Wednesday, October 31, 2007
Preememergence and postemergence herbicides are effective tools for managing weeds in nursery production. These chemicals can injury certain nursery crops, depending on the specific herbicide and formulation, specific nursery crop, ornamental growth stage, soil type, and weather conditions. This article will focus on ways to reduce the potential for injury associated with herbicide application.
Bedding plants and herbaceous perennials:
Certain herbicides cannot be used on most annual bedding plants and herbaceous perennials. This list includes the oxyfluorfen-containing products Goal, Rout, OH2, and Regal O-O. Dichlobenil (Casoron, Barrier), simazine (Princep, others), flumioxazin (BroadStar, SureGuard) and oxadiazon-containing herbicides (Ronstar, RegalStar, and Pre Pair) also cannot be used on most herbaceous ornamental species. Isoxaben-containing products (Gallery, Snapshot) can only be used on certain herbaceous perennials. Do not apply isoxaben to Danes rocket, oxeye daisy, the mustard family, sedum, ajuga, lambsear or Veronica. As with all herbicides, check the label for specific use restrictions.
Sprayable formulations of the dinitroaniline herbicides (pendimethalin, prodiamine, oryzalin, and trifluralin), especially oil-based (EC) formulations, can stunt bedding plants and reduce flowering. It is best to use granular forms of these products in bedding plants and herbaceous perennials. Pennant Magnum, an emulsifiable concentrate form of metolachlor, can burn tender foliage, especially in herbaceous ornamentals. Use directed sprays when possible and avoid applications during high temperature/high humidity conditions. Avoid herbicides altogether on Phlox paniculata. Currently no preemergence herbicides are registered for use in greenhouses or other enclosed structures such as over-wintering houses. Herbicide vapors could be trapped around ornamental foliage, resulting in nursery crop damage. Do not apply preemergence herbicides in enclosed structures; this applies to both herbaceous and woody ornamentals. The last application for the year should be applied at least 2 weeks prior to covering over-wintering houses.
Woody nursery crops:
The granular products containing oxyfluorfen, oxadiazon, or flumioxazin should not be applied to plants with wet foliage since they can cause a contact burn. Wet foliage causes the granules to stick and then release the herbicide, resulting in spotting of foliage. Since these chemicals are contact herbicides, these granules should not be applied to plants that could catch and funnel granules to their base, such as yucca. Avoid applications during budbreak since tender foliage is more susceptible to damage. Another concern with these products is injury following splashing of treated soil onto foliage. Applying a layer of mulch after application could make these products safer when applied to young plants growing in field soil. This could also be beneficial with herbicides that could cause injury through volatilization, such as oxyfluorfen.
Use lower rates when applying preemergence herbicide to sandy soils low in organic matter. Generally higher preemergence herbicide rates are needed in clay soils higher in organic matter. Emulsifiable concentrate formulations should not be applied overtop nursery crop foliage, especially during hot, humid weather. This applies to products such as Pendulum EC, Pennant Magnum, and the postemergence grass herbicides (Envoy, Fusilade/Ornamec, and Vantage). Avoid adding oil adjuvants to overtop applications during summer – use nonionic surfactants instead. For Fusilade/Ornamec, check the label for juniper, azalea and other cultivar restrictions Do not apply oryzalin (Surflan) to Douglas fir, hemlock, or true firs, especially on seedbeds, liner beds, and young plants. Isoxaben (Gallery) can injure dwarf burning bush (Euonymus alata compacta), hydrangea, and lilac. Simazine can injure dwarf burning bush, lilac, and mock orange.
BroadStar can injure wax myrtle, privet, butterfly bush, hydrangea, spiraea, and viburnum, although there may be differences in cultivar sensitivity and newly planted liners probably are more susceptible than older plantings. Do not apply SureGuard overtop broadleaf ornamentals; only conifers have tolerance to overtop application, and then primarily after new growth has hardened off or when plants are dormant. It is preferable to apply SureGuard or Goal to dormant shade trees. Dichlobenil (Casoron) can injure hemlock, fir, spruce or pines, especially if treated when young. Clopyralid (Lontrel, Stinger) can severely injure members of the aster, legume, and nightshade families, including such species as asters, mums, coreopsis, redbud, and locust, along with damaging English ivy. Certain species tend to be sensitive in general to herbicides. Test cultivar sensitivity using a few plants prior to widespread use for herbicide application to azalea, barberry, hydrangea, and dwarf burning bush.
From "You Better Watch Out!! – Herbicide/Ornamental Combinations to Avoid" by J.F. Derr, Virginia Tech in the 2006 Proceedings of the Annual Meeting of the Northeastern Weed Science Society meeting.
In October, during cloudy weather, light quality decreases and we often see a slowing of movement of calcium from the substrate into poinsettia leaves and bracts. If calcium does not move properly into the foliage, the deficiency will show up as bract edge burn in November and December. Many growers switch to mainly calcium nitrate based fertilizers and make foliar applications of calcium chloride to strengthen stems and prevent bract edge burn. Applying a fine mist of 200-400 ppm calcium chloride with a spreader sticker once a week is recommended. Final growth regulator applications should also be made by late October to avoid a decrease in the bract size.
Article modified from the Greenhouse TPM/IPM Weekly Report, University of Maryland Cooperative Extension, October 19, 2007 edition.
Tuesday, October 30, 2007
A common concern by laypersons during autumn concerns the color change and shedding of evergreen needles or leaves. Quite often it is difficult to convince the plant owner that yes evergreens do shed old foliage like the deciduous trees or shrubs during autumn. Sometimes the changes are so dramatic or occur so quickly that one will mistakenly blame a pest or other malfunction for normal foliar senescence and shedding.
Each year evergreen trees and shrubs will produce new foliage and they will shed some of their old foliage. Since the foliage of an evergreen can live from one to several years, the amount of shedding will vary with the individual evergreen species. In most cases the foliage will first turn yellow, then straw colored and eventually brown, at which time it drops to the ground. When viewed from a distance it appears as though the interior sections of foliage are yellow or brown and the only green foliage remaining is closer to the terminal end of the branch.
Pine (Pinus) trees produce needles in sets of 2 to 5 per fascicle (bunch). All of the needles contained in an individual fascicle will turn color and be shed off at roughly the same time. Pines shed their oldest needles in autumn. Most pines retain needles for 3 to 5 years. An exception is the white pine (Pinus strobus), which retains its needles for only 1 year. Hemlock (Tsuga) and yew (Taxus) produce individual leaves (needles) which are attached to a twig. These leaves will drop individually sometimes over an extended period of time. Hemlock and yew can retain needles for 3 to 5 years. Spruce (Picea) and fir (Abies) also produce single needles on twigs. Many of these species will retain needles for up to 5 or 6 years. On spruce and fir the shedding of foliage is not always restricted to the oldest needles but it does concentrate in that area. Arborvitae which bears its foliage as scale-like leaves that cover a tiny twig retains its leaves for only 1 year.
What about the broadleaf evergreens such as rhododendron and azalea (Rhododendron), holly (Ilex) and mountain laurel (Kalmia)? These plants produce leaves individually on their stems. Holly and laurel will retain their leaves for only one year. The Rhododendrons and azaleas will sometimes retain their leaves for 1 or 2 years. Holly, unlike most other evergreens shed their one-year-old leaves in the spring as soon as the new leaves start growing. Many species of rhododendron shed leaves in autumn, but it is not unusual to find some species shedding leaves at other times during the season. Leaf shedding on these plants is often influenced by environmental factors such as drought stress and severe winter weather.
Often leaf or needle shedding goes unnoticed in some seasons. This can occur when new leaves or needles conceal old foliage which is shedding on interior sections of the plant. But in some years it may be very noticeable, especially on white pine and arborvitae and this is often due to varying rates of growth from season to season. The length of stem and needle growth may be reduced during years when drought conditions prevail in comparison to a season where maximum stem and needle length occur. When this scenario occurs it is not uncommon to find that more than 50% of the needles/foliage will be shed in autumn on white pine and arborvitae. If the same length of growth occurs each year than 50% of the needles/foliage would shed in autumn. Some other factors which can affect the length stems, needles, and leaves in any one season are recent transplanting, root damage from construction or trenching, soil compaction, and poor soil drainage as well as disease and insect pests.
Old yellow and brown foliage/needles that shed and appear on interior sections of evergreens during late summer and autumn seldom indicate a serious problem. Occasionally, pests are involved. But more often than not we will diagnose this yellowing to be a normal phenomenon. Remember that normal leaf and needle drop occurs every year on every evergreen.
Article by Thomas Kowalsick, Extension Educator, Cornell Cooperative Extension - Suffolk County, NY. For the full publication with pictures go to http://counties.cce.cornell.edu/suffolk/HortFactSheets/factsheets/Normal%20Needle%20and%20Foliage%20Shedding%20on%20Evergreens.pdf
Monday, October 29, 2007
The beneficial effects of mulching landscape trees and shrubs are universally accepted. Mulch helps to protect plant roots against extremes in moisture and temperature; it improves general landscape appearance; and it suppresses weed growth within planting beds. Although all these benefits are important, the types of mulching materials and their impact on plants are far more complicated.
The Ohio State University Landscape Mulch Studies A three-year Ohio State University mulch study was designed to determine the effects of three basic options when selecting mulching materials. These included: 1) bare soils; 2) wood pallet mulch/hardwood bark; and 3) composted yard waste mulch (grass clippings, tree trimmings, and urea). All mulches were applied over the surface of the soil at a depth of 2-3 inches in order to determine the effects that the different mulch treatments (or lack of mulch) would have on the surrounding soils and plants. The plant material used in the studies included the River Birch ‘Heritage’ and two species of Rhododendron and Taxus.
Moisture & Temperature
Moisture level readings within each mulch type were determined by seasonal differences. Between April and June, the wood pallet mulch sites contained the highest moisture levels. As expected, the bare soil sites contained the lowest moisture. Interestingly, during the months of July and August the soil moisture levels were reversed. The highest moisture was then found within the bare soil study plots with the wood pallet mulch sites now containing the driest soils. This reversal in soil moisture levels in the wood pallet mulch was attributed to the formation of a fungal mat, which created a hydrophobic layer.
Despite the differences in soil moisture caused by the various mulch types, the researchers of this study did not believe it affected observed plant growth differences. The wood pallet and composted mulch treated areas also affected soil temperatures (i.e., they provided cooler temperatures in the spring as compared to the bare soils), but again these effects on observed differences in plant growth were not considered significant.
Soil Organic Matter & Microorganisms
How the different mulches influenced the percentage of soil organic matter over time was also evaluated. After two years, there were no significant increases in the % of soil organic matter within either the bare soils or the wood pallet mulched sites. Alternatively, and as expected, there were significant increases in the % of soil organic matter within the composted yard waste treated sites. The addition of nitrogen within the composted yard waste further increased the % of soil organic matter. The greater nitrogen availability enabled the microorganisms to break down carbon materials into even finer particles. The research determined that bacteria were significantly higher in both mulched treatment sites as compared to the bare soil site, and was attributed to the availability of carbon as an energy source. It is important to note that the increased microbial rates within the wood pallet treatments were only realized when nitrogen supplements were added. The research data suggested that neither soil temperature nor moisture differences caused by the specific mulch types significantly influenced microbial growth rates.
The reduced availability of nitrogen for use by plants was most pronounced in the wood pallet mulch treatments. After each site received supplemental nitrogen, the wood pallet mulched sites actually had less nitrogen available to plants than the plants in bare soils. The microorganisms feeding within the wood pallet mulched soils were starved of nitrogen and consumed the limited nitrogen before the plants could have access. However, nitrogen immobilization was reduced as compared to existing levels prior to the nitrogen supplements. There were no differences in the reported reduced availability of nitrogen between the fertilized and the unfertilized composted yard wastes (i.e., they both contained very low nitrogen immobilization levels). This shows that nitrogen supplements to landscape plants can be significantly reduced if landscape beds are treated with composted yard waste mulch (i.e., composted yard waste mulch treatments are already providing approximately 1# of N per 1000/sq.ft. /year).
The Ohio mulch data indicated that as nitrogen availability increased, the growth rates of plants also increased. The research showed the observed plant growth within composted yard waste mulch was greater because of a nutrient effect (primarily nitrogen). The trees growing in the composted yard waste mulched areas had between a 15% to 20% increase in trunk caliper in comparison to trees grown in bare soils!
Providing an environment that optimizes the growth of beneficial microorganisms will enhance their ability to naturally compete with pathogenic microorganisms. The build-up of suppressive beneficial microorganisms within the soil is encouraged by composted yard waste (“Build it and they will come”). Ultimately, natural biologic controls can occur and in some instances, the actual suppression of diseases.
The Ohio research data reinforced previous studies that discovered some diseases of nursery plants could be at least partially suppressed with composted mulches. For example, other studies have suggested that Verticillium wilt of maple trees could be suppressed with composted mulch materials. On the other hand, field studies have shown that bare soils (no mulch) will provide an even spread of the disease Phytophthora. A similar response has also been shown to occur with wood pallet mulches. Some studies have even indicated an increased spread of Phytophthora with wood pallet mulches. Insect Influences
The Ohio research has shown that composted yard waste increases plant growth. But does plant growth necessarily equal plant health? The environment and the amount of limited resources that are available determine the allocation of energy reserves by a tree. Plants with limited nutrient resources will typically invest a larger percentage of their energy into secondary defensive compounds (e.g., leaf tannins). Conversely, plants that have a larger amount of nutrient resources will usually devote a larger percentage of available energy towards growth.
The researchers also measured the growth of insects that fed on leaves of plants growing in the different mulch types. The trees growing within the composted yard waste mulch contained leaves with higher nitrogen levels. Insect growth rates increased when they fed on leaves containing higher nitrogen levels. The research indicated that leaf-feeding pests might not be attractive to extremely stressed trees, because the quality of the food would be too low.
Studies with white marked tussock moth caterpillars indicated that insects had less weight gain and grew slower when they fed upon trees growing in the wood pallet mulch as compared to trees growing in either the bare soils or composted yard waste mulch. The reason for this difference in insect growth was believed to be from the higher food quality. A significant correlation existed between the white marked tussock moth weight gain and leaf nitrogen levels.
Studies with Japanese beetle adults also indicated the greatest feeding occurred on plants growing in sites with composted yard waste and bare soils that were fertilized. The insects were therefore selectively feeding to a lesser degree on plants growing in sites having wood pallet mulch or on plants growing in bare soils that were unfertilized. It was uncertain if the adult beetles were cueing in on leaf volatiles from other beetle feedings, or if they were randomly feeding from leaf to leaf until they found a tree containing high quality food. The data from the study clearly showed that the beetles fed most heavily upon trees growing in soils with the highest nitrogen levels.
Although the mulching of trees and shrubs is an important plant health care practice, their effects can sometimes produce unexpected consequences. Different mulching materials should influence supplemental fertilizer practices. Nitrogen fertilizers can be applied to help reduce nitrogen immobilization where wood pallet or hardwood bark is found. Alternatively, where plants are growing in composted mulches, nitrogen application rates need to be adjusted to avoid overstimulation. It is generally best to apply composted products. It is most important to use these products when trees are first planted. If raw or fresh mulches are used, they are best applied in the late fall or winter in order to reduce their initial negative effects on plant growth and health. As soon as the organic matter is partially decomposed and the competition for nutrients begins among soil microorganisms, then the beneficial effects can begin.
Extracted from "All Mulches Are Not Created Equal" by Steven K. Rettke, Ornamental IPM Program Associate, Rutgers University in the October 6, 2005 issue of the Plant and Pest Advisory; Landscape, Nursery, and Turf edition.
Friday, October 26, 2007
Mesotrione is the common chemical name for a new herbicide to be released this winter as Tenacity. This will be a great material, giving good control of many problem weeds in turf. The following is an article on the subject. (currently, Tenacity is only labeled on golf courses and sod farms).
- Mesotrione is a new herbicide that will be registered soon for use in turf. Originally to be called Outplay, Syngenta has changed the proposed name to Tenacity. It is due to be released this winter pending registration approval.
- Mesotrione is a pigment inhibitor type herbicide (turning weeds white) that will have many uses for weed control in cool season turf. It has excellent safety on tall fescue, perennial ryegrass, and Kentucky bluegrass.
- With annual grass weeds, mesotrione is highly active against crabgrass both pre and post emergence, has shown the ability to control goosegrass at higher rates, and is active on annual bluegrass as a fall treatment pre and post emergence.
- What is noteworthy is that mesotrione can suppress or control certain weedy perennial grass species including nimblewill and creeping bentgrass in cool season turf.
- Another problem weed controlled by mesotrione is yellow nutsedge.
- Mesotrione has activity against many broadleaf weeds such as chickweed, henbit, plantain, and oxalis. It has good activity on dandelion and fair activity on clover. However, when combined with triclopyr (Turflon), clover control is excellent.
- Another feature of mesotrione is its safety on new turfgrass seedings. Research in New Jersey has shown that it can be used safely as a preemergence herbicide on new seedings. There is some risk of injury with early postemergence applications in the first 3 weeks of seedling growth, especially at higher rates so it is best used preemergence (after seeding but before emergence).
Gordon Johnson, Extension Agent, Commercial Horticulture, UD, Kent County
- DE soils naturally become more acid over time. Heavy N fertilization will hasten acidification.
- Liming is the practice of adding materials soils to reduce this acidity (raise the pH) and as a result make soils more favorable for plant growth.
- The most common liming material is ground limestone. Calcitic limestone which is mostly calcium carbonate is used for high calcium (HiCal) lime, dolomitic limestone has both calcium and magnesium carbonates and is often called HiMag lime.
- The finer that the limestone is ground, the more reactive it will be. Pelletized horticultural lime is made from this finely ground limestone that is formed into granules so it spreads easier.
- Lime should be applied only if called for by soil tests. It should never be applied routinely. Only add the amounts recommended. Over-liming can cause the tie up of certain micronutrients (manganese, zinc, iron).
- Soil samples (taken as recommended) should be sent to accredited laboratories that run standardized lime requirement tests along with pH (a buffer pH). You cannot determine lime requirements by running your own pH’s, even if you have a good pH meter because you do not know the buffering capacity of the soil (the reserve acidity of the soil).
- Use high calcium lime where magnesium levels in the soil are adequate. Where magnesium levels are low, use liming products based on dolomitic limestone that have both calcium and magnesium. Your soil test results will tell you which lime to use. Do not routinely use dolomitic lime.
- Hydrated and quick limes are faster acting but generally are not necessary and should not be used over top of existing turf or landscape plants due to potential phytotoxicity (they can be used in initial soil preparation).
- Alternative liming materials such as wet lime, industrial by-products, and lime stabilized biosolids need to be compared with standard liming products. Use Calcium Carbonate Equivalents (CCE) from laboratory tests of these materials to compare their neutralizing ability to standard lime. Gypsum is not a liming material.
- Keep limes away from plants such as azaleas, rhododendrons, and blueberries that flourish in acid soil.
- Apply lime evenly and avoid over-application in overlaps.
- Incorporate lime in newly prepared beds or areas to be seeded in turf. Applying lime during aeration is recommended in established turf areas to achieve some incorporation.
Fall applications are preferred if no incorporation is possible (topdressing).
- If large amounts of lime are recommended (>100 lbs/1000 sq. ft) then split applications half in fall and half in spring.
By Gordon Johnson, Extension Agent, Commercial Horticulture, Kent County.
Thursday, October 25, 2007
Wednesday, October 24, 2007
Plant growth retardants (PGRs) are commonly applied to container-grown plants to control stem elongation and produce high quality, compact plants. Flurprimidol (SePRO, Carmel, Ind.) was a molecule discovered over 20 years ago by Eli Lily and Company. It is a “Type 2” PGR, similar in its mode of action to A-Rest, Bonzi, and Sumagic. Flurprimidol has been labeled as Cutless for turf use in the U.S. and commercially introduced as Topflor in Europe for greenhouse crops. Cutless has been trailed extensively on nursery crops such as butterfly-bush (Keever and Gilliam, 1994), holly (Keever et al., 1994), and Mexican sage (Burnett et al., 2000) with growth control comparable to Bonzi and Sumagic.
Even though the initial Topflor trials were conducted in the United States on poinsettia, exacum, and pot chrysanthemum, the chemical was not introduced to the U.S market. In Europe, Topflor has been extensively trailed since the early 1990’s on a number of greenhouse plants such as chrysanthemum (Pobudkiewicz and Nowak, 1997), dianthus (Pobudkiewicz and Nowak, 1994), osteospermum (Olsen and Andersen, 1995), and streptocarpus (Pobudkiewicz, 2000). Commercial recommendations for applying Topflor foliar sprays to a number of greenhouse crops have been developed for European growers.
In Europe, a 1.5% Topflor formulation is used, while the new formulation that will be available in the U.S. is 0.38%. With reformulating Topflor, it has not been tested under U.S. growing conditions or on cultivars available in North America. Research is currently being conducted at a number of universities: North Carolina State, Purdue, Virginia Tech, University of Florida, and Cornell. The goal has been to determine optimal application rates for U.S. conditions. The following are research findings from the Southeast trials conducted at North Carolina State University and the Midwest trials conducted by Dr. P. Allen Hammer and Terri Kirk at Purdue University.
Foliar sprays of Topflor controlled growth of New Guinea impatiens. Southeastern U.S. growers should begin with 2.5 to 5 ppm sprays. Rates may vary by location and cultivar.
Topflor foliar sprays are effective in controlling growth of of pot mum sprayed once or sprayed twice,with the second spray applied 2 weeks after the first. Rates are between 10 and 30 ppm.
Substrate drenches of Topflor were an effective means of controlling "Ellen Houston" tuberous dahlia growth. Southeast U.S. growers should begin with 1 to 2 mg a.i./pot drenches. Rates may vary by location and cultivar.
Under Indiana growing conditions, Topflor foliar sprays of 80 ppm were required to control Easter lily growth. At 160 ppm, lower leaf yellowing occurred in North Carolina. Additional research is required to determine optimal rates.
Topflor foliar sprays of 5 ppm provided comparable growth control for fall pansies as Bonzi at 10 ppm, A-Rest at 10 ppm, or Florel at 50 ppm. Sumagic at 2.5 ppm provided a greater degree of growth control. The cultivar tested was Majestic Giants Yellow Blotch.
Topflor foliar sprays provide excellent growth control for bedding plants. Topflor rates of 2.5 ppm controlled growth of Pacifica White vinca grown in 1801 cell packs. Silverdust dusty miller growth was controlled with 10 ppm of Topflor when grown in 1203 cell packs.
Topflor foliar sprays provided growth control of zonal geraniums. For the less aggressive cultivar Samba, rates of 20 ppm applied once or 15 ppm applied twice (with the second application occurring 2 weeks after the first). Higher rates of 30 ppm applied once or 20 ppm applied twice also worked well for the more aggressive cultivar Noblesse 99. Rates may
vary by location and cultivar.
The response of Orion poinsettias to Topflor foliar sprays varied by location. Optimal rates appear tobe 2.5 to 5 ppm for Indiana and around 35 to 40 ppm for North Carolina. Additional research is required to determine optimal rates.
Both foliar sprays and substrate drenches of Topflor controlled growth of Pacino pot sunflowers. These plants flowered in January and slightly higher rates may be required for Southeastern U.S. locations during other times of the year. Rates may vary for other locations.
Information from Horticulture Research Series No. 156, Topflor: A New Plant Growth Regulator by Brian E. Whipker, Department of Horticultural Science, North Carolina State University, Raleigh, NC. For the full article with pictures go to http://www.pgrinfo.com/
Ever pull a seedling out of a poorly drained flat and find that it has no roots? Ever notice that diseases are more troublesome when pots are spaced too closely or when the humidity is too high? What do these two scenarios have in common? Moisture. Host plants, pathogens (or agents that cause disease), and the environment in which they occur have a close relationship that determines whether a disease will develop under a given set of circumstances. The environmental condition most likely to impact disease development in the greenhouse is moisture. Living organisms (plant hosts and pathogens alike!) consist chiefly of water, so the uptake of water is critical if these organisms are to grow.
From a host perspective, too little water in the soil (drought stress) or too much soil moisture (which leads to oxygen deprivation) places plants under stress, and plants with water stress are more susceptible to disease. Water is also important to facilitate movement of nutrients from the roots to aerial plant parts, as well as sugars, made in the leaves during photosynthesis, to the roots. Thus, any environmental condition or disease that affects the roots or vascular tissues also places undue stress on the host. Symptoms of plants with water stress include leaf wilt, yellowing (often of lower leaves), scorch, or premature drop, a decline in vigor, progressive branch dieback, and eventual death.
From a pathogen perspective, moisture extremes have a similar impact. Although too much water in the soil deprives pathogens of oxygen, too little water impedes pathogen survival and the infection process. Free moisture on leaf or root surfaces is necessary for fungal growth, germination, penetration, and dispersal of fungal spores to new hosts. Indeed, most pathogenic
fungi grow best in a damp environment.
For example, many pathogenic fungi secrete enzymes into leaf or root tissues to macerate, or soften up, host cells, releasing nutrients that are taken up by the fungi as food. Free moisture is needed to help move these enzymes and nutrients across the fungal cell wall.
Bacterial pathogens commonly enter plants through guttation fluid at the edges of leaves as water retreats within tissues during drier parts of the day. Water is also important for the fungal infection process, which is a series of steps that includes spore germination, penetration through the host epidermis, and fungal growth within the plant tissues. The pathogen can be particularly vulnerable to drying at this time.
For most aerial plant pathogens, such as Botrytis, prolonged leaf wetness facilitates the disease process. Free moisture and high relative humidity are important for infection of leaf and other above-ground tissues (such as petals, stems, or branches). This process requires a period of continuous leaf wetness — the duration of leaf wetness needed varies with the fungus. It stands to reason, therefore, that irrigation strategy would have a great impact on the development of leaf diseases.
For soil pathogens, water in soil pores is also needed for the motile spores (called zoospores) produced by the water molds (for example, species of Pythium and Phytophthora) to swim toward healthy roots. Finally, moisture, in the form of rain, splashing, and running water, is important for the dispersal of spores of all kinds of fungi, wherever they may attack, to new hosts. Only a few kinds of fungal diseases (powdery mildew and Botrytis blight) disperse easily without help from overhead irrigation.
Moisture management in the greenhouse environment
Moisture management is important from both a plant health and a pathogen point of view. Too much or too little moisture during production can have equally devastating results. Some ornamentals are prone to edema, a physiological disease that is generated by the water relationships of leaf cells. Corky, blister-like outgrowths on the lower surface of leaves occur on edema-prone plants during cloudy periods with abundant moisture. Certain nutritional and light factors may predispose plants to edema. When more water is supplied to leaf tissues than is lost during transpiration, the cells that line leaf stomates (where gas exchange occurs) become too full and burst. Some of the crops especially prone to edema are begonia, fern,
ivy geraniums, and pansy.
As a rule, even for crops not prone to edema, you should avoid prolonged periods of leaf wetness to curb the success of aerial plant pathogens. If using overhead irrigation, design and time watering events to minimize the length of time foliage stays wet. Consider using drip irrigation or aimed microemitters which do not place moisture on foliar surfaces. Water thoroughly, but less often, to keep the surface of the mix dry between waterings to reduce root and crown rots caused by Rhizoctonia and Phytophthora.
Reprinted from "Moisture and Those Troublesome Greenhouse Diseases!" by Ann B. Gould, Ph.D., Specialist in Plant Pathology, and Margery Daughtrey, Senior Extension Associate, Cornell University in the November 4, 2004 issue of the Rutgers Plant and Pest Advisory, Landscape, Nursery, and Turf edition.
Introduction: Star-of-Bethlehem (Ornithogalum umbellatum, L.) (SOB) is a bulbous perennial that resist mowing and is difficult to control. Plants reproduce primarily by small bulbs that are spread by tilling. Plants are poisonous and disrupt turfgrass uniformity and reduce sod value. SOB grows vegetatively from January to June but plants are not evident in summer and fall and may be overlooked on land rented for sod production until it is too late and turfgrass seed have already been planted. SOB is tolerant to most herbicides, including glyphosate, and Virginia Tech researchers have tested over 30 chemicals for its control in the past five years. Early research suggest that Gramoxone (paraquat) applied twice at 2.5 to 3 pints per acre effectively controls SOB. However, selective control measures are still not available. Our work suggest that rates of dicamba (Clarity) as high as one gallon per acre controls the majority of SOB plants without harming tall fescue and research conducted in Tennessee reported partial control with bromoxynil (Buctril) at normal labeled rates. Better selective controls are needed. Our goal was to evaluate a new herbicide, carfentrazone (Quicksilver) and Buctril in various combinations with Clarity to improve selective SOB control.
Research Methods: Experiments were conducted in April 2005 in Nelson County, VA to evaluate combinations and rates of Banvel, Buctril, and Quicksilver. Banvel was applied at 2 or 4 quarts per acre, Buctril at 2 pints per acre, and Quicksilver at 2 or 4 ounces per acre. Various combinations, such as Banvel followed by Buctril, were also evaluated. Plots were visually rated for effects on tall fescue turf and SOB weeds one month later and plots have been marked for evaluation next year. Our comparison treatments included Gramoxone applied twice at 3 pints per acre, Velocity applied twice at 45 g active ingredient per acre, and aminopyralid applied once at 3.8 ounces per acre or twice at 1.7 ounces per acre. Experiments were conducted in April 2005 in Nelson County, VA to evaluate combinations and rates of Banvel, Buctril, and Quicksilver. Banvel was applied at 2 or 4 quarts per acre, Buctril at 2 pints per acre, and Quicksilver at 2 or 4 ounces per acre. Various combinations, such as Banvel followed by Buctril, were also evaluated. Plots were visually rated for effects on tall fescue turf and SOB weeds one month later and plots have been marked for evaluation next year. Our comparison treatments included Gramoxone applied twice at 3 pints per acre, Velocity applied twice at 45 g active ingredient per acre, and aminopyralid applied once at 3.8 ounces per acre or twice at 1.7 ounces per acre.
Research Results: As in previous years, Gramoxone controlled SOB 96% but also injured tall fescue 95%. Treating with Clarity one week before treating with Buctril did increase the level of SOB control by 20% compared to either a single treatment of Clarity or Buctril but the best control observed with this combination was 63% at one month after initial treatment. An unexpected result of this research was that Quicksilver at 4 fluid ounces per acre controlled SOB 96% one month after treatment. Combinations of Clarity followed one week later with two treatments of Quicksilver, each at 2 fluid ounces per acre, also controlled the weed 96%. Quicksilver, Clarity, and Buctril did not injure tall fescue. Velocity and aminopyralid did not control SOB.As in previous years, Gramoxone controlled SOB 96% but also injured tall fescue 95%. Treating with Clarity one week before treating with Buctril did increase the level of SOB control by 20% compared to either a single treatment of Clarity or Buctril but the best control observed with this combination was 63% at one month after initial treatment. An unexpected result of this research was that Quicksilver at 4 fluid ounces per acre controlled SOB 96% one month after treatment. Combinations of Clarity followed one week later with two treatments of Quicksilver, each at 2 fluid ounces per acre, also controlled the weed 96%. Quicksilver, Clarity, and Buctril did not injure tall fescue. Velocity and aminopyralid did not control SOB.
Recommendations: After five years of research and the trial conducted in 2005, we can make the following recommendations:
• To avoid SOB problems, scout fields in April, avoid tillage of infested areas, and don’t attempt to renovate infested areas with glyphosate (Roundup).
• To control SOB selectively, apply Quicksilver at 4 fluid ounces per acre in late March.
• To renovate areas infested with SOB, use paraquat (Gramoxone) at 3 pints per acre applied twice at a three-week intervals starting in late March.
Article by Dr. Shawn Askew, Turfgrass Weed Specialist, Virginia Tech in the January 5, 2006 issue of the Virginia Turfgrass Journal
Cool Season Mites: Plan a dormant oil application on plants affected by these pests this fall. Oil sprays will kill the presently active adults as well as some of the overwintering eggs. Be sure to monitor for mites next season, since where it was a problem in the past it will most likely be a problem again, and the dormant oil application will probably not give 100% control.
Remember: Adult spruce mites (which attack conifers) will remain active into December and the overwintering eggs will typically hatch in April of next year. The two-spotted mites are warm season mites that overwinter as adults under the plant and will not become active again until the weather warms in late May. Dormant oil applications are not effective against the two-spotted mites.
Article by Steven K. Rettke, Ornamental IPM Program Associate, Rutgers Cooperative Extension (NJ), in the November 2, 2006 edition of the Landscape, Nursery, and Turf Edition of the Plant and Pest Advisory.
Fall Tree Transplanting is recommended for many tree species. Some trees, however, perform better when transplanted in the spring. These sensitive species include: birch, red maple, oak, dogwood, hornbeam, hawthorn, hemlock, golden-rain tree, tulip tree, plane tree/sycamore, popular, Prunus spp., willow, silver linden, and zelkova. If these species must be planted in the fall, be sure to allow for extra water at the time of planting and until the ground freezes in December/January.
From and article by Steven K. Rettke, Ornamental IPM Program Associate, Rutgers Cooperative Extension (NJ), in the November 2, 2006 edition of the Landscape, Nursery, and Turf Edition of the Plant and Pest Advisory.
Tuesday, October 23, 2007
In Delaware, dormant oils (3-4%) are typically applied during March and April. Many landscapers, however, also apply dormant oils during the late fall months. Dormant oils have proven to be an effective material against a wide range of immature insects/mites and their eggs. Common pests controlled include spider mites, soft scales (armored scales to a lesser degree), aphids, eriophiid mites and adelgids. Are there any potential problems associated with applying dormant oils during the months of November and December in Delaware?
Some advisors within our industry have stated that fall oil applications are not recommended. It has been suggested that spraying oils on deciduous trees just after leaf drop, when plants have not yet “hardened off” may interfere with interior growth of twigs, casing damage and even twig death. Also, it has been stated that spraying oils on conifers in November and December removes the protective waxy bloom necessary for winter protection, and should therefore be avoided.
Although the potential negative side effects need to be considered, they do not appear to be widespread problems. The use of a more conservative 2% oil mixture during the fall season on conifers may be a safeguard against undesirable side effects and yet still maintain spray effectiveness. Dormant oils are best applied when temperatures will remain above 40°F. for at least 24 hours. However, several university studies determined that no phytotoxicity occurred at lower temperature applications. When sprays are applied just prior to temperatures dropping below freezing, the emulsion breaks down, causing the oil to adhere to the bark/leaves instead of insects and thus produces poor results. Before applying dormant oils, monitor the plant to be sure of the susceptible life stage and location of the pest. Properly direct the spray to where the pest is located on the plant (underside of foliage, bark, new growth, etc.). When mixing, add water to the tank first, and then add the oil. The mixture should look like skim milk. Constant agitation is necessary during application (do not apply if the solution has been sitting 10 minutes or more without agitation).
Adapted and modified from "A Few Things to Remember When Applying Fall Dormant Oils" by Steven K. Rettke, Ornamental IPM Program Associate, Rutgers Cooperative Extension (NJ), in the November 2, 2006 edition of the Landscape, Nursery, and Turf Edition of the Plant and Pest Advisory.
Recommended Turf-Type Tall Fescue Varieties
2nd Millennium, Avenger, Biltmore, Bingo, Bravo, Cochise III, Constitution, Coyote II, Crossfire II, Davinci, Daytona, Endeavor, Falcon IV, Fidelity, Forte, Good-en, Grande, Greenkeeper WAF, Guardian 21, Houndog 5, Inferno, Justice, Kalahari, Magellan, Masterpiece, Matador, Matador GT, Onyx, Padre, Picasso, Penn 1901, Quest, Raptor, Rebel Exeda, Regiment II, Rembrandt, Rendition, Southern Choice II, SR 8250, Tarheel, Tarheel II, Tempest, Titanium, Turbo, Ultimate, Watchdog, and Wolfpack.
Promising Turf-Type Tall fescue Varieties
Blackwatch, Escalade, Grande II, Guardian 21, Hunter, Proceeds 5301, SR 8550, SR 8600
Recommended and Promising Fine Fescues – For general use in low maintenance areas or in partial to full shade.
Creeping red fescue – Recommended varieties: None. Promising: Cardinal, Epic, Fortitude, Garnet, Pathfinder, and Wendy Jean.
Chewings fescue – Recommended: Longfellow II. Promising: 7 Seas, Ambassador, Compass,
Culumbra II, Jamestown 5, SR 5130, and Zodiac.
Hard fescue – Recommended: Berkshire, Chariot, Discovery, Nordic(3), and Osprey(3). Promising: Firefly, Gotham, Oxford, Predator, Reliant IV, Spartan II, and SR 3000.
Sheep fescue – Recommended or promising: None at this time.
From the 2007-2008 Virginia Turfgrass Variety Recommendations Publication
Monday, October 22, 2007
Getting Green: Sustainable Energy Use for the Green Industry
Maryland State Fairgrounds, Timonium, MD
November 8, 2007, 7:45 a.m. to 4:30 p.m.
Sponsored by: University of Maryland Cooperative Extension In cooperation with: Maryland Greenhouse Growers Association and Maryland Nursery and Landscape Association
Registration/Check-in begins at 7:45 a.m. and the program starts at 8:25 a.m.
Topics and Speakers:
Electricity, Co-ops and Current Green Projects: Richard Anderson, CQI Associates, LLC
Growing Strategies and Technology Options to Reduce Greenhouse Energy Consumption: Dr. Erik Runkle, Michigan State University
The How and Why of Installing Effective Thermal / Shade Curtains: Scott Sanford, University of Wisconsin
When are technologies truly 'green’: David Tilley, Department of Environmental Science and Technology, University of Maryland
Switchgrass and Wood Burners: Andrew Ristvey, University of Maryland Cooperative Extension
Greenhouse Energy Efficiency; Reducing Natural Gas / Propane Use For Greenhouse Heating; Greenhouse Unit Heaters: Types, Placement, Efficiency: Scott Sanford
Clean Energy for Maryland, From Policy to Practical: Gary Skulnik, Clean Currents, LLC
Solar Power: John Shepley, Emory Knoll Farms
Biodiesel and Ethanol Fuels: Lynne Hoot, Maryland Grain Producers Association
To download the registration go to http://ipmnet.umd.edu/07Nov8C.pdf
Pythium root and stem rot is a common disease problem in poinsettias, and is often difficult to control. While there are numerous Pythium species that infect a wide variety of greenhouse ornamentals, Pythium aphanidermatum is the most common pathogen found on poinsettias in late summer and fall. This fast-growing species is favored by warm conditions, and can cause extensive root and stem rot very quickly. Successful disease management requires an integrated program with cultural and chemical components.
Cleanliness. Greenhouse sanitation is an important part of any disease management strategy, especially with soilborne diseases like Pythium root rot. Any soil particle or tiny piece of rotted root can potentially harbor the thickwalled, resistant spores called oopsores, which allow the pathogen to lie in wait until environmental conditions favor pathogen growth. Washing greenhouse benches and floors between crops helps to reduce the amount of pathogen material that persists from crop to crop. Keep hose nozzles off of the greenhouse floor, use clean pots and tools, and store potting media carefully to avoid contamination with soil or plant debris. Monitor for fungus gnats and shoreflies, insects that can carry Pythium from floor to bench. These seemingly mundane housekeeping chores are important in an integrated approach to Pythium root rot management.
Healthy plants. Plants that are under stress from over-fertilization or over-irrigation are more vulnerable to Pythium diseases. Cultural practices that promote overall crop health will help reduce Pythium problems, since healthy plants will produce more roots and the loss of a few roots due to disease will have less of an impact on plant growth.
Protection. Fungicides are another important tool in the battle against Pythium. Several products, such as etridiazole (Truban, Terrazole), thiophanate methyl + etridiazole (Banrot), fosetyl Al (Aliette), propanocarb (Banol), and mefenoxam (Subdue Maxx), are effective in protecting roots from Pythium infection. Resistance to mefenoxam is common among Pythium isolates (Dr. Gary Moorman and colleagues at Penn State University found more than one third of P. aphanidermatum isolates tested were insensitive to this fungicide), so rotating applications of different materials will maximize Pythium disease control. It is important to note that these compounds will not cure plants with extensive root or stem rot – wilted plants should be discarded.
Remember, it takes more than one weapon to win the fight against Pythium – use all of these strategies to maximize disease control.
Information reprinted from "Managing Pythium in Poinsettias" by Karen Rane, Director, University of Maryland Plant Diagnostic Laboratory in the Greenhouse TPM/IPM Weekly Report, University of Maryland Cooperative Extension,Central Maryland Research and Education Center, October 12, 2007
Sunday, October 14, 2007
Friday, October 5, 2007
Chrysanthemum white rust caused by the fungus Puccinia horiana affects cultivated chrysanthemum plants in the Family Asteraceae. The disease is not established in U.S. chrysanthemum production, and could have significant impact on both greenhouse and outdoor plants of chrysanthemum, as well as cut flowers. The disease has occasionally been found in United States nursery stock in greenhouses, but it is easily and quickly cleaned up when found. Symptoms include yellow spots on the upper surface of the leaves that are up to 5 mm in size. On the underside of the leaves, raised bumps or pustules develop which have a waxy, warty appearance and are light in color. If you see signs of white rust on leaves or flowers of a plant purchased recently in Delaware, please take it to your nearest County Extension Office or contact the Delaware Department of Agriculture. Plants should be destroyed.
From Nancy Gregory, Plant Diagnostician, Department of Plant & Soil Sciences, University of Delaware