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Hollyhock Pest Control: Are Hollyhock Nematodes Good Or Bad

Hollyhock Pest Control: Are Hollyhock Nematodes Good Or Bad


By: Laura Miller

You’re envious of other gardener’s hollyhocks.Their plants are nearly 6 feet (2 m.) tall with gorgeous blooms in shades ofpink, purple and yellow. Comparatively, your plants are stunted with poorflower production. They wilt easily and look yellowish.

You can’t find any signs of bacterial, viral or fungalinfections when you inspect your hollyhock. Pest control sprays haven’t helpedeither. You’re not sure why your hollyhocks are failing. Perhaps, it’s becausethe trouble lies under the soil. You may have hollyhock nematode problems.

How Do Nematodes Affect Hollyhocks?

Nematodesare tiny parasitic worms that feed on plant roots. They’re distributedworldwide and cause problems for commercial growers, greenhouse operators and thegarden hobbyist. These microscopic pests snack on the roots of many types ofplant, including cultivated flowers like hollyhocks.

Hollyhock nematode symptoms include poor development andgeneral decline during the growing season. The plant can appear stunted withyellowing or wilting leaves during the day, but recover at night. Digging upand examining the roots of an infected plant can give you the clues you need tosuspect the cause is hollyhock nematodes.

As parasitic hollyhock nematodes feed, the roots becomeknotted with visible galls or root swellings. The appearance of root knots andunderdeveloped root structures are classic hollyhock nematode symptoms.Nematode infested roots may also show signs of rotting.

Positive confirmation of a nematode infestation can be madeby the Nematode Diagnostic Laboratory. Your localcounty extension office can help you collect and send a sample for testingfor a minimal fee.

Methods for Hollyhock Pest Control

Commercial agricultural operations rely on chemicalnematicides to control nematode populations in their fields. But nematicidesare very toxic and expensive, making this type of hollyhock pest controlimpractical for the home gardener.

If you have hollyhock nematode problems, try these tips toreduce populations:

  • Choose nematode resistant plants whenever possible. Annual garden vegetables, such as peppers and tomatoes, are susceptible to nematodes. Growing resistant varieties of vegetables can protect your hollyhocks by reducing the population density of nematodes in your yard.
  • Rotate where hollyhocks are planted. Hollyhocks are short-lived perennials in USDA zones 3-8 and grown as annuals elsewhere.
  • Alternate hollyhocks with non-host species or those known to lower nematode numbers. These include broccoli, cauliflower and some varieties of French marigolds.
  • Never move soil from an area infected with nematodes to an uninfected one.
  • Practice cleanliness. Nematodes can hitch rides on tools, gloves, pots and garden equipment, like rototillers.
  • Remove dead plants from the garden. Properly dispose of diseased plants.
  • Keep flowerbeds and gardens weeded. Nematodes don’t discriminate between the roots of undesirable plants and prized specimens.
  • Till heavily infected areas often during the winter months to expose the hollyhock nematodes to cold weather.
  • Solarize the flowerbeds to reduce and eliminate hollyhock nematode problems.

Finally, healthy plants show fewer signs of nematode damage.Feeding, watering and proper soil amendment can help your hollyhocks grow intovibrant, colorful, flower specimens that are the envy of other gardeners!

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Hollyhock Nematode Problems – Do Nematodes Affect Hollyhock Plants

Du er misunnelig på andre gartneres stokkroser. Plantene deres er nesten 2 meter høye med nydelige blomster i rosa, lilla og gule nyanser. Sammenlignende er plantene dine stuntet med dårlig blomsterproduksjon. De vil lett og se gulaktige ut.

Du kan ikke finne noen tegn på bakterie-, virus- eller soppinfeksjoner når du inspiserer stokkrosen. Sprøytebekjempelsprayer hjalp ikke heller. Du er ikke sikker på hvorfor stokkroser mislykkes. Kanskje det er fordi problemene ligger under jorden. Du kan ha problemer med stokkrostnematoder.


Diagnosis

Positive identification is a critical first step in management. In the field, root-knot nematodes can usually be diagnosed by observing the symptoms described previously and by removing the plant and roots from the ground and looking for the diagnostic galls. If a nematode other than the root-knot nematode or another disease is suspected, laboratory root and soil sample analysis is necessary to identify the issue and the most effective control measures. For information and instructions on how to sample, contact your county Extension Center or visit North Carolina State University Plant Disease and Insect Clinic .

Look-alikes. Similar swellings can develop with clubroot disease of Brassica (Figure 5) and occasionally with crown gall on woody plants such as rose. Root swellings are part of the healthy anatomy of certain ornamentals such as liriope and daylily. By comparison, nematode galls on those hosts are small (Figure 6).

Root-knot nematode infection also can be mistaken for nodules formed on the roots of legume plants due to colonization by beneficial species of Rhizobium and related genera of nitrogen-fixing bacteria. Most other natural nodules or bumps are loosely attached to roots and have hollow centers. Active Rhizobium nodules have a milky fluid in their centers and are often pale pink in color. In contrast, root-knot nematode galls have a white or gray center.

Figure 5. Swollen brassica roots caused by clubroot disease.

NC State University Plant Disease and Insect Clinic

Figure 5. Swollen brassica roots caused by clubroot disease.

NC State University Plant Disease and Insect Clinic

Figure 6. (Left to right): Shrunken liriope root with root-knot galls, normal liriope tuber, pencil point.

NC State University Plant Disease and Insect Clinic

Figure 6. (Left to right): Shrunken liriope root with root-knot galls, normal liriope tuber, pencil point.

NC State University Plant Disease and Insect Clinic


Summary

Following the recommendations listed in this document can help you avoid or reduce problems with plant-parasitic nematodes in the landscape. However, there are no guarantees of success. County and state faculty with the University of Florida are continually exploring new nematode management options. The most current recommendations can be obtained from the UF/IFAS Extension website, Solutions for Your Life at http://solutionsforyourlife.ifas.ufl.edu/.

Tables

Root galling and reproduction of root-knot nematodes on 12 annual ornamental species. 1 Columns show reactions of each plant species to a root-knot nematode population in work done by C. C. Goff in the 1930s (more plants are listed in Table 2), common root-knot nematode (Meloidogyne incognita), javanese root-knot nematode (M. javanica), and "peanut" root-knot nematode (M. arenaria).


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