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Hort Update for July 20, 2018

Nebraska Extension Hort Update for July 20, 2018, https://communityenvironment.unl.edu/update07202018
Serious ConcernsMajor Symptom:
1. Fire blight Leaves on branch terminals wilting and turning brown or almost black
2. Herbicide drift on fruits & vegetables No research available on safety of produce from plants affected by herbicide drift
3. Bacterial wilt of cucurbits Remove and destroy infected plants
4. Squash vine borer Day flying, black & orange, clear wing moth lays eggs on cucurbits
5. Bagworm Insects are feeding; look for 1-1.5 inch bags on susceptible evergreens or those with a history of infestation
6. Japanese beetles Their season is peaking and plant damage in hot spots is severe
Minor IssuesMajor Symptom:
7. Shade tree anthracnose Minor disease causing brown blotches in ash, maple, sycamore
8. Kentucky bluegrass yellowing Warm soil issue, avoid overwatering and try straight iron application
9. Crabgrass breakthrough Mid-season crabgrass management and control
10. Tomato leaf blights Early blight, septoria and bacterial leaf spot, common diseases on tomatoes are active now
11. Blossom end rot Leathery to soft brown rot on the blossom end of tomatoes and other vegetables


1. Fire blightLeaves on branch terminals wilting and turning brown or almost black

This a bacterial disease infects pear, crabapple, apple, hawthorn, Cotoneaster and related species. The bacteria overwinters in branch cankers and is carried by insects and wind-blown rain from cankers to blossoms, natural openings (lenticils), or wounds from hail, mechanical injury, or pruning. Careless pruning also spreads the bacteria.

Key symptoms:

  • Leaves on branch terminals wilting and turning brown or almost black and remain attached. Typically up to a foot of the branch is affected.
  • Tender branch tips curling into a shepherd’s crook
  • Twig or branch cankers which are discolored often sunken areas
  • Blossoms turning brown and dying

Management/Control:

  • Plant resistant cultivars (see University of Missouri Extension link below for susceptible and resistant cultivars)
  • Prune out diseased branches during the dormant season and remove the material from the site. During the growing season, removed infected terminals. Prune at least 8 to 12 inches below cankers or infected terminals, but do not leave branch stubs. Remove branches at their point of attachment with another branch or the trunk. To avoid spreading bacteria, dip or spray pruning tools before each cut with a 10% solution of bleach (one part bleach to 9 parts water).
  • Avoid excessive applications of nitrogen fertilizer. Keep in mind fertilizers applied to lawns are available to trees. Rarely would any tree growing in a fertilized lawn require additional nutrients.
  • The bactericide Streptomycin can be applied during blooming. A minimum to two applications is needed. Follow label directions closely.

Fire Blight, University of Missouri Extension

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2. Herbicide drift on fruits & vegetablesno research available on safety of produce from plants affected by herbicide drift

Herbicide drift on fruits and vegetables is a concern leading to questions about safety when eating produce from drift affected plants. Drift occurs in two ways, particle or vapor. Particle drift occurs when small spray droplets are blown off the targeted site by wind. Vapor drift occurs when herbicides volatize or evaporate and move off site on air currents. Volatility increases when herbicides are applied during hot summer temperatures. Pesticide labels state at what temperatures, and other environmental conditions, it is not safe to apply the product. Follow label directions to reduce the risk of drift when applying products. Know that September and October are the key times for applying herbicides to broadleaf weeds so think twice about applying them during summer when hot temperatures are likely.  

Produce Safety Unknown

There is no available research to show produce from plants affected by herbicide drift is safe or not safe to eat. Also, how long an herbicide remains in plant tissues will vary with herbicide type. For some types, it may be a short period while for other products it could be months. Environmental conditions would also play a role, so even if there was a research based answer, it would vary with each situation. When customers ask about this issue, let them know there is no known research available to help in providing an answer. It would be best to play it safe and not eat produce from plants affected by herbicide drift. If they make the choice to eat the produce, advise them to at least not eat any edible portion that was present at the time of the drift.

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3. Bacterial wilt of cucurbitsRemove and destroy infected plants

Caused by a bacteria transmitted to plants by striped and spotted cucumber beetles. It infects cucumbers, squash, muskmelon, pumpkins and gourds, all members of the cucurbit family. Watermelon and some varieties of cucumbers and squash are resistant. The bacteria grows in the vascular systems of the vines, eventually gumming up the xylem and preventing movement of water in the plant. Once a plant is infected, there are no effective control measures. Promptly remove and destroy infected plants.

Key Symptoms:

  • Initially, wilting of individual leaves vines during the heat of the day with recovery overnight.
  • Fruit may have small, water-soaked patches on their surface.
  • Entire plants eventually wilt with leaves turning brown and dying.
  • Creamy white bacterial ooze in the stems. To distinguish bacterial wilt from other causes of wilting, such as squash vine borer or fungal disease, cut a stem cross-wise near the ground and squeeze it. Press a finger firmly on the cut surface and slowly pull away. If present, the bacterial ooze with string out in fine, slimy threads.

Management/Control:

  • Plant varieties more tolerant of bacterial wilt.
  • Control cucumber beetles by covering plants with floating row covers, or with labeled insecticides, until blooming. Monitor for beetles with yellow sticky traps. Keep in mind cucurbits rely on insects for pollination.
  • Cover soil below plants with reflective mulching to deter beetles.
  • Plant a trap crop, like green zucchini, two weeks prior to planting other cucurbits.
  • Promptly remove and destroy infected plants. Use crop rotation.

Bacterial Wilts of Cucurbit, Nebraska Extension

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4. Squash vine borerDay flying, black & orange, clear wing moth lays eggs on cucurbits

The larvae of a clear-wing moth. It is a serious pest of cucurbits, commonly attacking summer squash, winter squash and pumpkins. Cucumbers and melons are attacked less often. Borers feeds inside stems, causing vines to wilt and die. Adults emerge from overwintering cocoons from late June through July. Eggs are laid near the base of susceptible plants. Larvae bore into stems after hatching, feeding for 4 to 6 weeks. They then emerge and pupate in the soil to overwinter.

Key Symptoms:

  • Yellowing of leaves and wilting.
  • Sawdust-like frass near the base of plants. Plant bases may become mushy and rot.
  • Eventually, entire vines or plants may die.

Management/Control:

  • Plant resistant species. Plant a fall crop of summer squash in early July to avoid egg laying.
  • Once borers enter stems, control is difficult. Check squash for the day flying moths, which resemble a wasp and have an orange abdomen with black dots. They may also be trapped using a yellow container filled with water. Place traps in late June and check daily.
  • When moths or found, cover plants with floating row covers for about two weeks if the cucurbit is planted in an area where cucurbits have not been previously grown in the last 1 to 2 years.
  • If using labeled insecticides, begin application during late June or when moths are first seen. Repeat application as recommended. Two applications are usually sufficient.
  • Promptly remove and destroy plants killed by vine borer. Use crop rotation.

Squash Vine Borer Damage, Nebraska Extension

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5. BagwormsInsects are feeding; look for 1-1.5 inch bags on susceptible evergreens or those with a history of infestation

Feeding on conifer trees and shrubs justify control. Large populations are capable of seriously damaging or killing evergreens. Monitor spruce, Juniper, Arborvitae and pine for bagworms. Eggs hatch from mid-May through early June. Larvae are approximately 1-1.5 inches long, nearing full size. Bacillus thuringiensis, as well as other insecticides, can still provide effective control.

After hatching, larvae spin protective cases or “bags” around themselves. Bags are constructed of silk and fragments of needles or leaves. Bags are initially one-eighth inch long. As larvae feed and grow, they enlarge the bag. At this time of year, bagworms are between one-fourth and one-half long. By summers end, bags are up to two inches long.

Bagworms move around trees feeding on needles until early September. Early signs of damage are brown or stressed needles at branch tips caused by tiny, first-stage caterpillars etching needle surfaces as they feed. Heavy infestations of older bagworms can defoliate a tree or shrub. Less severe injury will slow growth and stunt plants. Bagworms are especially damaging to conifers because destroyed foliage is not regenerated.

Insecticides are most effective when applied from mid to late June targeting young caterpillars. Insecticidal spray applications require thorough coverage to penetrate the tree canopy. It’s best to use ground equipment capable of delivering higher spray volumes and pressure. Aerial applications may not provide thorough coverage. Insecticides containing Bacillus thuringiensis (Bt), spinosad, or neem oil (azadirachtin) and insecticidal soaps are effective against young larvae, but may require repeat applications. These products generally have minimal impact on beneficial insects.

Other insecticide options for bagworm control on conifers includes acephate, bifenthrin, chlorantraniliprole, carbaryl, cyfluthrin, dimethoate, esfenvalerate, fluvalinate, lambda-cyhalothrin, malathion, permethrin, and tebufenozide. When making an application, be certain the product is specifically labeled for both the target pest and plant species.

Bagworms, Nebraska Extension

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6. Japanese beetlesJapanese beetle season is peaking and plant damage in hot spots is severe

Unlike most insect pests, both adults and grubs cause plant damage. As beetles, they feed on leaves, flowers and fruits of more than 300 plant species. Linden trees, roses, grapes and soybeans are a few favorite foods. The beetles feed over a 4 to 6 week period beginning in late June. They eat green tissue between leaf veins causing leaves to appear lacy. Severe defoliation can stress trees and reduce yields in orchards and crops. 

As grubs, they feed on turf roots starting in July/early August and continue through summer. If grub populations are high enough, the turf may turn brown and can easily be rolled up like carpet. Note: Treating for the grubs will not prevent beetle damage since new beetles fly in.

Reduced risk beetle control consists of collecting beetles (7 PM at night seems to be a good time) and placing them in a bucket of soapy water or using plant covers to exclude them where feasible. Fine mesh nets can be placed over roses. Two organic sprays, Neem and Pyola, can protect plants but usually not beyond 3-7 days.

Chemically, adults can be controlled with pyrethroid products like Tempo and Bayer Advanced Lawn & Garden Multi-Insect Killer (cyfluthrin) or Ortho Bug B Gone (bifenthrin). Sevin (carbaryl) is another option. These all provide about 2 weeks of protection for foliage and flowers after thorough treatment. 

Because insecticides affect pollinators, try to spray in the evening only and after trees have finished blooming. Follow label instructions explicitly to avoid harming pollinators and damaging plants.

The grub stage are often kept in check by natural enemies like ants, parasitoid wasps, and disease. If they become a problem, insecticides, applied at the right time of year, can be helpful in controlling them. GrubEx (active ingredient: chlorantraniliprole; Scott’s Turf) applied in mid-June to mid-July can decrease populations of young white grubs. If dealing with an advanced infestation later in the season, products like Bayer Advanced Complete Insect Killer for Soil and Turf (active ingredient: imidacloprid; Bayer) can control > 50% of the grubs. 

Discouraging the Use of Traps for Japanese Beetle Control, Nebraska Extension
Japanese Beetles
, Nebraska Extension
Dealing with Japanese Beetles, Nebraska Extension

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