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Hort Update for June 16, 2015

Lawns Major Symptom:
1. Turf and "slip & slides" Pythium blight can develop in 2 hours
2. Broadleaf weed control Careful with herbicide use during hot temperatures
3. Second preemergence applications May be needed for control of annual weedy grasses
4. Post emergence crabgrass control Control of young crabgrass seedlings
5. Yellow nutsedge control Best to apply controls by summer solstice
6. Moss control Manage site conditions to reduce moss growth
Trees & Shrubs  
7. Wet weather related plant issues Yew dieback, Botrytis on Douglas fir, leaf yellowing
8. Sycamore anthracnose Blighted leaves, leaf drop, twig loss
9. Ornamental pear leaf diseases Multiple disease organisms cause pear leaf spots
10. Bagworm on evergreens Time to monitor evergreens for young bagworms
11. Giant bark aphids Large, gray and black in color; mass on bark
Landscape Ornamentals  
12. Grass control in flower beds Grass-Be-Gone and Over the Top recommended herbicides
13. Planting annuals Still plenty of time for planting the garden
14. Powdery mildew Whitish-gray powdery growth on leaf surfaces
15. Height reduction for perennials Cut back perennials prone to lodging to encourage stronger stem development 
16. 'Blonde Ambition' grama winter hardiness Winter survival problems on this popular ornamental grass
Fruits & Vegetables  
17. Cedar-apple rust Yellow leaf spots on upper surface; raised orange postules on leaf undersides
18. Apple & pear scab  Olive colored leaf spots and leaf yellowing
19. Fruit drop - causes Fruit trees may drop immature fruits for several reasons
20. Broccoli bolting Heat stress, overmature transplants may lead to bolting
21. 'Artwork' broccoli 2015 AAS Vegetable Award Winner 
22. Squash vine borer Day flying, black & orange, clear wing moth lays eggs on cucurbits
23. Squash bug Scount for eggs and immature insects; control early
24. Flooded gardens and food safety Use caution when harvesting food crops from flooded gardens
25. Blossom end rot Leathery, brown dry rot on base of the fruit
26. Grass clippings as mulch Many herbicide labels now state to never use clippings for mulch if herbicide have been applied this year
27. Weather effects on soggy plants Warmer days may cause heat stress symptoms


1. Turfgrass disease and "slip & slides" - When items such as children's wading pools or ‘slip and slides' are left on turfgrass, pythium blight can develop in under two hours. This fungal disease occurs during wet weather and in high maintenance landscapes that are frequently watered. Key symptoms are gray spots or streaks that appear water soaked and form suddenly. Affected turf may have a fishy odor, especially if a sample is bagged overnight. Some cultural practices to reduce pythium infection include not leaving items covering turf areas, providing good soil drainage, filling depressions where water stands, avoiding mowing and traffic when turfgrass is wet. See NebGuide for additional control methods for Pythium.


2. Postemergence weed control during high temperatures - Wet weather has encouraged an increase in broadleaf weeds in turf. Control involves good management to promote a dense, vigorous turf that competes with weeds. Use a tall mowing height of three inches to reduce seed germination and to shade out weed seedlings.

September is the best month to control broadleaf perennial weeds with herbicides. If herbicides are used during summer, read label directions for temperature ranges within which to apply. Hot temperatures will increase damage potential to nontarget plants. Whenever used, spot applications are best as they result in the smallest amount of herbicide being used; saving money and protecting the environment. Read and follow label directions. Labels are the law and herbicides should not be used outside of recommended temperature ranges.


3. Second premergence crabgrass applications, if needed, are typically made about six weeks after the first application. A second application may be needed if the first application was applied prior to late April; or in turf with a history of severe crabgrass issues. This year, cool spring temperatures may have delayed crabgrass seed germination and application made prior to late April may lose effectiveness by the time much crabgrass seed germinates. Our above average rainfall may have also reduced the period of control of initial applications.

Eleven Ways to Maximize Preemergence Control of Crabgrass, Nebraska Extension Turfgrass iNfo


4. Postemergence crabgrass control can be achieved with herbicides.  Preemergence herbicides are generally more effective and should be considered in areas with a history of crabgrass. Mowing at 3 inches dramatically reduces the risk of crabgrass infestation. Crabgrass that does germinate in non-treated areas, or even in areas that were treated with a PRE, can be controlled with herbicides containing quinclorac, mesotrione, and fenoxaprop. Dithiopyr is a PRE that has postemergence activity on young crabgrass. For all herbicides, control is much more effective on young/small crabgrass plants. Be careful applying herbicides when air temperatures at greater than 85°F and never mix fenoxaprop with 2,4-D to reduce the risk of damage to the desirable lawn grasses.

Crabgrass Control in Home Lawns, Nebraska Extension Turfgrass iNfo


5. Yellow nutsedge control - Yellow nutsedge is beginning growth from underground tubers. While it thrives in wet areas, once established it does well in dry areas where turfgrass is thin. Mow high to reduce yellow nutsedge pressure. Hand-pulling and herbicide controls are most effective when used prior to the summer solstice of June 21st. In July, the plants begin forming new tubers which herbicides typically do not affect. Cultural controls include mowing at the highest practical height, correct irrigation to prevent summer thinning, and fall fertilization to maximize turf density. Postemergence herbicides for nutsedge include sulfentrazone or halosulfuron.

Yellow Nutsedge Thriving in Lawn, Sports, and Golf Turf,  Nebraska Extension Turfgrass iNfo


6. Moss control - Moss can grow in shady areas with poor air circulation where low light and soil compaction have thinned turfgrass. Moss will not grow into areas with dense turf cover. Once moss develops, turfgrass will not grow into the area. While copper sulfate will kill moss, cultural controls are needed to prevent its return. If feasible, thin trees and shrubs to increase light penetration and air circulation to the area. Core aerate the turf to relieve soil compaction. Adjust irrigation in shady areas as these require less frequent irrigation than full sun areas. If the area is still too shady for dense turf growth and moss returns, replace grass with a mulched bed and/or shade adapted plants like Hosta or a groundcover like Adjuga.


7. Wet weather related plant issues range from saturated soils that restrict root growth and function resulting in yellow foliage or even wilted foliage to a variety of foliar diseases leading to leaf drop. When diagnosing plant issues, keep wet weather effects in mind. Check soils for saturated conditions. If needed, pull back mulch to allow soil drying via evaporation and redirect downspouts away from perennial plants and shrubs until rainy weather decreases. Remind clients that most foliar diseases are more aesthetic than harmful in the long term and to expect leaf drop. Fungicide controls are not recommended for minor foliage diseases of ornamental landscape plants.


8. Sycamore anthracnose - While anthracnose infects a number of trees like ash, maple and walnut, it causes the most defoliation in Sycamore. Infection is favored by relatively cool temperatures and prolonged periods of leaf wetness. In exceptionally cool, wet springs, sycamore trees leaf out and then defoliate heavily; as they are doing this year across Nebraska.

In Sycamores, anthracnose results in early spring is death of twigs and new shoots. Repeated killing of young twigs results in abnormal branching and gives the tree a ragged appearance. After bud break, sycamores show a scorching and wilting of new shoots and leaves. Later, fully expanded leaves develop elongated tan to brown lesions parallel with the midrib and veins. Infected leaves scorch and shed.

If favorable weather persists, disease development may continue throughout spring into early summer. As temperatures increase, anthracnose becomes less active and trees re-leaf. Preventive fungicide controls are available, but not necessary.


9. Ornamental pear leaf diseases - Pears are often infected with the bacterial disease fire blight. This disease also affects crabapple and hawthorn. Fire blight is promoted by conditions of high soil moisture, rapid shoot development, prolonged rainy or humid periods, and temperatures of 60 to 75 degrees F. Symptoms include blighted foliage on young shoots, tender shoots with a Shepard's hook appearance on the tip, blossom blight, and twig cankers that may exude sap. Control involves selecting resistant cultivars, pruning out infected branches about 8" below the affected area, and avoiding excess fertilization. The pesticide Streptomycin, if applied correctly and at the correct time, can be used to reduce fire blight.

Ornamental and fruiting pears are also susceptible to pear scab, Venturia pirina, affecting both leaves and fruits with symptoms similar to apple scab.  Leaf lesion begin as dark pin-point spots and may enlarge becoming velvety brown or olive green with indistinct margins. 

Cedar-apple rust also affects pears.  See #17 below.  Finally, pears are affected by Entomosporium leaf spot, a fungal leaf spot disease causing small reddish spots that age to develop a dark purple border with a grayish center. Severely infected leaves may drop prematurely. 

Fireblight, University of Missouri Extension
Apple and Pear Scab, University of California
Pear Scab, Michigan State University
Entomosporium Leaf Spot, University of California


10. Bagworms on evergreens - Bagworms are hatching on evergreens trees. Monitor evergreens for young bagworms. At this time of year, they can be as small as one-fourth inch long. Bagworms are small, brown,  triangular-shaped and covered with needles for camouflage.  At this size is the time when products like Bacillus thuringiensis will be most effective in controlling bagworms.

Bagworms, Nebraska Extension


11. Giant bark aphids are the largest aphid found in North America, averaging one-fourth inch long. They are grayish with black dots, long black legs and can be winged or wingless. They feed on a wide variety of trees by sucking sap from small branches. Serious damage is seldom reported, although heavy infestations could kill small twigs or branches. These aphids exude large amounts of honeydew that will create sticky conditions on sidewalks, patio furniture, cars, etc. Aphids can be present from late April into November as there are several generations.

Giant Bark Aphids, Oklahoma State University


12. Grass 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 a surfactant, commercial or dish soap, with these products as burning of desirable plants may occur. Be careful in mixed beds with ornamental grasses, contact of these products to desirable ornamental grasses will cause injury or death.


13. Planting annualsSpring and early summer conditions have been extremely wet so many homeowners have not gotten their normal spring plantings completed, particularly annuals and perennials, but also in the vegetable garden. Commercial landscapers many also be having a hard time getting all their plants in the ground due to wet soil conditions. Many homeowners are questioning if it's still OK to plant and the answer is a resounding Yes! There is plenty of time for perennial plants to get established or for annuals to provide flowers for the summer. If plantings were lost this spring, due to poor germination of seeded crops in wet soil or to cold conditions, reseeding is also a good idea.  There are still approximately 117 growing days left in the season for eastern Nebraska, so for longer term crops check seed packets for the approximate days to harvest.

Many nurseries still have a good stock of plants on hand, but its still a good idea for homeowenrs to inspect plants for quality before purchasing.


14. Powdery mildew causes grayish white powder-like patches on upper leaf surfaces. It is promoted by warm temperatures and high humidity. Extended wet conditions this spring and early summer have caused early infections on many garden plants.  Many types of plants are susceptible, such as Phlox, Monarda and Zinnia. If plants are heavily infected consider replacing them with resistant varieties.  Place susceptible plants in areas with good air circulation.  Avoiding overhead irrigation and excess nitrogen fertilizer. Fungicides will provide some protection as new healthy foliage emerges. Refer to the publication below for recommended fungicides. 

Powdery Mildew on Landscape Plants, Nebraska Extension


15. Height reduction for perennials - Some perennials in the garden are prone to lodging, falling over in the garden or opening up in the center. This occurs when plant grow quickly and don't develop strong enough stems to hold the plant upright.  Lodging is commonly seen in some ornamental grasses and tall sedum, along with other garden perennials.  One method that encourages strong stem development is to cut perennials back during mid-summer, removing about one-half of their height. Plants will regrow new top growth, while at the same time the remaining stems become thicker and stronger. 

Other methods that help reduce lodging, is to avoid high nitrogen or fast release nitrogen sources when fertilizing. Avoid overwatering, particularly since spring and early summer have been so rainy already. Stake tall plants. Ideally staking materials should be put in place in early spring just before or as new growth begins. If tall plants haven't been staked, do it now.  If tying stems to stakes, do so loosely with double loops to avoid wind whipping causing ties to damage stems.


16. 'Blonde Ambition' grama winter hardiness - Many reports have been received this spring of poor winter recovery on the popular ornamental grass 'Blonde Ambition' grama. In some cases plants died completely over winter.  In other cases, plants are very slow to regrow this spring. This grama cultivar will need further monitoring to determine its usefulness and success in Nebraska gardens. 


17. Cedar-apple and cedar-hawthorne rust are similar but different diseases for which it is too late to apply a fungicide. Cool, moist conditions this spring have increased infections on susceptible apple, crabapple and Hawthorne trees. Both diseases cause yellow spots on upper leaf surfaces and raised orangish-postules on leaf undersides. Both require two hosts to complete their life cycle, with one host being Juniper such as cedar trees. While it would take a number of years of severe infection to harm tress, infected leaves may drop resulting in unsightly trees and poor fruit production in apples. Repeated yearly infections can weaken trees and lead to other issues.

The best control of rust is selecting resistant trees. On susceptible trees with a history of infection, fungicides need to be applied in early spring just as buds are opening and applications repeated two or three times.


18. Apple & pear scab - Apple scab is infecting apples and crabapples. This fungal disease is favored by wet, humid weather occurring from late April through June. The disease decreases yields, reduces fruit quality, defoliates trees, and reduces tree vigor. The fungus can overwinter on or near trees so we often see this disease before cedar apple rust. Leaf lesions of apple scab are usually olive colored and turn brown.

Pear scab is very similar to apple scab, including leaf and fruit lesions, and is caused by a closely related fungus. 

As with rust, planting resistant cultivars is the best means of control. Fungicides can be applied, but applications need to begin in early spring to reduce infections.


19. Fruit drop - Homeowners are often concerned when their fruit trees begin dropping fruits, but this is actually a pretty common occurance. Fruit drop can happen for several reasons. 

  • Lack of pollination - The first occurrence of fruit drop happens right after blooming and petal fall when the new fruits are still tiny, approximately pea-sized. Fruits that did not pollinate properly fall from the tree. Cold or wet conditions during flowering reduces pollination due to a lack of bee activity. Cold temperatures during flowering may kill flowers and result in fruit drop. A lack of pollinators can also be a problem. 
  • Fruit load - A second round of fruit drop often occurs in early to mid summer when fruits are about marble sized.  This condition is often called June drop and is thought to occur due to competition between fruits for resources - water, nutrients and carbohydrates.  Trees often set many more fruits then they have the ability to bring to maturity. Trees are limited by their vigor and the amount of leaves present to photosythesize and create carbohydrates for fruit development. Fruit thinning by the orchardist can minimize June fruit drop. Apples and pears are particularly prone to June drop, but it is less common in cherries. Hot, dry weather in late spring or early summer contributes to June drop. Fruit drop at this time allows the remaining fruits to develop properly. 
  • Insect or disease problems - Fruits infected with diseases or insects often fall from the tree early. Check falling fruits for signs of common diseases or cut them open to look for wormy insects like immature codling moth or plum curculio larvae. 

Despite natural fruit drop, trees may still be in need of hand thinning to 1) prevent branch breakage of overloaded branches, 2) allow remaining fruit to develop good size, and 3) allow good fruit bud development for next year and prevent trees from developing an every-other-year bearing cycle. After thinning, apples should be spaced 1 fruit per every 8-10 inches of branch. Pears, plum, apricot and peaches should be spaced 1 fruit per 6-8 inches of branch. Apples and pears often bear fruits in clusters and should be thinned to allow only one fruit per cluster. 

Fruit Trees: Thinning Young Fruits, University of California


20. Broccoli harvest will begin soon. Head development is beginning for early spring plantings. Broccoli is usually ready to harvest 65-70 days after transplanting. The heads of broccoli are really flower buds. These must be harvested before the flowers open or show yellow. Mature heads measure 3-10 inches across. Cut the main stem about 6 inches below the main head. After the main head is harvested, lateral heads may develop from the leaf axil lower down the stem.  Although they will be smaller than the main head, they can also be harvested when the flowers have developed but are still dark green and closed.  

Early head development, or bolting, may occur before plants have had a chance to develop a good size if the plants are exposed to heat stress or if overmature transplants were used. If bolting occurs broccoli heads should be harvested small, then the plants should be removed from the garden. There is no way to "slow the plants down" or make the small heads develop more size before they become overmature. 

Growing Broccoli, Cauliflower and Cabbage in Minnesota, University of Minnesota Extension 


21. 'Artwork' broccoli is a unique and beautiful dark green stem broccoli that has only recently become available to home gardeners. Previously, stem or baby broccoli was exclusively available in gourmet markets and up-scale restaurants. Now home gardeners can make the art of gardening come alive with this delicious, long-yielding variety.  Artwork starts out similar to a regular crown broccoli but after harvesting that first crown, easy-to-harvest tender and tasty side shoots continue to appear long into the season, resisting warm temperature bolting better than other stem broccolis currently on the market

2015 All-America Selection Vegetable Award Winner


22. 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, Nebraska Extension
Squash Vine Borer Management in Home Gardens, Minnesota State University


23. Squash bug control - Squash bugs are one of the most damaging insect pest of pumpkins and winter squash. The adult is a brownish, shield-shaped bug about 5/8 inch long and 1/3 inch wide. Adults are very difficult to control; hence plants must be monitored closely for squash bug eggs and young nymphs to effectively control this insect. Eggs are brick red and found on leaf undersides in the V made by veins. Young nymphs are gray and tear drop shaped. Scout plants often for adults, eggs and young nymphs. Hand-pick adults and squish egg masses. When nymphs are present, carbaryl (Sevin) or permethrin can be applied for control in home gardens.

Squash Bug Control on Melons & Cucumbers, Nebraska Extension


24. Flooded gardens and food safety - Flood waters carry many contaminants, including bacteria and parasites, that can cause human illness.  Use of food crop from flooded vegetable gardens should be carefully considered. Preventing contamination of food crops is much easier than trying to remove contaminants. Bacteria and other pathogens naturally die over a period of time from exposure to sunlight, heat and beneficial microorganisms.  

The greatest risk is with food crops when their edible portion is in direct contact with the soil or came in contact with flood waters. In some cases, plants many not have survived the flood. Dead plants can be pulled out, or tilled back into the soil.  Crops can be replanted when soil is workable.

For crops that survived the flood or are replanted:

  • If the crop's edible portion is in direct contact with the soil and is usually eaten without cooking, such as baby carrots, lettuce or other greens, it is recommended that these crops not be harvested until 120 days have past after the flood. Check the predicted crop harvest times if replanting is needed, but follow the 120 days harvest restriction for the safest produce. If a home gardener decides to plant and harvest sooner, that's up to their discretion.
  • If the crop's edible portion is in direct contact with the soil, but is usually cooked before eating, such as potatoes and onions, then is it recommend that crops not be harvested until 90 days have past after the flood. 
  • If the crop's edible portion is not in direct contact with soil or flood water, it is recommended that crops not be harvested until 90 days have past after the flood. 

Food Safety and Flooded Vegetable Gardens, Backyard Farmer


25. Blossom end rot is a common problem of tomatoes, but also affects peppers, eggplant, squash and watermelon. It appears as a flat, dry, sunken, brown rot on the blossom end of fruits caused by a calcium deficiency in the fruit. In Nebraska, rarely is there a lack of calcium in the soil. Blossom end rot occurs when plants cannot pull calcium up quickly enough for developing tissues. Calcium must be dissolved in water to move within a plant, so dry soils can increase the problem.

Drought stress, low daytime humidity, high temperatures, and rapid vine growth favor blossom end rot. Applying calcium to the soil or to the plant is not beneficial. Instead, maintain a consistently moist but not saturated soil; use organic mulch near the base of plants; and avoid excess nitrogen fertilization with ammoniacal nitrogen sources.

Often the first ripe fruits are affected.  Remove them and later ripening fruits will usually be normal. 

Blossom End Rot of Tomato, Eggplant and Pepper, Ohio State University
Special Tomato Problems, Nebraska Extension


26. Grass clippings as mulch in the vegetable garden- Read the label. Many herbicide labels now have more conservative recommendations; stating grass clippings from lawns to which a herbicide has been applied should never be used as mulch. If this is stated on the label, it must be followed. If the label does not state this, our general recommendation has been to wait until after at least 3 to 5 mowings before using the clippings as mulch; however, it would be safest not to use clippings as mulch


27. Weather effects on soggy plants - Overly wet and cool conditions in spring and early summer may have limited root development on new ornamental plants, both annuals and perennials, and plants in the vegetable garden.  High levels of water in the soil drives oxygen out of soil pore spaces and limits root growth. Due to this limited root development, as summer conditions become hotter plants may struggle initially to maintain their internal water pressure.  Problems will be seen as plants wilt during warm sunny days.  Wilting may be slight or more severe, but plants will recover during the evening hours. If good soil moisture is present irrigation, or the addition of more water, will not help. Given time plants will develop better root systems enabling them to pull in water on demand to meet plant needs. 

If possible, provide temporary shade for several days to plants experiencing more severe wilting.  Shade will limit the amount of water lost through leaf surfaces, giving plants time to develop their root system without the risk of leaf scorch or plant death. A couple easy methods for providing temporary shade include 1) setting up snow fencing on the sunny side of plants, or 2) placing floating row cover fabric over plants.