Green Industry - A Knowledge Portal for Commercial Horticulture in Wisconsin (sponsored by University of Wisconsin-Extension)
- Animal damage ()
Animals that do the most damage to herbaceous plants include: deer, rabbits and woodchucks.
Deer damage is distinctive because deer only have teeth on their lower jaws, so when they bite down, they must tear the plant to pull off leaves. Thus, deer damage to plants is rough or shredded-looking. It may also be several feet off of the ground. Plus, if a large amount of plant material is damaged overnight, you should suspect deer.
Rabbit damage looks like someone used a pruner to cut the plant off at a clean, 45-degree angle.
Woodchucks will mow down plants, or sometimes just nibble on succulent material. They are diurnal, so keep on the lookout.
- Cucumber mosaic (Cucumber mosaic virus)
Viruses can only be definitively diagnosed in a lab under high magnification or with various serological test kits. Viruses can retard plant growth and change the appearance of foliage, flowers and fruits. Virus-infected leaves can become spotted, streaked or mottled; they may be distorted or stunted. Veins may lose their color or develop outgrowths. Flowers can be dwarfed, deformed, streaked, faded, or they can remain green and develop into leaf-like structures.
- Gray mold (Botrytis blight) (Botrytis cinerea)
Causes brown, water-soaked spots or decay on leaves or petals. Once diseased tissue encircles the stem, the shoot will wilt. Botrytis is easily diagnosed by the fluffy gray, tan or brown mold produced on blighted plant parts under moist conditions. It rapidly blights flowers. Infected petals that fall onto foliage or stems can cause additional blighting and dieback.
- Herbicide Damage ()
Herbicides can damage any type of plant and injury usually happens as a result of drift, careless application or evaporation during hot weather. Symptoms of herbicide injury may include: twisted plant stems; stem fasciation; narrow, curling or leathery leaves; or excessive callus formation on roots and stems along with secondary root growth. At extremely low application rates, broadleaf herbicides such as 2,4-D, MCPP or dicamba usually will not kill plants, although they will act as growth regulators.
- Inchworms (cankerworm, loopers, spanworms) (Geometridae family)
Inchworms are a collective group of caterpillars including cankerworms, loopers and spanworms. These larvae move distinctively, contracting their bodies into a hump, then extending straight due to only 2-3 sets of prolegs. Colors vary widely depending on species. Female adults are usually wingless and lay egg masses on small twigs, under bark or in trunk crevices. Larvae descend from trees on silk strands when they're ready to pupate, landing on anything in their path.
- Overwatering ()
Overwatering, whether acute or chronic, is usually a death sentence for plants, especially when accompanied with poor drainage. Waterlogged soils limit oxygen uptake by plant roots, which in turn affects the plant's metabolism, nutrient uptake, water absorption and photosynthesis. Symptoms vary from slow growth to plant death and can include: leaf necrosis, dieback, root discoloration, soil blackening, foul odors, slow growth, thinning canopy and chlorosis. Overwatered conifer symptoms are similar, except they can also exhibit needle drop. Overwatering is common in irrigated landscapes, plantings at the bottoms of slopes and in poorly drained containers.
- Powdery mildew (woody plants) (Several)
The upper and/or (less frequently) lower surface of leaves, as well as stems of infected plants, have a white, powdery appearance. They look as though someone has h pper and/or (less frequently) lower surface of leaves, as well as stems of infected plants, have a white, powdery appearance. They look as though someone has sprinkled them with talcum powder or powdered sugar.
- Root rot (woody plants) (Phytophthora species (W))
Gardeners often become aware of root rot problems when they see above ground symptoms of the disease. Plants with root rot are often stunted or wilted, and may have leaves with a yellow or red color, suggestareardenersadners often become aware of root rot problems when they see above ground symptoms of the disease. Plants with root rot are often stunted or wilted, and may have leaves with a yellow or red color, suggesting a nutrient deficiency. Examination of the roots of these plants reveals tissue that is soft and brown.
- Root rot (woody plants) (Pythium species (W))
Gardeners often become aware of root rot problems when they see above ground symptoms of the disease. Plants with root rot are often stunted or wilted, and may have leaves with a yellow or red color, suggesting a nutrient deficiency. Examination of the roots of these plants reveals tissue that is soft and brown.
- Root rot (woody plants) (Rhizoctonia species (W))
Symptoms on the above ground parts of larger plants include necrotic spots and blotches on the leaves, shoot blight and dieback.
- Root rot (woody plants) (Thielaviopsis species (W))
Uncommonly damages woody plants in the landscape. Symptoms include stunting, sparse foliage, poor foliar color and die back after the death of fibrous roots
- Soft scale (Coccidae family)
Soft scales are usually broadly oval becoming larger and more humped as eggs mature underneath the protective cover. Look for adults on twigs or small branches and immature stages on leaves or needles.
- Sooty molds (Several)
Sooty molds are dark fungi that grow on plant surfaces covered in honeydew excreted by insects with piercing/sucking mouth parts such as aphids, scale, mealybugs and whiteflies. It is generally harmless to plants, except when it is prolific, preventing light from reaching leaf surfaces, causing plants stress. This stress may make the plant more susceptible to other diseases or problems.
- Two-spotted spider mite (Tetranychus urticae)
This most common spider mite is miniscule (0.5mm) and prefers to colonize and lay eggs on leaf undersides of most host plants. When populations are high, these mites can be found on all leaf surfaces and stems.
- Whitefly (Aleyrodidae family)
Adult whiteflies are small (1-2mm), white, fly-like insects related to scales, aphids and mealybugs. Their color comes from wax they create to cover their bodies. All whitefly stages are usually found on the undersides of leaves. There can be several generations per year depending on the environment.
- Winter salt injury ()
De-icing salts accumulate in the soil along streets/sidewalks or may be dispersed in an aerosol spray by fast-moving traffic and high winds along wet, salted roads. Salt spray can travel hundreds of feet from the roads where it originated. Symptoms can be similar to other abiotic plant problems, but there are tell-tale indicators including: Damage is more severe on sides of plants facing roads/sidewalks; severity of damage increases with volume/speed of traffic and amount of salt used; plants downwind from roads show more damage than those upwind; most damage occurs within 60' of road and decreases with distance; branches covered by snow or otherwise sheltered show no damage; branches growing above spray drift zone show no damage. Symptoms in deciduous plants include: delayed budbreak; reduced leaf size/stem growth; off-colored foliage; scorched leaves; no flowering; bud/twig death; and branch-tip dieback leading to 'witches' broom' growth below the dead area. Symptoms on conifers include: tips of mature needles turn brown or yellow, discoloration moves down needle eventually killing all of it, then needles fall off; twig dieback; and symptoms manifest only on sides of plants facing roads/sidewalks.
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