Hort Update for June 6, 2014

Hort Update for June 6, 2014

slime mold
In This Issue:
Major Symptom:
1. Slime mold on leaf blades Promoted by moisture. Fungicide control is not needed.
2. White grubs If needed, apply preventive insecticides before mid-July
3. Ash rust Raised orange pustules on leaves; some leaf distortion
4. Anthracnose Blighted leaf areas on sycamore, ash, maple, oak, walnut
5. Maple bladder gall Raised red, bladder-shaped galls in upper leaf surfaces
6. Drip or micro-irrigation for trees Efficient method for watering trees and shrubs
7. Scout for spider mites Hot weather promotes rapid population growth
8. Abiotic problems of trees  Information pamphlet available from the Nebraska Forest Service website
9. Weed control in flower beds Mulch and preemergent applications
10. Deadheading annuals Remove spent blossoms, fertilize regularly
11. Aster yellows Stiff, bushy, yellowish green growth; no control
12. Strawberry sap beetle Small dark insects, damage fruit by their feeding and spreading disease
13. Squash vine borer Day flying, black & orange, clear wing moth lays eggs on cucurbits
14. Monitor for spotted wing drosophila  Small red-eyed fruit fly, closely resembling common indoor fruit fly.  Males have black dot near tip of each wing. 
15. Mosquito control Eliminate stagnant water in pools, tires; control adult mosquitoes
Articles

1. Slime mold in turfgrass has been promoted by recent rainfall. Symptoms of grass blade slime molds may be seen as irregular patches of discolored turf ranging in size from several inches to several feet in diameter. On close inspection, slime mold often appears as a raised, grayish to black growth on grass blades. This growth can easily be knocked off of the blade. While slime molds are fungi, they are not a turf pathogen and do not infect turfgrass. They simply use the grass blade as a structure to grow on. No treatment is needed.

Slime Molds on Turfgrass, Ohio State University

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2. White grub beetles (masked chafers and May/June beetles are in the egg laying stage. If a turf area had white grub damage last year, an insecticide application may be warranted this year. From now through early July, imidacloprid (Merit), halofenozide (Mach 2), or chlorantraniliprole (Acelepryn)  can be applied. Correct application and irrigation is important to effectiveness. Read and follow all label directions. For turf owners who choose not to apply a preventive grub treatment, the insecticides trichlorfon (Dylox) or clothianidin (Arena)can be applied in August or September as a rescue treatment if turf or animal feeding damage is seen. 

White Grub Management, University of Nebraska-Lincoln Extension

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3. Ash rust is a minor fungal disease that causes yellow/orange, raised areas on ash tree leaves. On ash, rust may also cause some twisting of foliage and leaf drop. It is not a serious disease and fungicides are not needed. If used, fungicides would need to be applied just as trees are leafing in spring to be effective. Applications made now will do very little to control this minor disease for which control is not necessary for tree vigor.

Ash Rust, University of Nebraska-Lincoln Extension

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4. Anthracnose has been promoted by recent rainfall on shade trees like sycamore, maple, ash, walnut and oak. Anthracnose is a generic disease name. While a variety of plants are infected, in each case it is a different fungus that causes the infection. The fungus causes leaf blighting or browning and in some cases twig cankers (i.e. sycamore and oak). Anthracnose lesions are typically large and irregularly shaped; often occurring between leaf veins. Severe infection can lead to defoliation. Otherwise healthy trees will tolerate some defoliation and many will develop secondary buds and produce new leaves. Fungicide spray applications are not feasible or very effective on large shade trees and are not often recommended. If their use is warranted, fungicides need to be applied in very early spring just as trees are beginning to leaf. Sanitation can help reduce the fungus. Rake and remove fallen leaves from the ground, 

Anthracnose, University of Minnesota Extension

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5. Maple bladder galls are harmless and require no control. They appear as raised, green, bladder-shaped galls or bumps that turn red, then black, on the upper surface of red and silver maple leaves. Leaves covered with galls may curl and drop off. The galls are caused by a small mite feeding on the leaves as they develop in spring. Like most leaf galls, maple bladder gall does not threaten tree health. Control is not practical or needed.

Maple Bladder Gall, Spindle Gall and Gouty Vein Gall, Ohio State University

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6. Drip or micro- irrigation is a water-wise method for new trees. It delivers water immediately above or below the soil. This minimizes water loss due to runoff, wind, and evaporation. Drip systems need to be designed correctly for the site and for the plant being irrigated. See the link below for information on drip irrigation systems for young and established trees.

Drip Irrigation, University of Colorado

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7. Scout for spider mites on variety of plants, especially evergreens: Mites can be difficult to detect. The first signs are yellowing and a whitish flecking on leaves. Check leaf undersides or between needles for spider mites or their webbing. A hand lens is needed to see them; or branches can be tapped over a white sheet of paper to check for active mites. Spider mites can be reduced with a strong spray of water directed at leaf undersides or needles and repeated on a regular basis to remove mites, webs and dust. If insecticides are used, the right insecticides must be applied or mite population can increase.

Insecticides Increasing Spider Mites: Spider mites frequently become a greater problem after application of insecticides. Such outbreaks can be a result of the insecticide killing natural enemies of mites or certain insecticides stimulating mite reproduction. For example, spider mites exposed to carbaryl (Sevin) in the laboratory have been shown to reproduce faster than untreated populations. Carbaryl, some organophosphates, and some pyrethroids apparently favor spider mites by increasing the level of nitrogen in leaves. Insecticides applied during hot weather appear to have the greatest effect on mites, causing dramatic outbreaks within a few days.

If insecticide treatment for mites is needed, use selective materials, preferably insecticidal soap or insecticidal oil. Petroleum-based horticultural oils or neem oils are both acceptable. Do not use soaps or oils on water-stressed plants or when temperatures exceed 90°F. These materials may be phytotoxic to some plants, so check labels and/or test them out on a portion of foliage several days before applying a full treatment. Oils and soaps must contact mites to kill them so excellent coverage, especially on the undersides of leaves, is essential and repeat applications may be required.

Spider Mites, Colorado State University

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8. Abiotic problems of trees - Useful for identification of problems not related to insects or diseases, such as herbicide injury, freeze injury, winter desiccation, chlorosis, overwatering, sun scald and more, is available from the Nebraska Forest Service.

Abiotic Problems of Trees, Nebraska Forest Service

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9. Weed control in flower beds - Perennial weedy grasses, such as brome grass, are difficult to control in flower beds. Other than hand-pulling and mulching, the herbicides sold as Grass-Be-Gone or Over the Top can be applied post-emergence to weedy grasses and provide decent control.

Note: These products contain a surfactant and it is not necessary to use an additional surfactant, such as commercial or dish soap, with these products as burning of desirable plants may.  occur. Be careful in mixed beds with ornamental grasses, because contact of these products to desirable ornamental grasses will cause injury or death.

In cases where a gardener has difficulty keeping up with weeding, mulch is especially important. In some cases, the use of Preen labeled for vegetable gardens may be justified. Preen needs to be watered in to be effective for about four weeks in controlling seedlings as weed seeds germinate.

Weed Control for the Garden and Landscape, Purdue University Cooperative Extension

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10. Deadheading & fertilizing annual flowers - Pinch off faded blooms weekly, or as often as possible, to stimulate continued blooming throughout the season. Trailing plants, such as petunias, ivy geraniums, trailing begonias and coleus, can be pruned to keep the plants compact and stimulate additional blooming. Removing faded flowers prevents the plants from forming seed. As a result, they will bloom again in an effort to complete the life cycle.

Deadheading spent flowers on perennial plants may encourage reblooming, but not in plants that have one specific bloom time, such as peonies, poppies or bearded iris. In this case, it allows plants to increase their vigor and store energy for next year's flowers by eliminating energy spent on seed development. Deadheading also prevents perennials that are prolific seeders from becoming problems in the garden.

Annual flowers require regular fertilization throughout summer to grow and bloom their best. Fertilize plants at a rate of 1/2 to 1 pound of 5-10-5 per 100 square feet every 4 to 6 weeks. Sprinkle the fertilizer lightly along the row and scratch it into the soil. Container plants should receive a weekly application of a water soluble fertilizer, like Schult's Plant Food, Miracle Grow, Peter's Fertilizer or any other water soluble fertilizer. Do not fertilize plants when they are wilted; instead water the plants with plain water first, then fertilize the next day after they have recovered.

Gardening With Annuals, University of Illinois Extension

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11. Aster Yellows is a common disease that affects many ornamental flowers. Susceptible plants include asters, Chrysanthemum, Coreopsis, Cosmos, Echinacea (coneflowers), Dianthus, Gladiola, marigold and petunias. Vein clearing, or loss of green pigment within the veins, is often the first symptom. Stunting, stiff extra bushy yellow growth, deformed or poorly developed flowers which remain green are all common symptoms. There is no cure for infected plants. Remove and discard them to reduce further spread.

Aster Yellows, Iowa State University

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12. Strawberry sap beetle has been spotted on strawberries.  They are a small, dark brown beetle, sometimes with blurry spots.  They are first attracted to rotting, damaged, or diseased fruits, but can also attack healthy fruit.  The larvae will feed on fruit, causing it to rot, or to become unmarketable.  The adults can also spread disease, so the damage is two-fold.  Strawberries are a favorite of the sap beetle, but can also be found on sweet corn and tomatoes.  Chemical control is difficult because they don't usually show up until fruit is ripened.  Removing wounded, rotting fruits is the first and best course of action in control.

Strawberry Sap Beetle, Purdue University Cooperative Extension

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13. Squash vine borer tunnels into plant stems (mainly squash, pumpkins, and gourds) and their feeding restricts translocation of water and nutrients. The point where a borer enters a stem, usually at the plant base, may have a sawdust-like frass around it and be decayed. Infested plants are weakened or die; depending on the number of borers. Control borers by practicing good sanitation, physically removing borers by slitting stems when borer activity is noticed, or applying insecticides labeled for vegetables during egg laying, usually about the time vines begin to run, and re-apply every 7 to 10 days for 3 to 5 weeks.

Squash Vine Borer Pictures, University of Nebraska-Lincoln Extension
Squash Vine Borer Management in Home Gardens, Minnesota State University

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14. Spotted wing drosophila is an invasive insect originally from Asia.  It was first detected in the U.S. in 2008 in California.  It was first found in Nebraska in 2013, in various counties across the state.  This fruit fly is different from others in the fruit it can attack - while most fruit flies are attracted to rotting or deteriorating fruit, the spotted wing drosophila female is capable of piercing healthy, ripening fruit and laying her eggs inside.  Once the eggs hatch, the larvae feed on the fruit making it unmarketable.  Raspberries, cherries, elderberries, blackberries and even grapes are susceptible.   Monitoring for this pest is essential, as is an integrated approach to its control.  Make sure to follow good sanitation in the orchard, such as removing rotten fruit from the ground, and harvesting ripe fruit as soon as possible.  Proper chemical applications are important, too.  For example, spinosad has proven to be effective, and has low-level effects on beneficial insects. 

Spotted Wing Drosophila, University of Nebraska-Lincoln Extension

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15. Mosquito control - Mosquito numbers are on the rise due to the large rain events we've had recently, resulting standing water.  Mosquito control involves:

  1. Applying larvicides, such as Bactimos or Vectobac which contain BTI (Bacillus thuringiensis israliensis) to stagnant water pools.
  2. Spraying grassy areas and shrubbery with insecticides such as permethrin or malathion (check label for use on the landscape plants to be sprayed.
  3. Preventing water from standing in containers such as flower pot basins, children's wading pools, bird baths, clogged roof gutters.
  4. And using personal repellents containing DEET (diethyl toluamide).

Residential Mosquito Control, University of Nebraska-Lincoln
Flies, Gnats & Moisquitoes, University of Nebraska-Lincoln
UNL Flood Resources Website

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