|Yard & Garden Line News
Volume 5 Number 14 September 1, 2003
The Considerate Gardener's Guide to Pesticides - Part 2.
Dean Herzfeld, Coordinator, Pesticide Applicator Training
Beth Jarvis, Yard & Garden Line
One often hears people talk about herbicides and pesticides. That's not exactly correct so before we proceed further:
2,4-D injury on left,
normal on right.
A pesticide is anything that kills, mitigates, or repels a pest. Not all pesticides are designed to kill. The term pesticide include herbicides for weeds, insecticides for insects, fungicides for fungi and molds, rodenticides for rodents and many more. (A more complete definition can be found in the April 1, 2001 issue of Yard & Garden Line News in our article about hiring a pesticide applicator:
One way pesticides may harm a neighbor's plant is by drift. What really is drift?
The EPA's definition of drift is 'the physical movement of a pesticide through the air at the time of application or soon thereafter, to any site other than that intended for application.' The definition generally excludes any pesticide movement, such as soil erosion that contains pesticides, that occurs after the pesticide is applied.
To reduce the potential for drift, pesticides should be applied when the wind is 3-5 mph, steady, and blowing in a safe direction and at moderate temperatures. Drift never happens up wind. Read the label and watch temperatures, as some products become more volatile at temperatures above 80 degrees F. Chance of drift goes up as wind speed approaches 10 mph, at which point no pesticides should be applied.
Recent research has shown the biggest culprit in causing drift are fine spray droplets less than 250 microns in diameter (250 microns is smaller than a toothbrush bristle but about 2 ½ times larger than the width of human hair). These small droplets can hang in the air a very long time. Unfortunately, most sprayers designed for home use can not be adjusted for pressure (lowering pressure increases droplet size) and do not use exchangeable nozzles. New types of nozzles are available for use on professional application equipment that significantly reduce the number of fine droplets produced and so reduce the chance for drift to occur.
Interestingly, volatility is not considered drift by the EPA. It makes sense, as even a conscientious applicator has no control over temperatures in the days following application or wind direction. Volatility is simply a solid or liquid turning into a gas. Herbicide volatilization can occur in the landscape when, for example, a 'weed and feed' granular fertilizer is applied that contains certain types of 2, 4-D, a broadleaf herbicide. The 2,4-D has the capacity to turn into a gas and move away from the original site. It still has herbicidal properties, so plant injury can occur elsewhere in that yard or in a neighbor's. (Liquid herbicides lose their ability to volatilize as soon as they have dried.) Some plants are more sensitive to 2,4-D than others. The most sensitive are: boxelders, tomatoes, lilacs and grapes.
ANYONE apply a pesticide should take care to reduce the chance for drift. It's clear that intentionally applying a pesticide in a manner that causes damage to a neighbor's property is prohibited. But it's also prohibited to apply to another's property even when no damage occurs.
Complaints regarding human or animal exposure, injury, or property damage caused by pesticide drift, careless application, or use that does not follow label directions should be reported to the Minnesota Department of Agriculture (MDA). Once an investigation is complete, the MDA
will then review the evidence to determine whether a violation has occurred and what action is
appropriate. For more information see the MDA's fact sheet 'Pesticide Drift and Misuse -
Reporting Procedures' on the MDA web site at: http://www.mda.state.mn.us/appd/pesticides/drift.pdf
As we said in the previous article, testing for pesticides residues is expensive and must be done immediately as many pesticides tend to break down quickly once they've been applied. So acting quickly in pesticide cases is essential.
SAFE TO EAT?
Perhaps the most commonly asked question that arises from accidental pesticide application is:
Are my fruits or vegetables safe to eat? The answer: If the pesticide isn't labeled for use on that crop, we can't say the sprayed food is safe because we don't know. The labels of pesticides often contain a Pre-Harvest interval during which the pesticide can not be applied to ensure safe levels for consumption.
You could have two seemingly identical bottles of insecticide, where each has the same percentage of the same active ingredient and are even manufactured by the same company. The only difference is one is labeled for houseplants and the other is labeled for vegetables. The label is the law and defines the only legal uses for that product. Therefore, it is illegal to use the houseplant insecticide on tomatoes or vice versa.
Sometimes, lawn or tree care products inadvertently wind up on a neighbor's vegetables or fruit plants. Some pesticides are sold to agricultural producers under one trade name and the nursery and landscaping industry under another. While the product formulations may be nearly identical, the labels are specific to the intended use, so, again, if it's not on the label, it's not a legal use.
Read the label before you buy the product, then before you use it, then after you've used it. If an insecticide label does not list maple trees as one of the plants for use, then don't use it on maple trees. A chemical company paid some university good money to find out that their product was phytotoxic to maples!
Clover-perennial weed to some
Photo credit: Sid Jarvis
If you accidentally get pesticide on a non-target plant, grab the hose and wash it off. The newer formulation of Round Up, for example, is rain safe after 2 hrs., which means you have 2 hrs. to wash off any misapplied Round Up. It's certainly something to try in the case of accidental application. If it's too late, it's too late, but it might help a bit.
Also, be sure to keep separate sprayer for different types of pesticides. Use the bright orange labels that generally come with the sprayers to mark them for herbicide use or insecticide use. We regularly hear about someone who put insecticide in a sprayer previously used for herbicide and gets fine control not only of the insect pest but the host plant as well.
Sprayers are inexpensive. Buy 2 if you need 2.
We recommend using 1 gallon tank sprayers with adjustable nozzles. Hose end sprayers don't mix the solution as accurately and increases the chance of poor results or unintended plant injury. If you use do use a hose end sprayers for fertilizer or pesticides, make sure you have back flow preventers on your exterior faucets. These will keep any tainted water from back-siphoning into your household (or city) water supply.
Here's a link to an article written in May 2001 by Roger Becker, a weed scientist, about how postemergence herbicides work in plants.
Postemergence Herbicide Use in Lawn and Garden, Roger Becker
Dry Some Flowers to Remind You of Summer
Deborah Brown, Extension Horticulturist
Flowers have been so lovely this year you might choose to preserve some of them. Dry arrangements – especially from your own garden – will remind you of summer as days grow shorter and colder. They also make thoughtful gifts at holiday time.
Air drying is easiest method of preserving blossoms, but it only yields an attractive finished product with some specific flowers. To air dry flowers, strip the leaves then hang them in small bunch upside-down from a rope or clothes hanger, using rubber bands to hold their stems together. Favorite flowers for air drying include globe amaranth, larkspur, goldenrod, mealycup (blue) sage, celosia, and statice. Grains and grasses also air dry easily.
If you want stems that arch gracefully, make a vase-like cylinder of hardware cloth (metal mesh) with chicken wire over the top and prop the flowers or grasses upright in it to dry. Either way, keep them in a well-ventilated, dark location till they're ready. If you expose them to much light, they'll fade excessively. Once dry, some people spray them with aerosol hairspray or laquer to keep them from reabsorbing moisture from the air.
Most flowers need to be covered in silica gel, a sand-like material that absorbs moisture, in order to preserve both their form and color. This is particularly true of blossoms that are "thick" or have many petals. Drying with silica gel requires a fair amount of practice to develop the skills needed to do a good job, so begin practicing now, while there will still be more flowers available as you master the technique.
You can buy silica gel at craft and hobby supply stores. Though it's not cheap, it lasts forever, and can be reused by heating it once it no longer absorbs moisture well. Complete instructions will come with the silica gel.
Yet a third way to preserve some flowers and leaves is to plunge their freshly cut stems into a mixture of two parts glycerine to one part warm water. As the glycerine is taken up by the stem, it will turn everything light brown, and leave the plant "rubbery" and flexible rather than dry and brittle. Often, hanging glycerine-preserved plant material out in bright sunlight will help bleach it to an attractive light tan or gold, especially if you've put a few drops of chlorine bleach into the glycerine solution to begin with.
Try glycerine on stems of perennial baby's breath and stems of interesting foliage. Be sure the leaves are still green, though. Once they start to turn fall colors, they won't absorb the glycerine mixture properly.
Soldier Beetles Common
Jeff Hahn, Assistant Extension Entomologist
People have noticed large numbers of soldiers beetles, Chauliognatha pennsylvanicus in gardens this summer. They are about ½ inch long, yellowish to tannish brown with soft wing covers. They have a black head, black legs with a black spot behind the head and an oval, black spot on each wing cover. Their wing covers do not completely cover the body, leaving a couple of abdominal segments exposed. Their head is clearly visible and like other beetles they have chewing mouthparts. Soldier beetles are related to fireflies but lack the light-producing organs that fireflies possess.
Firefly's cousin, the soldier beetle.
Photo credit: Jeff Hahn
Soldier beetles overwinter as larvae. During spring they are active in leaf litter, plant debris, loose soil, and other areas where high humidity occurs. They are predaceous, feeding primarily on insect eggs and larvae. Larvae resemble miniature alligators, are usually dark colored and can grow up to 3/4 inch long. Even though the adults are very conspicuous, people would rarely, if ever, see soldier beetle larvae.
Larvae pupate apparently sometime in early summer with adults first emerging in late July. They are active through August and into September. Adults will lay eggs some time at the end of the summer which shortly hatch into larvae. They remain in this stage for the winter. There is one generation a year.
Adult soldier beetles are commonly found on plant foliage and flowers of many (many) types of herbaceous plants. Just a few examples of where they have been seen include goldenrod, helianthus, coneflower, tansy, zinnia, marigold, and globe thistle. They feed primarily on pollen and nectar. There have been reports in the literature that they are also predaceous but current researchers believe that these observations are erroneous.
Two plus two.
Photo credit: Jeff Hahn
Soldier beetles are very active and readily fly, often resembling wasps in flight. They can also resemble bees by moving quickly and often between flowers. Because of their frequent contact with flowers, soldier beetles are important pollinators. Flowers must bring out the romantic side of soldier beetles as they are often found mating on them.
Although they are vulnerable out in the open, soldier beetles protect themselves by secreting defensive chemical compounds to make them a less tasty treat. In fact their yellowish color is thought to be a warning signal to predators that they don't taste good, much in the same way as monarchs are colored orange to advertise their distastefulness.
Some gardeners become concerned when they see so many beetles. They figure too many of one insect can't be good. But fortunately in this case, that isn't true. They do not damage flowers or other plants and are also harmless to people, making it unnecessary to control them. In fact they are beneficial because they are predators (larvae) and pollinators (adults). Just ignore them and they will go away on their own.
Get the low down on this month's insect pests at
Powdery Mildew-It's Hard to Resist!
Janna Beckerman, Extension Plant Pathologist
It's hard to resist bee balm (Monarda spp.). Bee balm is a plant that is adored for its flashy flowers in red, pink and purple. The flowers, particularly in shades of red, are magnets for hummingbirds. In addition to beautiful flowers, bee balm has a wonderful lemon-scented foliage that has been used in tea. As hard as it is for us to resist bee balm, it is even harder for bee balm to resist powdery mildew.
M. fistulosa with powdery mildew in July. It is now almost completely defoliated in August.
Powdery mildew is the most common disease problem associated with Monarda. The whitish covering coating leaves, stems and even flowers, can assist in the identification of powdery mildew . Severe powdery mildew infection can result in partial to complete defoliation of infected plants! It's axiomatic in politics that a lie, when repeated often enough, will eventually become accepted as the truth. It is unfortunate then, that the same axiom seems to apply to plants. The lie? That native plants are inherently more disease resistant. The reality? That nothing could be further from the truth! The proof? Figure 1 shows our native wild bergamot, Monarda fistulosa, absolutely covered with powdery mildew one month ago. That same bee balm is almost completely defoliated today. Compare this to Monarda cultivar 'Jacob Cline' in Figure 2. No, it is certainly not immune to powdery mildew, but it is a lot more resistant than the native wild bergamot growing just a few feet away!
Since the 1990's, over sixty cultivars of bee balm have been released. Many of these varieties are bred from two parents, even though over 16 species of Monarda exist in North America. The most common parents are Oswego tea (M. didyma), which has the bright red flowers, and red bracts, and the pink to lavender flowers of wild bergamot (M. fistulosa), a more common native bee balm with the widest geographical range. Oswego tea is commonly found in moister sites and can tolerate some shade, whereas wild bergamot is most commonly found in the open, dry land prairie. Other native monardas include the very showy horse-mint (M. punctata), which has pale yellow flowers with purple spots, emphasized by white leaf-like bracts, and white monarda (M. clinopodia), which has white flowers and pale bracts. Perhaps one of the showiest, but least planted bee balms is Monarda bradburiana, the Missouri bee balm, with purple-spotted pink flowers. Although listed as zone 4 hardy in some references, I suspect it is more zone 5. However, it does re-seed prolifically and should reward the enterprising grower.
Our very dry summer has greatly contributed to an unbelievable year for powdery mildew on landscape plants. Unlike most plant pathogens, powdery mildews do not free water to germinate, and can germinate and infect when the only available moisture is high humidity. Powdery mildew is a generic term encompassing a wide range of pathogens that produce similar signs-the white powdery coating on leaves, flowers and stems. For the most part, powdery mildew is very host specific. That is to say, the powdery mildew on your lilac is not the same as the powdery mildew on your roses, or your bee balm.
Hybrid Monarda 'Jacob Cline' is less susceptible to powdery mildew than its native counterpart. Photo by Janna Beckerman.
So, what can be done about powdery mildew on bee balm when even the cultivars bred to be resistant succumb? Plants should be situated in full sun to light shade. Keeping plants well watered to reduce drought stress will minimize severe infection and defoliation in most bee balms. Because bee balm is such a prolific grower, be sure to divide and thin your plants to improve air circulation. Despite this disease, bee balms have survived infection by powdery mildews for eons. As such, this disease does not warrant chemical control in most instances. Furthermore, fungicides, in general, prevent infections from occurring and do not cure existing infections. However, if you cannot tolerate this disease, it is important to treat for powdery mildew as soon as it appears to prevent additional infection. Some of the least toxic fungicides labeled for control of powdery mildew include potassium salts of bicarbonate, horticultural oils (which contain the active ingredients of neem, jojoba and mineral oil) and sulfur. Apply additional sprays as needed, according to the label.
Water Your Trees and Shrubs!!!
Beth Jarvis, Yard & Garden Line
For the second year in a row, our landscape trees and shrubs rnight be facing a dry fall. The Twin Cities has been toast dry most of August. The drought last fall and subsequent snow-less winter raised havoc with woody plants of all ages. This spring many leafed out poorly or late, if at all.
with early fall color.
Photo credit: Beth Jarvis
Most people will remember to water newly planted (and paid for) woody plants, at least
at first, Why risk the time and money expended, for want of some water? Established plantings are less likely to get watered, but they can generally get by with weekly rainfall, when there is rain. We tend to think of shade gardens and wooded areas as cool and damp but we forget that soil moisture there can be in short supply due to all the plants that grow in the shade and compete for water.
Drought stressed trees and shrubs are more prone to injury caused by even a normal winters because they are too stressed to go through the long, slow process of shutting down for winter dormancy. They will suffer more dieback, stem cracking, and bark splitting among other things. If your woody plants are already turning fall color, it means they are shutting down from stress, not winter dormancy.
Gary Johnson, Extension Specialist in Urban and Community Forestry, urges folks to keep the upper 6-8" of the soil around their trees and shrubs moist. If you've not been watering your woody plants, it may take a good bit of water to attain that depth of soil moisture.
For newly planted trees and shrubs, Johnson advises watering every 2 to 3 days. For every inch of stem caliper, apply 1.5 gallons of water and just pour it over the rootball area. So a "2 inch" tree needs 3 gallons every two to three days. If the soil is poorly drained, the plants may need water less often. In drier soils, they may need to be watered daily. Mulch will help conserve moisture.
Laying a hose against the trunk of the established tree in the front yard doesn't do much good as the feeder roots are located away from the trunk. For every inch of trunk diameter, as measured 4.5 feet up from the ground, you need to water one to 1.5 feet of root radius. So, for a tree that is five inches in diameter, you need to water 5 to 7 feet out from the tree trunk. The tree roots reach further than that but many fine feeder roots are located within this area.
Johnson prefers to use soaker hoses and says he leaves his run for several hours at a time in his yard. Overhead sprinklers lose a lot of water, but if that's who you have, use them. Right now, the most important thing is to provide water to your woody plants.
In the September 15 Y & GL News, we'll hear from Stan Hokanson on the most winter hardy Japanese maple available to us. We return to monthly publication with the October 1 issue. Dave Hanson, Urban & Community Forestry, will provide the truth about tree roots Do they heave sidewalks, see out sewer pipes and imperil basement walls?
Looking ahead, after Christmas, Dave Ragsdale will expound on the changing face of insecticides. Scientists are finding new insecticides that are more narrowly focused to target specific pests. The general purpose, broad specturm, ecologically harmful insecticides may one day be a thing of the past.
In the future, you'll also get to meet Dr. Tim Kurtti, who does deer tick research.
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.
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