Extension Educator, Local Food Systems and Small Farms
Extension Educator, Horticulture
September 27, 2011
It's fall leaf time again, and those interested in the phenomenon of fall leaf color should be happy with the fall colors we achieve this year. We are entering the peak color period for this season. Frost is often credited with causing the great fall colors, but it actually kills leaves producing dull earth tone colors. Bright fall colors are caused by chemical reactions in leaves, and these reactions are triggered by shortening day length and cool temperatures. This year, the stress conditions of water, no water, and hot temperatures have caused an early coloring.
To understand the process that creates color, we need to know a little about basic tree growth. A tree has two parts in its vascular system, the xylem and the phloem. A tree's xylem cells can be thought of as thousands of minute soda straws packed end to end, going from the roots to the leaves. Water and nutrients are taken up by the roots and transported to the leaves through the xylem cells in the tree's sapwood. In the leaves, water and nutrients are converted into sugar, the energy that feeds the tree's growth. This conversion process, known as photosynthesis, happens in the presence of chlorophyll and sunlight.
The phloem is a thin layer of cells found in the inner bark of the tree. This is where the sugars move from the leaves to the roots and other storage sites within the tree. The location of the phloem shows how a tree can be severely injured or killed if its bark is damaged. If the phloem is disrupted, food can't flow through the phloem and the roots starve to death.
Fall coloration starts with the onset of senescence, a natural process that disrupts the tree's vascular system. This is the orderly process in which the light gathering and carbon capturing substances in the leaves, including the pigments that capture sunlight and the proteins that use the captured energy are disrupted and broken down. The change is started by the tree's genetic ability to "sense" day length and temperature variations. Fall's shorter days with less light and different light intensity, along with the cooler and longer nights affect the production of growth regulators that trigger senescence.
The long and warm days of summer produce high levels of the auxins and gibberellins that stimulate tree growth and low levels of growth inhibitors. These stimulate a variety of changes, including the formation of corklike cells at the base of the leaf petiole, which produces a brittle zone around the vascular tissue so that it is easy for the leaf to break off from the branch. Eventually only the dead xylem cells are left holding the leaf on the tree. Heavy winds or rains can easily break this fragile connection, causing leaves to fall to the ground.
The shorter days and cooler temperatures get the tree ready for dormancy. Chlorophyll production drops dramatically from the high levels of the growing season to virtually nothing. The tree's priorities then switch to the production of sugars that will be stored for next season's growth. This reduction in chlorophyll production starts the visible fall colors. Chlorophyll is the predominant pigment and makes the leaves green during the growing season. Chlorophyll is also very fragile and must be replaced by plants on a continual basis until the days grow short and temperatures fall. The fading of the green color, due to much lower chlorophyll production, causes the other pigments once masked by the green chlorophyll to come through. These other pigments include yellow, orange, and buff colors of the carotenoid, xanthophyll, and tannin pigments.
Carotenoids are always present in the leaves, so fall's yellow to orange colors are usually fairly consistent from year to year. Xanthophyll is a yell to tan colored pigemtn and tannins are responsible for the brown earth tones found in oak leaves. A fourth pigment called anthocyanin does not naturally occur in the leaves, but is a product of senescence and concentrated sugar sap in the leaf cells. Anthocyanins appear red and generate the varying shades of blue, purple, and red that provide some of the most vibrant color displays. The actual color depends on the pH of the cell sap, with acidic saps causing red to orange and neutral to alkaline saps will appear purple to blue. Not all trees produce anthocyanins with sugar and red maples, dogwoods, sumac, blackgum, sweetgum, scarlet oak, sassafras, persimmon, hawthorn, and white oak producing the most brilliant shades of red, maroon, purple, and blue.
Hopefully this somewhat scientific explanation of fall colors will cause you to understand a little better what went on within trees to bring about an abundance of fall color.
September 21, 2011
When the entire tree looks like it is dying, the injury, disease, or insect logically must be affecting the trunk or the roots. These areas would cut off the water supply to the entire tree. Look at the entire tree and compare it to nearby trees. Also consider when the problem started and what changed on the site about that same time. Healthy trees don't suddenly die because they are old. Many below ground reasons may cause tree decline. Drought, flooding, compaction of the root zone, poor soils, planting too deeply, inadequate space for roots and many other things could be involved. We have definitely had more than our share of stressful weather the past few years, with alternating flooding and drought. Often, diagnosing such a problem is a process of elimination. One of the possibilities more difficult to eliminate is root rot. Most gardeners believe that they cannot possibly know the health of a mature tree's roots.
Cankers on the stems, stem tip dieback, off-color foliage, early fall color and early defoliation are also clues that a tree may be stressed by underground causes. To detect the wood rots and root rots, look for mushroom-like fungi growing at the base of the tree or shrub. In wood rot fungi, the conks (also called shelf fungi or fruiting bodies) may be found growing on the trunk or main branches. These are signs of the disease. The actual fungus is probably growing in or on the roots, or inside the wood. One of the most common examples is Ganoderma root rot, which produces a shelf type of fungal structure at the base of many trees, especially honeylocust. The structure is reddish-brown and appears to have been varnished. Its presence indicates invasion by a root rot. Other fungi may indicate wood rots. Wet weather often triggers the formation of these structures. They could easily be confused with fungi growing on dead organic debris near a tree. If, however, they are growing from the tree itself, they are excellent signs of wood rot or root rot.
No chemicals help a tree in decline. Use approved cultural practices, such as proper watering and fertilizing to improve vitality. Cut out dead branches in the dormant season, fertilize in late fall or early spring and keep traffic off the root system. For very old or large trees, fertilization and watering may have no benefit, but these practices sometimes help the tree survive for years.
September 21, 2011
September 21, 2011
Most fall defoliators come to us as the larval stage (caterpillars) of a moth. When we talk about controls of the larvae, the fact that they are larvae of moths or butterflies makes them susceptible to the use of B.t. products such as Thuricide. Other control options include the standbys such as Sevin, permethrin, bifenthrin, Othene, malathion, and others.
The way that insects live also dictates some of the control do's and don'ts. Fall webworms live inside a "web" all the time. They actually expand the webbing as they need to have more leaves to eat. They are usually worst on fruit and nut trees. You can even clip the nest (and the branch it is around) off the tree and burn it. I guess this tells you that defoliation caused by the insect isn't that great of a threat to the tree or you wouldn't cut the branch area off. If you want to spray fall webworms, you need to get the spray through the web. This may be a little harder than you think. If you don't have enough pressure, the spray just runs off the webbing.
In the case of Eastern tent caterpillars, they hatch out of a common nest. They then leave the nest to feed, but generally return in the evening to congregate in the area of the nest. They are not covered by webbing, and the time they are congregated is a great time to spray since they are usually in one area on the trunk or main branches of trees.
In summary, control of fall defoliators isn't usually justified from the plant's standpoint. Forested areas have heavy pressure from this group in insects every year, and the trees are still thriving. The exception is newly transplanted or struggling plants. If appearances are important, consider a control spray.
September 21, 2011
You may have noticed a very large number of brown needles on evergreens this fall. That may even have translated to large piles of needles under your evergreens in the past few weeks, especially white pines. Not to worry. Evergreens usually only keep one to four years of needles (one to two years growth for white pines) on the ends of branches. Depending on weather, the old needles will turn brown and drop off. Usually this is a gradual process that isn't noticed too much. This year it happened all at once, mainly due to the hot and dry weather. If the buds on branch tips are plump and green, odds are your tree is fine.
Several calls have come in concerning the proper time to prune or cut things back. Let's start with some flowers. Keep in mind that perennials keep building their food reserves until all the leaves and stems are brown. For peonies and other similar flowers, you want to wait until all the above ground plant parts are brown. Then you can mow them off, or cut them at ground level. This same principal goes for most perennial flowers – wait until the above ground parts are no longer green. For trees and shrubs, pruning is best done at other times. Flowering shrubs should be done after they flower, high sap flow trees are best done in December, and most other trees are best done in February. The evergreen trees and shrubs are best done in late June.
Crabgrass is nearing the end of its lifecycle. It comes up from a seed about the first of April each year, depending on temperatures. Seed has been viable for several weeks already, and that is what will make next year's crop. The seedling germination inhibitors do the best job on the annual grasses, and they can stop the cycle anytime you apply them. For now, let nature run its course since you really don't have any options anyway.
September 7, 2011
Everyone seems to be having troubles with "sweat bees" these days. Or are they sweat bees? Sweat bees are about a quarter of an inch long, and are usually a metallic green in color. The yellow and black insects that are commonly called sweat bees are actually flies. Syrphid flies to be correct.
Syrphid fly is a generic name given to an entire group of flies. There are some differences in appearance and color, but the yellow and black color is the major one in our area. The other names for syrphid flies are hover flies or flower flies. They tend to hover around your arms and face when you have been perspiring, and land to lap up the sweat. They are also commonly found on flowers, hence the flower fly name, and do a good job of pollinating.
Syrphid flies are actually beneficial insects.They help pollinate, larvae feed on dead organic matter, and the larvae are predators of aphids.They cannot sting, but their mouthparts can usually be felt when lapping up sweat from sensitive areas. You may feel a slight pinch.
Yellowjackets are the other common yellow and black insect this time of year. Yellowjackets can be very aggressive in biting and stinging. They are usually about twice the size of the syrphid flies, and the easiest way to tell them apart (without getting stung) is to count the wings. Flies have one pair, and bees and wasps have two pairs.
Yellowjackets are most frequently encountered when they scavenge for food. Their habit of feeding on nectar and sugar can create a nuisance. Yellowjackets are attracted to open cups and cans of soda and other sweet liquids. They are also attracted to open cans of garbage, bright flowery clothing, and floral scented perfumes. All outside garbage cans must be kept clean and well covered, to reduce yellowjacket problems. Contact with the wasps can be decreased by reducing these attractions at picnics and other outings. In situations closer to home, the elimination of overripe fruit from gardens and orchards will dramatically decrease the number of scavenging yellowjackets. Holding gatherings indoors and using screens on windows will also help avoid yellowjacket problems.
There are a variety of traps on the market that claim to attract yellowjackets. These traps are baited with the scent of rotting fruit or other odors equally as appetizing to the yellowjackets. It is questionable whether these traps can out-compete the natural and man-made attractants described above. However, it is certain that through proper sanitation and removal of natural and man-made attractants, yellowjacket contact can be reduced. However, in situations where the potential for repeated contact exists, other management methods may be necessary. These traps can also attract more yellowjackets if placed close to the home or patio, so place them to attract the insects away from where you'll be.
As for the syrphid flies, no controls are going to be very effective. On the other hand, there really isn't much need for control. They are really a nuisance pest that is very agile. They will probably be able to avoid that aerosol spray. Inside the home, a swatter and a vacuum cleaner are probably the best tools.