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Even though Labor Day weekend often signals the end of summer, the approaching fall season is an excellent time to clean up those dandelion plants still hanging around.  Or, maybe the plantain, creeping Charlie or clover that is beginning to take over some areas.   Whatever the situation, early to mid-fall is an excellent time to control many of our perennial broadleaf lawn weeds.  The careful and discriminate use of chemical weed killers can be very effective tools to gain an upper hand in lawn weed management.  Once initial control is achieved, future applications can be done on a spot treatment basis or plants can even be removed by hand.

One of the reasons why fall control programs for these weeds are usually quite successful   is that our perennial broadleaf weeds such as dandelion, clover, plantain or  creeping Charlie are all actively growing during early fall.  If chemical weed killers are going to be used to control the weeds, having the plants actively growing is a requirement for good control.  If the late summer, early fall period is dry but cool, watering the lawn with a ½ inch of water a couple of days before applying the product will usually improve control. 

Most broadleaf control products available to the homeowner contain one or more of the ingredients: 2,4-D, MCPA, MCPP, and dicamba.  In addition, formulations for more difficult to control weeds such as creeping Charlie and violets often include the chemical triclopyr.  Generally these products require that they be applied during calm conditions, no rain or watering for 24 – 48 hours and temperatures be at least 55 to 80oF.  However, always read the product label for exact application instructions.  It’s the law!

Here are some control tips for a few common lawn weeds for which late summer to early fall is a good time to treat with chemical control products along with some hints on non-chemical removal:

Dandelion: 

Short-term perennial, survives by regrowth from a fleshy taproot, usually removal of at least 2/3 of the taproot is necessary to prevent regrowth from appearing; seedlings emerge from late spring to early autumn with most emerging within several weeks of seed being shed; most broadleaf weed control products for lawns will provide good results with 1 or 2 applications; controlling both young, first year plants as well as more mature plants is an advantage to fall treatments.

Creeping Charlie: 

Perennial with vigorous creeping stems known as stolons; hand removal is very difficult as each point (node) where a leaf arises on the stolon will also send down roots into the soil; each one of those rooted “nodes” has the capacity to generate an entirely new plant;  best controlled in the fall;  susceptible to broadleaf herbicides containing two or three different chemicals; products containing the chemical triclopyr are reported to provide better control; repeat applications spaced about two to three weeks apart (See specific label directions for spacing of applications.) are usually more effective.

Wild Blue Violets: 

Perennial with vigorous, but short spreading underground stems known as rhizomes; often considered a desirable groundcover plant; does particularly well in shaded conditions, hand removal is possible providing all of the rhizome material can be completely removed; herbicides containing the chemical triclopyr generally give better results, repeat applications may be necessary.

White “Dutch” Clover: 

Perennial with vigorous above ground stems (stolons) that root at the nodes (similar to creeping Charlie); will not compete as well in lawns where there is sufficient nitrogen available for vigorous grass growth; historically it was considered a desirable component of lawn mixes but fell out of favor when chemical control for it became possible shortly after WWII; difficult to hand remove due to the stoloniferous nature of its growth – pieces left behind can root and begin to regrow;  susceptible to most common broadleaf weed control products – especially those designed specifically for clover control and contain higher concentrations of the chemical MCPP.

 

 

 

 

 

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Before going into some details of seed collection and storage, let’s reflect first on the purpose of seeds.  Seeds are small, well-packaged plants and are primarily the result of sexual reproduction.  Genetic material is recombined from female and male parents in the resulting new plant.  Vast variability can be found among seedlings through unique combinations of genes, just as we may or may not look quite different than our siblings even though we share the same parents.  In nature variability among plants is valuable because as different climatic or other stressors influence a plant population, there will hopefully be at least some members that will be able to survive whatever challenges arise.    Some of the potential challenges can be disease, drought, herbivores, etc. 

Some plants, like those with an annual life cycle, especially rely on seed propagation to persist.  They grow, flower, produce seeds, and die all in one growing season.  Annuals typically have very high seed production rates and tend to have longer flowering periods than perennials.  They also tend to leave a lot of dormant seeds in the seed bank that can persist from year to year.  Perennial plants, on the other hand, while also relying on seed propagation, typically have additional methods and strategies to reproduce themselves.  Perennials persist from year to year and have the advantage of multiple opportunities at producing seeds. Therefore, perennials tend to produce less seeds on average in a single season than typical annuals.  There are of course exceptions. Many perennials also invest in vegetative means of propagation to spread themselves as well.

Saving seeds from open-pollinated varieties and hybrids

As gardeners, we purchase many of our flower and vegetable varieties as seeds or as transplants from the garden center where they were started from seed for us.  Depending on the background of each of these varieties, saved seed may or may not come true to type.  Typically, varieties that have the phrase F1 hybrid next to the name, although uniform themselves, will display a lot of segregation and variability among their seedlings.  There are also many varieties, typically open-pollinated varieties, that will come relatively true from seed as well.  For many gardeners, some variability among especially flower seedlings is welcome because some variability fits nicely into informal plantings, while in other situations variability may be less tolerated.  One example where variability could be unwelcome is in the case of hybrid vegetables where preserving flavor and other culinary traits would be important. A demonstration bed comparing seedlings from the original variety of various flowers and vegetables along with seedlings from saved seed from that same variety was planted at UMore Park in Rosemount, Minnesota this year.  Data on how the original versus saved seedlings compared has been collected and will be presented in an upcoming Yard and Garden News article.

Most species that are commonly raised from seed by gardeners are relatively easy to save seed of and store.  If this were not the case, they would not be so reliable and grown so widely.  Typically, seeds of species one typically finds on the garden center seed rack can be stored relatively dry and cool and should be able to germinate when we are ready to plant them in spring.  Other species, like those of many of our native perennials, trees, and shrubs, often have specific environmental cues they need to perceive before germinating.  Some of these cues include a cool, moist treatment (stratification) to signify winter has come and gone and it is safe to germinate.  Other species need to retain a relatively high moisture content such as many of the nut trees.  If their seeds dry down too much they can die.  Saving seeds and propagating species that we don’t typically find on the garden center seed rack can be a rewarding challenge.   One very useful resource to learn how to effectively propagate different species is the Seed Germination Database (www.backyardgardener.com/tm.html). There are many books and other resources devoted to propagation of various species as well.  Following are some general tips that should be useful for seed collection and storage of most seeds.

Seed collection

Collect when seeds are ripe

It is important to collect seeds when they are mature.  Prematurely collected seeds may have reduced storage life due to reduced amounts of stored energy.  They also may have a relatively high moisture content before naturally drying down, which can lead to greater incidences of pathogen attack during storage.  For some species there is a narrow window between when seeds are ripe and when they shatter or are otherwise dispersed from the parent plant.  Besides keeping a close eye on developing seeds in order to harvest them when ripe and before they naturally are dispersed, one can use bags or netting around the seed heads or fruits to help contain seeds. These coverings can also serve to deter animals from eating seeds before we are able to collect them as well.

It is typically beneficial to remove debris from around seeds

Ripe, healthy seeds can be surrounded by or found among chaff, nonviable seeds, or fleshy fruits.  Removal of such materials is often necessary in order to better handle and store seeds.  For instance, planting excessive amounts of chaff and other debris with seeds can encourage fungal growth.  In addition, remains of sugary, fleshy fruits can encourage bacterial and fungal growth and also may contain germination inhibiting chemicals.  Germination inhibiting chemicals from fruit tissue can actually be an advantage in nature for the species by keeping some seeds dormant and in the seed bank for multiple years before germinating.

For dry seeds, forced air is often a useful means to quickly separate relatively heavy, healthy seeds from lighter chaff and empty, aborted seeds.  One can use screens to aid in the process and forced air.  Seeds can be placed on a screen that has holes smaller than the seeds so they do not fall through and a fan can be positioned underneath.  The amount of air forced through the screen can be varied by how far from the fan the screen is held.  The goal is to have enough air being forced through to blow the light chaff away, but not enough to blow the viable seed away.  The use of air and the fact that seeds are often heavier than debris has been used for millennia to clean wheat and other grain kernels.  Another technique that has worked well for me with species like zinnias, heliopsis, and tithonia is to gently rub the seeds and chaff in order to break the chaff into smaller pieces and then put the mixture into a standard business envelope.  With the envelope open, gently angle and tap the seed/chaff mix from one end of the envelope to the other blowing gently to remove the chaff. Wearing safety glasses is wise to protect ones eyes from debris and it is nice to work outside or indoors where it would be easy to sweep up fallen chaff. Chaff can be blown out of the envelope, while the heavier seeds remain.

Fleshy fruits are often eaten by animals and the seeds are cleaned through the digestion process.  Physically opening the fruit and separating the seeds is easy to do for most species with moist fleshy fruit.  For soft fruit like berries (blueberries and raspberries) and tomatoes one can cut the fruit open pressing the fruit to dislodge the seeds with their fingers in a container of water.  Leaving the fruit in the water for a day or more can encourage fruit softening and/or fermentation and easier separation of fruit tissue from seeds.  The mixture can be stirred and the seeds often settle to the bottom of the container first.  Fruit remains can carefully be decanted off.   Additional water can be added, the mix stirred, and the remaining fruit pieces decanted again in order to get cleaner and cleaner seeds.  For those seeds that tolerate dry storage, like tomato, one can then pour out the mix on something like coarse paper towels or a screen to dry and then the seeds can be scraped off and packaged.  Seeds of other species like blueberries and cranberries can germinate right away and the mix of seeds and remaining water in the container can be poured over the top of germination mix.  For hard seeds within a fleshy fruit, like roses and strawberries, a blender can be useful and easier than processing each one individually.  It can be tricky to find the balance in blender speed and blade sharpness for the fleshy tissue to be removed from the seed without damaging the seed.  However, if there are a lot of fruit and one can spare some seeds, it is a great time saver.  Seeds generally sink and the fruit pieces can be stirred and carefully decanted off.

Seed storage

Seeds of some species are naturally short-lived, while seeds of other species can remain viable for extended periods of time, especially when environmental conditions are favorable.

Moisture level within seeds and humidity in the storage environment

Moisture level within the seed is especially critical for storage and extended survival.  Seeds of some species are recalcitrant (sensitive to drying out) and need to be maintained above a certain percent moisture content in order to survive.  During dry storage of such seeds if the moisture content dips below the minimum for survival (the threshold can be as high as ~30-35% moisture) the seed can die.  Many nut species (oak, hickory, and walnut) fall into this category as well as fleshy seeds of many tropical fruits including avocado.  Such species benefit from being planted right away.  The moisture in the soil should allow our temperate species to maintain an appropriate moisture level and also be stratified if left outdoors over winter.  Otherwise such species can be stored in a moist substance like peat and stratified indoors in a root cellar or refrigerator in plastic bags.  In early spring such seeds can be moved to a warmer location in the house and be given a jump start on the growing season before being planted outdoors.  Avocados and citrus species typically germinate right away and seedlings can make attractive houseplants.  

Many of the standard species grown from seed are very desiccation tolerant and low moisture content (3-5%) can aid long term storage.  For many desiccation tolerant seeds, not allowing seeds to dry down sufficiently after harvest can result in increased pathogen attack and reduced storage life.  Paper envelopes or bags versus plastic bags tends to be a better storage environment for such seeds as paper can allow excess moisture to dissipate.

Humidity during storage will affect seed moisture.  Moisture from humid air can enter seeds and increase seed moisture content and low humidity can lower it.  Commercial seed storage facilities are careful to control humidity and seed moisture in order to preserve seed viability.

Proper temperature is critical to help extend seed viability

Temperature is very important for seed storage because it influences the rate of respiration.  Respiration is constantly happening in live seed tissue and is the burning of stored energy for survival.  During germination, respiration increases dramatically to fuel the germination process.  Higher temperatures are associated with increased respiration rates.  Storing seeds in a cool place can reduce the respiration rate and help conserve limited energy reserves.  Many seeds that are desiccation tolerant can be frozen to help preserve viability over the extended durations. When I worked for the USDA Forest Service this is how we stored seed of many of the coniferous tree species.

For desiccation tolerant seeds, storing them cool with a desiccant (something that reduces humidity in the air) can help maintain and extend seed viability.  This can be accomplished in the home in the refrigerator with an airtight jar and desiccant (an easy place to find desiccant is your local pharmacy).

Saving ones own seeds and seeing what comes of it can be very fun and rewarding. Don’t miss the opportunity available this time of year to save some seeds.

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It is common to find large, black and yellow spiders during late summer in the center of big, round, flat webs.  They have bodies measuring one inch long and counting their legs, can be several inches in length. These spiders belong to the family called orb weavers (Araneidae) and are known as argiope (ar‑JYE‑o‑pee) spiders or garden spiders.

There are two common species in Minnesota, the black and yellow argiope, Argiope aurantia and the banded argiope, Argiope trifasciata.  Both are strikingly colored spiders.  The black and yellow argiope has a black body and yellow markings on its abdomen, somewhat resembling flames.  The banded argiope has a series of thin yellow, white, and black transverse (side to side) bands on its abdomen. Garden spiders are typically found building their webs in gardens or in tall grassy areas.

People assume because these spiders are large that they must be dangerous to people.  They actually are very shy (as nearly all spiders are).  They stay in their webs, eating insects they capture, and rarely, if ever, are found off of them.  Orb weavers would not do well if they fell to the ground.  They would move very slowly and have very poor vision, even for a spider.  They would be extremely unlikely to bite people, a person would have to handle one carelessly for an argiope to have any chance to bite.  This spider is not dangerous to people and should be left alone.  They are fascinating to watch and people should enjoy any argiope spiders they find.

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Honeylocust trees (Gleditsia triacanthos) are valued landscape trees for several reasons. They will tolerate air pollution, salt and a wide range of soil conditions; all common challenges to the urban tree. In addition, the light airy leaves of honeylocust trees allow light to filter through. This provides enough light to successfully grow a lawn underneath the tree canopy, a much desired trait for yards and city street trees.
    
Problems arise, however, when a passing lawn mower comes too close to the natural flare at the base of the tree. Honeylocust trees are highly susceptible to a root and butt rot fungi called Ganoderma. This wood rotting fungal pathogen commonly occurs on wounded or stressed trees. Lawn mower wounds provide the perfect entry point for the Ganoderma fungi.

Roots serve two functions for the tree. They take up water and nutrients needed by the tree from the surrounding soil, and they anchor the tree, providing structural support for the trunk and branches above. The Ganoderma root rot fungi affect both of these functions. Trees infected with Ganoderma root rot often have yellowing leaves, a thin canopy, and even dead branches. All of these indicate that sufficient water and nutrients did not make it to the canopy above. In addition, infected wood in the roots and the butt (the natural flare at the base of the tree) is stringy or spongy due to rot. This weakens the tree. Trees suffering from root rot commonly break or fall over due to wind or storms.

Although yellowing leaves and dead branches in the canopy may first alert a gardener to potential problems with Ganoderma root rot, it is the fungal conk growing out of the base of the tree or roots that confirms the disease. Ganoderma fungi produce conks (also known as shelf fungi) that are kidney shaped to disk shaped. The top of the conk is shiny reddish brown, almost lacquered in appearance. The lower surface of the conk is white and a rim of white is often visible around the edge of the conk. These structures produce fungal spores in the summer months that allow the fungi to spread to new trees.

Many commonly grown deciduous shade trees and a few conifers are susceptible to the Ganoderma fungi, including maple, oak, birch, hackberry, beech, ash, honeylocust, cottonwood, willow, elm and pine. The disease progresses very slowly in many of these trees. Oak trees have lived 30 years with the fungal infection before showing symptoms in the canopy. In contrast, honeylocust and sassafras trees decline very rapidly once infected with Ganoderma.

Once a tree is infected with Ganoderma root rot, little can be done. Infected honeylocust trees should be evaluated as potentially hazardous trees that could break or blow over in a storm. Dead branches or severely infected trees should be removed if they are located in areas where they may fall and cause damage to people or valuable property.

Prevention is the best strategy for dealing with Ganoderma root rot. Reduce stress on trees by providing extra water during times of drought. Do not compact soil by driving heavy equipment over the root zone, especially if soils are wet. Most importantly take care not to wound the roots or the base of the tree with a lawn mower or any other garden machinery. Simply replacing the turfgrass around the base of the tree with an organic mulch like wood or bark chips, greatly reduces the risk of injuring a tree with a passing lawn mower. Mulch should not be mounded around the base of the tree in a volcano form. Rather an even 2-4 inch deep layer of mulch should be laid at the base of the tree with a few inches of air space separating the trunk of the tree from the mulch.
For more information about how to properly mulch a tree, visit the International Society of Arboriculture’s website http://www.treesaregood.com/treecare/mulching.aspx

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Happy gardening!

David C. Zlesak, Ph.D.
Editor
Extension Educator