Green Industry Resources
Hort Update- Seasonal Information for the Green Industry
Hort Update for the Week of August 9, 2013
|1. Yellowing of Kentucky bluegrass||Yellowing of new foliage|
|2. Overseed cool season grasses||Begin overseeding cool season grasses soon|
|3. Yellow nutsedge||Notes on late season control|
|Trees & Shrubs|
|Late season herbicides have minimal effectiveness|
|5. Leaf scorch on maple||Browning of leaf edges|
|6. Pear leaf spots||Leaf and/or fruit spots on pears; sanitation important|
|7. Fall webworm||Large, webbed nest filled with caterpillars and/or frass|
|8. Oak twig girdler||Small clusters of brown leaves at twig tips|
|9. Japanese beetle||Identification tips and pictures|
|10. Genista broom caterpillar||Yellowish green caterpillar commonly seen feeding on Baptisia|
|Fruits & Vegetables|
|11. Blossom end rot||Flat, brown, dry, sunken patch at base of tomatoes|
|12. Harvesting vegetables||Know proper harvest time to ensure ideal storage and quality|
|13. Bitter cucumbers||Common during heat and enviromental stress|
|14. Fall vegetable gardening||Now is the time! NebGuide available for recommended timing and vegetable selection.|
|15. Peach split pit||Seen on fruit starting on the stem end|
|16. Orchard sanitation||Rotting fruit provides overwintering sites for insects & diseases|
|17. Fruit tree defoliation||Sanitation is important for control|
|18. Tree replacement||Tree species recommendations for replacing Scotch Pine and Ash trees|
|19. Spider webs on grass||Sign of a beneficial insect, not a pest|
1. Yellowing of Kentucky bluegrass - Similar to previous summers with adequate rainfall, Kentucky bluegrass has turned an off-color yellow in the last few weeks. UNL turfgrass specialists are unsure of the exact cause, but do know:
- Only the young leaves are yellow, so it is probably not related to nitrogen or other nutrients mobile in the plant. However, iron deficiency could explain the symptoms because Fe is relatively immobile in the plant.
- There are no obvious lesions present so it is not mediated by above-ground diseases.
- We do not see it in tall fescue, perennial ryegrass, and some cultivars of Kentucky bluegrass.
- We see it when soil temperatures are at their seasonal highs.
We see it almost exclusively on irrigated turf and most frequently during wet summers. We know from past experience that this
a visual effect and long-term health of the plant is not an issue. Therefore, immediate action is probably not needed other than to improve aesthetics. Reducing irrigation in the short should help. Increasing drainage and reducing compaction with more frequent aerification should also help in the long-term.
We would not recommend a fungicide, insecticide, or > 0.5 lbs N/1000 sq ft (avoid almost any N in August except on greens or sports turf in use). We often see symptoms similar to this in the spring, but those are usually attributed to denitrification and Fe applications do not help then. However, a low rate of iron may be effective now. Since most the chlorotic leaves are the youngest and higher in the canopy, mowing should remove much of the yellowing.
Yellowing of Kentucky Bluegrass, UNL Turf iNfo
2. Overseed cool season turfgrasses - If cooler temps continue, seeding of turfgrasses could take place a little earlier than usual this year, and the earlier cool season grasses can be seeded, the better. The rule of thumb is that for each week grasses are seeded before Labor Day, maturation is speeded by two weeks. August 15 to September 15 is the optimum window to seed cool-season turfgrasses. Winterkill and/or poor establishment by winter/next summer could result when seeding outside of this window.
Overseed Kentucky bluegrass at a rate of at .75 to 1.0 lb. seed per 1,000 sq. ft. with improved cultivars, but this is effective only on thin turfs since Kentucky bluegrass is not very comptetitive. Use a blend of improved turf-type tall fescue cultivars with resistance to brown patch, and seed at 4 to 6 lbs/1,000 sq. ft.
When overseeding, it is critical to seed to soil contact. If seed is just scattered over living grass and debris, little will germinate and grow. One way to achieve good results is to use a slit-seeder that will plant seed through existing grass right into soil or to core aerate the lawn prior to overseeding. Vertical mowers, or dethatchers, can be used, but these can be destructive to existing grass and after using these machines, plant debris must be raked away before overseeding. Mowing the lawn at 1-1.5 inches prior to seeding and for the next 6 to 8 weeks after seeding will favor the seedlings.
3. Yellow nutsedge - late summer applications will kill the foliage, but will have little affect on tubers. Repeated applications are still necessary for control. For a listing of herbicides and their effectiveness on nutsedge, see the publication linked below. Yellow nutsedge is a grass-like weed with yellowish-green, waxy, triangular shaped, blade-like leaves, and produces underground tubers.
4. Annual broadleaf and grassy weeds are prolific this year, especially in lawns thinned by last summer’s drought. Common summer annual broadleaf weeds include knotweed, spurge, purslane; grassy annual weeds include crabgrass and foxtail. Annual weeds growing now will die this fall. Continue mowing to reduce seedhead development, and postpone control until next spring when pre-emergence herbicides can be applied. Weeds do not have to be killed before thin lawns can be overseeded. Traditional broadleaf herbicide applications made in Sep and Oct will control perennials and winterannuals, but not the summer annuals.
- Poor regional adaptation in some maple species, specifically Norway, Japanese and Red maple, is a contributing factor. Planting them in hot, windy, dry locations makes them susceptible to scorch.
- Leaf scorch may be seen on young trees with unestablished root systems; particularly those grown in very dry areas.
- Anything that reduces root or trunk function can contribute to scorch as uptake or movement of water within the tree is restricted. Root or trunk function can be affected by planting depth, stem girdling roots, and bark damage from physical injury, sun scald, or cankers.
- Reflected heat from hard surfaces, such as streets, driveways, or buildings, contributes to leaf scorch.
- Excess mulch can cause death of bark sections on the trunk or death of roots, and could also lessen a tree’s ability to move sufficient amounts of water.
Proper planting of new trees, considering both planting depth and elimination of stem girdling roots, is critical to their overall health and vigor. To manage leaf scorch, 1) follow good watering practices, 2) apply a 2-3 inch layer of wood chip mulch applied over roots but not piled against tree’s trunk to conserve soil moisture, and 3) avoiding excess nitrogen fertilization. These practices can help reduce leaf scorch on otherwise healthy trees.
- Ccedar-hawthorn rust, Gymnosporangium globosum
- Pear scab, Venturia pirina
- Fabraea leaf and fruit spot, F. maculata, (synonym Entomosprium leaf spot)
- and Black rot, Botryosphaeria obtuse.
Leaf spots noticed late in the season cannot be controlled by fungicide applications. Heavily infected leaves may fall from the tree early, but does not cause serious damage to the tree.
Diseases overwinter on infected leaves and fruits, so sanitation beneath and around trees is very important, and the best means for reducing disease problems next year. Collect and discard all debris from the tree, including leaves and fruit each year. Also prune out and destroy dead or diseased branches and twigs each spring.
7. Fall webworm appears as large, unsightly webbed nests in fruit, ornamental and shade trees from late summer through fall. The webs are filled with caterpillars, dead leaves, frass and worm excrement. While unsightly, they are fairly harmless to established trees at this time of year. Mechanical removal of the nests on small or newly planted trees is the best control method. Insecticides applied when the webbed nests are small will reduce fall webworm numbers.
Controlling Fall Webworm, University of Nebraska-Lincoln
8. Oak twig girdler is now causing twig dieback in oaks. Agrilus angelicus, has a two-year life cycle. In our area, it prefers red oak, but also attacks live oaks and several introduced oaks. The small, slender, bronze-to-black beetles emerge from May to September and deposit eggs on twigs at the junction between the current and previous year's growth. Larvae that hatch bore into twigs, and as they grow, they mine spirally so that terminal clusters of dead leaves ("flags") appear during August and September. During the next year, larvae continue to mine deeper into twigs and complete development, pupating in the autumn.
While damage is obvious, it is rarely severe, and there is rarely a need for control. Pick up and discard dead twig sections that fall to the ground to eliminate the larvae inside. Squirrels clipping tree twigs may be confused with girdler damage.
Flat Headed Borers, University of Nebraska-Lincoln
9. Japanese beetles are copper brown and metallic green beetles, with a white grub larval stage. Proper identification is important, however, and there are several metallic green beetles that can be confused with Japanese beetles. The UNL Entomology department has developed a publication with pictures of Japanese and Emerald Ash Borer beetles, along with several other insects with which they could be confused.
Emerald Ash Borer & Japanese Beetle Look- Alikes, UNL Entomology
10. Genista broom caterpillar is a relatively new insect in Nebraska, causing damage to Baptisia, a popular perennial plant commonly know as False blue indigo, along with other plants in the pea family, including shrubs like honeysuckle (Lonicera spp.). The adult insect is a moth, with medium brown wings and a very pronounced snout. Their caterpillars are the culprits causing plant damage, and are yellowish green with white and black markings.
They often begin feeding on Baptisia's newest foliage, just as the flowers are fading. By August, they have finished or are nearing the end of their feeding. Terminal clumps of skeletonized or missing leaves are seen now, intermingled with webbing and shed skins. The caterpillar's feeding has little impact on your plant's health, but you can maintain their appearance by pruning out the damaged sections.
Genista Broom Moth/Caterpillar, University of Minnesota
11. Blossom end rot is a common problem of tomatoes, but also occurs on peppers, eggplant, squash and watermelon. It appears as a flat, dry, sunken, brown rot on the blossom end of the fruit, opposite the stem end. The size of the rotted area varies, but can cover up to 50% of the fruit. In rare cases, small sections of black tissue may develop on the inside of a tomato that are not visible from the outside.
This problem is a physiological disorder associated with a calcium deficiency in the developing fruit. Rarely is the problem a lack of calcium in the soil. Drought stress, low daytime humidity, high temperatures and rapid, vegetative plant growth caused by excess nitrogen applications favor blossom end rot development. To reduce it, prevent drought stress, mulch with organic mulch and avoid excess nitrogen fertilization.
12. Harvesting fresh fruits and vegetables brings great satisfaction to home gardeners. To obtain a quality food product from your garden for fresh use or storage, you must harvest fruits and vegetables at their proper stage of development. Improper harvesting influences quality and storage ability as well as continued productivity of the plant.
13. Bitter tasting cucumbers are most common during periods of heat, or other environmental stress. All cucurbits produce a group of chemicals called cucurbitacins, which cause the vegetables to taste bitter, and the higher the concentration of cucurbitacin the more bitter the vegetable will taste. Mild bitterness is fairly common in cucumbers resulting from higher levels of cucurbitacin triggered by environmental stress, like high temperatures, wide temperature swings or too little water. Uneven watering practices (too wet followed by too dry), low soil fertility and low soil pH are also possible stress factors. Over mature or improperly stored cucurbits may also develop a mild bitterness, which is often not severe enough to prevent gardeners from eating them. For more information,
Bitter Cucumbers, University of Nebraska - Lincoln Extension
14. Fall vegetable gardening time is here. Cool season vegetables can be planted to mature during the cooler weather of fall. For tips on fall gardening and information on what and when to plant, check out these resources from UNL Extension.
Fall Vegetable Gardening, University of Nebraska - Lincoln Extension
Fall Gardening, Backyard Farmer on YouTube
Fall Garden Tips, Backyard Farmer on YouTube
Fall Clean Up, Backyard Farmer on YouTube
Fall Garden Calculation, Backyard Farmer on YouTube
15. Peach split pit is a physiological problem. It is often accompanied by openings of the peach flesh, followed by entry of insects or secondary rot into the peach, which makes them unusable. Affected fruits can sometimes be spotted due to flattenng at the blossom end, and a larger than normal diameter of fruits across the suture.
Conditions that favor development of split pit include, cold or freeze damage during flowering and early fruit development, and cultural practices that encourage very rapid growth. Irregular watering, and excessive fruit thinning during the pit hardening stage, 50-60 after bloom, are also factors. This disorder is most common in early cultivars ripening before Redhaven, and for tree with light crops and very large fruit.
Peach and Nectarine Varieties for Virginia, Virginia Cooperative Extension
16. 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.
17. Fruit tree defoliation can be caused by several fungal diseases, such as cedar-apple rust, apple scab, cherry leaf spot, and several more. Apple and crabapple trees severely defoliated by cedar-apple rust are a common site in late summer. Infection by fungal diseases occurs early in the season, just after blooming or during early growth. That is when control measures should be done. Fungicide applications now are not effective, and unless a tree is heavily infected several years in a row control is not needed. Rake up and discard infected leaves as they fall to minimize disease pressure next spring.
18. Tree replacement recommendations - When replacing or planting new trees, choose species that are well-adapted to Nebraska's extreme climate conditions. Increasing tree species diversity is essential for limiting pest impact.
Homeowners should be aware of the potentially serious problems caused by Emerald Ash Borer, before planting ash. The insect has not been found in Nebraska yet, but will be here eventually. We caution people against planting ash at this time. Also, Scotch pine trees are currently dying in large numbers from Pine wilt, so planting of Scotch pine is not recommended.
20. Spider webs on plants and in turf are a sign of beneficial arthropod activity, not a damaging pest. Chemical control of spiders associated with lawns and shrubbery is not needed. If webs appear unsightly, remove them with a broom.
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