Green Industry Resources
Hort Update- Seasonal Information for the Green Industry
Hort Update for the Week of July 12, 2013
|1. Bluegrass billbug||Browning of turf, resembles drought injury|
|2. Bindweed & other perennial weeds||Fall herbicide applications most effective|
|Final timing for early season treatment, rescue treatments|
|4. Zoysia fertilization||Timing of warm season grass fertilization|
|Trees & Shrubs|
|5. Bagworms||Inspect now; control while insects are small|
|6. Care of young trees||Deep infrequent watering needed when soils are dry|
|7. Japanese beetles||Watch for copper brown and metallic green beetles on rose, apple, maple|
|8. Aphid control||Curling leaves on trees, sticky honeydew on objects beneath tree|
|9. Two-spotted spider mites||Yellow and stippled leaves|
|10. Hollyhock rust||Orange- red spots on leaves|
|11. Aster yellows||Stunted, distorted flowers that fail to open|
|12. Phlox plant bug||White or pale green spots on leaves and deformed flower buds|
|13. Tobacco budworm (geranium & petunia)||Small green-to-brown colored worms; small holes in flower buds and leaves|
|Fruits & Vegetables|
|14. Tomato leaf spots||Vigorous plant growth, fruit bud initiation requires water|
|15. Tomato herbicide damage||Leaf yellowing, distortion and cupping|
|16. Cucumbers flowering, no fruit set||Consider rotating solanaceous crops with other veggie types|
|17. Squash vine borer||Apply a stump treatment to prevent regrowth; follow herbicide recommendations|
|18. Powdery mildew on squash||Grayish white powder on leaf surfaces|
|19. Potato flowering & fruit set||Small green, round fruit at the top of the potato plants|
|20. Raspberry canes wilting & dying||Brown to black stems, wilt and die|
|21. Rabbit control||Protect plants from rabbit nibbling|
1. Bluegrass billbug is the species that damages turf in eastern Nebraska. When control is needed, insecticides also need to be targeted at adult weevils present from April into June and September into October. Bluegrass billbugs are smaller at 1/4 inch long and also brownish-black. Pit-fall traps are the best way to monitor.
Rocky Mountain billbug (also known as Denver billbug) causes damage to Kentucky bluegrass lawns in western Nebraska. Billbug injury can be mistaken for white grub or sod webworm damage, disease, or drought stress. Newly-hatched larvae tunnel in grass stems, hollowing out the stem and leaving fine sawdust-like debris and excrement. Infested stems discolor and when pulled, readily break away at or near the crown. Subsurface feeding by older larvae can damage root systems, causing lawns to appear drought stressed.
Larvae are cream colored, legless with reddish heads. They look like a puffed up rice kernel. Under heavy billbug pressure, turfgrass turns brown and dies.
When control is needed, insecticide applications need to be timed for when adults are present in May and June. Rocky Mountain billbug adults are 1/3 to 1/2 inch long brownish-black weevils. They may be observed on sidewalks or monitored using pitfall traps (see link).
2. Bindweed is a perennial vine with an extensive rhizomatous root system, and can be found in thin turf, ornamental beds and the vegetable garden. Fall applications provide the most effective control. Recommended herbicides include clopyralid, quinclorac, 2, 4-D and/or dicamba. Spot applications are best with care taken to prevent these broadleaf herbicides from damaging ornamental plants.
Bindweed spreading through thin turf, ornamental beds, UNL Turf iNfo
- imidacloprid (Merit),
- halofenozide (Mach 2),
- chlorantraniliprole (Acelepryn)
- clothianidin (Arena)
As a rule, these products are best applied from June 14 to July 4th. Correct irrigation is important to effectiveness. Read and follow label directions.
After mid-July, or on situations where preventive insecticides fail to provide adequate control or preventative products were not used and populations have reached 8 grubs per square foot, turf managers may need to use a rescue treatment. Curative treatments are with fast acting, short residual products such as carbaryl (Sevin) or trichlorfon (Dylox).
Post‐treatment irrigation is critical in these situations. To optimize the effectiveness of any these products, irrigate with ½ inch of water immediately following application. If conditions have been very hot and dry and grubs are deeper in the soil, a pretreatment irrigation of up to 1/2 inch applied 48 hours before the insecticide application should encourage grubs to move closer to the soil surface and enhance the level of white grub control.
4. Zoysia fertilization- A zoysia lawn may be fertilized three times during the summer; May 30th, July 1st, and August 1st. This coincides with the period of most active growth. If a zoysia turf is fertilized before the grass is actively growing, much of the fertilizer is wasted and may encourage weed growth. Apply ¾-1 lb of nitrogen per 1,000 sq. ft. at each application, using a complete fertilizer with nitrogen, phosphorus and potassium. Fertilizers with at least 50% slow-release nitrogen are preferred.
Zoysiagrass Lawn Calender, University of Nebraska - Lincoln
5. Bagworms have hatched. Control is most effective while the insects are still small, ideally 1/4-1/2 inch long. Monitor evergreens and other landscape ornamentals for their presence. If only small numbers are found, they can often be control through handpicking. Drop the caterpillars in a bucket of soapy water. If many trees are affected or many insects are present, then insecticides can be used for control. Spray trees thoroughly with bifenthrin, Bacillus thurengiensis (Dipel) or permethrin.
6. Care of young trees - The care trees receive during the first few years after planting is critical. Many recommendations have changed drastically in recent years in light of new and more thorough research. Refer to the UNL NebGuide for updated care practices of young trees. The NebGuide explains the correct mulching, pruning, watering, wrapping, staking, and fertilizing practices that will promote healthy growth and development of young trees.
7. Japanese beetles are showing up on ornamentals in extreme eastern Nebraska. Japanese beetles are prodigious feeders on the foliage and fruit of nearly 300 species of landscape plants. Japanese beetles feed on the upper leaf surface, removing the soft green tissue and leaving the veins in a lace-like pattern. Japanese beetles release a strong aggregation pheromone that attracts additional beetles to a food source. The larva (white grubs) of Japanese beetles feeds on the roots of plants from late summer into early fall. Grub control in lawns is the same as for other annual white grubs.
For control of adults, see:
Management of Japanese Beetle Adults, University of Nebraska- Lincoln
8. Aphids are small, pear-shaped, soft-boded insects that feed by sucking sap from plants through their straw-like mouth. They can reproduce very quickly, with multiple generations of insects each summer. Despite their small size, large colonies of aphids can greatly reduce plant vigor. Their feeding often causes leaf cupping or rolling, distortion, and their secretion of excess plant sugars, called “honeydew”, frequently results in a black, sooty mold.
Almost every plant has some type of aphid that feeds on it. Aphids are a major prey insect species, serving as a food source for ladybug and lacewing larvae, spiders, and many more. Often these predatory insects will show up after aphid populations have built up to a high level.
Syringing, or spraying plants off with a strong jet of water, can often bring aphid populations under control while preserving beneficial insects. Chemical control is seldome necessary, but if needed applications of insecticidal soap, bifenthrin or permethrin, either alone or in conjunction with a soil drench of imidacloprid, can be used.
Insect Pests of Broadleaf Trees, Nebraska Forest Service
9. Two-spotted spider mites - This warm season pest has been seen on a variety of plants, so it would be wise to be alert for signs of damage on a variety of plants from ornamentals to evergreens to vegetables. With return of warm weather, populations can build quite rapidly and early control is best way to prevent damage.
10. Hollyhock rust is caused by a fungus that, unlike many other rust fungi, completes its life cycle on one host. The fungus survives winter in infected plant debris. In spring, spores are rain splashed or wind-blown to leaves. Initial symptoms are yellow to orange spots on upper leaf surfaces; then red to brown pustules develop on lower leaf surface and release orange spores to infect nearby leaves throughout summer.
Hollyhock rust can be managed during dry years with cultural controls. Remove all plant debris in the fall to reduce the amount of overwintering fungus. Use healthy transplants or start disease-free seeds each year. Keep plants growing vigorously in a sunny location with good air circulation. Avoid overhead watering. Routinely check hollyhocks for leaf spots and remove infected leaves as they appear. Rust can become severe during wet seasons and may require chemical control. Fungicides like Myclobutanil or Propiconazole must be applied early, with applications repeated according to label directions to protect leaves from rust infection.
Hollyhock Rust, University of Minnesota Extension
11. Aster yellows is a common disease affecting many ornamental flowers. Susceptible plants include Aster, Chrysanthemum, Coreopsis, cosmos, Echinacea (coneflowers), Dianthus, Gladiola, marigold and Petunia. 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.
12. 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.
13. Tobacco budworm feed on flower buds and may cause petunias, geraniums and other annual flowers to stop blooming. The budworm's droppings, sometimes described as small black seeds, are often seen before the worms are noticed. On close inspection, small green-to-brown colored worms can be found nibbling small holes in flower buds and leaves. Treat with a Bt product (Bacillus thuringiensis) such as Dipel or Thuricide or carbaryl (Sevin) or permethrin (Eight).
14. Tomato early blight and septoria leaf spot are fungal diseases that begin as leaf spots on lower leaves, then work their way up the plant causing leaves to die; often leading to fruit sunscald. Avoid overhead irrigation and increase air circulation around plants with proper spacing and caging. Mulch the soil around tomatoes to reduce soil splash of fungus onto lower leaves. Plant resistant varieties and avoid planting tomatoes in the same area each year. Severely infected plants are best pulled and destroyed. Use fall sanitation to reduce the amount of overwintering fungus.
Both can be reduced with fungicides labeled for use on tomatoes. For best results, begin applications as soon as symptoms first appear on lower leaves. Repeat applications every 7 to 10 days.
15. Tomato herbicide damage - Leaf yellowing, distortion and cupping, can be caused by herbicide drift. Herbicide drift on tomatoes appears as leaves that are cupped, thickened, distorted or leathery, and which develop an uncharacteristic fan shape. To determine whether herbicide damage is to blame, look at surrounding herbicide-sensitive plants such as potato, pepper, grape and redbud to see if they also show twisting or distortion. Some broadleaf herbicides such as 2,4-D are volatile, especially during hot weather, and may drift across the yard or even from adjacent yards in concentrations sufficient to cause injury. Avoid applying herbicides for weed control during August to avoid injury to non-target plants.
Herbicide Drift Injury, Iowa State University
16. Cucumbers flowering, but no fruit set is being reported by many gardeners. Cucumbers produce separate male and female flowers, and it's common for male flowers to be produce first with female flowers following later. Cool night temperatures and cloudy days anytime during the growing season favor male flower development. However, eventually, the plant produces female flowers and fruit develops.
If female flowers are present, with no fruits set, then lack of pollination could be a problem. Either a lack of insect pollinators, or very hot (90° F and above) temperatures, with dry conditions could be the cause. Hot, dry conditions prevent germination of the pollen tube, or cause it to dry up before pollination can occur.
Some cucumber cultivars, termed gynoecious plants, produce all female flowers. With gynoecious varieties, one or two seeds of varieties with male flowers are included in the seed packet to provide pollen for pollination. The pollinator seeds may be dyed, or placed in a separate packet. In this case, a lack of pollen may be causing the problem.
17. Squash vine borers tunnel into plant stems, mainly squash, pumpkins, and gourds. Their feeding restricts water and nutrient movement. 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 1) practicing good sanitation to eliminate overwinter sites, 2) physically removing borers by slitting stems when borer activity is noticed, or 3) applying insecticides labeled for vegetables during egg laying, usually about the time vines begin to run. Reapply insecticide as labeled, or every 7-10 days for 3-5 weeks.
18. Powdery mildew is the name given to a group of diseases caused by several closely related fungi. Their common symptom is a grayish-white, powdery mat visible on the surface of leaves, stems, and flower petals. There are many hosts; and although this disease is not considered fatal, plant damage can occur when the infestation is severe.
Squash and Pumpkin Varieties Resistant to Powdery Mildew, University of New Hampshire
Treating Powdery Mildew, University of California
19. Potato flowering and fruit set - Gardeners are often astounded when they see, for the first time, true fruits on potato plants. They might think that somehow their potato is reverting to a tomato, or that the fruit formed by cross pollination with a tomato. Neither of these theories is correct. The true fruits are a normal structure that produces potato seeds and appears more often on some potato varieties than others. 'Yukon Gold' is a variety that sets true fruit more heavily than other cultivars.
Normally most potato flowers dry up and fall off after blooming without setting true fruits. But it makes sense that the fruits of potatoes and tomatoes would look very similar since they are in the same family. The part of the potato that we normally eat is an enlarged, underground stem section called a tuber. Potatoes do not come true from seed so saving seed is not recommended and the fruits of potato are not edible so don't harvest them.
20. Raspberry canes wilting & dying may be caused by raspberry cane borer, anthracnose, or root rot. The raspberry cane borer damages raspberry plants from early June to late August. Females puncture two rows of holes in raspberry stem tips and lay their eggs between them. The punctures restrict sap flow resulting in wilting, blackening and finally death of the tip.
Raspberries with root rot have similar symptoms. Roots are rotted and lack fibrous roots. After hot, dry periods, older leaves may wither or become bronzed and scorched. Affected leaves flag. Fruit stems usually are shortened and berries, if formed, remain small and often wither before ripening
Anthracnose causes slightly raised spots with gray centers and purplish margins on raspberry canes. These eventually girdle and kill canes. Infection can occur throughout the season during wet periods. If needed, apply labeled fungicides to susceptible raspberries. Sanitation is important for control. After harvest, remove and destroy all old fruited canes (floricanes) and any new primocanes that are infected. It is best to remove old canes during the dormant season before new growth begins in spring.