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Hort Update for September 19, 2017

Nebraska Extension Hort Update for September 19, 2017
Eriophyid mite damage to coneflower's central cones, could be confused with aster yellows.
LawnsMajor Symptom:
1. Irrigation Fall irrigation is important; continue well into October
2. Fertilization Still time to make September application; use combination of slow/fast release N
3. Aeration/overseeding Ideal window for overseeding is or has closed; weed very soon 
4. Broadleaf weeds Fall is most important time to apply herbicides for perennial broadleaf weeds
5. Preemergence weed control Use now on turf with a history of little barley, henbit, or other winter annuals
6. Perennial weedy grass Apply herbicides before weedy grasses go dormant 
7. White grubs Timely irrigation is more important than insecticide applications 
Trees & ShrubsMajor Symptom:
8. Spruce issues Needle yellowing, needle browning and shedding, branch dieback
9. Leaf scorch Leaves turn brown on edges; needles brown from tips back
10. Hackberry decline Early leaf yellowing and shedding
11. Bagworms Easy to see now; but feeding has stopped and insecticides will not work
12. Aphids and sooty mold Black sooty mold growing on sticky aphid honeydew – not harmful now
13. Transplanting trees Evergreens in September; deciduous trees from leaf drop into November
14. Natural needle drop Uniform and sudden yellowing of interior needles on evergreens
Landscape OrnamentalsMajor Symptom:
15. Hollyhock rust Yellow to orange leaf spots; causes early leaf drop
16. Division & transplanting of perennials Fall is ideal time to divide and transplant
17. Rose winterization - when to cut back Mulch, prune if needed after plants are dormant; best to prune in spring if possible
18. When to cut back - other perennials Providing habitat for beneficial insects
19. Coneflower eriophyid mites Microscopic mites cause deformed central flower cone
Fruits & VegetablesMajor Symptom:
20. Rhubarb red leaf disease Bacterial disease causes crown rot; leaves may be dull yellow or red
21. Are any vegetables poisonous after a frost? Do not harvest rhubarb after a hard freeze
22. Cutting back asparagus Allow stems to stand over winter provides some benefits
23. Planting garlic Fall best time to plant for production of larger bulbs
24. Low tunnels for season extension Easy structures to build provide fall and winter vegetable garden season extension
25. Harvest & storage of fruits & vegetables Harvest at proper time and store at correct temperature/humidity
26. Garden clean up Helps control pests and diseases
MiscellaneousMajor Symptom:
27. Average fall freeze dates October 10 in eastern Neb.; September 20 in western Neb. 
28. Vole control Protect trees and use traps for vole monitoring
29. Solitary wasps - western Nebraska Gone in eastern Nebraska; but still causing concern in western Nebraska 

1. Turf irrigationFall irrigation is important; Continue well into October 

Still important during late summer/early fall; especially with this year’s warm, dry early September.  Cool season turfgrass is increasing density through tillering and/or rhizome production and sufficient moisture promotes this.  Adequate moisture at this time of year also decreases the risk of winter kill.  If white grubs are feeding, irrigation will promote root growth and reduce/prevent turf damage.  Enough irrigation should be applied to prevent visible drought stress without overdoing it.  Excess moisture can delay dormancy. Too wet, or poorly drained soils, leads to less vigorous roots. 


2. FertilizationStill time to make September application; use combination of slow/fast release N

On older lawns (10 to 15 or more years), the first fall application should be made very soon if it has not yet been done. A fertilizer with a slow release nitrogen source can be used. 

On younger lawns, two fertilizer applications during fall are recommended; one in late August/ early September and one in mid-October.  

For the first one, use a slow release nitrogen source. For the last one, use a fast release nitrogen source.  Applications much past November 1 are less efficient because plant uptake is low. This causes nutrients to leach away during winter or linger in soil until spring; resulting in too early succulent growth.  A specific winterizer-type fertilizer is not needed, but have homeowners buy a fertilizer with their particular fertilizer spreader settings listed on the label.

Improving Turf in Fall, Nebraska Extension 
Fertilizing Home Lawns, Nebraska Extension


3. Aeration/overseeding

Ideal window for overseeding is or has closed; seed very soon 

Can still be done, however, it is past the ideal window for doing this without increased risk of winter injury on young grass stands. For increased success, seed ASAP, buy quality seed and maximize seed-to-soil contact by using an aerator or power rake/dethatcher to press the seed into the soil.  A mechanical slit seeder also increases seed to soil contact. Research at UNL showed all three methods were equally effective, though the pattern of seedling emergence varied greatly. 

Seed to Soil Contact Essential, Nebraska Extension


4. Broadleaf weed controlFall is most important time to apply herbicides for perennial broadleaf weeds

Fall-applied herbicides are preferred for broadleaf weed control because:

  1. winter annual weeds are smaller and more easy to control than when they mature in spring,
  2. perennial broadleaf weeds are translocating stored energy (and properly applied herbicide) below ground, and
  3. cooler temperatures reduce the likelihood of injuring turf or ornamental plants.
For best control that will be noticeable this fall, herbicides should be applied by mid to late October. Herbicides applied later in fall can still be effective provided soil moisture isn’t limiting at the time of application, but control will likely not be perceivable until next spring. Herbicides are most effective when applied to actively growing weeds not stressed by extreme temperatures, drought, etc. It is also generally recommended that turf is not mowed within 3 days before or after herbicide treatment.

Effects of Mowing on Broadleaf Herbicide Efficiency, Nebraska Extension


5. Preemergence weed controlUse now on turf with a history of little barley, henbit, or other winter annuals

Preemergence herbicides applied in fall are only for control of winter annuals like little barley, henbit and speedwell.  Winter annuals are or will soon be germinating.  Other management options for winter annual control include maintaining a healthy and vigorously growing lawn that competes. 

Not Yellow Foxtail. Little Barley, Nebraska Extension


6. Perennial weedy grass controlApply herbicides before weedy grasses go dormant

Still can be done prior to these grasses going dormant. Information for control of weeds like windmill grass, nimblewill, tall fescue and others can be found in the publication below.   

Perennial Grassy Weed Control, Nebraska Extension   


7. White grubsTimely irrigation is more important than insecticide applications

Damage may show up in lawns due to our early September warm, dry spell. Since white grubs are nearing the end of their feeding cycle for this year and larger grubs are more difficult to kill with insecticides, the best approach now is to use timely irrigation to encourage new root growth and recovery.  If homeowners complain of something digging in their yard, i.e. turning over sod, tearing up grass, this could be skunks or raccoons foraging for white grubs. The sod should be reset and watered to promote root growth and recovery. 


8. Spruce issuesneedle yellowing, needle browning and shedding, branch dieback

Problems on spruce tree have been seen this fall, with the syptoms of discolored  needles, needle drop and branch dieback. Some are water stress related. Others are pests like needle cast or Siroccocus shoot blight or spider mite damage. Positively identify the cause of a tree issue before attempting control. Water stress often appears as yellowing of needles, at least initially. With Rhizophaera needle cast, older needles turn reddish-brown and shed. With Sirococcus shoot blight, needles on the very tips of branches turn brown and drop off. Shoots may droop. Be aware spruce tips may also droop if the herbicide Dicamba is applied near the tree and absorbed by tree roots. Spider mite injury appears as a general bronzing or browning of needles, often localized on the tree. Based on issue identification, adjust watering and/or follow label directions for herbicides. If one of the diseases is identified, fungicide applications are made during spring when new needles are one-half to two inches long and again 3 to 4 weeks later. If mites are confirmed and still present on trees, apply a miticide according to label direction.

Diseases of Evergreens, Nebraska Forest Service


9. Leaf scorchLeaves turn brown on edges; needles brown from tips back

Being observed in western Nebraska as dry conditions continue. Scorch appears as browning of leaf margins on deciduous trees. In more severe cases, the browning may extend down between leaf veins. On evergreens, it appear as a uniform browning of needle tips. Fall irrigation is critical for drought stressed trees. Keep the soil moist, but not overly wet, as long as conditions remain warm and dry, and soils are not frozen. Mulch with wood or bark chips using a three to four inch layer in a 4 to 6 foot diameter ring around the tree. Do not pile mulch against the trunk. Do not use weed mat beneath the mulch. Allow it to decompose and improve soils over time.

Abiotic Problems of Trees, Nebraska Forest Service


10. Hackberry declineEarly leaf yellowing and shedding

Hackberry leaf yellowing is being observed in western Nebraska. This could be signs of hackberry decline brought on by drought stress; which include yellowing leaves, leaf drop, and branch dieback. Decline is suspected to be the result of a combination of stresses such as weather extremes, repeated herbicide injury, drought, poorly drained soils and more. Provide good growing conditions for trees with correct mulching and irrigation. Use herbicides safely.


11. BagwormsEasy to see now; but feeding has stopped and insecticides will not work

Bagworms are easy to see now but insecticide controls will no longer be effective. Bagworms have stopped feeding, attached their bags to twigs, and are pupating. Once feeding stops, insecticides are no longer effective. Advise homeowners to pick off and discard bagworms on small trees to reduce overwintering. If needed next season, insecticides are most effective when applied after eggs hatch and before bagworms do much feeding; typically from mid-June into early July.

Bagworms, Nebraska Extension


12. Aphid honeydew and soot moldBlack sooty mold growing on sticky aphid honeydew – not harmful now

Aphid populations were high this season. As aphids feed on sap, they exude a sticky honeydew that remains on leaves or drips onto nearby plants. A black sooty mold often grows on the honeydew causing leaves to appear black. The mold is not infecting the leaf, just growing on the surface. This late in the season, it is not an issue as the leaves have done their job of photosynthesis for the season and will soon be senescing and dropping. Homeowners may be concerned but no controls are needed of either aphids or sooty mold.


13. Transplanting treesEvergreens in September. Deciduous trees from leaf drop into November

When fall transplanting is done, evergreen trees are best transplanted in September. Deciduous trees and shrubs are typically transplanted from leaf drop into November. The sooner the better to allow for root growth prior to soil freezing. Smaller trees transplant better than larger trees. When digging the tree, a wide root ball is more important than a deep root ball. Dig only 8 to 12 inches deep, but about 2 feet or more wide, if feasible.  Do not transplant the tree any deeper than it was in its original location. Planting too deep is a common problem and a major source of stress for trees, leading to slower growth and increased susceptibility to pests. Avoid nitrogen fertilizer at transplanting time but keep the soil of the root ball and surrounding soil moist up until the soil begins to freeze. 


14. Natural needle dropUniform and sudden yellowing of interior needles on evergreens

Natural needle drop will soon begin.  Evergreens do not keep all of their needles forever. They retain one to seven year old needles. Natural needle drop typically begins in September with interior needles suddenly and uniformly turning yellow from the top of the tree to the bottom. These yellow needles are easily knocked off of the tree by hand, wind or rainfall. Natural needled drop is just that; natural and not of any concern. As a rule, pines hold their needles for two to three or more years and spruce trees hold needles five to seven years. Natural needle drop is most noticeable on white pines.


15. Hollyhock rustYellow to orange leaf spots; causes early leaf drop

Hollyhock rust symptoms are seen as yellow to orange spots on the upper leaf surface followed by red to brown pustules on the lower leaf surface. This disease is spread by wind and splashing water, which includes rain and a sprinkler. The best way to control rust is through sanitation, meaning removal of infected plants and leaves in fall to minimize overwintering of the disease. 


16. Division & transplanting of perennialsFall is ideal time to divide and transplant

Dividing perennials is an important management practice for many species, helping to encourage vigorous growth and optimum blooming. Many perennials benefit from division once every 3-5 years. Dividing is also a good way to propagate perennials.

Dividing Perennials, Backyard Farmer on YouTube


17. Rose winterization - when to cut backMulch, prune if needed after plants are dormant; best to prune in spring if possible

Pruning is not needed during fall for shrub and hybrid tea roses unless some pruning is needed for a rose to fit beneath a winter protection method, such as a rose cone. Wait until April and then prune to remove winter killed wood.

Hybrid tea roses benefit from extra winter protection, but shrub roses usually do not require it. Do not add winter protection to roses until the soil begins to freeze or night temperatures are consistently dropping into the 20s at night. One good mulching method is the encircle the rose with a chicken wire cage, staked to hold it in place, then fill the cage with coarse leaves. Soil can also be mounded up around the base of a hybrid tea rose to provide extra cold protection for the graft union.


18. Cutting back perennialsProviding habitat for beneficial insects

Insects, depending on their species, overwinter is a specific life stage – adult, egg, larva, nymph, pupa, etc. Many insects enter diapause, a stage of extended dormancy, to enable them to survive winter conditions. They seek out sheltered locations that provide some winter protection, such as hollow plant stems, leaf litter around the base of shrubs, tree bark flaps, or grass and perennial plant crowns. Or they may nest in the ground, in tree or shrub cavities or in wood. Plants with pithy or hollow stems like ornamental grasses, elderberry, raspberry, blackberry and sumac serve as good overwintering sites for solitary bees.

When working with clients on cutting back ornamental grasses and perennials in fall, landscape managers should recommend leaving 12-18” of stems in the garden to allow for increased beneficial insect overwintering habitat. Pollinators and butterflies will benefit from these additional amounts of winter cover.

Where Do Insects Go In Winter?, Smithsonian


19. Coneflower eriophyid mitesMicroscopic mites cause deformed central flower cone

These microscopic mites are carrot shaped, white or yellow, with two pairs of legs. The coneflower mites feeds deep inside flowers causing the central cone to become enlarged and deformed. But there are no symptoms in the flower petals or plant leaves, which helps distinguish this insect damage from aster yellows - another common disease of coneflowers. Deadhead flowers showing symptoms to reduce mite numbers in the garden.   

Eriophyid Mites, Missouri Botanical Garden


20. Rhubarb red leaf diseaseBacterial disease causes crown rot; leaves may be dull yellow or red

Also known as bacterial soft sot, this disease is suspected to be vectored by plant feeding insects or through infected root stock. Infected plants develop a browish, cavity-forming rot of the plant crown. During wet weather, the rot may extend up into the base of the stalks of mature leaves, causing them to become dull yellow or reddish and eventually collapse. Rogue out and destroy infected plants. Avoid replanting in the same area. 

Rhubarb Red Leaf, Pacific Northwest Pest Management Handbook


21. Are any vegetable poisonous after a frost?Do not harvest rhubarb after a hard freeze

This is a common question from home gardeners in fall. The only vegetable of concern is rhubarb, which should not be harvested or eaten when leaves are wilted and limp after a hard frost. Oxalic acid in the plant's leaves may move from the leaves into the leafstalk, making them toxic.  All rhubarb leaf stalks that have been exposed to freezing temperatures should be removed and discarded. 

The texture and storage potential of other vegetables are affected by freezing temperatures, such as lettuce, peppers, summer squash and sweet potatoes.  Some vegetables actually improve in flavor following freezing temperatures, including parsnip, Jerusalem artichoke and horseradish.


22. Cutting back asparagusAllow stems to stand over winter provides some benefits

Cutting back asparagus in fall is a common practice for many gardeners. But allowing asparagus stems to stand does provides some benefits to plants.

  • Standing asparagus fronds trap snow during winter, providing moisture for the crown as the snow melts.
  • Nutrients in the stems are transported into the plants' crown if stems are allowed to stand until later winter, February or March. By then the stems will be brown and all nutrients will have moved into the plant crown.
  • Allowing asparagus fronds to stand in late winter delays new stem emergence, which can be a useful technique where late freezes are common.

However, if you have an older female cultivar of asparagus, such as Mary or Martha Washington, asparagus seedlings can become a problem in the garden. In this case, cutting back stems in the fall and removing as much seed as possible from the garden minimizes asparagus weed problems next year.


23. Planting garlicFall best time to plant for production of larger bulbs

Mid-September through mid-October is a good time to plant garlic for harvest next summer. Plant at least one month before the soil freezes. The bulbs will root and begin to sprout, then go dormant to continue growth next season. Garlic is started by planting small cloves, or divisions of the large bulb. The larger the clove, the larger the mature bulb will be at harvest. Do not divide the bulb into cloves until just before planting.

Garlic grows best in loose, loamy, fertile soil high in organic matter. Apply three pounds of 10-10-10 fertilizer per 100 square feet at planting time or use organic fertilizers such as blood meal. Plant the cloves 3 to 5 inches apart with points up and 1 to 2 inches deep. Allow 18 to 30 inches between rows or plant 5 inches apart in a wide bed row. Mulch fall planted garlic with 8 to 12 inches straw after the soil freezes.


24. Low tunnels for season extensionEasy structures to build provide fall and winter vegetable garden season extension

Low tunnels are simple structures made from plastic stretched over hoops. They are usually 2 to 3 feet high, as opposed to high tunnels, which can be 12-15 feet tall in the center. Low tunnels are temporary garden structures and are particularly easy to work with for home gardeners who have raised beds. In the vegetable garden, they can provide enough temperature buffering to allow production of cool season crops, like salad greens, radishes and carrots, even when unprotected outdoor gardening is not possible in late fall and winter. 

Extending the Gardening Season with High Tunnels, Penn State Extension 
10 Reasons Why Low Tunnels Beat Cold Frames for Winter Gardening, Mother of a Hubbard


25. Harvest & storage of fruits & vegetablesHarvest at proper time and store at correct temperature/humidity

Storing fruits & vegetables is most successful if produce is harvested at the correct stage of maturity, cured or otherwise prepared properly for storage, and then stored at the temperature and relative humidity needed by each vegetable and fruit. For specifics on curing and best storage conditions for each fruit and vegetable, see:

Canning, Freezing and Drying, Nebraska Extension


26. Garden clean upHelps control pests and diseases

Garden sanitation during fall involves cleaning up or tilling under plant debris in the vegetable garden and around fruit trees to reduce overwintering pests. The sooner this can be done after a plant dies or after fruit drops to the ground, the better. Plant pathogens are less likely to survive if organic matter is quickly decomposed. Remove plant debris or infected plant parts after each growing season.

  • Turn the soil after harvest to help break down small roots that may harbor nematodes, fungi or bacteria.
  • Gardeners may compost dead plants if they have a good composting system; otherwise, these piles may serve as a source of pathogens.
  • Prune or remove twigs and branches of woody plants affected with fire blight and other bacterial or fungal canker diseases.
  • Keep gardens weed free. Weeds often are another source of pathogens. Eradicate weeds to break the life cycle of pathogens and control them. Weed removal also can increase air movement and thus decrease conditions that favor disease development.
  • So that pathogens do not spread from one area to another, always disinfest machinery and other tools with steam, hot water under pressure, or a 10 percent solution of household bleach diluted with water.

Orchard sanitation is essential for good maintenance of fruit trees and small fruit plantings. Insects and diseases can overwinter on dead or infected plant material. Dried fruits or "mummies" carry disease organisms through the winter to attack next years' crop. Remove and destroy any fruits that have fallen to the ground, or those appearing to rot on the branches.

Non-chemical Control of Disease, Colorado State University


27. Average fall freeze datesOctober 10 in eastern Neb.; September 20 in western Neb.

A map of Nebraska showing fall freeze dates.

Average fall freeze (32° F) dates are a measure of when the average first frost will occur in a region. They indicate that half of all autumn freezes will occur before the dates shown and half will occur after, based on 47 years of data from 1949-1995. In southeastern Nebraska that average autumn freeze date is approximately October 9 and September 21 in the northwest corner of Nebraska's panhandle. These dates are guidelines only. Freezing temperatures may occur before the dates listed below. Also remember that local microclimate conditions can significantly affect the occurrence of frost in your landscape.

These dates can be used as guidelines for gardeners growing late season vegetable crops. Frost sensitive plants will not tolerate freezing temperatures and must be taken inside before a freeze occurs or allowed to succumb to the end of the season.


28. Vole controlProtect trees and use traps for vole monitoring

If we receive enough snow cover this winter, voles may turn to trees and shrubs for a food source, gnawing on tree bark and roots, and potentially killing plants. To help prevent this, keep tall grass and weeds removed from around the trunk of trees and avoid mulch layers deeper than three inches. Placing hardware cloth around tree trunks will prevent vole feeding. Check for and trap voles by placing baited mouse traps inside PVC or other pipe near trees. Insert the traps far enough into the pipe so that pets, birds and other animals are unable to reach the trap. Check the stations once a week and reset traps as necessary.

Vole Damage, Nebraska Extension