Urban Orchards : Orchard Diseases

Contents:
Disease in Fruit and Nut Plants
Urban Orchards Pest and Disease Control Practices
Common Orchard Diseases

Disease in Fruit and Nut Plants

There 3 types of disease that attack plants:
1.) Fungi: Most thrive in cool, wet weather (exception: Powdery Mildew); Examples: Apple Scab, Black Knot, Peach Leaf Curl
2.) Bacteria: Can multiply and spread very quickly (a few days) under the right conditions (see Fireblight); Examples: Fireblight, Bacterial Canker
3.) Viruses: Develop more slowly (over a few years) than other types of disease; sometimes difficult to identify at onset because symptoms resemble other problems (mineral deficiency, fungus, general weakness); Examples: Stony Pit Virus, X-Disease

Urban Orchards Pest and Disease Control Practices

Steps that you can take toward prevention of pest damage and orchard disease:
1.) Select varieties of plants bred for high pest/disease resistance.
2.) Select appropriate plants for each site, and select an appropriate site for each plant.
3.) Maintain plant health and minimize stresses by being sure to regularly water, fertilize, feed, and mulch your plants. Install rodent guards, keep the plants and surroundings clean of diseased, dying, and dead plant material, including dropped fruit, fall leaves (from fruit, nut, and berry plants). You can compost these only if the compost gets hot enough (3 x 3 x 3 foot minimum with proper moisture, air, and carbon-nitrogen ratio). The safest treatment is to double bag infested fruit so it pickles and kills the larvae.

*Stressed plants release chemicals into the air that attract pests. A healthy plant is less likely to attract pests because its immune system is strong. When a healthy plant is attacked by pests/diseases it produces natural toxic compounds that ward off or contain diseases and pest attacks.

4.) Remove pruned branches from the orchard. If you chip them into mulch, remove diseased branches first, and compost the mulch before using in the orchard.
5.) Encourage native beneficials by planting flowering ground covers (small-flowered species in compositae, umbelliferae families). Don't mow, or do so infrequently (once per year) to allow the ground covers to re-seed. Marigolds inhibit nematodes, which feed on roots.
6.) Eliminate plants that attract/harbor pests or disease.
7.) Pull off the loose bark on older trees so insects can't overwinter in them.
8.) Paint the trunk of young trees (use watered-down light-colored latex paint) to prevent sunscald and/or Southwest winter injury. In hot, sunny summer areas, also prune very low branches to stubs for the first few years, which will help them to leaf out enough at the top to shade the trunk.

If a plant is infested, diseased, or otherwise damaged:
1.) Remove as much diseased/dead material as possible.
2.) Remove/deter pests:: Handpick pests off the plant and hand-crush or drown them.; Shake the plant off and hand-crush or drown the pests that come off.; Spray the plant off with a strong stream of water.; Place tree bands, ant barriers, traps, lures, and rodent guards.
3.) Attract appropriate beneficials using insectary plants, water, birdbaths, suet, toad shelters, and bird feeders.
4.) Continue to water plant well, mulch, fertilize, and spray foliar food.
5.) If a plant is badly diseased and dying, remove it to prevent contamination of other plants.
6.) As a last resort, you may decide to spray. If so, please become well educated before doing so. Consult books such as The Orchard Almanac by Steve Page and Joe Smillie, AgAccess, 1995, or Fruits and Berries for the Home Garden by Lewis Hill, Storey Communications, 1992. These examples follow “Integrated Pest Management”, a whole-system approach which minimizes toxic sprays. EarthWorks advises strongly against any toxic sprays, especially in urban areas.

Spray Tips for the Desperate:
There is little need to use the organic control sprays unless growing commercially. When you first notice a pest or disease, determine whether it is a “no-spray situation”. Chances are, the beneficials are already present and dealing with the imbalance, or can be encouraged or introduced. Foliar feeding sprays generally do not harm beneficials, nor do non-toxic oils and soaps.

For almost any type of spray, the best time is early morning, when leaf pores are more open. Morning dew helps spread the spray over the plant and hold it on, as well.

Foliar feeding sprays (nutrients are absorbed through leaves) quickly help stressed plants recover. Seaweed emulsions provide a balance of nutrients including trace elements. Liquid Seaweed extract is recommended at 1/4 lb. dry per acre. Ground horsetail plant also contains silica, which increases light reaching leaves and fruit. Mix 1-2 oz. dry in 3 gallons of water, warm on a stove or as “sun tea.” Mix this solution 1:5 in water before spraying. Make nettle tea by placing leaves or whole plants in a 5 gallon bucket for at least 24 hours. Mix with water depending on strength, and spray every 2 weeks.

Organic Control Sprays: Tracking “degree days” (cumulative temperature excess over some base temperature, usually 40 or 50 degrees Fahrenheit) is crucial for timing spraying with insect or disease pressure. Included here is a list of organic control sprays that EarthWorks has found to be the least harmful to plants and beneficials in the orchards:
Neem: A botanical derived from satree in India and Africa, neem is used as toothpaste ingredient in India as well as by native people as a repellant and growth regulator which functions by interrupting insect metamorphosis (of both pests and beneficials). Neem is used in combination with crushed or powdered garlic. Pre mix 1 pint of each in 5 gallons of water and dilute 1:10 (use 1/2 cup vinegar to lower water pH, as garlic-neem breaks down in alkaline water).
Bacillus thuringiensis is a protein that breaks down the stomach lining of insects, but may also kill or repel beneficials.
Horticultural oil should be sprayed at bud break. These smother foliar pest eggs (aphid, scale), but are usually not needed if other pesticides which kill beneficials haven't been used. Dormant oil can be made using 2 qt. light motor oil, 1 lb. fish oil soap or l/2 cup liquid detergent. Mix this solution 1:20 with water.
Baking soda and oil help to prevents powdery mildew. In 1 quart of water, dissolve 1 teaspoon baking soda and 1-2 teaspoons horticultural oil.

Check the Organic Materials Review Institute website for a current list of allowed sprays if you’re selling any organic produce – the list keeps changing.

Common Orchard Diseases

Apple Scab
Type: Fungus
Affects: Apples, pears, crabapples
Symptoms:: Leaves – Olive green spots, which develop into large, black blotches. Possible leaf drop.; Fruit – Green to velvety-brown spots, which become raised and corky. Possible fruit distortion.
Conditions: Thrives in areas of cool, moist summers. Innoculum overwinters in leaves, not fruit.
Controls: Rake up and compost fallen leaves. Plant disease resistant varieties.

Bacterial Canker (resembles Cytospora Canker)
Type: Bacteria
Affects: Sweet cherries, peaches, plums, tart cherries
Symptoms:: Branches – Fail to leaf out, wilt, and die. Cankers ooze sour-smelling gum.; Fruit – Develop dark, sunken areas (susceptible to Brown Rot Fungus).
Conditions: Occurs after bloom in cool, wet weather.
Controls: Spray trees with copper spray, early-mid spring.

Black Knot
Type: Fungus
Affects: Plums, cherries
Symptoms: Branches – Black, knobby swellings develop, and eventually girdle and kill branches.
Controls: Try to contain disease by removing infected branches 9-12” below knots and burning. Removal is best done during winter dormancy, when disease is dormant. If done during growing season, disinfect pruners between cuts with bleach-water solution (1 part bleach:9 parts water). Prevent infection of healthy trees by removing badly infected trees and nearby hosts (i.e. wild cherry trees). Plant disease resistant varieties.

Botrytis Blight (also known as Bitter Rot, White Rot, “Dry” Rot)
Type: Fungus
Affects: Strawberries, raspberries, grapes, many woody plants
Symptoms:: Fruit of strawberries, raspberries, grapes – Patches of fuzzy gray-tan mold.; Tree fruits – Small, sunken brown lesions that work their way to core.
Conditions: Thrives in cool, wet weather and at high levels of soil nitrogen.
Controls: Remove and destroy infected fruit. Reduce nitrogen fertilizer. Promote dry foliar conditions: prune foliage to improve air circulation.

Brown Rot
Type: Fungus
Affects: Peaches, cherries, plums, apricots
Symptoms:: Flowers – Brown, wilted, covered with light brown spores.; Branches – Small cankers near tips.; Fruit – Small brown spots that develop into patches covered with grayish-brown spores. Fruit persists on tree as rotted, shriveled mass.
Controls: Remove and burn infected shoots and fruit. Promote dry foliar conditions by pruning foliage to improve air circulation. Plant disease resistant varieties.

Cedar-Apple Rust
Type: Fungus
Affects: Apples (alternate hosts: Eastern Red Cedar, Juniper, Hawthorn)
Symptoms:: Apple leaves – Tiny yellow-orange spots on upper surface, may have brown spots on lower surface. Can defoliate tree.; Fruit – Tiny yellow-orange spots on calyx (blossom) end.; Alternate hosts' branches – Spiny, reddish-brown galls near tips.
Conditions: Thrives in wet weather.
Controls: Needs an alternate host to spread, so plant apple trees 4 miles away from alternate hosts if possible. Promote dry conditions by pruning foliage to improve air circulation. Prune off and destroy galls in late winter. Plant disease resistant varieties.

Chestnut Blight
Type: Fungus
Affects: American and European Chestnuts, some American-Chinese hybrids. Currently resricted to east of the Rocky Mountains.
Symptoms: Branches, trunk – Blackening/blistering/cankering of bark, death of infected limb/trunk, extensive suckering at base of trunk.
Conditions: Spread by rain splashing on infected areas.
Controls: None known. Plant disease resistant varieties (such as pure Chinese, or Layeroka, an American-Chinese hybrid).

Cytospora Canker (resembles Bacterial Canker)
Type: Fungus
Affects: Peaches, plums, apples, pears
Symptoms:: Branches – Yellowing/wilting/dieback of new shoots. Inner bark shows reddish brown-black.; Discoloration. Gummy cankers swell to girdle and kill infected limb/trunk.
Controls: Remove and destroy infected branches during dry weather, disinfecting pruners between cuts with bleach-water solution (1 part bleach:9 parts water). Keep trees growing vigorously, since fungus does not attack healthy trees. Avoid injury by not making unnecessary wounds in bark. Avoid late season growth which leads to winter dieback (do not fertilize or water in late summer-fall).

Eastern Filbert Blight
Type: Fungus
Affects: Corylus species
Symptoms:: Branches – Fail to leaf out, bark is blackened/shriveled to soil line, can kill entire plant.; Roots – Rotted such that dead stems pull out of soil easily.
Controls: Remove and destroy infected part upon detection. Plant in well-drained soil (sandy loam). Plant disease resistant varieties (such as American hazel, Beaked hazelnut).

Fireblight
Type: Bacteria
Affects: Pears, apples, quince, hawthorn, mountain ash
Symptoms: Branches – Major shoots blacken/wilt/curl downward in less than one week, dead leaves persist on twigs. Cankering.
Conditions: “65/65 rule” – Temperatures above 65 degrees Fahrenheit + humidity greater than 65% can lead to Fireblight. Blossoms and tender shoots are most susceptible. Spread by rain splashing on infected branches.
Controls: Remove and burn infected branches, cutting 9-12” into healthy wood. Best done during winter dormancy, when disease is dormant. If done during growing season, disinfect pruners between cuts with bleach-water solution (1 part bleach : 9 parts water). CAUTION: Overpruning will induce vegetative growth, which is disease susceptible – only lightly prune pears in dormant season. Plant disease resistant varieties, and avoid planting Bartlett pears. Grinding or composting fallen leaves prevents innocculum from overwintering in them.

Peach Leaf Curl
Type: Fungus
Affects: Peaches, nectarines
Symptoms:: Leaves – Yellow/reddish/gray puckering and thickening. Possible leaf drop.; Branches – New growth stunted.; Fruit – Deformed.
Conditions: Thrives during cool, wet springs.
Controls: Remove and destroy infected leaves. Plant disease resistant varieties.

Powdery Mildew
Type: Fungus
Affects: Apples, cherries, grapes
Symptoms:: Leaves – Look like they've been dusted with flour.; Fruit – Skins may crack, develop raised webbing, or have white powdery coating.
Conditions: Thrives in hot weather, especially with cool nights. Contrary to common believe, the disease is not aggravated by wet weather.
Controls: Prune foliage to improve air circulation. Spray foliage thoroughly with a solution of 1 teaspoon baking soda and 1-2 teaspoons horticultural oil:1 quart water as a preventative measure. Plant disease resistant varieties.

Sooty Mold
Type: Fungus
Affects: Many woody plants
Conditions: Mold grows on honeydew - a sticky sweet liquid exuded by sap-sucking insects, indicative of aphids, scales.
Controls: Control sap-sucking insects. Mold is not harmful, but if unsightly, wipe off foliage with damp cloth.