stabilize all open soil and maintain windbreaks. Cover dirt roads with gravel or oil.

3. Require equipment moving between nursery blocks to pass through a central area where soil is washed off. The equipment can be parked on a bed of cobblestones, and the soil particles will be carried down through the cobbles. A steel grating over a pit is a better arrangement for a permanent wash-down area.

4. Clean boots and hand tools as you do mechanical equipment.

5. When roguing diseased plants or pruning diseased parts of plants, destroy or bury the discards unless you are assured of no hazards.

6. Do not allow surface water to run from one nursery block to another. Divert it into ditches or culverts.

7. Remember that irrigation water can carry pests and pathogens. Select a clean source and keep it clean.

8. Allow no direct traffic from outdoor areas to indoor propagation areas. Use foot baths containing a germicidal agent such as Amphyl at entrances.

9. When collecting cuttings in the field, inspect stock plants carefully, and avoid any plants showing disease symptoms or abnormalities. For many leaf diseases, inspect stock plants late in the growing season before cuttings are actually to be taken, when leaf diseases are most apparent.

3.3 Diseases of General Importance or Occurrence

3.3.1 Crown Gall

Crown gall, caused by Agrobacterium tumefaciens, occurs in nurseries and outplantings throughout New York State. The list of woody plants susceptible to the disease includes plants in at least 77 genera and 32 families.

The disease becomes established in nursery crops when clean stock is planted in infected soil and when infected stock thought to be free of the causal bacteria is planted in previously clean soil. Once in the soil, the bacteria can persist indefinitely in decomposing debris from galls on susceptible plants. The wounds necessary for entry of the pathogen occur during planting, cultivating, grafting, and pruning.

Table 3.3.1. Provisional list of woody plant genera not susceptible to crown gall

Scientific name	Common Name	Scientific name	Common Name
Berberis	barberry	Buxus	boxwood
Carpinus	hornbeam	Catalpa	catalpa
Cedrus	true cedars	Cephalotaxus	Japanese plum yew
Cryptomeria	cryptomeria	Fagus	beech
Ginkgo	ginkgo	Ilex	holly
Koelreuteria	goldenrain tree	Larix	larch
Liriodendron	yellow poplar, tuliptree	Magnolia	magnolia
Mahonia	mahonia, Oregon grape	Nyssa	black gum
Picea	spruce	Pinus	pine
Pseudolarix	golden larch	Pseudotsuga	Douglas-fir
Tamarix	tamarisk	Taxodium	bald cypress
Tilia	linden, basswood	Tsuga	hemlock

3.3.2 Verticillium Wilt

A fungus, Verticillium dahliae, causes this disease, which occurs in at least 46 genera of woody plants grown in New York State and adjacent areas. Maples comprise the most important group of highly susceptible woody plants. The pathogen is soilborne and can persist many years in soil without host plants. The disease is common in nurseries that have been established on land formerly devoted to fruit, bramble, vegetable, or field crops, many of which are also susceptible. If Verticillium wilt has occurred in previous crops on a particular site, susceptible plants should not be planted.

There is no guaranteed way to rid soil of V. dahliae once the soil has been contaminated. Soil fumigation may help but is probably a bad investment if done for the sole purpose of controlling Verticillium. Instead, prevent the disease from getting started by planting clean stock on sites where previous occurrence of the disease has not been noted. Seek guarantees from suppliers that stock you receive is Verticillium-free.

If a tree or shrub already established in a landscape becomes infected with Verticillium, it may still live and be a serviceable plant for many years. Trim symptomatic parts from the plant, disinfecting tools between cuts. Be sure the plant has adequate water and nutrition because Verticillium spreads more quickly in plants growing in less than optimal sites.

If an established tree or shrub must be removed because it is dying from Verticillium wilt and a replacement is desired, use a resistant plant. Yews and conifers are not affected by Verticillium wilt. Many broadleaf trees and shrubs commonly planted in New York also seem to be resistant.

Although maples are generally thought to be highly susceptible to Verticillium wilt, red and sugar maples appear to be much more resistant than Norway maples. ‘Jade Glen’ and ‘Parkway’ are reported to be more resistant than other cultivars of Norway maples. ‘Charlotte,’ ‘Tryon,’ and ‘Union’ are moderately susceptible, but have not been widely field tested for other performance characteristics.

Table 3.3.2 Some Verticillium wilt resistant genera

Scientific name	Common Name	Scientific name	Common Name
Betula	birch	Carpinus	hornbeam
Cornus	dogwood	Crataegus	hawthorn
Ginkgo	ginkgo	Gleditsia	honeylocust
Liquidamber	sweetgum	Malus	apples
Morus	mulberry	Platanus	sycamore, plane
Pyracantha	firethorn	Quercus	oak
Salix	willow	Sorbus	mountain ash

3.3.3 Shoestring Root Rot

Several different species of fungi, once all lumped together under the name Armillaria mellea, cause this disease, which can be lethal to hundreds of kinds of woody plants. The fungus kills by girdling trees and shrubs at the butt or root collar. Two conditions must usually be satisfied before lethal attack occurs: (1) the pathogen must have access to a large energy source or food base such as a colonized tree stump or root and (2) the tree or shrub must be under physiological stress such as from water shortage, defoliation, or construction damage. Control depends on optimizing growing conditions and eliminating food bases. Keep trees and shrubs vigorous by protecting against defoliation and water stress.

Fertilize at regular intervals. Remove the stump and roots of a killed plant if others of value are nearby. If disease is detected in a valuable living tree or shrub while confined to one root or to one side of the butt, expose the entire root collar area and as much of the butt as possible to the air for several months. Remove all dead roots and dead bark. Fertilize and water as needed to promote vigorous growth.

3.3.4 Powdery Mildew

Many species of fungi that have certain morphological features in common are classified as powdery mildews. These fungi have similar life cycles, parasitize only the outermost cells of leaves and succulent stems, and can be controlled by the same methods. In general, wait until symptoms appear. Then, if necessary, apply an appropriate fungicide according to label directions. Powdery mildews on most woody plants intensify during the latter half of the growing season and have little effect on overall plant health. Thus, fungicide application is often unnecessary except to preserve the appearance of the foliage. Thiophanate-methyl, triadimefon, and myclobutanil are effective in controlling powdery mildews on a wide array of trees and shrubs. Powdery mildew on rose is also controlled with applications of copper or propiconazole. Horticultural oil is registered for control of powdery mildew on rose.

3.3.5 Chlorosis Caused by Manganese or Iron Deficiency

In areas where soil pH is high (i.e., > 6.5), root uptake of essential nutrients, especially iron and manganese, may be inhibited. Maples, oaks, and ericaceous plants (e.g., rhododendrons, azaleas) are highly intolerant of such conditions, but other species may also show chlorotic foliage if they lack sufficient amounts of these nutrients. Because deficiencies of either iron or manganese cause symptoms that look alike, it is advisable to have both soil and foliage tested before treatment.

It is usually not feasible to lower pH by adding chemicals to the soil. Thus, the needed nutrients must either be applied directly to the plant through injection into the vascular system or spraying onto the foliage, or to the soil in a chelated, more readily available form.

3.3.6 Cutting Rots Caused by Several Species of Fungi

To prevent rot in recently stuck cuttings, pasteurize or sterilize the rooting medium with steam and take precautions to ensure that it does not come in contact with untreated soil. Use sharp tools and heat them briefly in a flame periodically to minimize chances for disease spread on dirty tools. Drench rooting medium with etridiazole per label directions.

3.4 Fungicide Information

Table 3.4.1. Some fungicides, bactericides, and nematicides registered for use on trees and shrubs in New York State
Material and Some Trade Names		EPA Reg. No.	Use ††	REI§
Azoxystrobin
	Heritage Fungicide	100-1093	N, L	4

Remarks: Warning: Azoxystrobin is of the strobilurin chemical class. To discourage development of resistant pests, alternate sprays with another product that has a different mode of action between every one or two treatments, as directed on the label.
Calcium Polysulfide
	Lime Sulfur Solution	66196-2-72	N, L	48

Remarks: Broad-spectrum protectant fungicide. May be phytotoxic to some plant species if temperature exceeds 75° F. at application.
Chlorothalonil
	Applause	50534-188-34704**	N	12
	Bravo Ultrex Agr. Fung.	50534-201-100**	N	12
	Bravo Weather Stik Agr. Fung.	50534-188-100**	N	12
	Chloronil	50534-188-100**	N	12
	Concorde	72167-24-1812	N, L	12
	Concorde DF	72167-25-1812	N	12
	Daconil Ultrex Turf Care	50534-202-100	N, L	12
	Daconil Weather Stik	50534-209-100	N, L	12
	Daconil Zn Flowable	50534-211-100	N, L	12
	Docket DF	50534-202-100	N, L	12
	Docket WS	50534-209-100	N, L	12
	Manicure 6 Flowable	50534-209-100	N, L	12
	Manicure Ultrex T&O	50534-202-100	N, L	12
	Manicure 6FL	60063-7-10404	N, L	12
	Manicure Ultra	60063-3-10404	N, L	12

Remarks: Chlorothalonil labels are extremely variable. Before purchasing, be certain product is labeled for both the host and the disease you wish to control. Where noted (), conifers are the only ornamentals appearing on product labels. Note:** Where a 12 hr. REI is recommended, see additional precautions required for 6.5 days after treatment. Some products are not for residential use. See labels. Manicure 6 Flowable and Ultrex T&O have been discontinued and their registrations are due to expire 12/31/2008.
Chlorothalonil + Thiophanate-Methyl
	Spectro 90 WDG	1001-72	N, L	12

Remarks: Broad-spectrum fungicide for control of specific leaf spot, rust, scab, and blight diseases.
Copper, Elemental
	Basicop	1812-300	N	24

Remarks: General protectant fungicide and bactericide.
Copper Hydroxide
	Kocide 2000	1812-358	N, L	24
	Kocide 2000 T/N/O	1812-358	N, L	24

Remarks: General protectant fungicide for control of leaf diseases. May be toxic to foliage of some deciduous trees and shrubs.

Pest Management Guidelines A Cornell Cooperative Extension Publication	Cornell Guide for Pest Management of Trees and Shrubs
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