\m 13 4 26 2 1 'Introduction' \m 27 9 66 2 1 'Symptoms of Nematode Injury' \m 96 43 20 3 1 'Management of Nematode Pests in the Landscape' \m 197 91 37 6 1 'Susceptibility of Some Woody Ornamentals to Four Common Nematodes' \t'January 1988' 'II C-' \a Dr. Robert A. Dunn, Extension Nematologist \a \a LANDSCAPE ORNAMENTALS Dr. Robert A. Dunn, Extension Nematologist \h 1 'Introduction' LANDSCAPE ORNAMENTALS Ornamental plants permanently placed in the landscape accumulate pest problems as do other perennial crops. If there are serious nematode infestations in the roots or soil ball or in the planting site, the chances of satisfactory growth are slim, and the longevity of the planting may be substantially reduced. Although there are few or no "cure" treatments, the kind of start given a planting and the care it is given can have a substantial effect on its performance. The information which follows is adapted from Nematology Plant Protection Pointer 21, "Nematodes of Landscape Plants." \h 1 'Symptoms of Nematode Injury' Symptoms of Nematode Injury ABOVE GROUND SYMPTOMS are similar to those resulting from many kinds of root injury. Foliage loses its luster and wilts more readily than it should. Prolonged stress because of nematode injury to the root system may result in yellowing and eventual loss of foliage. New flushes of growth are weak, with fewer and smaller leaves than healthy plants. There may even be twig dieback if the stress continues. The unthrifty condition may persist despite use of extra fertilizer and water. The distribution pattern of damage is usually irregular, since nematodes are usually not distributed evenly in the soil. ROOT SYMPTOMS vary widely. Some kinds of nematodes cause the tissues on which they feed to grow strangely (root-knot and some foliar nematodes, for instance); some stop the growth of the roots; other kill the cells on which they feed, leaving patches of dead tissue as they move on. Fungi and bacteria which cause root rots, wilt, and other plant diseases often infect nematode- damaged roots earlier and more severely than uninjured roots. Therefore, depending on the kinds of nematodes involved, nematode damage to landscape ornamentals may include galls, stunting, and decay of roots; roots are often darker in color than healthy roots. Among the dozens of nematode species which have been associated with landscape ornamentals, relatively few seem to cause most of the serious problems. The root-knot nematodes (Meloidogyne spp.) are by far the most important in Florida. Their easily-recognized galls on roots make their presence obvious. Galls result from growth of plant tissues around juvenile nematodes which feed near the center of the root. Root-knot gall tissue is firm without a hollow center, and is an integral part of the root; removing a root-knot gall from a root tears root cortical tissue. Nodules formed on roots of many legumes because of beneficial Rhizobium spp. (nitrogen-fixing bacteria) and most other natural nodules or bumps are loosely attached to the roots and have hollow centers. Active Rhizobium nodules have a milky fluid in their centers. \v \bNot only is their damage the most easily recognized, but root-knot nematodes actually cause more serious damage to more kinds of ornamentals than other nematodes. Among popular plants known to be susceptible to root-knot nematodes in Florida are many hollies (Ilex spp.), ixora (Ixora coccinea), hibiscus (Hibiscus spp.), Barbados cherry (Malpighea glabra), ti plant (Cordyline terminalis), most Gardenia spp., Pittosporum spp., boxwoods (Buxus spp.), rose (Rosa spp.), and figs (Ficus). Many plants, such as Citrus spp., may occasionally be damaged by root-knot nematodes even though normally unaffected by them. We do not know why these unusual infections occasionally happen, but it is likely that plant stress from environmental factors or other pests may promote them. The less distinct discoloration, stunting, and decay of roots that are caused by nematodes other than root-knot are easily masked by or confused with the effects of numerous pathogens and other root problems. Nematodes such as lesion (Pratylenchus spp.), burrowing (Radopholus similis), and reniform (Rotylenchulus spp.) probably cause far more damage to landscape plantings than is recognized because their effects are not as readily recognized as those of root-knot nematodes. Susceptibility to one kind of nematode is not necessarily related to the reaction of the same plant to other nematodes. Susceptibilities of 21 common woody ornamentals to four widely distributed nematodes are compared in Table 1. Many plants that are rated susceptible (S) or highly susceptible (HS) to root-knot nematodes are tolerant (T) to one or more of the others, and vice versa. This table is based on many years of research at the North Carolina State University Research Station at Clayton, N.C. The same plants may suffer greater damage from the same nematodes in Florida than in North Carolina, because of the extreme sensitivity of plants to drought stress in our sandy soils. That is, some plants rated T in the chart for North Carolina probably deserve an S in Florida. \h 1 'Management of Nematode Pests in the Landscape' Management of Nematode Pests in the Landscape First, it is important to realize that there are a few plant parasitic nematodes in nearly every square foot of foil in Florida. However, it is obvious that most plantings of landscape ornamentals in Florida are healthy assets to their surroundings. So, don't panic! There is not an army of nematodes just waiting to gobble up every sapling and bulb you plant. In most cases, there are many attractive plants which could be planted into any particular site without serious damage or immediate losses. However, new ornamentals sometimes never really get started after planting. If nematodes attack a young plant as soon as its roots are in the ground, the plant may decline fairly rapidly and eventually die or remain so unattractive that it must be removed. In another case, a long-established specimen or hedge gradually declines, and a great deal of root-knot nematode galling is found on the roots. The following suggestions should help minimize these cases in which a common species in the soil fauna gets out of hand. \v \b 1. Prepare new planting sites properly to give plants the best chance to become rapidly established. 2. Use nematode-free stock. No matter how perfect and pest-free the planting site, a nematode infection already started in the roots is right where it must be to do the most damage. Buy only top quality plants. Reject any that have clear evidence of nematodes or other hard-to-control pests. 3. Use plants that are well adapted to the location: region, soil type, shade, drainage, etc. Plants that are "out of place" are more likely than well-adapted ones to suffer environmental stress at any given time and to be under stress more of the time. Just as you may be more apt to catch pneumonia when a cold places unusual stress on you, stress makes plants more susceptible to potential pests which are common in their environment. Moreover, the characteristics that make a plant species "well adapted" to an area probably include some degree of tolerance or resistance to locally common pests, such as nematodes. Avoid using plants known to be susceptible to a specific kind of nematode known to occur in a planting site. Most references to "nematode susceptibility" in magazine articles and extension literature refer to one or more root-knot nematode species, unless they specify others. Such lists are often incomplete, but it is quite likely that any plant identified as "nematode susceptible" should not be planted where root-knot nematodes are known to be serious. 4. Keep other pests under practical control. Stress from pests can set plants up for nematode infection just as readily as over- or under- supply of nutrients or water. Overuse of pesticides can also injure plants, so use judgement in their application. 5. Give the plants optimum care from the start and for as long as you want them to perform well. "Optimum" does not mean "Maximum". Fertilize as needed to maintain healthy growth, not to produce excessive, weak, succulent growth which invites attack by many kinds of pests above and below ground, including nematodes. Water deeply, to encourage development of a deep root system which can exploit a large volume of soil for water and nutrients. Frequent shallow watering causes plants to develop a shallow root system. A large root system can better withstand a small amount of nematode damage without major compromise to the overall health of the plant than can a shallow, already minimal root system. 6. Do not allow maintenance to lapse. Sudden dry periods or pest outbreaks can weaken plants in an incredibly short time. Even under normal conditions, erratic or inadequate watering can weaken a plant so that it can no longer tolerate a modest nematode population that had existed on/with it for years. \b 7. If nematodes had built up to high levels on a plant that was removed, or if vegetables or other plants that are especially favorable for nematodes were recently removed from the site, do not plant without treating the soil to give the new plant a fighting chance. Metam-sodium products (e.g. Vapam, Fume-V) may be used by anyone as long as label directions for soil preparation, chemical application, and post-treatment waiting period are followed. Methyl bromide products (e.g. Brom-O-Gas), available in 1 lb and 1.5 lb cans for treating small areas, may be used in many situations--read the label carefully. Either chemical will satisfactorily control nematodes and many other soil-borne pests if used according to label instructions. 8. Keep the plant root zone mulched to keep roots cool in hot weather and minimize evaporation of water from the soil surface. Organic mulches also contribute organic matter to the soil, thus enhancing the capacity of the soil to retain water and nutrients. Mulches reduce stress on the plant as a whole and the root system specifically, which improves the plant's chances to do well despite some nematode damage to roots. Greater soil organic matter content is also associated with increased activity of natural enemies such as certain fungi, predatory nematodes, etc. which apparently help keep popula- tions of plant parasitic nematodes from exploding. 9. Conspicuously lacking is any recommendation of a nematicide to treat nematode problems of plants established in the landscape. There is presently no chemical effective against root-knot and other hard-to-control nematodes that may be applied legally to landscape plants. Several nematicides which are registered for ornamental plants are restricted to the commercial production nursery because they are extremely toxic. Metam-sodium, the only effective nematicide which can be used legally in most sites, is highly toxic to plants at the rates which are effective for nematode control. Therefore, it can only be used to treat planting sites before planting (point 7, above). \v \v \v \b\v \h 1 'Susceptibility of Some Woody Ornamentals to Four Common Nematodes' Susceptibility of Some Popular Woody Ornamentals to Four Common Nematodes at the NCSU Central Crops Research Station, Clayton, NC.* Table 1: HS - Plants highly susceptible (severe stunting, branch die-back and death) S - Plants susceptible (some stunting but plants will grow satisfactorily) T - Plants will grow satisfactorily O - Have not been tested ------------------------------------------------------------------------------- Nematode Reaction ---------------------------------------- Host Plant Root-knot Stunt Lesion Ring _______________________________________________________________________________ Azalea T S O T Aucuba japonica HS S O S Buxus microphylla (Japanese Boxwood) HS O O O Buxus sempervirens (American Boxwood) O T HS O Camellia japonica T T O O Camellia sasanqua T T O O Gardenia jasminoides S T T T Gardenia radicans HS T O T Ilex cornuta (Chinese Holly) cv. Burfordi T T O T cv. Rotunda S S O S Ilex crenata (Japanese Holly) cv. Compacta HS T O S cv. Convexa HS T O S cv. Helleri HS S O S cv. Rotundifolia HS S O S Ilex vomitoria nana T T O T Juniper sp. Blue rug T T HS T Shore juniper T T O T Spiney Greek T T S T Ligustrum (Privet) T T O T Nandina domestica T T T T Photinia fraseri (red tip) T T O T Rose S S S T ------------------------------------------------------------------------------- ------------------------------------------------------------------------------- *Reproduced by permission from "Nematodes and Their Control in Woody Ornamentals in the Landscape," by R.H. Jones, D.M. Benson, and K.R. Barker. Pathology Information Note #63, Department of Plant Pathology, North Carolina State University at Raleigh.