Green Industry Resources
Hort Update- Seasonal Information for the Green Industry
Hort Update for the Week of April 19, 2012
|1. Crabgrass control||Apply preemergence herbicides now|
|2. Dandelions||Spring flowering season 2nd best time to control|
|3. Violets||Triclopyr for homeowners. Triclopyr or fluroxypyr for commercial.|
|4. Yellow nutsedge||Early emergence. Treat earlier and with multiple applications.|
|5. Use of clippings for mulch||Many newer herbicide labels state to never use clippings for mulch if herbicide have been applied this year|
|6. Seeding||Tall fescue better for late spring seedings|
|7. Summer patch control||Apply fungicides when soil temperatures reach 65 F.|
|Trees & Shrubs|
|8. Frost damage||Most damage cosmetic in nature only|
|9. Careful herbicide applications||Windy, warm conditions lead to damage to nontargets|
|10. What not to prune||Avoid pruning during leafing. Do not prune oaks now.|
|11. Winter desiccation||Browning of evergreens|
|12. Cedar-apple rust & apple scab control||Plant resistant cultivars. Fungicides have limited control.|
|13. Spruce spider mites||Monitor evergreens for mites|
|14. Euonymus scale||Apply controls when yellow crawlers are present|
|15. Vole damage||Gnawing on base of trees and root surfaces|
|16. Rose clean up and pruning||Remove winter killed portions of canes when pruning|
|17. Fertilizing perennials||Now is time to fertilize some perennials|
|18. Weed control in perennials beds||Use a combination of controls|
|19. Mulching perennials||Apply a 2 to 4” deep layer. Keep away from plant stems.|
|20. Staking perennials||Put staking materials in place before much growth occurs|
|21. Iris borers||Overwinter in egg stage on old foliage. Sanitation important.|
|Fruits & Vegetables|
|22. Rhubarb soft stalks & safety after frost||Warm, dry conditions or frost may cause|
|23. Asparagus weed control||Avoid salt. Use a combination of methods.|
|24. Cool season crops & warm temperatures||May lead to bolting and bitter tasting or tough produce|
|25. Ticks||Numbers are high. Refer to Tick Control NebGuide|
|26. Eliminating weedy trees & shrubs||Apply a stump treatment to prevent regrowth; follow herbicide recommendations|
1. Crabgrass control- Soil temperatures have moderated but remain warm enough for crabgrass seed to begin germination. For the most reliable control, a preemergence herbicide should already have been applied; with a second application to be made in early to mid-June. Recent research indicates the same active ingredient is not required for both applications and any of the preemergence herbicides can be used for the first and/or second application as long as one-half of the high label rate of each product is used.
For those who chose to wait, an application should be made as soon as possible; or when very young crabgrass is first seen and products containing dithiopyr should be used for PRE and POST control. Even if the application is made in early May, one application is usually not sufficient in difficult summers, thinned turf, hotspots, etc.
2. Dandelions- The optimum time to control dandelions and other perennial broadleaf weeds (white clover, ground ivy, violets, and/or plantain) is in the fall. The second most effective time is in late spring, at or shortly after flowering. Herbicides applied at spring flowering do not translocate as effectively and usually do not provide as effective control as when fall applied. Herbicides containing the traditional active ingredients (ai’s) 2,4-D, MCPP and dicamba are effective for control of dandelions and other broadleaf weeds. Relatively “newer” ai’s like carfentrazone, triclopyr, fluroxpyr, quinclorac, and sulfentrazone combined with the traditional ai’s can increase the speed of burn down, expand the spectrum of weeds controlled, and/or improve overall effectiveness depending on the product used. Whenever possible, spot-apply herbicides rather than treating the entire lawn. This is expensive and can be less effective. Be careful when applying herbicides near ornamentals or trees as these are easily damaged by direct overspray or indirectly by volatilization of herbicide.
Dandelion Turf iNfo, University of Nebraska-Lincoln
3. Violets are a cool-season, broadleaf weed. Like dandelions, fall is the optimum time to control violets with spring being the second most effective time. For violets, a good herbicide for homeowner use is triclopyr. For commercial applicators, triclopyr or fluroxypyr are recommended.
4. Yellow Nutsedge has been germinating for over two weeks in hotspots in Lincoln, at least six weeks or more ahead of normal. Recent cold temperatures may slow germination for a short time. Herbicide applications are traditionally recommended to be timed just prior to summer solstice (June 21). This is because tubers start forming about that time of year and applications at that time limit tuber formation, potentially reducing future populations. Since a tuber can germinate multiple times in a growing season, herbicidal control of young plants earlier than the summer solstice could trigger re-germination of the tuber.
This year, however, early germinating plants will be extremely robust and difficult to kill by the time June applications are made. Therefore we recommended applications for nutsedge control starting in April and now May, realizing the tubers may re-germinate. Then, a second application near the summer solstice should be more effective on smaller nutsedge plants.
5. Use of grass clippings as mulch- 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.
6. Seeding cool-season turfgrasses- Fall is the best time to seed cool-season turfgrasses. When it needs to be done in spring, the window for seeding Kentucky Bluegrass is April 1 to April 30 and for Tall Fescue, April 15 to May 15. For later May seedings, recommend to homeowners to consider turf-type tall fescue instead of Kentucky bluegrass because it germinates and matures faster than bluegrass.
Spring Seeding Tips for Cool Season Grasses, University of Nebraska-Lincoln
7. Summer patch disease control- On lawns with a history of summer patch, begin preventative fungicide applications once soil temperatures at a 2 inch depth reach 65 degrees F in mid-afternoon for 5 consecutive days; typically sometime in May. Make a second application 30 days later.
Summer Patch Disease Control, University of Nebraska-Lincoln
8. Frost damage on trees/shrubs- The tender growth of some trees and shrubs has been damaged by cold temperatures. In most cases to date, the damage is cosmetic and not harmful to plant vigor. If leaf buds are killed or severely damaged by cold temperatures, a healthy plant will develop secondary buds and continue to leaf.
- If leaf buds are slightly damaged by frost, as leaves unfurl damage may be seen as browning, leaf tatter from wind blowing out freeze damaged areas, etc. Remind people this is likely freeze damage and not insects or disease and so pesticide applications are not needed.
- If a tree or shrub were to die, it was probably not fully hardy to our area or had other issues that had lowered the plants food reserves and the freeze was “the straw that broke the camel’s back”.
- If leaf buds or leaves are killed, leafing may be delayed and stored food reserves used by the plant to develop secondary buds.
- If a terminal bud is damaged, some “odd growth” might be seen down the road.
Avoid unnecessary pruning so the plant does not have to deal with pruning cuts as well as secondary bud development.
Avoid fertilization so additional growth is not forced and additional food reserves used.
Follow best management practices and control pests as needed during the summer to avoid additional stresses. If flower buds are killed or damaged, the tree will not develop new flower buds for this season, but will develop flower buds for next year.
9. Safe Herbicide Use- With warmer than average and windy conditions, the risk of herbicide injury to non-target plants increases. Read the label before applying herbicides to reduce the risk of injury to non-targets and the potential for lawsuits. There are a number of herbicides that cannot be applied at certain temperatures, near water, over the roots of trees and so on.
Keep in mind tree roots can extend away from a tree up to two to three times the trees height, i.e. a 30’ tree could potentially have roots growing 60’ away from the tree and possibly beneath a gravel lot that may be sprayed with herbicide that will injure the tree. Read pesticide labels before, not after, applying herbicides. Especially avoid application on hot, windy days
10. When and what not to prune- Pruning deciduous trees is best avoided during spring growth. Pruning can resume in June. Stop pruning from mid-August up until leaf drop. Spring flowering shrubs are best pruned just after they stop blooming. Trees that are infected with or susceptible to fireblight should not be pruned now. Oaks, especially white oaks which are more susceptible to oak wilt, should not be pruned now.
11. Winter desiccation on evergreens showing up in southwestern part of state. It appears as fairly uniform browning, often on the south or west facing side of a tree and on outer plant parts. Evergreens lose moisture on warm, sunny winter days. If the soil does not contain enough moisture to replace the loss, needles dry out and turn brown from the tip down. When soil is moist, roots may not be able to absorb it due to cold or frozen soil or damaged roots. To reduce winter desiccation, provide adequate moisture to plants throughout the growing season and well into fall.
For now, wait o prune winter damaged areas until after new growth begins to better evaluate the extent of damage and to avoid pruning healthy buds the plant needs to repair damage. Keep in mind if an evergreen is pruned beyond where there is green needle tissue, it will not produce new growth to fill in the area.
12. Cedar apple-rust & Apple scab- Trees leafed out earlier than usual this year and the ideal timing of fungicide sprays for these two diseases may have been missed. However, windy and dry conditions are also not conducive to high infection rates. Still, the best control of these two diseases is to select and plant resistant cultivars. See the NebGuides for a listing of cultivars. If needed, continue to apply fungicide to susceptible cultivars, especially if rainfall increases.
Cedar Apple Rust and Related Rusts of Apples and Ornamentals, University of Nebraska-Lincoln
Apple Scab, University of Nebraska-Lincoln
13. Spruce spider mites have been confirmed in Lancaster County. Spruce mites are typically active in April into May and September into October. They spend the summer in the egg stage. Monitor evergreens for mites. If mites are detected, a hard spray with water will help keep populations down. Insecticides to apply include a horticultural (growing season) oil (these will temporarily remove blue needle color on blue Spruce), insecticidal soap, or a registered insecticide. Repeat treatment 7 to 10 days after the first application.
Spruce Spider Mites, University of Minnesota
14. Euoymous scale can be found on Euonymous, boxwood, honeysuckle, Pachysandra, holly, lilac, bittersweet and English ivy. If white overwintering scales are found on plants, monitor for yellow to orangish crawlers by wrapping some of the infested stems with black electrical tape with the sticky surface facing out. Regularly inspect the tape over the 2-3 week egg hatch period for crawlers, typically from mid May into June; but likely earlier this year. When crawlers are found, repeated applications of insecticidal soaps will reduce scales somewhat. Chemical options include the insecticides Acephate, permethrin and malathion or horticultural (growing season) oils. Read and follow label directions.
Euonymous Scale, University of Nebraska-Lincoln
15. Vole damage to the base of trees has been found in Platte County. Voles gnaw on tree bark and cambium during winter. Once the damage occurs, little can be done to repair it. Reduce vole damage on trees during winter with the use of hardware cloth cages placed around trees. Avoid deep layers of mulch around trees. Mulch should be used, but kept at a 2 to 4 inch depth and not piled against tree trunks.
Controlling Vole Damage, University of Nebraska-Lincoln
16. Rose garden clean up and pruning- On all roses, first prune out the winter killed portion by making a cut just above the nearest healthy bud. Also prune out canes showing blackish cankers caused by the disease black spot. If needed, thin out and shape the rose bush, especially shrub roses. Rake and remove leaves to reduce overwintering fungus.
17. Fertilizing herbaceous perennials- With proper soil preparation before planting and the use of organic mulches, many perennials require little additional fertilization. For established plants, an application of a balanced, slow release nitrogen fertilizer in May, and again one month later, can be beneficial.
Fertilizers high in nitrogen should not be used as nitrogen promotes excess foliage at the expense of flowers and roots, causes floppy stems, and can increase disease susceptibility. Perennials grown in wood mulched beds may require a little more nitrogen as soil nitrogen is used to decompose mulch.
When fertilizing, use slow release nitrogen sources, avoid contact with leaves when using granular forms, water in fertilizer after applications, apply fertilizer when the soil is moist and stop fertilizing after August 1. Fertilize native and/or drought-tolerant perennials only when the plants show signs of diminished vigor or chlorosis (leaf yellowing).
18. Weed control in perennial flower beds includes mulching and hand weeding. Preemergence herbicides like Preen can be used to control seedlings during and just after seed germination. Preemergence herbicides need to be applied to the soil of weed free beds and applications repeated according to label directions. Hard to control established weeds like field bindweed and dandelions can be spot treated carefully with products containing Glyphosate. Perennial grassy weeds can be controlled post emergence with products containing fluazifop, such as Grass-B-Gon.
19. Mulching perennials during summer will help conserve soil moisture and keep weed growth to a minimum. Apply 2-4 inches of chipped or shredded bark, straw, grass clippings or other suitable material. Keep mulch away from plant stems and crowns as this can create an environment conducive to crown and root rots.
20. Staking perennials- Some perennials have weak stems, grow tall, become top heavy and fall over. For such plants, place stakes or wire cage within or around the plant in early spring. New growth will hide the support. Use stakes or support frames made from twigs, wood dowels, bamboo, wire, or plastic. Stakes should be 6 to 12 inches shorter than the full height of the plant. Place the stake behind the plant and sink it into the ground far enough to be firm. Tie the plant loosely to the stake with soft cloth ties or wire covered with paper or plastic. Tie the plant with one loop around the plant and another around the stake rather than a single loop around both the stake and plant.
Growing Perennial Flowers, Purdue University
21. Iris borers are the most destructive insect pest of iris and can be found throughout Nebraska. This pest overwinters as eggs attached to the previous year’s iris leaves. Eggs begin to hatch in late April. The young borers move up the leaf, feeding as they go and leaving jagged leaf edges. Later, the iris borer caterpillar chews a small hole into the leaf and tunnels inside down to the rhizome. This feeding causes distinctive water streaks in the leaves. Once in the rhizome, the borers continue to feed and can completely destroy the rhizome. In mid-summer, the borers pupate then emerge as moths in late summer to early fall. Female moths attach their eggs to nearby iris leaves, thus completing their seasonal cycle.
Sanitation is the key to controlling this pest. Once iris leaves have turned yellow, remove the current year’s dead foliage and compost it. This should reduce problems next year by eliminating the overwintering egg stage.
A well-timed insecticide application in the spring (when leaves are about 4 to 6 inches tall) will reduce iris borer damage. Treat foliage with bifenthrin, cyfluthrin, permethrin, or spinosad to destroy newly hatched borers before they can tunnel into the plant. A second application should be applied after 10 to 14 days. A single application of the systemic insecticide imidacloprid (Merit, Bayer Advanced) also should provide satisfactory control. In addition, small caterpillars can be killed by squeezing them while they are inside the leaves.
Culture of Iris, University of Nebraska-Lincoln
With frost still a possibility, if rhubarb is hit by a hard frost or freeze, it can still be eaten provided the stalks are firm and upright. Leaf injury would appear as brown or black discoloration along the margins. If the stems are soft and mushy, don’t eat them. Severe cold injury may cause the oxalic acid crystals in the leaves to move into the stalks, increasing the chance of poisoning. If in doubt about the safety of eating the stalks, don’t eat them. Cut the damaged stalks off and compost them. Allow new stalks to develop for eating.
Growing Rhubarb in the Home Garden, Ohio State University
23. Asparagus weed control- Do not use salt. Use a combination of methods including mechanical (hand pulling, hoeing, shallow tillage), cultural (3 to 4 inch mulch layer) and chemical (herbicides). For preemergence control, apply Preen Vegetable Garden Weed Preventer to weed free soil. For postemergence control, once harvest is finished, snap all spears off slightly below ground level, then spot treat weeds with glyphosate to kill existing weeds before applying mulch and then allow the ferns to grow.
Asparagus Weed Control, University of Nebraska-Lincoln
24. Cool season crops and warm temperatures- Unusually warm air and soil temperatures may lead to bolting (early flowering) of cool season crops such as broccoli. These conditions can also reduce produce quality leading to bitter tasting, stringy, and tough produce.
Controlling Ticks, University of Nebraska-Lincoln
26. Eliminating weedy trees & shrubs- To remove weedy trees and shrubs, cut the plants down close to the ground and paint the freshly cut stumps with one of the mixtures below. If the stumps are not treated, they will resprout and grow back.
A number of herbicides are recommended for this. For the best results, apply them immediately after cutting to the freshly cut surface. Treatments include:
- 2,4-D Ester mixed with diesel
- 50 - 100% solution of Glyphosate
- Tordon RTU
Use caution when applying Tordon, due to its long residual in the soil and the high risk of injury to nearby trees. It is best avoided in landscape situations or wherever there are nearby trees.
2012 Guide to Weed Management, University of Nebraska - Lincoln