4. NEMATODES

Nematodes are microscopic, non-segmented worms. They are filamentous in shape, however, females in some species may become swollen at maturity and exhibit round or pear shaped bodies. Plant parasitic nematodes have a hollow stylet which penetrates plants cells. This stylet is visible under a light microscope and sometimes under a dissecting scope. Nematodes have well developed digestive and reproductive systems.

Nematodes are placed into different classification based on how they live their lives. For example, ectoparasitic nematodes live freely in soil, do not enter plant tissue and feed superficially on roots. Migratory endoparasitic nematodes live freely in sod, enter plants and move through plant tissue feeding internally. And sedentary endoparasitic nematodes have a free living juvenile stage, but as adults they attach to the root and feed in one location.

A. Diseases of Ornamentals, Vegetables and Turfgrass Caused by Nematodes (examples):

1. Root-Knot Nematode

Root-knot nematodes (Meloidogyne incognita) can be a serious pest in home gardens and field grown crops. The pest is most serious in warm, light soils. Root-knot nematodes have an extremely wide host range (over 2,000 species) which includes most vegetables, many cereals and field crops, some trees, and weeds.

The severity of symptoms depends on the host, the nematode and the age at which the plant was infected. Younger plants are more severely damaged than mature plants. Above ground symptoms are not unique, and in fact may be reminiscent of diseases caused by many other pathogens and abiotic disorders. Common above ground symptoms include stunting, chlorosis, wilting (particularly during the heat of the day), and reduced yield. Roots of infected plants exhibit characteristic galls, and may be distorted. These galls are usually visible with the unaided eye, and can clearly be seen with a hand lens or dissecting microscope. The size and number of galls is dependent on the type of host, the age of infection and the nematode population. Because nematodes are sensitive to sod type, damage may be "spotty" rather than uniform across a field or garden.

Root-knot nematodes live in soil as eggs and juveniles, and in plants as adults. Juvenile nematodes invade roots of susceptible hosts. Once inside the host root, the nematodes swell and become pear-shaped, disrupting the developing root tissue. As the nematodes feed on root cells, the cells enlarge creating what is called "giant cells". It is the formation of giant cells and the presence of the nematodes in the roots which creates the characteristic root galls. Female nematodes lay their eggs (200-500 per female) in a gelatinous matrix on the outside of the root. Eggs hatch in the soils and new juvenile nematodes invade other roots. During favorable conditions, the life cycle of this pest is completed in about one month, so there may be up to four or five generations per season. Therefore, populations can build up in soils very rapidly.

Several management practices can be used to reduce nematode populations. Never plant transplants which exhibit nematode galling (remember that legumes form root nodules for nitrogen fixations which may look similar to small nematode galls). Avoid areas known to be heavily infested with nematodes. Crop rotation may be helpful, but the wide host range of the pest limits its effectiveness. There are chemicals registered with can be used to control nematodes, however most are soil fumigants which can only be used prior to planting and they are "Registered Use Materials" which means that they need to be purchased and applied by a licensed pesticide applicator. Some success controlling nematodes has been had in relatively small areas with the incorporation of soil amendments containing crushed seashells. The seashells are made of chitin which is the same protein which makes up the nematodes exoskeleton. The addition of chitin to the soil stimulates beneficial soil microbes which can degrade chitin. This increase in beneficial organisms will help to reduce the nematode population by destroying the nematodes cell wall.

2. Turfgrass Nematodes

Plant parasitic and saprophytic nematodes are components of every turfgrass ecosystem. The importance of these microscopic worms in the overall health of the turf varies depending on the type of nematode, the nematode population, and the environment. While some nematodes can be beneficial in controlling some pests, others can cause serious diseases in turf. Nematodes are more likely to cause disease in warm temperate or subtropical regions, although disease can occur in cooler regions as well.

All turfgrass species are susceptible to nematodes. Several different species of nematodes can cause damage in turf. Some of the common species in warm climate species are:

a. Meloidogyne spp. - root-knot nematode

b. Trichodorus spp. and Paratrichodorus spp. - stubby root nematode

c. Belonolaimus spp. - sting nematode

d. Dolichodorus spp. - awl nematode

e. Helicotylewhus spp. - spiral nematode

f. Hoplolaimus spp. - lance nematode

Some of the common species in cool climates are:

a. Xiphinema spp. - dagger nematode

b. Pratylenchus spp. - lesion nematode

c. Macroposthonia spp. - ring nematode

d. Tylenchorhynchus spp. - stylet nematode

e. From species above; a, b, e and f.

Nematode injury might appear as areas of low fertility, even when adequate fertilizers have been applied. Symptoms will be slight to severe chlorosis, declining growth, gradual thinning, wilting, and in severe cases, death. Turf which is under stress, particularly from high heat, drought, low fertility, or excessive thatch, is more susceptible to nematode injury.

Chemical treatment with a nematicide is available to professional sod growers, nursery operators, and professional pesticide applicators. Retail nematicides are not available to homeowners.

5. PARASITIC HIGHER PLANTS

Parasitic higher plants are flowering plants which live off other plants. True and dwarf mistletoes and dodder are examples of parasitic plants.

Mistletoes have chlorophyll, but no roots and thus, rely on host plants for water and nutrients. True mistletoes parasitize hardwood trees, such as cottonwoods, elms, oaks, and locusts. This pathogen is disseminated by birds which feed on the seed-baring mistletoe berries. Dwarf mistletoes attack conifers and are an important pathogen in conifer forests. This pathogen forcibly discharges its seeds and is disseminated by wind currents.

Dodder has no chlorophyll and no true roots. It depends on its host for water, nutrients and carbohydrates. Dodder is a soilborne vine-like plant which twines around its host. It is mostly a problem in agricultural fields, but can be troublesome in home gardens and landscapes, particularly in newly developed areas which were once used for agriculture.

1. NUTRIENT DEFICIENCIES

Nutrient deficiencies occur when essential elements are not available in the required amount. The effect on plants is dependent on the host plant and element(s) that is deficient. Some general symptoms include, stunting, chlorosis, small leaves, malformed leaves, poor root growth, weak plant growth, poor turfgrass stand establishment, etc.

Common nutrient deficiency descriptions:

Nitrogen: slow growth, stunted plants, chlorosis (particularly older leaves).

Phosphorus: slow growth, stunted plants, purplish coloration of foliage on some plants, dark green coloration with tips of leaves drying, delayed maturity, poor fruit or seed development.

Potassium: leaf tips and margins "burn" starting with the older leaves, weak stalks, small fruit, slow growth.

Iron: interveinal chlorosis of young leaves (veins remain green except in severe cases), twig dieback.

Zinc: decrease in stem length, rosetteing of terminal leaves, reduced bud formation, interveinal chlorosis, dieback of twigs (if deficiency lasts more than one year).

Magnesium: interveinal chlorosis in older leaves, curling of leaves upward along margins, marginal yellowing with green "Christmas tree" area along midrib of leaf.

Calcium: death of growing points (terminal buds and root tips), abnormal dark green, premature shedding of blossoms and buds, and weak stems.

Sulfur: light green color of (mostly) young leaves, small and spindly plants, slow growth, delayed maturity.

Manganese: interveinal chlorosis of young leaves - gradation of pale green coloration with darker color next to veins. No sharp distinction between veins and interveinal areas as with iron deficiency.

Boron: death to terminal buds, thickened, curled, wilted and chlorotic leaves, reduced flowering and improper fertilization.

Soil availability of nutrients is influenced by soil characteristics. The pH of the soil has a profound effect on nutrient availability. For example, iron, though plentiful in the soil, is mostly unavailable to plants in alkaline soils (pH above 7.5). Likewise, phosphorus, manganese, copper and zinc are also less available in alkaline soils. Boron, which is needed by plants in very small amounts in almost completely unavailable at pH between 7.5 and 8.5. A soil pH between 6.5 and 7.5 gives a maximum availability of the primary nutrients (nitrogen, phosphorus and potassium), and a ‘relatively high degree of availability of the other essential elements. Unfortunately, much of the soil in the southwest is alkaline.

Some elements such as nitrogen are readily leached through the soil and therefore need more frequent application to provide the plants with an adequate amount of the element. Additionally, the relative amounts of different elements effect nutrient availability. The excesses of certain nutrients may result in the plants inability to take up another essential element.

Soil tests are needed to determine the base nutrient content and other important soil characteristics. The results of soil test will help to determine the type and amount of fertilizers needed for different plants. Nutrient toxicities can occur with over fertilization or with improper application of fertilizers. In most cases, application of a balanced fertilizer with essential micronutrients is beneficial to plant growth. In some areas, additional foliar applications of some microelements such as iron might be needed to keep plants green.

2. PESTICIDE INJURY

All pesticides, if used inappropriately, can be toxic to plants. In most cases, damage results from improper application or from pesticide drift. Failure to thoroughly clean spray equipment can also result in injury to nontarget plants.

Common symptoms of pesticide injury include: leaf burn, leaf distortion, chlorosis, flattened or enlarged stems and roots, plant death, etc. Symptoms type and severity are dependent on the type of pesticide and the concentration of the chemical. In turf situations, damage appears in patterns associated with application of the chemical.

When any pesticide is used, it is imperative that the material be applied carefully and in accordance with the pesticide Label. It is also important to avoid spraying on windy and/or hot days.

3. TEMPERATURE EXTREMES

Temperature extremes, both high and low, can cause injury to plants. High temperature Results in excess transpiration, wilting, heat stress and sunscald. The plants are unable to cool themselves by evapotranspiration. In turf, heat stress is intensified by objects covering blades, high humidity, dry soil, and lightning strikes.

Low temperature injury causes leaf epidermal cells to separate from underlying tissue giving the affected tissue a silvery appearance. The affected herbaceous tissue will wilt and turn black. On trees, frost or freeze damage results in splits and cracks in trunks branches and twigs, eventually causing cankers to develop. These cankers become entry sites for secondary organisms such as fungi and bacteria.

4. SALT INJURY

Salt injury occurs when excessive salts from either the soil or the irrigation water are taken up by the plant. Damage results from a loss of feeder roots. Symptoms include marginal necrosis, leaf, stem and twig necrosis. Salt injury is often seen in association with heat stress.

5. LIGHT EXTREMES

Light affects germination, growth and shape of plants. Lack of light causes etoliation (elongation) between nodes and results in poor color. Excess light can result in sunburned foliage or fruit.

6. WATER EXCESS

Excess soil moisture results from excess irrigation, rainfall or poor soil drainage. These sods have reduced oxygen levels which inhibits plant growth. Plants may be chlorotic, have small or thin foliage, and have numerous dead or dying roots. Roots may die from a lack of oxygen or from soilborne fungi which are favored by high soil moisture. The final result may be plant death. Chronically wet soils may become black in appearance and have a foul odor.

Water soaked above ground plant parts are predisposed to many diseases. Additionally, excessive moisture on the foliage favors many foliar diseases which require either free water or high humidity for germination and infection.

7. DROUGHT INJURY

Drought injury results from a chronic lack of water. Affected grasses turn bluish in color and the leaves curl before turning brown. Shrubs and trees wilt in the afternoon and recover at night until they wilt permanently. New foliage is small and pale in color. Plant growth is restricted and plants are more susceptible to heat stress.

8. WIND AND SAND INJURY

Wind Injury results from excess air movement. Damage is more severe if temperatures are high. Plants become desiccated, and may become radically altered in shape due to directional force of wind. Leaves become tattered either from the force of the wind whipping the foliage around, or from wind blown sand. Wind may lead to problems associated with wind blown pathogens.

9. HAIL DAMAGE

Hail causes necrotic spots on foliage and fruit. Severe hail may cause holes in leaves or leaves to become tattered. Hail striking the crown of young plants can cause plants to fall over and die.

10. AIR POLLUTION

Air pollution which results from a lack of sufficient air currents can cause problems on many different types of plants. Combustion of fuels, auto exhaust, coal burning, interaction of sunlight and nitrogen oxides make up different air pollutants. The common major pollutants are: nitrogen oxides, ozone, hydrocarbons,. peroxyacetyl-nitrate (PAN), and sulfur dioxide.

Symptoms of air pollution vary somewhat depending on the type of pollutant, however common symptoms include, flecking of upper leaf surface, bronzing of the lower leaf surface, interveinal bleaching, or damage may be invisible.

11. IMPROPER CULTURAL PRACTICES:

A. Management Practices that Impact the Health of Ornamentals

a. Planting:

i. Choice of location.

ii. Soil preparation

iii. Root preparation.

iv. Planting depth.

b. Irrigation:

i. Timing.

ii. Amount applied.

iii. Frequency of irrigation.

iv. Application method (coverage).

c. Fertilization:

i. Selection:

- macronutrient ratio

- addition of micronutrients

ii. Timing.

iii. Frequency of application.

iv. Application method:

- water soluble

- slow release

- foliar sprays

- injection

d. Cultural Practices:

i. Pruning; timing and method.

ii. Sanitation; removal of debris, clean tools, weed and insect control

iii. Staking

iv. Mulching/Cultivation

B. Management of Turfgrass

Turf diseases are best controlled with good management of the turfgrass. For maximum disease control, turfgrass should be maintained at moderate rate of growth. Turf which is very lush or under stress is more susceptible to disease than turf which is grown at a. moderate pace. Management, practices include, irrigation, fertilization, mowing, and de-thatching (aeration).

a. Water

Turfgrass is best watered in the early morning. This allows for efficient use of the water and for the grass blades to dry before nightfall. Water thoroughly so that water penetrates several inches into the soil. It is better to water less frequently and for longer periods than to water frequently for short periods of time.

The amount of water needed will vary depending on the time of year and the weather conditions. You can determine the amount of water you are applying with each irrigation by placing a few empty food cans in various locations on the lawn. Turn on the sprinklers for a designated amount of time. After irrigation, measure the amount of water which has accumulated in the cans. This will tell you how much water in inches that you are applying in that specified amount of time. You can then adjust the duration of irrigation to provide the desired amount of water.

b. Fertilizer

The use of slow release nitrogen fertilizers can help to reduce the rapid flush of lush growth after fertilization. Slow release fertilizers releases nitrogen slowly over a long period of time. This avoids disease problems which may by associated with large amounts of nitrogen available all at one time. Fertilization is best applied four times a year.

C. Mowing

Mow the lawn as high as is practical for the use of the turf. Low mowed or scalped grass plants are more susceptible to diseases. Be sure that your mower blades are sharp and that they are making nice clean cuts of the grass blades. Dull mowers tear or shred leaf blades, leaving jagged tips of injured leaves straw colored. Overall appearance of turf is ragged and grayish in color. In addition to poor appearance, the jagged cuts made by dull blades are more attractive to many disease organisms. Scalping injury (mowing grass so short that yellow or brown stem tissue is exposed) is caused by infrequent mowing, weedy grass areas, and uneven areas. Scalping weakens turf plants making them more susceptible to diseases.

If you are mowing your lawn appropriately, you can leave the clippings on the surface of the lawn and this will help with the overall balance of nutrients and microorganisms in die thatch and soil. If you mow infrequently you do not want to leave the clippings because the large amount of clippings will mat on the surface of the lawn reducing the amount of water and air penetration to the soil.

d. Dethatching and Aerification

Thatch is the layer just below the grass blades and above the soil. It is made up of decomposing grass plants - leaves, shoots, rhizomes and roots. A small amount of thatch is desirable, however if thatch accumulates over 2 cm it impedes water penetration and can cause detrimental affects to the grass. Roots tend to grow in the thatch layer instead of the soil, increasing risk of drought or high temperature damage. Excessive thatch is caused by keeping turf too wet or too dry, high soil acidity or alkalinity, high nitrogen fertilization, and repeated pesticide applications.

Thatch accumulation is controlled with periodic aeration of the grass. Aeration is achieved by poking holes in the lawn, by vertical mulching, slicing or power raking. You should aerate your lawn at least once a year.

Benefits of aeration:

Exchange of air and water

Reduce water runoff

Water penetration/retention

Increase root/shoot growth

Improve drainage/reduce thatch

Disease and insect control

e. Fungicides for Turf Disease Control

Several broad spectrum and disease specific fungicides are available to help control turf diseases. It is important that the disease be identified as best possible to help in selecting the proper chemical. Only use registered fungicides and use them only when absolutely necessary as repeated fungicide application will reduce the effectiveness of the chemical due to the development of resistance in the fungal population. Keep in mind that fungicides typically do not kill the fungus, they stop the activity of the fungus and allow for the turf to get a head start on filling in the diseased areas. However, if conditions which initiated the disease problem reoccur, repeat treatment may be necessary.

1. Many living and non-living factors cause abnormalities in plants.

2. The host, the pathogen and the environment must all work together to cause disease.

3. Strong, healthy, well-managed plants are less susceptible to disease than plants under stress.

4. Effective control programs disrupt the interactions between at least two of the interacting components

5. The best disease management programs utilize an integrated approach to control.