Yard & Garden Line News Volume 2 Number 12                                                              August 1, 2000

Features this issue: Repotting Houseplants Understanding Soil pH Fairy Rings: Curse or Curiosity Too much of a Good Thing? Nuisance Weevils in Homes Earwigs In and Around Homes Concealed Wasp Nests in Homes Jumping Oak Gall Pine Root Collar Weevils Editorial Notes

Repotting Houseplants
Deborah Brown, Extension Horticulturist

Potbound.

Begonia. Photo credit: U of M Ext. Scv.

Increased light levels in spring and early summer spring may have caused some of your houseplants to put on enough new growth that they require repotting into larger containers. The rule of thumb is to choose pots only one size larger than currently in use. Going from a small containers to ones much larger increases soil volume to the extent that it will stay wet a longer time when you water, and roots may suffer.

Pick a container with at least one drain hole, then cover that drain hole with an irregularly shaped pebble or piece of broken clay pottery to keep soil in, but allow excess water out. Add fresh potting soil, transfer the plant -- roots, soil, and all -- then firm more soil gently between the root ball and sides of the container. Unless you press this soil in, water will run too quickly down the inside walls of the container, rather than thoroughly soaking the entire soil mass.

You can also root prune some houseplants to control their growth and keep them in the same containers year after year. Knock the plant out of its pot and shave 1/2 to 1 inch off the soil and roots from both the bottom and sides of the soil mass. Add fresh potting soil and replace the plant, firming soil along the sides as described above.

When root pruning, it's important to also also prune the topgrowth slightly in order to keep the roots and foliage "in balance." Not all houseplants may be pruned, however. It's not a good idea to prune palms, Norfolk Island Pines, yuccas, or most houseplants that have a strong central trunk with little or no branching.


Understanding Soil pH
Carl Rosen, Department of Soil, Water, and Climate

pH shows up twice on the form. Image credit: Y & GL

Nutrient deprived white pine. Photo credit: Beth Jarvis

Pink hydrangea in high pH soil. Photo credit: Beth Jarvis

Healthy blueberries. Photo: Beth Jarvis

Iron-deficient blueberries. Photo: Carl Rosen

One of the most important measurements on a soil test report is soil pH. The soil test report will provide you with the pH level of your soil and in some cases the "buffer index". The significance of these measurements and implications for plant growth and pH adjustment are discussed below.

Soil pH: The pH of a soil is a measure of soil acidity or alkalinity and technically is a measure of the hydrogen ion concentration on a logarithmic scale from 1 to 14. A pH of 7 is neutral, a pH below 7 is acid, and a pH above 7 is alkaline. A low pH has a high amount of hydrogen ions and a high pH has a low amount of hydrogen ions. Soil pH is an important chemical property because it affects the availability of nutrients to plants and the activity of microorganisms in the soil.

Availability of nitrogen, phosphorus, and potassium decreases as pH decreases. In addition the activity of bacteria that fix nitrogen for legume plants also decreases as the pH drops below 5.5. As the soil pH increases above 7.0, the availability of phosphorus and many micronutrients, especially iron decreases. In most soils, iron is present in large amounts but as the pH increases it becomes tied up and is not available for plant uptake. Typical symptoms of iron deficiency are yellow leaves with green veins and usually seen first on the youngest leaves.

While many plants can tolerate pH ranges between 5.2 and 7.8, most plants grow best in mineral soils when soil pH is between 6.0 and 7.0 (slightly acid to neutral). This general rule applies to most of the commonly grown fruits, vegetables, flowers, trees, and shrubs. Most turfgrass tends to grow best between 5.5 and 6.5. Many evergreen trees and shrubs prefer a pH range of 5.0 to 6.0. Potatoes tolerate a wide range in soil pH, but potato scab, caused by an actinomycete, can be a problem if the pH is above 5.3.

Some important exceptions include blueberries, azaleas, and rhododendrons (acid loving plants) that require acid conditions between pH 4.5 and 5.2. Iron deficiency in acid loving plants can occur when the pH is less than 7.0 Blue hydrangeas also require a pH lower than 5.0 to induce the blue flower color.

The buffer index and raising soil pH: The buffer index is a laboratory measurement used to determine how much lime (calcium carbonate or dolomite) is needed to raise the pH of a given soil. The soil pH value reported in a soil test indicates whether lime is needed, but cannot be used to determine how much lime is needed. The amount of lime to apply depends upon reserve soil acidity, which is measured by the buffer test and reported as the buffer index. The lower the buffer index, the larger is the quantity of lime required to raise soil pH to the desired level. The buffer index is only determined for soil samples with a soil pH less than 6.0. For most landscape plants, your soil test report will tell you how much lime to apply if your soil pH is less than 6.0. If your soil pH is above 6.0 a buffer index is not needed because your soil will not require any lime.

In many areas of Minnesota and especially in urban landscapes, the soil pH is alkaline and will NOT need lime. Do not apply lime unless your soil test indicates a need. Application of lime when it is not needed can cause micronutrient deficiencies.

Lowering soil pH (soil acidification): For most plants, soil acidification is unnecessary, but lowering soil pH is frequently required to grow blueberries, azaleas, and rhododendrons successfully. These plants require an acid soil with a pH between 4.5 and 5.2. If soil pH is above this range, it is usually desirable to lower soil pH to 4.5 prior to planting. Over time pH will tend to increase, especially if the water supply used for irrigation is alkaline as it is in many parts of Minnesota and in most municipal water supplies.

Elemental sulfur, iron sulfate, and aluminum sulfate are amendments that can be used to lower pH. Recommendations are provided on the soil test report to lower pH only for acid loving plants.

Fine-textured clay and silt loam soils, and high lime soils such as those in western Minnesota with a pH greater than about 7.3, require high rates of acidifying amendments. These soils are not recommended for growing acid-loving plants, because the amendment rates required to lower soil pH initially result in excessive levels of soluble salts and the soil pH will eventually increase. The best strategy for soils with a pH greater than 7.0 is to select plants that are adapted to high pH conditions. Refer to the appendix of BU-1731-F Soil Test Interpretations and Fertilizer Management for Lawns, Turf, Gardens, and Landscape Plants for soil pH preferences of selected landscape plants.

Fairy Rings: Curse or Curiosity
Jon F. Powell, Department of Plant Pathology

Where fairies danced... Photo credit: Jon Powell

Fairy rings are those rings or arcs of grass that appear greener in color and grow faster than neighboring turf. Normally this is the extent of the effect of the grass, however in southern states and less commonly in Minnesota, fairy rings produce rings of dead grass with the vigorous growth at the margins of the dead ring. Fairy rings may vary in size from being just a couple of inches to several hundred feed in diameter. Under favorable conditions mushrooms may be produced from many of these rings.

Originally, fairy rings were believed to be the after effects of a site where fairies had danced in a circle and the rings were an after effect of their magical presence. However, we now know that fairy rings are the result of work of fungi. In particular, by one of over 60 species of fungi that are members of the basidiomycetes, the same group of fungi that are responsible for producing mushrooms.

Fairy ring mushrooms. Photo credit: Jon Powell

Fairy rings can occur on just about any turf, whether a native grasslands, parks, home lawns, or golf courses. They common occur at areas that were previously forested or where woody materials have been buried. The fungi begin from a point and grow radially, increasing the diameter of the ring by up to 2 feet per year. Interestingly, if two fairy rings run into one another, the rings will cease growing in that region as the fungi inhibit the growth of one other.

The main factor that promotes the growth of these fungi is the presence of organic matter in the thatch or soil which the fungus uses as a food source. As the fungus decomposes the thatch and organic matter it releases nitrogen which results in stimulated growth of the grass in the area. In turf with particularly heavy thatch build-up, it is sometimes possible to feel the reduction of thatch on the inside of these rings where the fungus had degraded the thatch layer. Due to the loss of thatch, the grass inside the rings may be better quality than outside the rings.

Turf wilts where fungi colonize. Note greener grass inside ring. Photo credit: Jon Powell

While fairy ring fungi do not generally infect grass plants, or do so weakly when they do, they are often considered to be a nuisance by affecting the uniform appearance of the turf or were they do cause plant death. One of the causes of plant death has been attributed to the production of toxins by the fairy ring fungi. The other negative side effect that is observed with many fairy rings is induction of drought stress at the zone of stimulated growth. This is the result of the body of the fungus (mycelium), often visible as white strands in a cross section of the soil through a ring. When the fungus heavily colonizes the soil surface, it has a water repelling (hydrophobic) effect which prevents water from penetrating into the soil resulting in wilting of the grass plants which may result in death.

So what are your choices if you wish to get rid of a fairy ring? The most reliable method is to dig it out. In order to do this, you would need to dig out the entire ring to a 1 foot depth and to an additional foot beyond the zone of stimulated growth. The soil and turf needs to be removed from the site and new soil brought in and reestablished from new seed or sod. There are two fungicides, flutolonil (ProStar) and azoxystrobin (Heritage), that are labeled for the management of fairy rings. These products must be drenched into the soil and have met with mixed results.

Cross section of fairy ring showing mycelium in soil Photo credit: Jon Powell

An alternative strategy to limit the undesirable effects of fairy rings is to manage the symptoms. One such strategy is to saturate the ring with water for 48 hours. This treatment probably works by leaching the nitrogen thereby limiting the stimulation of growth, but the ring will likely reappear the next season as the fungus is still present in the soil. If the problem with the ring is primarily drought stress and wilting of the turf in the zone of stimulation, the soil may wetted by drenching the ring with a wetting agent or with soapy water (1 teaspoon dish soap/gallon). This will help break down the hydrophobicity of the fungal mycelium and permit the water to soak into the soil. It is important to water the area to a depth of 4-6 inches to prevent further wilting. The uneven growth of grass due to a fairy ring may be masked by increasing the nitrogen fertility program that the turf is receiving. With the understanding that fairy rings thrive on thatch and organic matter in the soil, efforts to reduce thatch accumulation, such as aerification can help minimize the effects of fairy rings.

Due to the minimal effects fairy rings have on turf, perhaps the best way to deal with fairy rings is to simply appreciate this curiosity of nature.

Too much of a Good Thing?
Beth Jarvis, Yard & Garden Line Project Coordinator

Photo: AAS

If your garden overwhelming you?? Too many tomatoes? Billions of beans? A zillion zucchini?

Some of the local foodshelves would love to take that surplus off your hands! To find out which foodshelves have facilities to handle fresh produce, call the Minnesota Foodshelf Association:

Local number 612-870-9170
Out of Metro 1-800-782-6372

Nuisance Weevils in Homes
Jeffrey Hahn, Assistant Extension Entomologist

Strawberry root weevils. Photo: Y&:GL

Longhorned weevils. Photo: Y&:GL

Throughout Minnesota in July, several different species of weevils have been found indoors. Sometimes these weevils have been described as aphid-like with hard shells or in other cases as having a large bulb-like or pear shaped abdomen. Some people confuse these weevils for ticks. However, insects have six legs, (don't count the antennae as legs), while ticks have eight legs. These weevils are not very big, ranging in length from 1/8 inch (Barypeithes pellucidus) to 1/4 inch long (strawberry root weevil). They are generally dark-colored, although Polydrusus impressifrons is iridescent green.

As larvae, these weevils feed on the roots of plants. For example, Sciaphilis asperatus larvae feed on the roots of sugar and red maple, yellow birch, hazel and hophornbeam. Adults generally feed on leaves, often on edges, of various plants. Neither weevil adults or larvae are considered to be serious landscape pests.

During the summer, It is common for adult weevils to accidentally enter homes, sometimes in large numbers. Dry weather can drive weevils indoors as they search for moisture. Strawberry root weevils in particular are often found around sources of moisture in homes, such as sinks, basins, tubs.

These weevils are harmless to people and pets and cause no damage to food, clothes, furniture or property. Nuisance weevils do not reproduce indoors and are present for a short time before they go away on their own. However, not all weevils are innocuous in homes: rice and grainery weevils can infest dry food products while Hexarthrum ulkei, can infest conifers similar to powderpost beetles. These weevils generally have longer, more slender snouts than nuisance weevils.

Despite their harmless nature, controlling nuisance weevils is often challenging. Start outside around the home's exterior. Check the foundation and around windows and doors for cracks, spaces, gaps, and tears in screens that may allow insects to enter homes. Repair or seal any that are found. If too many weevils continue to enter the home that can't be tolerated, consider an insecticide application. Residents have access to products containing permethrin, bifenthrin and diazinon to treat the exterior of buildings. For weevils that are found indoors, vacuum them or remove them by hand. Insecticides are not recommended for nuisance weevil control indoors. These weevils go away on their own by August.

Earwigs In and Around Homes
Jeffrey Hahn, Assistant Extension Entomologist

European earwigs (female-left, male-right). (Red color caused by scanner.) Photo: Y&GL

About ten years ago, earwigs were rarely seen in Minnesota. Today the European earwig has become very common in the Twin Cities and other areas in Minnesota. An earwig is about 5/8 - 3/4 inch long, reddish brown with very short wings. It is flat and has conspicuous antennae and legs. It does bear a resemblance to a cockroach or a beetle. However, it‘s easy to identify an earwig from its forcep-like pincers on the tip of its abdomen. You can distinguish the gender of earwigs from the shape and size of these pincers: males have stouter, curved pinchers while females possess more slender, straight pincers.

Earwigs prefer to be in dark, confined damp areas and are found under stones, firewood, potted plants, welcome mats, newspapers, and similar objects. They are mostly active at night. Earwigs are scavengers feeding on decaying plant tissue, live and dead insects, as well as live plants.

Despite their name and reputation, earwigs are harmless to people. They do not crawl into people ear's or bore into their brains. They can grab onto objects with their pincers but they can not squeeze very hard. When they are found around homes, they are just a nuisance.

People are most concerned about earwigs when they come into their homes. To keep them out, caulk and repair spaces and cracks around the outside of your home, especially at ground level. Also clean up debris around the house, such as firewood and stones which can give earwigs places to hide close to your home.

If you still find a lot of earwigs inside, spray around the foundation of your home with permethrin, bifenthrin, or diazinon. However, if earwigs are determined, some will still get inside your home. Just remove those with a dust pan or vacuum. Fortunately, they don't reproduce indoors and are a problem just during the summer.

Concealed Wasp Nests in Homes
Jeffrey Hahn, Assistant Extension Entomologist

Yellowjacket nest in building. Photo: Jeff Hahn

As a result of the early spring we enjoyed earlier this year, yellowjackets are occurring in above average numbers. Nests are becoming large enough that residents are discovering them sooner than normal. When nests are in wall voids or other hidden sites, you don't see the nest, although you do see the wasps flying back and forth from the entrance.

The worse thing a person can do is to seal the nest opening while the wasps are still alive. They will search for another way out which usually means they find their way into the interior of the home. The same can happen if you spray an insecticide into the nest opening. Because the nest probably isn't directly adjacent to the opening, you will kill some wasps, but aren't likely to eliminate the nest. However, you are likely to irritate the wasps which may also drive them indoors.

The best method for eliminating a yellowjacket nest in a wall is to apply an insecticidal dust. Boric acid or diazinon are available to the public for use indoors, but they can be hard to find. You may also consider an experienced pest control service to dispatch those hard to reach nests.

Jumping oak gall
Jeffrey Hahn, Assistant Extension Entomologist

Jumping oak galls on bur oak. Photo credit: Jeff Hahn

Galls are abnormal plant growths caused by a variety of organisms, including insects. Oaks, in particular have many different types of galls on them. One common type of gall is the jumping oak gall, caused by a tiny cynipid wasp, Neuroterus saltatorius. In Minnesota, jumping oak gall is found on white and bur oaks. In early spring, adult females emerge from last year's galls. They lay eggs on opening leaf buds which forms blister-like galls. Later in the summer, male and female adults emerge. After mating, females lay eggs on mature leaves. Seed-like galls form on the upper leaf surface. There is one insect in each gall.

When mature, these galls fall to the ground. The larva remains active inside the gall and can cause the gall to "jump" several inches off the ground. This is very similar to a Mexican jumping bean which is due to the activity of a Mexican bean beetle larva moving inside the bean. When these ‘jumping' galls are encountered, they are just a curiosity and are harmless to people.

Jumping oak gall rarely, if at all, has any lasting effect on oak trees. Although these galls can be abundant, they are not likely to remain so more than a year or two. No control is necessary.

Pine Root Collar Weevils
Jeffrey Hahn, Assistant Extension Entomologist

Pine root collar weevil damage. Photo credit: Dept. of Entomology

Pines are subject to attack from a small insect known as pine root collar weevil. The larvae infest and girdle the root collar (where the roots meet the stem). Pines that are attacked put out large amounts of pitch which darken the root collar and the adjacent soil. Needles on infested trees turn yellow to red throughout the tree. Small trees can be killed while older trees can be so seriously injured that the tree falls over. Trees grown in open fields (like young plantations) are most susceptible to pine root collar weevils.

Adults lay eggs during spring and summer at the base of the pine. After hatching, the larvae bore into the inner bark of the root collar and large roots. They feed until fall and remain inactive during winter. The following spring the larvae resume feeding. By summer, they pupate in chip cocoons constructed of sawdust and other debris. Adults emerge in late summer. They are not strong fliers and do not travel far to attack new trees. Adult weevils prefer to feed during the evening when temperatures are cooler and they can avoid direct light. All stages of this insect may be found throughout the growing season.

If you have a problem with pine root collar weevils, you can take advantage of the fact that adult weevils are sensitive to light and temperature. Remove the lower one or two whorls of the tree to allow more light to the root collar. Also remove leaf litter and the soil at the base of the tree. Do not mulch if there is a problem with pine root collar weevils.

You can supplement this with an insecticide application. Spray in mid-May when adults are first laying eggs and again in mid-August when adults start to emerge. Spray the root collar and the soil in a foot radius from the tree. Homeowners can apply chlorpyrifos (Dursban) or contact a professional service to make the application.

Editorial Notes

Bell flowers. Photo credit: Rebecca Jarvis

The Campanula sp. at left was photographed at Enger Tower, Duluth, in late July. Plants bloom a week or two later there than here in the (relative) banana belt. Speaking of relatives, the photographer is my niece.

With summer pretty much at its peak, we must start anticipating fall chores. Weed control in lawns is best accomplished in fall. In the next issue, Roger Becker, a horticulturist and agronomy weed specialist, will talk about herbicides--how they work, etc. It should cover at least selective herbicides (dandelion control) and may cover non-selective (eg: RoundUp). The non-selective herbicides might wind up waiting for a subsequent issue. Closer to spring, Roger has promised to do a piece on pre-emergents for crabgrass and annual weed control.

Jon Powell, turf pathologist, will return this fall to discuss other lawn diseases.

Remember the apple bagging experiment from last year? Larry Zilliox has completed a second year and has promised an update. He had more orchards more widely distributed over the state. This could be the best non-chemical apple production method yet--for homeowners, anyway.

This winter, Carl Rosen will discuss soluble salts test levels. Doug Foulk will talk about growing grapes in Minnesota and varieties to seek out when perusing garden catalogs. George Heimpel will return to talk about conservation biocontrol.

As soon as the data's analyzed, we'll also be hearing from Carl Rosen on using treated lumber in garden beds. He has a graduate student testing garden soils adjacent to treated lumber to see if arsenic leaching is a problem.

The plant pathology supervisor position at Yard & Garden search continues. Application deadline is August 15. If you know someone with at least a MS in Plant Path., who loves to teach and write, point them our way! To see a copy of the listing, click here on job opening. In the mean time, we'll probably be a bit light on plant disease articles.

I rely on your comments and questions for ideas for future articles. Please, keep the story ideas coming! We really try to be responsive to your needs.

Please feel free to cut and paste any of the articles for use in your own newsletters. All we ask is that you give our authors credit.

Back issues Yard & Garden Line News are on the Yard & Garden Line home page at www.extension.umn.edu/yardandgarden/. Our home page has clickable links to most of the components of the Yard & Garden Line, such as Bell Museum of Natural History, INFO U and the Soil Testing Lab.

Deb Brown answers gardening questions on Minnesota Public Radio's (MPR) "Midmorning" program on the first Thursday of every month at 10 a.m. Katherine Lanpher hosts the program that is broadcast on KNOW 91.1 FM, and available state-wide on the MPR news radio stations.

If you would like to receive an e-mail reminder when the next issue of the Yard & Garden Line News is posted to the web, just send an e-mail to: listserv@lists.umn.edu (note: the second E in listserve is omitted), leave the subject line blank, then in the body of the message, type: sub yglnewslist
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Happy gardening!

Beth Jarvis
Yard & Garden Line Project Coordinator

Websites
Sustainable Urban Landscape Information Series. This site contains everything from landscape design planning and lawncare to both herbaceous and woody plant selection databases. The URL is:http://www.sustland.umn.edu


For pesticide info, for both home owner and professionals, check out:

http://www.crc.agri.umn.edu/~mnhelps/

There's also some very interesting reading at Forest Products website. To get there from here, click on: http://www.cnr.umn.edu/FR/extension/
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