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Hort Update for June 18, 2020

Hort Update for June 18, 2020, Nebraska Extension,
Newly hatched bagworm caterpillars creating protective bags out of the juniper on which they are feeding. At this stage they are less than 1/2 inch long. Image by James Kalisch.
Serious ConcernsMajor Symptom:
1. Shade trees not leafing out Slow or poor canopy development in shade trees
2. Curled leaves in tomato & pepper Several possible causes
3. Oak anthracnose Brown shriveled leaves or leaves with dead sections
Minor Issues
4. Cedar-apple rust and apple scab Bright yellow or olive-green leaf spots on apples and crabapple
5. Small twig and leaf drop in trees Larger than normal numbers of individual leaves and small trig sections
6. Little barley in turf Blue-green grass early season grass, turn tan/brown in early summer
Timely Topics  
7. Brown patch in turf Irregularly shaped tan leaf lesions with red margins; roughly circular brownish patches in turf
8. Dollar spot in home lawns Leaf blades exhibit straw-colored dead spots with reddish-brown margins; lesions pinched at center into an hour-glass shape; 4-6 inch dead spots in turf
9. White grub control timing in turf Time to control
10. Nutsedge control in lawns Apple-green, grass-like plant with waxy blades and a triangular-shaped stem
11. Bagworms hatching Time to control
12. Invasive Asian jumping worms If found, monitor and report

1. Shade trees not leafing outPoor or slow canopy development in shade trees

Reports of trees not leafing out this spring or beginning to leaf and then stopping have been fairly common across the state. This could be cold temperature injury. Freezing injury to trees can occur in the fall when there is a sudden drop in temperature prior to a tree becoming fully acclimated for winter. Injury can also occur in late winter if above average temperatures occur, such as those we experienced in February and March, and a tree begins to break dormancy. Subsequent cold temperatures may then injure trees. If only leaf buds are damaged, otherwise healthy trees can develop secondary buds and leaf out. However, if a tree has not developed leaves by now, it is not likely too.


2. Curled leaves in tomato & pepperSeveral possible causes

Curled and/or distorted leaves on tomatoes and peppers may be caused by weather extremes, a virus disease, or herbicide drift. It is important to distinguish which is the cause. With weather extremes, leaves may be curled or rolled but otherwise appear fairly normal. On hot, windy days, leaves curl to reduce transpiration of water from their leaves. With herbicide drift, other plants in the garden or nearby are likely to show signs of leaf curling/distortion as well. On these plants, new growth will be normal. With a virus disease, leaves are curled, distorted and may be off-color. New growth will continue to be affected. Some viral diseases include curly top, tomato mosaic virus, and tomato yellow leaf virus. With herbicide injury and virus diseases, plants are best removed and destroyed.


3. Oak anthracnoseBrown shrivelled leaves or leaves with dead sections

Oak anthracnose attacks many species of oaks. Susceptibility varies among species, with white and bur oaks usually most severely affected. The first symptom seen in the spring is usually shoot blight, which can develop suddenly following rain. Young leaves and shoots appear brown and shriveled. Leaves that have already expanded may become cupped and distorted with large areas of dead tissue. Some leaf drop may occur. Mature leaves are fairly resistant and infection causes only small necrotic spots. The fungus also infects twigs, producing cankers and causing twig dieback during the winter and early spring. Most otherwise healthy trees will tolerate anthracnose infection and control is not needed or effective now.

Oak Anthracnose, Iowa State University Extension and Outreach


4. Cedar-apple rust & apple scabBright yellow or olive-green leaf spots on apples and crabapple

Symptoms of cedar-apple rust are bright yellowish-orange leaf and fruit spots, which often have a band of red or yellow around the outer edge. Apple scab causes olive to greenish-black leaf spots. Similar cracked, scabby spots appear on the fruits with heavily infected fruits becoming misshapen.

Fungal infections by these two diseases occur mainly during spring as trees are leafing out and spring rains are providing moisture needed for infection. It is during the infection period (April into June) that fungicides need to be applied to reduce summer leaf drop. Fungicides applied after leaf drop have very little affect. Encourage customers to wait until the following spring to apply a fungicide. Cedar-apple rust and apple scab will not kill a crabapple or apple tree; but repeated infections will reduce tree vigor and health. The best control of these two diseases is to plant resistant cultivars of apple and crabapple.


5. Small twig and leaf drop in treesLarger than normal numbers of individual leaves and small trig sections

This can be caused by the heat and high winds we had when trees were not prepared for such conditions; hence they dropped some leaves. If the tree is an oak, this might be due to squirrels or the twig pruner insect. Homeowners can be assured these issues are not a long term concern for trees.

Twig Girdler and Twig Pruner, University of Missouri


6. Little barley in turfBlue-green grass early season grass, turn tan/brown in early summer

This winter annual grass has been confused for yellow foxtail causing concern that premergence herbicides are not working. Little barley is a winter annual grass that seeds in June, and may be confused with foxtails. However, yellow foxtail (and others) are summer annual grasses, which are just now germinating in southeastern NE and will seed later in summer. Little barley is best managed by encouraging a dense turf stand or with a preemergence herbicide applied in fall. We generally don’t recommend post emergence herbicides for control of little barley. The species will thin and die as temperatures warm this summer. Overseeding thin areas this spring (and especially in late summer for cool-season grasses) will improve turf density and limit little barley establishment in future years.

Little Barley, University of Missouri


7. Brown patch in turfIrregularly shaped tan leaf lesions with red margins; roughly circular brownish patches in turf

Symptoms are reddish brown circular patches with grass blades in or near the patch having irregular shaped tan lesions with red margins. Unlike lesions of dollar spot, these usually do not encircle the leaf blade. Brown patch may be more noticeable in tall fescue lawns but Kentucky bluegrass is also affected. Brown patch is most often found in slower growing turf, but can show up in fast growing lawns after fertilization with fast release nitrogen sources. Fungicide control in home lawns is rarely needed. Use a fertilizer with slow release nitrogen sources or one with at least 50% of the nitrogen being slow release or water insoluble (WIN). Know that younger lawns, 10 years old or younger, require more nitrogen fertilization than older lawns. Leave grass clippings when mowing.

Brown Patch Disease of Turfgrass, Nebraska Extension


8. Dollar spot in home lawnsLeaf blades exhibit straw-colored dead spots with reddish-brown margins; lesions pinched at center into an hour-glass shape; 4-6 inch dead spots in turf

This is a minor disease for most home lawns. The best way to manage dollar spot in residential lawns is with a June application of fertilizer to help it grow out of the damage. To identify dollar spot, symptoms appear as four to six-inch, straw-colored patches of blighted turf. A bleached lesion in the shape of an hour glass is present on the leaf blade. The lesion has a characteristic reddish-brown margin. In early, dewy mornings, a cobweb-like mycelium is visible in the affected area.

Dollar Spot Disease, Nebraska Extension Turf iNfo


9. White grub control timing in turfTime to control

June into early July is the time to apply preventive insecticides to lawns with a history of white grub damage last summer. If a lawn did not have confirmed white grub damage last season, preventive insecticides do not need to be applied. Instead, encourage monitoring of lawn during August for signs of white grubs. These signs include dry or brown spots, flocks of birds, particularly starlings, feeding in the turf, and animals, especially skunks and raccoons, foraging in an area. In August, if 8 to 10 masked chafer or Japanese beetle grubs can be found per square feet, or 3 to 5 June beetle grubs per square foot; then an application of Dylox or carbaryl (Sevin) is justified at that time.

White Grub Management


10. Nutsedge control in turfApple-green, grass-like plant with waxy blades and a triangular-shaped stem

Yellow nutsedge grows rapidly in summer, becoming quite noticeable in mid to late June through the end of summer. However, early June to just past mid-June is the best time to apply herbicides for management. When herbicides are applied after June 21, the plant may be killed but it will have already produced many small underground tubers that will regrow this year or in future years. For yellow nutsedge to be effectively managed, herbicide control programs must be implemented early in the season and used in consecutive years. Late applications and/or not sticking to a multi-year strategy often results in no net gain against this troublesome perennial weed. For information on herbicides to use, see the TurfInfo linked below.

Yellow Nutsedge: It’s Time to Treat, Nebraska Extension


11. Bagworms hatchingTime to control

Once overwintering eggs on trees begin to hatch, insecticide control can begin. Upon hatching, bagworms are about one-eighth of an inch long and difficult to detect. When small, Bacillius thuringiensis (kurstaki) and spinosad are biorational insecticides that can be applied to foliage to kill young caterpillars as they feed. Biorational insecticides kill caterpillars without causing harm to natural enemies. They must completely cover foliage and be consumed by bagworms to be effective. After the month of June, when bagworms are bigger, conventional insecticides need to be used and these may include malathion, acephate, carbaryl, bifenthrin, permethrin etc. Preventive or systemic insecticides containing dinotefuran are applied to the soil but these must be applied weeks before hatching, hence it is too late to use these products now.

Bagworms on the Loose, Nebraska Extension


12. Invasive Asian jumping wormsIf found, monitor and report

This new invasive species was found in Douglas, Sarpy, Lancaster and Platte Counties last year. Activity of this worm can deplete soil of nutrients and alter the soil's capacity to hold water. While Asian jumping worms look similar to European earthworms, there are distinct differences to aid identification. See links below.

Unlike European earthworms, Asian jumping worms do not create channels in soil nor do they recycle nutrients into soil. Instead, they feed near the surface on leaf litter and mulch leaving behind a dry, grainy soil that deprives trees and other plants of essential nutrients. As a new pest, research is being done on the best way to manage them. One way to slow their spread is to discourage clients from sharing plant materials from yard to yard.

If you suspect jumping worms, take a video and/or photo of them to submit to your local Extension office and/or the Nebraska Invasive Species program.

A New Can of Worms, Nebraska Extension


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