Hort Update for August 15, 2016

Lawns
Major Symptom:
1. Summer turf diseases Disease pressure high; many lawns showing symptoms of infection
2. Irrigation management Water management key to disease control
3. Yellow nutsedge control Weeds growing strongly; unfortunately now is not a good time for control

4. First fall fertilizer application

Current recommendations for fall fertilization
   
Trees & Shrubs  
5. Japanese beetles - follow up Severely defoliated trees are not dead
6. Bagworm - follow up Insecticide applications no longer effective
7. Fall and mimosa webworm Webbed nests in deciduous trees containing caterpillars and frass
8. Oak tubakia leaf spot & bur oak blight Brown leaf blotches and defoliation; too late for control
9. Lacebug damage on oak Discoloration and drying of tree leaves
10. Twig girdler Small terminal twigs turn brown; variety of trees affected
11. Rhizosphaera needle cast Inner needles of spruce turn brown and fall early
12. Twospotted spider mite damage - burning bush Yellowing of leaves along mid-vien
   
Fruits & Vegetables  
13. Poor tomato ripening in heat, yellow shoulders Temperatures above optimum for ripening causes a slow down in fruit production
14. Strawberry sap beetle Small dark insects, damage fruit by their feeding and spread disease
15. Fall vegetable gardening Time to plan/plant the fall vegetable garden

1. Summer turf diseases are rampant right now, due to warm temperatures and plenty of moisture. Humid air and warm days followed by nighttime temperatures that cool to the dew point result in surface moisture that favors infection. Preventive fungicide applications are most effective for disease control, but at this point many lawns have active infections. So prevention is too late. Home lawns can often tolerate a low level of damage without justifying the need for fungicide applications. Lawns will recover on their own from leaf spot diseases like dollar spot and brown patch once weather conditions dry out and cool. “Curative” applications may stop a disease outbreak from spreading further, but the damage will have been done. Additionally, higher rates are required for curative applications and environmental conditions suitable for disease infection may subside following the initial outbreak, meaning that a curative application may be completely unnecessary.

  • Dollar spot - Chlorothalonil, boscalid, demethylation inhibitors (e.g. propiconazole), dicarboximides (e.g. iprodione), and thiophanate-methyl provide preventive dollar spot control.
  • Brown patch - Use high label rates of propiconazole or thiophanate-methyl to provide three to four weeks of protection.
  • Gray leaf spot - Azoxystrobin, chlorothalonil, mancozeb, propiconazole, thiophanate-methyl, triadimefon.
  • Rust - Two or three applications at 7 to 21 day intervals beginning in late July, or when rust is first detected, should provide adequate protection. Some of the products that will control rust on turfgrass include chlorothalonil (Daconil 2787), maneb, mancozeb, propiconazole (Banner) and triadimefon (Bayleton).

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2. Irrigation management is one key factor in minimizing turf disease. When air is humid, dew will likely be present in mornings, and disease will probably develop in unprotected turf. Do everything possible culturally to reduce leaf wetness and reduce the likelihood of infection. Reduce or eliminate irrigation cycles following precipitation, irrigate during early morning hours to reduce the duration of leaf wetness and knock dew off of leaves, improve air flow, and even pole, mow, or drag a hose across turf to remove dew in the morning. 

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3. Yellow nutsedge control - Plants are growing strongly, but unfortunately this is not the best time of year for control. Plants are mature and have already begun producing tubers that will allow recovery following herbicide applications this year. If plants haven’t already been treated, it may not be worth treating at this point. Herbicide applications may aesthetically reduce yellow nutsedge, but likely won’t reduce tuber incidence in soil which is the true measure of control.

Next year, plan to treat problematic areas in spring to early summer, before plants mature and produce tubers. Sulfentrazone, imazosulfuron, and halosulfuron provide good postemergence control, and are safe on most cool- and warm-season turfgrasses. Mesotrione is another option for control in some coolseason turfs, and active ingredients such as flazasulfuron and metolachlor may be used in warm-season turf. Because of tuber persistence in soils, herbicide applications in successive years are often required for control.

Yellow Nutsedge Management Basics, Nebraska Extension Turf iNfo

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4. First fall fertilizer application - Fall is still the most important time to fertilize cool-season turfgrass. Fall fertilization helps promote recovery, builds roots, and increases sugar reserves going into winter. Here are the current recommendations for fertilizer applications.

  • Newly seeded areas: Starter fertilizer with higher levels of P2O5 should be applied at or slightly after seeding. A second application of starter fertilizer should then be applied 4 weeks after emergence or mid-October (whichever occurs first). Newly seeded golf or sports turf can also benefit from frequent applications of soluble nitrogen (urea or ammonium sulfate) every 10 to 14 days to accelerate establishment.
  • Newer turf areas (<10 years old>: New stands of turf require more fertilizer than older turf areas. Additionally, turf areas that are thin or were damaged by a pest will also benefit from additional fall N to accelerate recovery prior to winter. For these sites apply a balanced (50% soluble and 50% slow-release) nitrogen fertilizer in late-August to early-September. Then make a follow-up application of a quick release fertilizer in mid-October. Again, aim to apply 0.5 to 1.0 lbs N per 1000 ft2 or buy a fertilizer with your spreader setting on the bag.
  • Established turf (10+ years old): One application of a balanced released nitrogen source in midSeptember. Look for a fertilizer product with 30 to 50% of the total nitrogen as quickrelease/soluble nitrogen. This will provide even release during the fall. Aim to apply 0.5 to 1.0 lbs N per 1000 ft2 . If unable to calibrate your spreader, then buy a fertilizer with spreader settings for your particular fertilizer spreader on the bag.

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5. Japanese beetles follow up - The majority of adult insects have died and their feeding damage is done for another year. Linden trees are a favorite food source of Japanese beetle adults and in some cases have suffered severe defoliation. In most cases, trees will recover next year. Trees have NOT been killed by the beetle feeding, even if they have lost most or all of their leaves, so these trees should not be cut down. Healthy living buds for next year's new growth are present even on leafless twigs. Defoliation is most harmful to newly planted (in the last 2-3 years) or trees already in poor health. Trees that develop a history of severe damage may warrant control next year when the adult beetles are again present.

Is beetle control with milky spore effective? Milky spore is a bacteria that can infest and kill the grub stage of Japanese beetles. (Only Japanese beetles; it does not affect other white grub beetle larva such as our native masked chafer.) Grubs in the soil will eat the spores of this disease as they feed on turf roots. Once the disease infiltrates the white grub it causes the grub to lose its stores of body fat and it slowly turns the grub a milky white (hence the name).

It is a natural disease that helps to suppress grub populations but releasing it en mass in commercially bought milky spore packets doesn’t help. The issue is that this disease needs hosts in order to survive. When you release it into the environment, if there aren’t enough grubs for it in an area the disease will not be able to propagate in your lawn. This removes its utility as a preventative treatment for grubs. It can be released as a curative agent later in the year, but again it will not last once the grubs are gone.

See page 188 of this publication for more information - Biology and Management of Japanese Beetle, 2002 Annual Review of Entomology

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6. Bagworm follow up -  Immature bagworms are no longer feeding, so pesticide applications at this time are no longer effective. They have moved into the pupal phase and have retreated into their bags. Their bag protects them from insecticide applications. Bags, which have been permanently attached to plant branches, can be removed by hand from small plants. This will eliminate eggs for next year's generation. Large trees with serious infestations should be sprayed next year in late May to mid June when the next generation of insects is active.

Bagworms, Nebraska Extension

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7. Fall webworms have been appearing as webbed nests on the ends of branches in cottonwood, crabapple, walnut and other trees. A similar insect, called mimosa webworm, is very common on honeylocust.

Caterpillars hide in the webbed nests during the day and feed at night. The nests are unsightly, but caterpillars cause little harm to otherwise healthy trees. Tree health is usually not affected until more than 50 percent of the foliage is eaten. If there are enough nests, almost one on every branch, a tree could be completely defoliated. If you can safely reach the nest, use a broom to break up the bag of webworms. Follow up by spraying with a strong stream of water or an insecticide such as permethrin or Spinosad. Prune out the webbed nests when feasible. There are natural parasites and pathogens of fall webworm that often bring these infestations under control.

Fall Webworm, PennState Department of Entomology
Mimosa Webworm, PennState Department of Entomology

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8. Oak tubakia leaf spot & bur oak blight - One of the more serious leaf spot diseases showing up now is tubakia leaf spot of oak, caused by the fungus Tubakia dryina. Affecting mostly bur oak, it causes large brown leaf blotches, often along the viens. Affected leaves drop and can result in significant leaf loss. Young shoots may die. Symptoms are often more extensive in a tree's lower branches than higher in the tree.

Control is rarely needed and its too late for preventive fungicide applications now. In trees with a history of repeated infection, spray the tree with mancozeb (Dithane, Fore) or propiconazole (Banner Maxx, Infuse) at budbreak (April) and repeat twice at 10-14 day intervals.

Another, more serious disease, caused by a related fungus is bur oak blight, Tubakia iowensis  sp. novi. Leaves on affected trees become discolored in late summer, around mid-August, with purple-brown leaf lesions along the mid-vein and yellow wedge-shaped blotches on the leaves. Infected leaves also have black pustules at the base of the petiole. Infected leaves tend to persist on the tree through winter. Symptoms usually start in the tree's lower canopy, but spread and worsen after several years of infection to affect the whole canopy. Infected trees are more susceptible to secondary pests, such as two-lined chestnut borer and may show extensive canopy dieback after a few years of infection. Bur oak blight, along with the secondary pests it opens the tree up to, can result in tree death if left untreated.

Trees suspected of bur oak blight infection should be injected with propiconazole (Alamo) early in the growing season (May or June) to protect it from additional infections. 

Oak Leaf Blotches, University of Minnesota
Bur Oak Blight, USDA Forest Service

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9. Lacebug damage on oak - Significant lacebug damage can now be seen on the leaves of many oak trees. Lacebugs are small insects with white lacy wings that cluster on leaf undersides of oak, sycamore and other trees. Sapsucking insects, they pierce leaves to feed causing tiny light colored flecks on upper leaf surfaces. If heavily infested, leaf undersides appear dirty with dark spots or stains, and leaves turn yellow or brown. Lace bugs are prevalent in late summer. In most cases, the damage is minor enough, or occurs late enough in the season, that control is not needed. Also, natural enemies can keep lace bug populations down unless insecticides kill predators, allowing lace bug populations to build. A water spray from a high pressure hose can be used to knock lace bugs off of smaller plants to reduce populations

Lace Bugs on Deciduous Trees and Shrubs, University of Minnesota

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10. Twig girdler causes terminal leaves to turn brown; a symptom called'flagging'. It also causes twig dieback and the girdler can attack oak, elm, linden, hackberry, honeylocust, poplars, hickory, pecan, persimmons and some fruit trees like apple. The girdler is a long-horned beetle that emerges in late summer. As part of egg laying, the female girdles the twig to kill it because the larvae cannot develop in healthy wood. The dead tip may fall to the ground or hang in the tree until wind knocks it out. While damage is obvious, it is rarely severe, and there is usually no need for control. Larvae overwinter inside twigs. Pick up and discard dead twig sections that fall to the ground to reduce this insect. Squirrels clipping tree twigs can be confused with girdler damage.

Twig Girdler, Kansas State University
Twig Girdler and Twig Pruner, University of Missouri

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11. Rhizosphaera needlecast is a common fungal disease affecting Colorado blue spruce and other spruces.  Trees in eastern Nebraska are more commonly affected than those in the west. Needles are infected in spring, but symptoms do not become evident until a year later when the needles turn yellow, then a reddish brown which is being seen in trees now.  Older needles on the interior of the branch are affected.  Black fungal fruiting structures can be seen with a hand lens protruding from the stomata of infected needles. 

Infections can be high due to extended wet weather last season and now this spring. Saturated soils increase air humidity around the tree's lower canopy and also contribute to good conditions for disease development.   The disease can be controlled with an application of chlorothalonil in spring when new growth is one-half to two inches long.  Follow-up applications should be made every 3-4 weeks if frequent rains occur during spring and early summer.

Diseases of Evergreen Trees, Nebraska Forest Service

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12. Twospotted spider mite damage on burning bush- Spider mites are not insects, but are more closely related to ticks and spiders. They feed by removing liquid chlorophyll and other cell components from leaves with their piercing mouthparts. Damaged leaves develop yellow stippling; as damage progresses leaves turn yellow or silvery especially along the mid-vien. Very tiny webbing may be found on the underside of leaves along the mid-vien. Many generations of spider mites occur each summer, approximately one every 5-7 days when temperatures are above 75 degrees F. Adults overwinter in protected locations near host plants.

Monitor for live mites by shaking a branch over a white piece of paper. The mites can be seen as tiny specks of dust that move around on the paper. Spraying affected plants down with a strong jet of water can reduce mite populations and slow their reproduction. Continue to spray affected plants daily for several days or weeks to reduce mite populations without pesticiedes. Or spray plants, especially the undersides of leaves, as soon as mites are found with horticultural oil, insecticidal soap, abamectin, spinosad. Or use a specific miticide such as bifenthrin, permethrin or malathion. Repeat applications as often as monitoring shows live mites, or as directed on the pesticide label.

Two-spotted Spider Mites in the Home Garden and Landscape, University of Minnesota Extension

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13. Poor tomato ripening in heat/ yellow shoulders- Optimum temperatures for ripening of mature green tomatoes is 68-77 degrees F. The further temperatures vary from optimum, whether hot or cold, the slower the ripening process will be. Tomatoes do not produce lycopene and carotene, the pigments responsible for ripe tomato color, when temperatures are above 85 degrees F. So extended periods of extreme heat cause tomatoes to stop ripening. Tomatoes during this time may appear yellowish-green to yellowish-orange.

Yellow shoulders is a related problem and seen as areas at the top of tomatoes that never ripen properly. These areas stay green or yellow as the fruit ripens, having a firm texture and poor flavor when the tomato is eaten. Heat, environmental stress and variety susceptibility are all factors in the development of yellow shoulders. As mentioned above, high temperatures within the tomato prevent the development of lycopene and carotene needed for proper ripening. Areas of the tomato exposed to direct sunlight, like the top shoulders, get hottest and are most prone to the disorder.

Keep plants well-watered during hot periods and maintain adequate fertility when plants are fully loaded with fruits. Once temperatures cool, the ripening process should get back on track. Alternately, gardeners can harvest tomatoes at the pink stage and allow ripening to finish indoors. Development of yellow shoulders can sometimes be avoided if fruits are brought indoors to complete ripening away from high heat and other stresses.

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14. Strawberry sap beetles are small, dark brown beetles, 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 they 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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15. Fall vegetable gardening- Though often overlooked by gardeners, planting vegetables in July and August for fall production is an excellent practice. For those who love to garden, extending the harvest time helps ward off the dreariness of cloudy autumn days and extends the growing season of quality produce. Most cool-season vegetables grow as well as, or better than, those planted in the spring because they mature during shorter, cooler days. Flavors of vegetables maturing in the cool, crisp days of autumn are often sweeter and milder than those grown during thot summer weather. For tips on fall gardening and information on what and when to plant, UNL Extension has a NebGuide on fall gardening available.

Fall Gardening, Nebraska Extension

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Seasonal information for Nebraska's green industry professionals.

Continuing Issues

Lawns

Trees & Shrubs

  • Emerald Ash Borer Resources - EAB was confirmed in Omaha, NE 6/8/16 and Greenwood, NE 6/17/16. It is recommended homeowners wait to begin treating their ash trees until the insect is confirmed within 15 miles of their location. 
  • Basic EAB Information

Landscape Ornamentals

Fruits & Vegetables

Local Conditions

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Dry conditions are a frequent condition in Nebraska.  Stay informed on current conditions, and public water utilities restricting water use. Visit UNL Drought Resources.

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