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| Landscape Alert newsletter | |||||||
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| Vol. 23, No. 14, July 25, 2008 |
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| In this issue Landscape and nursery Japanese beetles are now out in full force Fall webworms beginning to appear New publication on organic growing of ornamentals Scouting for weeds: prostrate knotweed, prostrate pigweed, prostrate spurge and common purslaneTurfgrass Submitting samples for vascular wilt of woody ornamentals Heat tracks on lawnsChristmas trees and forestry Christmas trees and forestry disease update Christmas trees and forestry insect updateAround the home Armyworms marching across the northwest Lower Peninsula Northern black widow outbreak? Cicada killers starting nest construction European chafer confirmed in Mackinaw CountyOther news Weather newsNext issue August 8 |
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| In order to protect susceptible types of trees, shrubs and flowers from Japanese beetle, spray them with Sevin (carbaryl) or Bayer Multi-Insect Killer (cyfluthrin) as soon as they start stripping leaves. Spray again every week to two weeks, until late August, if necessary. The Japanese beetle traps are a great way to find out if you have Japanese beetle, but do little to prevent plant damage. | |||||||
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| Fall webworms beginning to appear In the last two to three years, webworms have been abundant throughout southern Michigan in late summer. Silky tents made by webworm caterpillars are beginning to appear now on the branch tips of walnut, hickory, ash, elm, crabapples and other types of trees. The small yellowish-gray webworm caterpillars hide in the webs during the day. Some trees have actually been defoliated from having a tent on nearly every branch. But in most cases, each tree has three or four tents. They look bad, but cause little harm. Tree health is not affected until more than 50 percent of the foliage is consumed, and even then, the trees usually come back just fine the following spring. Pruning-out infested branches is the best strategy if you can reach them. Spraying the foliage around tents with B.t., Sevin, Orthene, or a pyrethroid insecticide will prevent further feeding injury, but the old tent will remain visible for several months. We have many natural parasites and pathogens of fall webworm that will eventually bring infestations under control. Outbreaks usually last two or three years.
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| New publication on organic growing of ornamentals Editor’s note: MSU plant pathologist Willie Kirk advises that he likes this publication for the way it promotes integrated pest management (IPM) and clearly states the limits of the products. Thanks to Purdue for its development. Disease control on ornamentals is a significant problem for the homeowner, nursery and greenhouse grower, and the landscape professional. By definition, these plants are to be “ornamental,” however, diseases often mar the beauty of these plants, and growers are often puzzled by the many different chemicals, and how to use them. To address this use, we published a new brief in the Disease Management Strategies Series titled, “Using Organic Fungicides.” This brief is available online at: http://www.extension.purdue.edu/extmedia/BP/BP-69-W.pdf. This publication offers strategies for properly using organic fungicides and describes a number of organic fungicides growers can use to prevent plant diseases. |
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| Scouting for weeds: prostrate knotweed, prostrate pigweed, prostrate spurge and common purslane Landscape professionals and homeowners may encounter some common weeds in landscape beds, gardens and driveways with a prostrate, mat-forming growth. Four of the most common low-growing, summer annual weeds include prostrate knotweed, prostrate pigweed, prostrate spurge and common purslane. While similar in habit, these plants have specific characteristics that aid in their identification (see below). Just as with any other pest, correct weed identification is the first step to creating an integrated weed management program. Editor’s note: The identification information is from the new field guide An IPM Pocket Guide for Weed Identification in Nurseries and Landscapes. For ordering information, call 517-353-6740 or visit: http://www.ipm.msu.edu/pdf/pocketGuidesLandsc07.pdf Prostrate knotweed: Polygonum aviculare L. Life cycle: Prostrate, mat-forming summer annual. Leaves: Alternate, narrow oval to oblong leaves with pointed tips, smooth margins and short petioles. Stems: Prostrate, tough, wiry stems with distinct nodes are highly branched and mat-forming. Plants perform well in compacted areas. A membranous sheath (ocrea) surrounds the stem at the base of each petiole Flowers and fruit: Small, inconspicuous flowers are white to pinkish and clustered in the leaf axils. The seed is enclosed in a single-seeded, dark reddish brown, three-sided fruit. Reproduction: Seeds.
Prostrate pigweed: Amaranthus blitoides S. Wats. Life cycle: Prostrate, mat-forming summer annual. Leaves: Alternate and pale green to shiny, dark green leaves are oblong, oval to egg-shaped with pointed, rounded to slightly indented leaf tips. Leaf margins are smooth and usually whitish. Leaves are numerous at the stem ends. Stems: Prostrate and nearly smooth, light green to red-dish stems form thick, circular mats. Stems may be 1 to 3 feet long and mostly erect at the tip. Flowers and fruit: Small, greenish flowers are found in dense clusters in the leaf axils. Flowers have bracts as long as the sepals and yield small, round, shiny black seeds. Reproduction: Seeds. Photo caption: Prostrate pigweed seedling. Prostrate spurge: Chamaesyce humistrata (Engelm. ex Gray) Small Life cycle: Prostrate summer annual. Leaves: Cotyledons are oval with maroon undersides and short petioles. Opposite, pale green, egg-shaped leaves with rounded tips have small, irregular teeth along the margins and short petioles. The upper leaf surface often has a maroon watermark. Stems: Prostrate, densely hairy stems are highly branched from the base, forming circular mats up to 16 inches in diameter. Stems may root at the lower nodes and exude a milky sap when damaged. Flowers and fruit: Inconspicuous flowers are formed in the leaf axils. Fruit are hairy, three-lobed capsules that contain three wrinkled, three-sided, pale brown seeds. Reproduction: Seeds. Similar weeds: Spotted spurge [Chamaesyce maculata (L.) Small] Differs by having stems that do not root at the nodes, narrow oval to oblong leaves, and ridged, not wrinkled, seeds.
Common purslane: Portulaca oleracea L. Life cycle: Prostrate, mat-forming summer annual. Leaves: Cotyledons are oblong, hairless and succulent. Cotyledons and young leaves are maroon-tinted on the undersides. Thick, fleshy, succulent leaves are hairless, spatula-shaped and about 1 inch long or less. Leaves are alternate but appear opposite and are often crowded near the stem tips. Stems: Prostrate, purplish red or green stems have multiple branches that form circular mats. Stems are thick, fleshy, succulent and hairless and up to 20 inches long. Flowers and fruit: Small, yellow, star-shaped flowers with five petals are produced in the leaf axils, opening only on sunny mornings. Fruit are egg-shaped capsules that split around the middle, scattering many tiny, black, shiny seeds. Reproduction: Seeds. |
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| Submitting samples for vascular wilt of woody ornamentals Woody ornamental vascular wilt diseases such as Verticillium wilt, Dutch elm disease and oak wilt can be frustrating, not only for our clients but also for lab staff. They can be challenging to diagnose and downright impossible without a quality sample. The accuracy of results relies heavily on the sample itself. Improperly collected, stored, or shipped samples decrease the chances of isolating a pathogen. Following the procedures outlined below will help to ensure sample quality and increase the likelihood of an accurate diagnosis.
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| Heat tracks on lawns |
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| Christmas trees and forestry disease update
Spruce needle rust Spruce needle rust is showing up now in Christmas tree fields and blue spruce in the landscape in the Cadillac area. Needles have yellow bands with small yellow-orange pustules on them. Spruce needle rust overwinters on Labrador tea and leather leaf, and spores from those alternate hosts are now infecting spruce trees. In July and August, yellow current-year needles with whitish-orange blisters filled with yellow spores on Colorado blue, black and white spruce will appear. This will be followed by shedding of infected needles. These alternate hosts are members of the Heath family and are found in bogs and damp thickets. Care should be taken to plant spruce away from wetlands, especially the rust-susceptible Colorado blue, black and white spruce. Norway spruce is more resistant. Scouting for alternate hosts, rouging infected branches and trees, and planting resistant stock can reduce the impact of many of these rust diseases.
Lophodermia needlecast Management of Lophodermia needlecast disease of Scotch and red pine, caused by the fungal pathogen Lophodermium seditiosum, is slightly different than the needlecast diseases found on Douglas fir and spruce that I have written about in other reports. This disease can kill red pine seedlings, and causes browning and massive amounts of needle loss on Scotch pines. Scotch pines infected with this disease have needles with brown spots surrounded by yellow margins, yellow needles or brown needles, especially at the bottom of the tree. Lophodermium is a severe needlecast of Scotch pine, which in some cases can cause the entire tree to brown in the spring. Even though we see the symptoms of Lophodermium in the spring, the most important time to protect trees is from the end of July through September. This is when needles are infected from spores being released by the small, shiny, football-shaped, black fruiting bodies that form on the fallen needles. The dead needles currently falling off the trees this summer (June, July, and August) will be providing the inoculum (spores) that will spread throughout the trees in your plantation or nursery. These spores will infect this year's crop of needles from August to October. And, even though you won't see the result of those infection events until next year, the fungus will stay in those healthy looking needles all winter until spring, when, again, those needles will begin the process of yellowing, browning, and dropping off. To break this disease cycle, the time to manage this disease is in late July and throughout August, even into Fall, if it stays warm and moist. To initiate control, you must begin now. Look for needle spots and brown foliage on the lower branches of 50 or more trees scattered throughout the plantation. If ten percent of the trees are infected, consider treating the entire plantation by the first week of August. To reduce Lophodermium needlecast, remove the branches of pine from cut stumps where spores are likely to be produced. Apply a registered, preventative fungicide three or four times, once every two to three weeks from late July through October. Make sure all the older pines have been removed from windbreaks near nurseries or plantations. These pines can serve as sources of fungal spores. |
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| Christmas trees and forestry insect update Cooley spruce gall adelgid Douglas fir growers should be actively scouting the trees near harvest age for Cooley spruce gall adelgid. Check for white, cottony balls dotting the undersides of needles on Douglas-fir. If you look under the cottony material, you will find pale peach-colored eggs or possibly the first emerging nymphs. Eggs will hatch about 1500 - 1600 degree days base 50. In most years, this has been the last part of July. Insecticide can be applied once these eggs hatch to control nymphs that will overwinter. On spruce, we are beginning to see the first nymphs emerging from galls. These nymphs will either continue their life cycles on blue spruce or fly to Douglas-fir to lay eggs. So if you are planning to cut off and destroy galls, you will need to do that quickly before they open and a new generation of adelgids emerges. Pine needle scale The second generation of crawlers should be hatching in northern lower Michigan and the Upper Peninsula. Research at MSU indicates that the summer generation eggs can begin hatching at roughly 1,280 GDD50 (usually early to mid- July). Hatching may continue over two to three weeks. Don't load up the sprayer as soon as you see the first scale. It's best to wait until nearly all scale eggs have hatched and many of the crawlers have settled and started to feed. The ideal timing control window is generally around 1,500 GDD50. They will turn from a reddish-pink color to more of a yellowish color. This is the hyaline stage. It occurs before they start secreting the hard, white armored covering. The hyaline stage is quite vulnerable to insecticides or horticultural oil. Also, just because you see a few scales on a few trees, don't assume that an insecticide is necessary. You may not need to spray, especially if the trees are at least a year from harvest or the population is low to moderate. There are lots of natural enemies out there that will attack pine needle scale. Pine tortoise scale We are still finding crawlers active under the reddish-brown, roundish scales of pine tortoise scales. So if you have had problems with this scale you will want to keep checking your fields. What makes this even more of a problem is that it excretes amazing amounts of sugary honeydew and black sooty mold, then grows on the honeydew that coats the needles and branches. Trees can look pretty awful if the scale population builds up to even moderate levels, making the trees unsalable. Pine shoot beetle The new generation of pine shoot beetle can be found feeding in tunnels in the center of new or one year old shoots on various pine species. They will spend the rest of the summer feeding in the shoots. Look for broken branches, needles on the tips of branches turning brown and a round hole seen on the outside of the shoot which is often surrounded by pitch. Some shoots will have only one tunnel while others may have several short tunnels.
Weevils We are finding the first adult weevils of white pine weevil. These adults emerge from late July to late August. Adults feed on the bark of small branches before dropping to the litter to over-winter. If you are having problems with white pine weevil an insecticide application between mid-August and September may help to control the newly emerged adults. |
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| Armyworms marching across the northwest Lower Peninsula Hungry hordes of armyworms are eating their way through corn and alfalfa fields in the northwest Lower Peninsula. Counties reporting problems are Benzie, Manistee, Mason, Missaukee and Osceola, but other places are likely infested. Fields with poor weed control, as well as edges of corn fields near ditch banks, fences, or neighboring pastures and legume/grass stands are most at risk. Armyworm, Mythimna (= Pseudaletia) puncta (Lepidoptera: Noctuidae) is a grass loving caterpillar whose numbers can wildly fluctuate from one year to the next. One year it’s difficult to find any of them and then the next year they are seen in the millions marching from one field to another eating all the grass that lie in their path. Steve Gower described this year’s outbreak as “biblical” in proportion.
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| Northern black widow outbreak? That’s the question that two reporters from the northern Lower Peninsula asked me this week. Apparently, many people in this area of the state are finding this spider around their homes and several reported finding many of them. I have never thought of spiders as having outbreaks, like the armyworms discussed above. I can’t imagine what the reaction of people, who are prone to arachnophobia anyway, would be if armies of black widow spiders were seen marching across the countryside destroying everything in their path. Outbreak is a relative term that depends on the perceived threat of the bug. Maybe finding a dozen or so widow spiders in one’s yard is the functional equivalent, outbreak-wise, of having a million or so armyworms devouring your cornfield. Anyway, outbreak or not, it appears that northern black widow spiders are more numerous in certain parts of the state than in past years. The northern black widow spider, Latrodectus variolus (Araneae: Theridiidae), is found throughout the eastern United States, from southern Canada south to Florida, and west to eastern Texas, Oklahoma and Kansas. In Michigan, they appear to be more common in the western Lower Peninsula. Outdoors, they are found in old stumps, hollow logs, under fallen fence posts, in abandoned animal burrows or piles of brush, and in the corners of sheds and crawlspaces. In the northern black widow, the distinctive hour glass marking on the underside of the abdomen is incomplete or split in the middle. Northern widows also have a series of red spots along the dorsal midline of the abdomen, and many have a series of lateral white stripes on the abdomen. The web of the black widow is an irregular mesh of strands in which the spider hangs in an inverted position. Surprisingly, as common as this spider is, black widow bites are infrequent because the spider is actually very timid and prefers fleeing when disturbed. That’s a good thing because the venom of a widow spider is 15 times more toxic than that of rattlesnakes. However, due to the small amount of the venom injected into the bite, widow bites are far less serious. There is less than one percent mortality (mostly children) of persons bitten by black widows. The toxin affects the central nervous system and the severity of the bite depends on many factors including the age, size and sensitivity of the victim, location and depth of the bite, and when the spider last used her venom. Pain is felt almost immediately after the bite, and increases for one to three hours, but may last for 24 hours. In severe cases, large muscles become rigid with spasms, there is a rise in body temperature, blood pressure, profuse perspiration, and a tendency to be nauseous. If a person has been bitten by a widow spider, keep the bite victim calm and under observation. Immediately take the victim to a doctor or emergency room. If the spider can be safely captured, take it to the doctor for verification of the type of bite. The bite victim may need to be hospitalized. Fatalities are uncommon and healthy victims usually recover quickly. See photos of a northern black widow at http://bugguide.net/node/view/184137/bgimage. |
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| Cicada killers starting nest construction A gentleman from Lansing brought in the year’s first cicada killers this week. These impressive wasps had dug several burrows in his yard before he sprayed them. He brought three into the lab to have them identified. It was a pretty easy call: these wasps are enormous! Read more than you will ever care to know about cicada killers at: http://ww2.lafayette.edu/~hollidac/cicadakillerhome.html
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| European chafer confirmed in Mackinaw County For those keeping track, the first European chafers from Mackinaw County in the Upper Peninsula were confirmed last week. |
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| Weather news A large area of high pressure over the eastern United States Friday morning (July 25) will bring one more day of fair and dry weather to Michigan before the passage of a frontal system overnight Friday into Saturday bringing the next chance for showers and thunderstorms to the state. Best chances for rainfall with this system will be Friday evening through Saturday afternoon. At this point, widespread rainfall is not expected with this system, with only scattered 0.10-0.25-inch totals where rainfall occurs. Some areas of the state will remain dry. High temperatures Friday and Saturday should range from the upper 70s far north to the mid-80s south with lows from the upper 50s into the mid-60s. Slightly cooler temperatures are expected by the end of the weekend and early next week, with highs from the low 70s north to the low 80s south and lows from the mid-50 south to low 60s far south. High pressure is forecast to dominate weather across the region early next week with fair and dry conditions expected. Rainfall should be possible again by the middle of next week. In the medium range period, forecast guidance suggests upper air troughs across northwestern and northeastern sections of the United States with a broad ridge across the Great Plains region. In general, this would suggest a drier than normal pattern for Michigan and much of the Great Lakes region. Both National Weather Service 6 - 10 day, covering July 30 through August 3, and 8 - 14 day, covering August 1 – August 7, outlooks call for below normal precipitation totals statewide. Mean temperatures during the 6 - 10 day time frame are forecast to range from near normal levels across Lower Michigan to above normal levels across the Upper Peninsula. The outlook calls for the 8 - 14 day period calls for temperatures to warm to above normal levels statewide. |
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