What are lichens? Lichens are organisms that arise from mutually beneficial interactions between certain filamentous fungi, algae and yeasts. The filamentous fungi provide the physical structures of the lichens, as well as protection for the algae and yeasts. The algae produce food for the fungi and yeasts via photosynthesis. The yeasts are thought to produce compounds to fend off disease-causing organisms and insect pests.
What do lichens look like? Lichens come in four basic growth forms. Crustose lichens are crust-like and adhere tightly to the surface upon which they grow. Foliose lichens are leaf-like and composed of flat sheets of tissue that are not tightly bound together. Squamulose lichens are composed of scale-like parts. Fruticose lichens are composed of free-standing branching tubes.
Where do lichens come from? Lichens are everywhere. There are an estimated 13,500 to 17,000 species of lichens, and lichens can be found growing in tropical, temperate and polar regions throughout the world. Lichens will grow on almost any surface that is stable and reasonably well-lit. In temperate regions, lichens can often be found growing on the bark of trees or old fence posts. Others lichens grow in less hospitable places, such as bare rock surfaces or old headstones in graveyards, where they aid in the breakdown of rocks and the formation of soil.
How do I save a tree with lichens? DO NOT PANIC! Lichens do not harm trees; they are not pathogens or parasites, and do not cause disease. Lichens are self-reliant, with the algal component of the lichen producing food for the organism via photosynthesis. Lichens absorb water and minerals from rainwater and the atmosphere, and because of this, they are extremely sensitive to air pollution. As a result, the presence or absence of certain lichen species can be used as an indicator of levels of atmospheric pollutants. Information on the abundance and species of lichens growing in an area can give a good indication of the local air quality.
For more information on lichens: Contact your county Extension agent.
What are stinkhorns? Stinkhorns are mushrooms that are found from the tropics to more temperate regions such as Wisconsin. They can suddenly appear in mulch, lawns, and areas with bare soil. These visually-shocking fungi get their common name from their characteristic, unpleasant odor. Although they are often unwanted additions to home gardens, stinkhorns do not cause plant disease. Because stinkhorns can grow on dead organic material, they actually are beneficial in that they contribute to the recycling of plant debris into nutrients that improve soil fertility and can be used by garden plants.
What do stinkhorns look like? Stinkhorns grow into various shapes, but they are best known for looking like horns or penises. A few species grow several appendages, resulting in an octopus-like appearance. Some species have a veil attached below the cap that resembles a lacey skirt flowing from the mushroom’s hollow stalk. Stinkhorns can range in color from white, beige, and olive to bright orange or red with black accents. The tips of mature stinkhorns are usually coated in a spore-containing slime. Gardeners often discover immature stinkhorns as they dig in the soil. The immature forms appear as whitish to pink or purple, egg-shaped masses. Stinkhorns develop rapidly sometimes growing up to four to six inches per hour, and can generate enough force to break through asphalt.
Where do stinkhorns come from? Stinkhorns are often first introduced into a garden in organic materials (e.g., soils and mulches) that contain microscopic hyphae (i.e., fungal threads) of stinkhorn fungi. Once stinkhorns mature, they produce a pungent, off-putting odor that is reminiscent of rotting flesh or dung. This smell may disgust people, but it attracts insects, particularly flies. Flies and other insects eat the slimy material at the tips of stinkhorns and carry spores in this slime to new locations as they move around in the environment. In many ways, this process is comparable to the distribution of pollen by bees (but of course without the more appealing scents associated with most flowers).
How do I control stinkhorns? Stinkhorns are short-lived and will naturally disappear quite rapidly. If stinkhorns are too unsightly, if their smell becomes too putrid, if they attract too many insects, or if there is concern about small children or pets eating them, pluck them from the ground and discard them as they appear. Keep in mind however, that removing stinkhorns will not eradicate them. Stinkhorn hyphae will remain in the soil or mulch and will eventually produce other stinkhorn mushrooms. In addition, flies and other insects carrying stinkhorn spores can introduce these fungi to new locations.
How can I prevent problems with stinkhorns in the future? No fungicide treatments or other methods are available to prevent stinkhorns from appearing in a garden. Removing organic matter (e.g., mulch) or reducing soil moisture may reduce the number of stinkhorns that appear. However, these strategies are unlikely to eradicate stinkhorn fungi. Therefore whenever stinkhorns appear, consider embracing their unique beauty and enjoy their brief time in your garden.
For more information on stinkhorns: Contact your county Extension agent.
What are the benefits of wood mulch? Wood mulch is typically available as chipped wood, or shredded or chunked bark, and can contribute to tree health in many ways. When high quality, composted mulches are applied two to four inches deep in a ring three to six feet in diameter (or greater) from the trunk of a tree, mulch can help preserve moisture, control weeds, limit damage to the trunk from mowers and string trimmers and moderate the soil temperature. Use four inches of mulch when soils are light and well-drained, and two inches of mulch on heavier, clay soils.
Can wood mulch harm trees? Use of improperly composted mulches (some-times called “sour mulches”), can lead to tree nutrient deficiencies. Sour mulches can also produce gases like methane and ammonia that can be toxic to plants. Foliage on trees surrounded by sour mulches may initially turn yellow, then brown, die and fall off. If your mulch smells like vinegar, ammonia or sulfur, it is likely a sour mulch and should be removed. Replace the sour mulch with a high quality, composted mulch and consult with your local Extension agent about testing the soil for nutrient deficiencies. Fertilize appropriately based on the results of these tests.
Improper application of mulch can also lead to problems. Piling wood mulch up against the trunk of a tree can keep the bark underneath excessively wet. This wetness can contribute to bark decay. In addition, use of thick mulch layers (greater than four inches) can lead to overly wet soils that are favorable for development of root rots (see UW Plant Disease Facts D0094, Root and Crown Rot). To avoid these problems, make sure mulch is applied at least four inches away from the trunk of a tree and that the mulch layer is the appropriate thickness for the soil type in your landscape (see above).
Does woody mulch harbor or attract insects? Insects such as earwigs [see UW Bulletin A3640, Controlling Earwigs (available at https://learningstore.extension.wisc.edu/)], centipedes (see University of Wisconsin Garden Facts XHT1113, Centipedes), millipedes (see University of Wisconsin Garden Facts XHT1108, Millipedes) and sowbugs (see University of Wisconsin Garden Facts XHT1110, Sowbugs) can feed on decaying organic matter in mulches. While these insects are often only nuisances, earwigs can feed on and cause damage to a variety of ornamentals, particularly to flowering plants. If mulch is used near entrances to a home or around basement windows, these unwanted insects may get inside. Termites ingest wood and can be attracted to wood mulch, but new termite colonies are not likely to become established due to use of wood mulches. Typically, termites are not a problem in Wisconsin, and when colonies are found, they occur only in the southern half of the state.
Carpenter ants [see UW Bulletin A3641, Controlling Carpenter Ants (available at https://learningstore.extension.wisc.edu/)] and powderpost beetles (see University of Wisconsin Garden Facts XHT1053, Powderpost Beetles) are unlikely to utilize mulch as a food source because conditions required for their development would not be satisfied by wood mulch. Carpenter ants do not ingest wood as a food source; instead, they chew non-living wood (in trees or landscape timbers, etc.) to excavate galleries in which they live and raise their young. Since wood mulch is composed of small wooden pieces, it would not serve as a home. To avoid potential insect problems, keep mulch as far away from the foundation of your home as possible and seal all holes and crevices that insects might use as entry points. Also, periodically inspect landscape timbers and the house for termites.
Does woody mulch harbor tree pathogens? Wood mulch may come from many sources, including trees and shrubs that have died from a wide range of diseases. To be harmful to your trees, disease-causing organisms (pathogens) would have to survive in mulch and these organisms would have to move from the mulch either directly, or through the soil, to their new host – your tree. There is currently very little research on this topic.
Elm trees killed by Dutch elm disease (see UW Plant Disease Facts D0045, Dutch Elm Disease), can serve as breeding areas for native and European elm bark beetles. Bark beetles that breed in logs or firewood from these trees can pick up the fungi that cause Dutch elm disease (Ophiostoma ulmi and Ophiostoma novo-ulmi) and carry these fungi from tree to tree. Chipping infected elm trees creates an unfavorable environment for bark beetles yet there is no scientific literature that describes the level of risk of transmitting the Dutch elm disease fungi from wood chips or bark chunks to healthy elms.
Oak trees killed by oak wilt (see UW Plant Disease Facts D0075, Oak Wilt) can be attractive to several sap-feeding beetles that can potentially pick up the oak wilt fungus (Bretziella fagacearum) and move it in the landscape. This process is affected by moisture and temperature and would likely be disrupted by the chipping and composting process yet there is no scientific literature that describes the level of risk of transmitting the oak wilt disease fungus from wood chips or bark chunks to healthy oaks.
Research at the University of Wisconsin-Madison suggests that wood chip mulches produced from trees suffering from Verticillium wilt (see UW Plant Disease Facts D0121, Verticillium Wilt of Trees and Shrubs) can serve as a source of the fungus (Verticillium dahliae) that causes the disease. These studies show that Verticillium can survive for at least one year in mulch and that use of this contaminated mulch can lead to Verticillium wilt in both woody and herbaceous plants. Therefore use of mulches produced from trees with Verticillium wilt should be avoided.
For more information on wood mulch and tree health: Contact your county Extension agent.
What are slime molds? Slime molds are members of a shape-shifting group of organisms called myxomycetes. These organisms are found all over the world, even in deserts, high altitudes, and on the edges of snowbanks. Although they often resemble fungi, slime molds are more closely related to amoebas and certain seaweeds.
What do slime molds look like?A slime mold spends most of its life as a lumpy mass of protoplasm, called a plasmodium, that moves and eats like an amoeba. It may be white, yellow, orange, or red. The color of a particular species can vary slightly with temperature, pH, and the substances the plasmodium eats. One very common slime mold, Fuligo septica, looks like dog vomit or scrambled eggs, from which it derives its common names. Others resemble a network of veins or a fan. In the course of a few hours a slime mold can transform from its amoeba-like phase into its fungus-like phase, which produces spores.
Where do slime molds come from? The most common slime molds in Wisconsin love moist, shady places like crevices in rotting logs, leaf letter, and bark mulch. Spores of slime molds are resistant to adverse conditions and will germinate after a heavy rain. The plasmodium forms from many individual swimming cells called swarm cells. The plasmodium can move at a very slow rate, feeding on bacteria, other microorganisms, and organic matter. Changes in moisture or temperature, or exhaustion of its food supply can cause the slime mold to move to a drier, more exposed location to produce spores.
What do I do with slime molds in my garden or lawn? Slime molds do not cause diseases. However, they do use leaves and stems of plants as surfaces on which to grow and can block sunlight leading to leaf-yellowing. The best way to get rid of slime molds is to break them up and dry them out. Rake up and dispose of slime molds on bark mulch. For slime molds on turf, mow the lawn, and rake up the thatch. Alternatively, you may want to enjoy slime molds, if you find one in your yard. These complex organisms are fascinating to observe with a hand lens and can be “captured” and grown indoors as a science project.
What is huitlacoche? Huitlacoche is the Native American name for the mushroom-like masses found on the ears of corn and corn relatives (collectively called teosinte). Huitlacoche can be a major problem for sweet corn growers where it is referred to as common corn smut (see UW Plant Disease Facts D0031,Common Corn Smut), causing yield and quality losses. However, huitlacoche is also considered a culinary delicacy in many cultures. In Mexico, huitlacoche is considered a gift from the gods, and is commercially available in many markets. In the United States, huitlacoche is less common commercially, but can be found in the ethnic sections of some grocery stores.
What does huitlacoche look like? Huitlacoche is a tumor-like growth (called a gall) that forms from corn kernels. Galls can swell to ½ to 11 inches in diameter. Huitlacoche initially has a streaked, silvery appearance, but eventually develops a scorched, blackened look. Huitlacoche galls remain smooth until they rupture releasing a black, inky material that eventually becomes sooty, coarse and dry.
Where does huitlacoche come from? Huitlacoche is actually a corn disease, caused by the fungus Ustilago maydis. The black, inky material released by huitlacoche is a mass of spores produced by the causal fungus. These spores can be easily moved by wind and can survive for many years in soil. Normally U. maydis infects unpollinated corn silks, but the fungus also can infect through wounds caused by heavy wind, heavy rain, or hail.
What can I do with huitlacoche if I find it? Huitlacoche is edible, has a smoky, earthy taste, and is an excellent source of carbohydrates, proteins, fats, vitamins and minerals. To enjoy the flavor of huitlacoche to its fullest, harvest galls before they begin to dry, but after they have turned dark grey. DO NOT use galls that are powdery inside when split open. If you prefer not to harvest your own huitlacoche, you can purchase canned hutlacoche at your local Mexican market. Although use of hutlacoche as a food originated in Mesoamerica (i.e., parts of Mexico and Central America), like many other gourmet mushrooms, chefs have begun to incorporate huitlacoche into non-traditional dishes including macaroni and cheese, and even ice cream. See http://www.sweetcorn.illinois.edu/Common-smut/Recipes.htm for sample huitlacoche recipes.
How do I encourage more huitlacoche to form? While huitlacoche can be harvested from naturally infected ears of corn, you can increase your yield by artificial inoculation. Prior to pollination, soak corn silks with huitlacoche spores mixed with water. After inoculation, water and fertilize corn plants for optimal growth. If your inoculation is successful, galls should start to form within two weeks. Galls are usually best if harvested 16 to18 days after inoculation.
For more information on huitlacoche: Contact your county Extension agent.
What is dodder? Dodder is the name of several species of parasitic plants that are widely distributed in North America and Europe. Plants parasitized by dodder include alfalfa, carrots, onions, potatoes, cranberries, a variety of herbaceous and woody ornamentals, and many weed species. Parasitized plants become weakened, have reduced yields (in the case of agronomic crops), and can potentially die.
What does dodder look like? Dodders lack roots and leaves, and also lack chlorophyll, the green pigment found in most plants. Dodders have slender, yellow-orange stems that cover infected plants in a spreading, tangled, spaghetti-like mass. From May through July, dodders produce white, pink, or yellowish flowers.
Where does dodder come from? Dodders produce large numbers of seeds that germinate in the spring to produce shoots that attach to suitable host plants. Dodders penetrate host tissue, and absorb nutrients via specialized structures called haustoria. Once established on a host, the bottom of a dodder plant dies (thereby severing its connection with the soil), and the dodder plant becomes dependent on the host plant for water and nutrients.
How do I save plants parasitized by dodder? On woody ornamentals, simply prune out dodder-parasitized branches. When small patches of dodder occur among herbaceous plants, apply contact herbicides such as 2,4-D early in the season, preferably before dodder seedlings have parasitized host plants. Keep in mind that use of contact herbicides will likely also kill host plants. Alternatively, cut or burn dodder and parasitized plants to keep dodder from spreading, and to prevent seed production. For widespread dodder infestations, a combination of frequent tilling, burning and herbicide applications may be needed to achieve control. Be sure to read and follow all label instructions of the herbicide that you select to ensure that you use the product in the safest and most effective manner possible.
How do I avoid problems with dodder in the future? Dodder’s wide host range and ability to survive as dormant seeds in soil make eradication difficult. Preventing introduction of dodder is the best method of control. Use dodder-free seed, and be sure to clean equipment thoroughly after working in a dodder-infested area. Try to restrict animal movement between infested and non-infested areas as well. Depending upon the specific crop or location, use of pre-emergent herbicides containing DCPA, dichlobenil, propyzamide, or trifluralin may be possible to prevent germination of dodder seeds. Destroy actively growing dodder and any parasitized plants before the dodder produces seeds. In agricultural settings where dodder has been a problem, rotate away from susceptible crops and grow non-host crops (e.g., corn, soybeans, or small grain cereals). In conjunction with rotation, adequate control of weed hosts is critical to achieve control.
For more information on dodder: Contact your county Extension agent.
What is black walnut toxicity? Black walnut trees (Juglans nigra) produce a toxic substance (called juglone) that prevents many plants from growing under or near them. Related trees like butternut (J. cinerea) and shagbark hickory (Carya ovata) also produce juglone, but in lower concentrations than black walnut. Juglone occurs in all parts of black walnut trees, but especially in buds, nut hulls and roots. The toxic effects of a mature black walnut tree can extend 50 to 80 feet from the trunk of the tree, with the greatest toxicity occurring within the tree’s dripline. In this area, plants susceptible to juglone may wilt or die; plants tolerant to juglone will grow normally. Vegetables such as tomato, potato, eggplant and pepper, and ornamentals such as lilac, peony, rhododendron and azalea are particularly sensitive to juglone.
What do the effects of black walnut toxicity look like? Plants sensitive to juglone may be stunted, have yellow or brown, twisted leaves, exhibit wilting of some or all plant parts, and die over time. Often, the vascular (i.e., water-conducting) tissue of affected plants will be discolored. Symptoms may occur rapidly, even within a few days after sensitive species are transplanted into a walnut tree’s root zone. Alternatively, some plants may survive for years near a young walnut tree but then wilt and die as the tree increases in size. Black walnut toxicity can be confused with wilts caused by bacterial and fungal pathogens (e.g., see UW Plant Disease Facts D0121, Verticillium Wilt of Trees and Shrubs, and D0122, Verticillium Wilt of Vegetables), herbicide injury (see UW Plant Disease Facts D0060, Herbicide Damage), or drought.
How do I avoid problems with black walnut toxicity? There is no cure for a plant affected by walnut toxicity. Removing a walnut tree may not be practical, as the tree could be the focal point in a landscape. In addition, even if a walnut tree is removed, juglones will not immediately be eliminated, because it is next to impossible to remove all root pieces from the soil and remaining pieces may continue to exude toxins for several years as they decay.
When establishing a garden around a walnut tree, try to plant species that are tolerant to juglone (see table on the reverse side). If you are growing sensitive species near a walnut tree, transplant them elsewhere in your garden. If you must grow sensitive plants near a black walnut, keep beds free of walnut leaves and hulls, and remove walnut seedlings as they appear. Grow shallow rooted woody and herbaceous plants, and improve drainage to help diminish the effects of juglone. Alternatively, consider building raised beds with wood, stone, or concrete barriers that limit root growth through and under the beds.
When disposing of bark and wood from a walnut tree, do not use these materials for mulch.
The information in the following table is intended to provide guidance in selecting plants to grow near walnut trees. Inclusion of plants in this table is based on observation, not on formal testing. In addition, the plant lists in this table are by no means exhaustive. Oftentimes the juglone sensitivity or tolerance of specific plants has never been observed or documented. Finally, sources often disagree on whether particular plants (e.g., columbine, lily, narcissus, tulip) are juglone sensitive or tolerant. Some varieties may be susceptible while others may be tolerant. Most plant species with conflicting information regarding their sensitivity or tolerance to juglone have not been included in the table.
What are bird’s nest fungi? Bird’s nest fungi are a group of organisms named for their resemblance to miniature bird’s nests. These fungi are found all over the world, growing and reproducing on decomposing organic matter. In temperate regions, bird’s nest fungi can be found virtually anytime there are damp, shady conditions, but they are most commonly seen in the autumn.
What do bird’s nest fungi look like?Bird’s nest fungi can be identified by the appearance of a brown, gray, or white outer “nest”, with brown or white “eggs” inside. The “eggs” are actually spore-containing structures called peridioles that rest inside the cup-shaped fruiting body (reproductive structure). Individual fruiting bodies are usually only ¼ to ½ inch in diameter and vary in shape, size, and color depending upon species.
Where do bird’s nest fungi come from? Bird’s nest fungi are classified in the fungal group gasteromycetes. Cyathus spp., Nidula spp., Crucibulum spp., Nidularia spp., and Mycocalia spp. are the most common genera of bird’s nest fungi. These fungi are often found in moist, shaded areas, and typically survive on soil, plant remains, decaying wood, or horse and cow excrement. The characteristic “cup and egg” structure of the bird’s nest fungi provides a unique method of dispersing spores. In a storm, the “eggs” are splashed out of the “cups” by raindrops. “Eggs” can travel a three feet or more before sticking to another object. When the “egg” dries, it splits open releasing fungal spores.
What do I do with bird’s nest fungi in my yard? Bird’s nest fungi are not harmful to living plants, and control of these fungi is typically not necessary. In fact, bird’s nest fungi can be fascinating organisms to observe when you find them in your yard. On occasion, bird’s nest fungi can be a nuisance, particularly when the “eggs” stick to objects such as houses or cars where they are difficult to remove. If bird’s nest fungi become a nuisance, the number of fruiting bodies can be reduced by decreasing irrigation and raking the affected area. The use of non-mulch groundcovers, such as ivy, can also reduce the occurrence of these fungi. Fungicides are not recommended for treatment of bird’s nest fungi.
For more information on bird’s nest fungi: Contact your county Extension agent.