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| Landscape Alert newsletter | ||||
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| Vol. 22, No. 11, June 22, 2007 |
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| In this issue Landscape and nursery  Toxic mulch Downy mildew on Veronica Scouting for pests: Tarnished plant bug Scouting for pests: Iris borer Scouting for pests: Rose chafer Scouting for diseases: RhizoctoniaTurfgrass Leaf spot and crabgrassChristmas trees and forestry Maintaining soil moisture levels throughout the growing season in Fraser fir plantations Christmas trees insect update Gypsy moth spray window datesOther news Weather news |
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Toxic mulch It seems that every year we hear from homeowners having problems with recently spread mulch (view images). The problem is rapid desiccation of foliage of all plants in landscape beds and grass along these beds within a day or two of spreading the mulch. This problem has been termed toxic mulch, sour mulch or hot mulch. Toxic mulch typically has a very sour, pungent, vinegary odor. A mulch sample submitted recently to the lab had a pH of 4.1. Toxic mulch results from poorly processed, managed, stored or “green” mulch. Chemicals produced by fermenting organisms in the mulch pile under oxygen-deficient conditions can cause significant injury on annual and perennial landscape plants. These toxic substances can include ammonia, alcohol, methanol, acetic acid or hydrogen sulfide. These chemicals often escape, or volatilize, soon after spreading the mulch. |
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| Desiccation or dying of leaf tissue will first be observed on the bottom leaves of plants and then progress upward. Large perennial plants may have injury only on the lower leaves and will most likely recover over time. The volatizing chemicals may be too much for smaller annual plants. Mulch with a pungent odor should not be spread in landscape beds. If lower leaf injury is observed soon after spreading mulch, quickly remove it in hopes of preventing further damage. Toxic mulch can be spread out in a driveway and watered in for a few days to leach out the toxic chemicals. | ||||||||||||||||||||||||||||||
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| Downy mildew on Veronica Downy mildew problems have been showing up on perennials (view images). The name downy mildew refers to a group of related fungal pathogens that cause similar symptoms on a wide variety of plants. Downy mildew is not the same as powdery mildew, do not confuse the two. Each downy mildew fungus affects a limited group of plants, also know as a host range. For example, downy mildew on Veronica sp. is caused by Peronospora grisea; plants in the genus Veronica are the only known host of this pathogen. Downy mildew on Salvia sp. and Lamium sp. is caused by Peronospora lamii, a different fungus that is only known to infect plants in these two generas. Symptoms caused by downy mildew fungi are fairly similar regardless of the host. There are chlorotic or necrotic lesions on the upper surface of infected leaves. Lesions may have angular edges, some lesions are bordered by veins. Also there is fuzzy gray to black mold on the underside of infected leaves. Infected foliage may be cupped and new growth may become distorted. Severely affected plants may also be stunted. Warm days and cool nights with high humidity are favorable conditions for downy mildew spore production. Spores are released from the plants and dispersed by air currents. Hot dry weather will slow the development of downy mildew. Susceptible hosts such as Veronica should be scouted for disease, especially as new plant material arrives. Maintain good air circulation with good plant spacing to make the environment slightly less favorable to disease. Once a downy mildew problem is present disease control is difficult. Consider removing and destroying plants that are heavily infected. This will reduce the number of spores in the growing areas. This can be especially helpful where disease is detected early and has not yet spread extensively. Fungicides for disease control are best used preventatively on especially susceptible crops. Downy mildews are capable of developing resistance to several effective systemic fungicides. Systemic fungicides should be used in rotation with protectant products to slow the development of resistance. Products labeled for downy mildew control on ornamentals include mancozeb, Stature DM, Aliette, Compass and Heritage. Refer to the product labels for specific application information. |
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| Scouting for pests: Tarnished plant bug Feeding by tarnished plant bug adults and nymphs causes yellowing of terminal growth, which becomes twisted and distorted. In addition, leaves may appear ragged and discolored. Flowers may fail to develop, or the flower buds may abort. Tarnished plant bug overwinters as an adult. (view images) Management: Remove weeds and plant debris from adjacent areas. Contact insecticides may be applied when nymphs and adults are present. |
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| Scouting for pests: Iris borer Iris borer larvae initially feed at the tops of plants, chewing holes in leaves and giving leaves a ragged appearance (view images). They eventually create dark-streaked areas that appear watery. Larvae migrate down the plant, and then mature larvae bore into leaves a few inches above the growing medium surface. Mature larvae then feed within the rhizome, creating large tunnels. The tunneling causes plants to wilt severely and eventually rot. The adult iris borer is a nocturnal moth with dark purple front wings and yellow-brown hind wings. Females lay eggs in plant debris. Iris borer overwinters in the egg stage. Management: Remove debris from adjacent areas. Clip and remove dead iris leaves and stems to eliminate any overwintering eggs. Contact insecticides need to be applied before the larvae enter leaves. Frequent applications may be necessary in the spring. |
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| Scouting for pests: Rose chafer Rose chafer: Macrodactylus subspinosis (view images) Hosts: Rose, flowering cherry, crabapple, hydrangea, elm, elder, wisteria and several herbaceous perennials. The larvae overwinter as grubs in the soil, pupate in early spring and emerge in June. Look for adults as beautybush and European cranberrybush (Viburnum opulus) are blooming. Grubs feed on the roots of grasses, weeds, trees and shrubs, and are found in sandy soil. Rose chafers particularly favor feeding on rose flowers. Leaves skeletonized by rose chafers look very similar to those damaged by Japanese beetles. Management: Floating row covers or netting may be used as barriers to protect plants, but may not be practical where plants are large or numerous. A pheromone trap specific for rose chafer is commercially available. This insect has few natural enemies and is poisonous to birds. Target the adult stage with a registered insecticide. |
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| Scouting for diseases: Rhizoctonia Pathogen: Rhizoctonia solani (view images). Hosts include: Achillea, Aconitum, Aquilegia, Aster, Campanula, Chrysanthemum, Coreopsis, Delphinium, Dianthus, Digitalis, Gaillardia, Gypsophila, Helianthus, Hemerocallis, Hosta, Iberis, Lathyrus, Lilium, Limonium, Lysimachia, Nepeta, Oenothera, Papaver, Phlox, Platycodon, Potentilla, Primula, Salvia, Sedum, Veronica and Viola. Symptoms: Rhizoctonia causes a variety of symptoms, including damping-off, stem lesions, stem rot, root rot, crown rot and aerial web blighting. Infection causes wilting, stunting and possibly plant death. Some vegetatively propagated plants are susceptible to rot at the base of the cutting. Spread: This is a soil-borne pathogen. It persists in soil as mycelium and sclerotia (small, brown, long-term survival structures). The disease is spread when contaminated soil, plant material, tools and equipment are moved. Management: Good sanitation practices are important to minimize disease introduction and spread. Rhizoctonia spp. tend to be more prevalent on stressed or wounded plants. Stress factors such as an excess or deficiency of water and fertilizer are important considerations in preventing Rhizoctonia diseases. Avoid periods of wet conditions followed by dry conditions. The fungus is favored by warm, moist conditions. Severely affected plants should be removed promptly. Research on efficacy of biological control through soil amendments is ongoing. |
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| Leaf spot and crabgrass High temperatures, lack of rain in many places and high humidity, have put the hurt on turfgrass in many areas across the state. The early season sightings of diseases on lawns, such as red thread, have now been replaced by sightings of leaf spot. Leaf spot is generally active during warm summer weather. The symptoms are water-soaked spots on leaf blades that turn purple/brown/black. Turf infested with leaf spot will appear yellowish to reddish-brown, and a general thinning of the turf with no distinct pattern may occur if conditions are ideal. The best management strategy to alleviate damage is to irrigate lightly and frequently, preferably around mid-day (noon) and apply a light fertilizer application (0.5 lb. N/1000 ft.2 or less). Avoid irrigating at night because it results in the leaf blades remaining moist throughout the night and, therefore, more susceptible to disease infection. Another cultural management option is to raise the mowing height to reduce turfgrass stress. Fungicide applications to home lawns are generally not recommended, as they can be expensive and often give unpredictable results. One grass that is currently thriving in the summer heat is crabgrass. In most areas, crabgrass is really cutting loose and control with Dimension, active ingrediant dithiopyr, which has early postemergence activity is probably past. Probably the most common postemergence crabgrass killer in the homeowner market contains the active ingredient MSMA, usually sold as a product that has the phrase “crabgrass killer” somewhere in the title. If you are going to use products that contain MSMA, beware that at high temperatures (greater than 80º F) these products might burn the turf a little, so you might need to decide how important it is for you to eliminate the crabgrass from the turf. Remember that sometimes green is better than brown even if it is a weed! Another active ingredient that is now available in homeowner products and is very effective for postemergence control of crabgrass is quinclorac. Please remember that when using any pesticide to read and follow all label directions. |
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| Maintaining soil moisture levels throughout the growing season in Fraser fir plantations Most areas of Michigan have just gone through the first extended period of dry and hot weather for the 2007 growing season. At our two irrigation research sites (Montcalm and Jackson counties), no rainfall was recorded from June 6 to June 20. During that period, tensiometer readings (soil moisture potential) measured at 12 inches, increasing from 10 to 20 centibars in non-irrigated plots. (Around 20 centibars, growers should be thinking about turning on their irrigation system.) We also monitored the gravimetric soil moisture (total soil moisture content) at the Jackson farm, and it decreased from 13 to 6 percent at 10 cm below the surface. Note that on sandy soils, 5 percent soil moisture could result in permanent wilting in just a few days depending on plant rooting and condition. (view photo) We haven’t observed any significant plant mortality; however signs of wilting were present especially in sites transplanted this year. Keep in mind that maintaining good soil moisture is essential for maintaining good health and enhancing all the physiological functions of your trees. If you have access to irrigation, we recommend putting at least 0.5 inch of water per week on transplant and younger trees, especially in sandy soil if there has been no rainfall, and none is forecasted for the week. Don’t forget to factor in the time you need to run your system through all your irrigation zones before it is too late for the areas you reach last. You should irrigate early in your first zones to be just on-time when you get to the last block. For more information on using tensiometers to help determine soil moisture, see MSU Extension bulletin E2977 Using Tensiometers for scheduling Irrigation of Fraser fir in Christmas Tree Production. To order this publication, please visit http://www.emdc.msue.msu.edu/intro.cfm or call 517-353-6740. |
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| Christmas trees insect update Feeding time for sawflies Keep an eye out for sawflies on your conifers. Larvae of several sawfly species feed in late June through late July. Watch for yellowheaded spruce sawfly on young, open-grown white spruce; larch sawfly on larch (tamarack) trees; and redheaded pine sawfly on red, Scotch and jack pine, balsam fir sawfly on balsam and Fraser fir and introduced pine sawfly primarily on white pine but can be found on Scotch, red and Austrian pine. Sawfly larvae are often mistaken for caterpillars, but are actually a primitive group of insects related to wasps and bees. The larvae usually feed in colonies of 10 to 50 individuals and typically eat all of the needles or leaves from a single branch. The adult is a brownish or black fly-like, non-stinging wasp. When populations are high, these summer feeding sawflies can cause serious defoliation because they eat both new and old foliage. If sawflies are in small numbers, you can usually clip out the colony and mash or otherwise destroy the larvae. Insecticides will also kill these larvae, but be careful and only use these products if it is truly necessary to protect the tree since most sawfly populations are controlled by parasitoid wasps, and the wasps will be very susceptible to any insecticide that you use. Note that Btk, a product often used to control leaf-feeding caterpillars, will not be effective on the sawfly larvae. Balsam gall midge The small oval galls from balsam gall midge are visible on the needles of the new growth of balsam fir. Growers in Wisconsin have also reported having problems with this in Fraser fir. Adult female midges lay eggs on newly emerged shoots in May. The larvae feed on the new needles causing the small galls to form. Mature larvae will drop from the needles in the fall and over-winter in the soil beneath the tree. If growers have had heavy damage this year, they will need to time their insecticide next May when the adult females are laying eggs. Adult emergence traps can be placed beneath previously affected trees to estimate timing of the adult. |
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| Gypsy moth spray window dates Growers should note the closing dates below for Zone 4 and Zone 5. Degree day accumulations have been well ahead of normal in most areas. This has resulted in earlier spray window dates this year. Growers are cautioned to pay close attention to degree day accumulations and larval development in their area. The chart below shows open/close dates for application of the two groups of pesticides used for regulatory treatment of gypsy moth in nursery stock and Christmas trees. Next week’s Landscape CAT Alert will contain the final announcement for Zone 5 - all other compounds.
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| Weather news Showers and thunderstorms associated with a cool front moving across Michigan Tuesday, June 19 and Wednesday, June 20, helped ease moisture shortages in some areas of the state following a dry spell more than two weeks in length. Unfortunately, the rainfall was scattered in nature and some areas remain unfavorably dry. Climatologically, the recent sunny, warm and dry weather pattern was unusual. Between June 7-18, summed potential reference evapotranspiration (the amount of evapotranspiration from a reference well-watered, 4-inch grass-covered surface) generally ranged from 2.5-3.0 inches, or about 0.20-0.25 inch per day. Such rates over a more than one week continuous period are unusual for Michigan (they would be more typical of arid or semi-arid western locations in the western United States) and in many cases led to significant soil moisture depletion in the upper layers of the soil profile. While the actual rates of evapotranspiration during this period were generally less than the reference potential rates (due to the gradual drying of the soil profile), remember that the top 3 to 4 feet of most soils in the state only hold on the order of 3 to 8 inches of plant available water. Soils are entering the period of the growing season with highest water needs with a somewhat depleted moisture profile. (This would be more true for relatively deep-rooted perennial crops than for annual crops.) Looking ahead, the outlooks in general suggest a return of warmer than normal weather with continued dryness. In the near term, the frontal boundary that moved through the state late Wednesday and Thursday is forecast to return northward through the state as a warm front this weekend. The front will lead to widespread showers and thunderstorms in areas of the central Corn belt just south and west of Michigan during the next few days. Some of this activity may reach into far southwestern sections of the state late Friday and Saturday, otherwise dry weather is expected. Any precipitation that does develop with this weather system is expected to be widely scattered in nature with most amounts remaining less than 0.25 inch. Dry conditions are expected over most all of the state Sunday and Monday. A second frontal system will approach the state from the northwest by late Tuesday, bringing the next best chance for significant rainfall, initially across northwestern sections of the state overnight Tuesday and across southern and eastern sections of the state by Wednesday. Temperatures during the next couple of days will gradually warm to much above normal readings by the late weekend into early next week. Some of the warmest temperatures of the year thus far are possible by next Monday and Tuesday across southern and central sections of the state. Look for highs ranging from the mid 70's north to low 80s south Saturday, increasing into the 80's statewide by Sunday. High temperatures in the low to mid 90s are possible in the southern Lower Peninsula by Monday through Wednesday with upper 70's and low 80's in northern lakeshore locations. Low temperatures will range from the upper 40's north to low 50's south through Thursday, increasing into the 60's by the weekend. Medium range forecast guidance is suggesting the formation of an upper air ridge across the Great Plains and western United States with troughing across the eastern United States. With the ridge in place, both the 6-10 day and 8-14 day outlooks covering June 27-July 1 and June 29-July 5, call for above normal temperatures state- and region-wide. Precipitation totals during the 6-10 day time frame are forecast to range from near normal levels across Lower Michigan to above normal levels in the western Upper Peninsula. Below normal precipitation totals are expected statewide during the 8-14 day period. |
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