Green Industry Resources
Hort Update- Seasonal Information for the Green Industry
Hort Update for the week of 6/4/2010
Bold items are new in this issue of Hort Update
|1. Sod webworm (western Nebraska)||Overwintering larvae causing some early season damage|
|2. Powdery mildew||White, powdery growth on surface of grass blade; some thinning|
|3. Golfcourse issues||Diseases not typically found in some bentgrass greens|
|4. Ascochyta tip blight||Browning of turf. Similar to drought. Grass blade tips are white.|
|Trees & Shrubs|
|5. Storm damage (western Nebraska)||Wind and hail damage to limbs and leaves|
|6. Monitor for bagworms|
Time to monitor for egg hatch; treat in mid to late June
|7. Small maple leaves/numerous seeds||Ideal conditions for seed production; restricted leaf growth|
|8. Anthracnose on shade trees||Browning of leaves and defoliation in ash, sycamore….|
|9. Oystershell scale||Branch and twig dieback with scales covering woody tissue|
|10. Tiny holes in leaves, i.e. Linden||Chill damage when leaves unfurling from bud|
|11. Minor leaf galls||Reddish bladder galls on maples; spindle galls on Linden|
|12. Ash rust||Raised orange spots on leaf undersides; some leaf curling|
|13. Pine sawflies||Numerous small caterpillar-like insects eating last year's needles|
|14. Rose slugs||Leaf holes or skeletonized leaves|
|15. Rose rust||Raised orange pustules, spots, on leaves|
|16. Rose mildew||Powdery white growth on leaves and buds|
|17. Rose black spot||Black spots on leaves, leaf yellowing, defoliation|
|18. Serviceberry showing fall coloration||Orange fall color most likely due to basal stress|
|19. Herbicide injury||Curling, cupping, twisting of leaves on non-target plants|
|20. Phlox plant bug||White or pale green spots on leaves and deformed flower buds|
|21. Rose mosaic||Yellow lines or streaking in leaves; stunted plants|
|Fruits & Vegetables|
|22. Tomatoes with stunted growth||Slow growth, leaf yellowing,|
1. Sod webworm overwinter as partially grown larvae. In spring, they move to the surface and feed until mid to late May when they pupate and emerge as adults. Most sod webworm damage occurs in July and August in Nebraska from the next generation. When overwintering populations are high, some damage may occur to lawns in spring. This year, damage is being reported in the Panhandle.The close clipping of grass blades by sod webworm does not kill turfgrass directly but exposes the crown to heat stress; thus, injury is much worse during hot, dry weather. If damage is not too severe, lawns recover from spring feeding without treatment.
Monitor lawns in June for buff colored moths flying low over the lawn and again in August. Seeing moths fly up while mowing or walking around the lawn does not confirm larvae will cause damage. The adult moths can fly considerable distances and may be coming from other infested areas. If you suspect sod webworm but are unable to find the larvae or their frass, use a soap disclosing drench. Mix up two gallons of tap water with two tablespoons of liquid dishwashing detergent. Sprinkle this mix over one square yard of affected turf. Within a couple of minutes, the flesh-colored, spotted larvae will wriggle to the surface. If you find 10 to 15 larvae in a one square yard of turf, treatment is warranted in June/July.
Sod webworm, Kansas State University Extension
Sod Webworm Management in Lawns, Ohio State University
2. Powdery mildew appears as a whitish powder on grass blades. It is found in shaded turf areas with reduced air movement and high moisture or humidity levels. The fungus grows on leaf surfaces, shading the underlying leaf blade and reducing photosynthesis. Some yellowing and thinning of turf may be seen in heavily infected areas. Reduce shade and improve air movement through pruning where possible. Preventative fungicide applications may be needed in areas with a history of mildew, but are not typically recommended on home lawns.
Powdery Mildew Disease in Turfgrass NebGuide, University of Nebraska- Lincoln Extension
3. Golfcourse bentgrass greens are showing two diseases this spring which are not typically seen. They are Take All Patch and possibly Bentgrass Dead Spot. Take All has been isolated on three golf courses. Confirmation of Bentgrass Dead Spot is in process. For information on dealing with these in golf courses, see:
Take All Patch, University of Missouri Extension
Bentgrass Dead Spot (pdf) ,United States Green Section Record
4. Ascochyta Tip Blight- Patches or large areas of lawn suddenly turn straw or tan color; resembling drought stress. Leaf blades have bleached white tips and the blade is constricted where dead tissue merges with green tissue. Considered a minor disease related to environmental and poor management stress. Turfgrass usually recovers in one month or less without treatment. Fungicides are generally not recommended or needed.
Ascochyta Leaf Blight, Colorado State University Extension
5. Storm damage in western Nebraska involves wind damage to limbs and hail damage to leaves and limbs. Broken limbs need to be pruned correctly and carefully. Remove broken branches where they attach to the trunk or another branch. When cutting, leave the branch collar but do not leave a stub. Where hail stripped leaves from trees, otherwise healthy trees will develop secondary leaves and most will be fine in the long term. Avoid fertilizing storm damaged trees.
Nebraska Forest Service Storm Damage Series (pdf)
6. Bagworms will begin to hatch in late May and early June. Now is the time to monitor for their presence. The time to treat evergreens for bagworm is from mid to late June. At this time of year, young bagworms are about ¼ to ½" long.
Bagworms, University of Nebraska- Lincoln Extension
7. Heavy maple seed crop/small maple leaves- Without a spring freeze to kill maple flowers, trees produced a heavy seed crop. Much of the trees energy went into seed production, resulting in smaller than average leaves and thinner tree canopy's. For most trees, this is not an issue. Rake and remove seeds as the drop to help keep them out of storm drains and surface water. Be alert for tree seedling weeds in shrub and flower borders. Pull when young. Tree seedlings in lawns will be killed by mowing. There is no need to fertilize trees that had a heavy seed crop.
8. Anthracnose is a common fungal disease on ash, maple, sycamore and oak that causes irregular brown areas on leaves. Leaves may curl slightly and minor to severe defoliation of a tree can occur. It is too late to treat trees effectively. Anthracnose is rarely a serious problem for otherwise healthy trees. Most trees will produce new leaves to replace lost leaves, if needed.
Anthracnose Diseases of Shade Trees, Kansas State University Extension
9. Oystershell scale can be hard to notice but easy to see once observed. They attack a variety of plants but are common on dogwood and lilac and have been seen on river birch and aspen this year. Scales attach to twigs and branches and grow a waxy covering that camouflages them as they feed on plant sap. Branch dieback occurs when high populations of scale are present. Prune and destroy heavily infested branches. Insecticides such as bifenthrin, malathion or Orthene need to be applied to young crawlers soon after egg hatch, usually in May, to be effective. Monitor plants in August for a second generation of young crawlers. Read and follow label directions as Acephate (Orthene) is NOT recommended for some maples.
Oystershell scale, University of Nebraska- Lincoln Extension
10. Small holes in leaves this spring are most likely due to young leaves having been damaged slightly by chilling as they unfurled from the leaf bud. High winds have since caused the damaged areas to drop out of the leaves.
11. Leaf galls like reddish bladder galls on silver maple, nipple galls on hackberry, green, round galls on oak and spindle galls on Lindens are harmless to trees. They may cause some leaf curling and minor leaf drop, but do not require insecticide control. They are caused by the feeding of various mites or tiny wasps.
Most Leaf Galls Don't Hurt Trees, University of Nebraska- Lincoln Extension
12. Ash rust causes yellow/orange, raised spots on leaves. Not a problem for trees. No fungicide control is needed and it's too late to treat.
View pictures of this disease at- Ash Rust , Kansas State University Extension
13. Pine sawflies have hatched. They are very small, and can be found clustered in the terminal growth of pines. You'll see an area of chewed-off needles, and below it, the black-headed caterpillar-like insects. The easiest control is also the greenest: take a stick and lightly tap the branch, knocking the critters to the ground. Few if any will crawl back into the tree. If a chemical treatment is preferred, products containing permethrin (Eight), carbaryl (Sevin), insecticidal soap, or neem oil will work. The smaller the caterpillar, the easier they are to control.
Pine Sawfly, University of Nebraska- Lincoln Extension
14. Rose slugs & Rose Chafer - Brown, skeletonized leaves on roses are often caused by either rose slugs or rose chafer. Rose slugs damage leaves by feeding on the green tissue and leaving behind the veins. Rose slug adults are sawflies- small; non-stinging wasps. The larvae are greenish, with a tan head and look much like butterfly or moth caterpillars. If they are not present there is no reason to treat. Most garden dusts or sprays will work. Insecticidal soaps must contact slugs to have an effect.
Rose Chafers are scarab beetles approximately 3/8 inch long, slender, and light tan. Adults feed on rose flowers and foliage. Inspect roses for skeletonized leaves and adult beetles. Rose chafers can be hand picked if the population is small. The insecticides carbaryl (Sevin) and acephate (Orthene) will control these beetles. However, the beetles are quite mobile and new beetles may replace those killed by insecticides.
Defoliators/leaf feeders of roses, University of Minnesota
15. Rose rust produces yellow-orange spots on leaves. No alternate host needed so fungus can keep re infecting the rose. Sanitation important -remove infected stems and leaves at first appearance. Preventative fungicides include chlorothalonil (Daconil 2787) or systemic fungicides such as triadimefon or triforine (Funginex).
Controlling Rose Diseases Ohio State University Extension
16. Rose powdery mildew causes a whitish powder-like growth on leaf surfaces. Fungicides are usually not needed. Select mildew resistant cultivars and improve air circulation around plants. For a list of fungicides to use, see:
Powdery Mildew on Landscape Plants (pdf), University of Nebraska- Lincoln Extension
17. Black spot of roses causes small black spots on leaves with yellowing and defoliation. Cultivars resistant to black spot need to be selected. Fungicides need to be applied from leaf emergence in spring through July.
Black Spot of Roses, University of Nebraska- Lincoln Extension
18. Fall color in serviceberry has been reported in Hall and Platte County. This is most likely due to environmental stress or mechanical damage. Basal injury to the trunk that damages the cambium layer, such as from a weed trimmer or rabbit gnawing, can lead to stress. Use mulch around the base of trees to protect from lawn mowers and weed trimmers. Protect tree trunks from rabbits feeding during winter with hardware cloth.
19. Herbicide injury appears as curling, cupping or twisting in leaves as well as distorted veins and leaf yellowing. If herbicide is suspected, inspect other plants in the area as herbicide injury will typically be found on more than one type of plant. Whether long term injury will occur is difficult to assess as there is usually no way to know how much herbicide the plant received. In most cases, otherwise healthy woody plants recover. We cannot recommend affected produce from vegetables and/or fruits are safe to eat if exposed to herbicide drift.
20. Phlox plant bug feeding occurs on upper leaf surfaces of young phlox leaves and buds. Injury appears as white or pale-green spots that later become yellow-stippled areas. Blossoms may be deformed. In extreme cases, plants become stunted and die. Adult bugs generally have contrasting colors, i.e. orange and black or red and black, sometimes gray and white or yellow; all with black legs. Nymphs are orange or bright red. This insect overwinters in the egg stage with nymphs emerging in early May. Remove infested plant parts. The use of insecticidal soaps, horticultural oils, or systemic insecticides will reduce damage.
21. Rose Mosaic Virus causes yellow lines or streaks in rose leaves. Plants may also be stunted, with or without leaf discoloration. Virus infected plants cannot be cured. Select roses resistant to virus when possible. Try to control insects, particularly aphids, as they help spread the virus. If pruning virus-infected plants, don't prune healthy plants unless the pruners are disinfected between each cut by dipping the pruner into a 10% bleach solution (one part bleach to 9 parts water). Severely infected plants are best removed and destroyed.
22. Stunted growth in tomatoes is most likely due to planting when soils were cool, followed by the cool, cloudy conditions in May. Warmer weather should increase growth rate. If tomatoes remain stunted, they may have chilling injury or possibly be infected by a virus. It is best to remove and discard these plants.